Drive waveform generation device, drive waveform generation method, program, liquid discharge device and printer

Abstract

To provide a drive waveform generation device which suppresses a stringiness length and satellite generation, a drive waveform generation method and program, a liquid discharge device, and a printer.SOLUTION: A drive waveform generated by a processor includes, in one drive cycle, a discharge pulse group which discharges droplets from a nozzle and a voltage swing that does not discharge the droplets from the nozzle. Three or more voltage swings are placed after a first discharge pulse which is the last discharge pulse in the discharge pulse group. A starting end of the first voltage swing immediately after the first discharge pulse is arranged at a position apart by about a resonant pulse cycle from the starting end of the first discharge pulse. A starting end of the second voltage swing immediately after the first voltage swing is arranged at a position apart by about a resonant pulse width from the starting end of the first voltage swing.SELECTED DRAWING: Figure 12

Description

[Technical field]

[0001] The present invention relates to a drive waveform generating device, a drive waveform generating method and program, a liquid ejection device, and a printing device, and in particular to a technique for stabilizing the ejection of liquid from nozzles. [Background technology]

[0002] It is known that the flight shape of ink droplets in inkjet printing varies greatly depending on the ink properties. Depending on the ink properties, the ink threads tend to become long, resulting in the generation of satellites. Satellites are unnecessary droplets that are generated when the ink threads separate from the droplets.

[0003] Long strings make the ejection unstable and cause bending. Furthermore, if satellites occur, the dot shape may not be clean when the droplets land, and they may land in unintended locations. This can lead to deterioration of image quality and equipment failure, so it is necessary to suppress strings. Furthermore, mist, which is a mist-like droplet smaller than a satellite, and reverberation of the meniscus after ejection affect the stability of ejection, so these must also be suppressed for stable ejection.

[0004] Patent document 1 discloses a technology that enhances the satellite shortening effect at the trailing end of an ejected droplet by placing a non-ejection pulse that has a satellite suppression effect in the first half of a waveform within one cycle and applying only the non-ejection pulse to the blank area.

[0005] Patent Document 2 discloses a technique for outputting a micro-vibration pulse after an ejection pulse in a waveform within one cycle in order to improve the state of the meniscus of the nozzle. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2020-093535 A [Patent Document 2] JP 2014-028447 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the technology described in Patent Document 1, since a non-ejection pulse that has a satellite suppression effect is not applied when ejecting continuously, there is a possibility that satellites may occur. Also, in the technology described in Patent Document 2, there is a problem that the satellites cannot be suppressed by the micro vibration pulse.

[0008] The present invention has been made in consideration of the above circumstances, and has an object to provide a drive waveform generating device, a drive waveform generating method and program, a liquid ejection device, and a printing device that suppress thread length and satellite occurrence. [Means for solving the problem]

[0009] In order to achieve the above object, a drive waveform generating device according to a first aspect of the present disclosure includes one or more processors and one or more memories in which instructions to be executed by the one or more processors are stored, the processor generates a drive waveform for driving a droplet ejection element of a liquid ejection head having a nozzle for ejecting droplets, a pressure chamber communicating with the nozzle, and a droplet ejection element for pressurizing a liquid in the pressure chamber in response to a supplied drive waveform, the drive waveform including, within one drive cycle, an ejection pulse group including one or more ejection pulses for ejecting droplets from the nozzle, and a voltage swing that does not eject droplets from the nozzle, and three or more voltage swings are arranged after a first ejection pulse that is the last ejection pulse of the ejection pulse group. a starting point of the first voltage swing immediately after the first ejection pulse is located at a position separated by a first time from the starting point of the first ejection pulse, a starting point of the second voltage swing immediately after the first voltage swing is located at a position separated by a second time from the starting point of the first voltage swing, and if a period of two ejection pulses at which the speed of the ejected droplets is the fastest in the two ejection pulses is taken as a resonance pulse period, the first time is 80% to 120% of the resonance pulse period, and if a pulse width of one ejection pulse at which the speed of the ejected droplets is the fastest in one ejection pulse is taken as a resonance pulse width, the second time is 80% to 120% of the resonance pulse width. Driving the droplet ejection elements of the liquid ejection head with the drive waveform generated by this aspect makes it possible to suppress the stringing length and the occurrence of satellites.

[0010] A drive waveform generating device according to a second aspect of the present disclosure is the drive waveform generating device according to the first aspect, in which the start of a third voltage swing, which is the voltage swing immediately after the second voltage swing of the drive waveform, is located at a position separated by a third time from the start of the first voltage swing, and the third time is preferably 80% to 120% of half the resonance pulse period. By driving the droplet ejection elements of the liquid ejection head with the drive waveform generated by this aspect, it is possible to suppress the string length and the generation of satellites, and reduce mist.

[0011] A driving waveform generating device according to a third aspect of the present disclosure is the driving waveform generating device according to the first or second aspect, in which the start of a fourth voltage swing, which is a voltage swing immediately after the third voltage swing of the driving waveform, is arranged at a position 4 hours away from the start of the first voltage swing or 5 hours away from the start of the third voltage swing, and the fourth time is preferably 80% to 120% of an even multiple of the resonant pulse width or 80% to 120% of an integer multiple of the resonant pulse period, and the fifth time is preferably 80% to 120% of an even multiple of the resonant pulse width or 80% to 120% of an integer multiple of the resonant pulse period. By driving the droplet ejection elements of the liquid ejection head with the driving waveform generated by this aspect, it is possible to suppress the stringing length and the generation of satellites, reduce mist, and suppress reverberation of the meniscus.

[0012] A driving waveform generating device according to a fourth aspect of the present disclosure is the driving waveform generating device according to any one of the first to third aspects, wherein the starting end of the second ejection pulse, which is the ejection pulse immediately before the first ejection pulse of the driving waveform, is located at a position 6 hours away from the starting end of the first ejection pulse, and the pulse width of the second ejection pulse is 7 hours, the 6th time being 80% to 120% of the resonance pulse period, and the 7th time being 80% to 120% of the resonance pulse width. By driving the droplet ejection element of the liquid ejection head with the driving waveform generated by this aspect, satellites can be merged into droplets ejected by the first ejection pulse and droplets ejected by the second ejection pulse, thereby suppressing satellites.

[0013] A driving waveform generating device according to a fifth aspect of the present disclosure is the driving waveform generating device according to the fourth aspect, in which the driving waveform is a position before the second ejection pulse and a non-ejection pulse that does not eject droplets from the nozzle is not arranged between a position 8 hours away from the start of the second ejection pulse, and the 8th time is preferably 80% to 120% of the resonance pulse period. In other words, the voltage is constant between a position before the second ejection pulse and a position 8 hours away from the start of the second ejection pulse. By driving the droplet ejection element of the liquid ejection head with the driving waveform generated by this aspect, the second ejection pulse can be stably ejected and satellites can be suppressed.

[0014] A drive waveform generating device according to a sixth aspect of the present disclosure is the drive waveform generating device according to any one of the first to fifth aspects, wherein the liquid preferably has a surface tension of 35 mN / m or less.

[0015] A drive waveform generating device according to a seventh aspect of the present disclosure is the drive waveform generating device according to any one of the first to fifth aspects, wherein the liquid preferably has a surface tension of 30 mN / m or less.

[0016] In order to achieve the above object, a droplet ejection device according to an eighth aspect of the present disclosure includes a drive waveform generating device according to any one of the first to seventh aspects, a liquid ejection head having a nozzle for ejecting droplets, a pressure chamber communicating with the nozzle, and a droplet ejection element for pressurizing the liquid in the pressure chamber in response to the supplied drive waveform, and a processor for ejecting droplets from the nozzle by supplying the drive waveform generated by the drive waveform generating device to the droplet ejection element. According to this aspect, it is possible to suppress the string length and the occurrence of satellites.

[0017] In order to achieve the above object, a printing device according to a ninth aspect of the present disclosure includes the liquid ejection device of the eighth aspect, and a relative movement mechanism for relatively moving the liquid ejection head and the substrate, and the processor prints an image on the substrate by relatively moving the liquid ejection head and the substrate and ejecting droplets from the nozzles. According to this aspect, it is possible to suppress the string length and the occurrence of satellites.

[0018] In order to achieve the above object, a drive waveform generation method according to a tenth aspect of the present disclosure is a drive waveform generation method executed by one or more processors, the drive waveform generating method including generating a drive waveform for driving a droplet ejection element of a liquid ejection head having a nozzle that ejects droplets, a pressure chamber communicating with the nozzle, and a droplet ejection element that pressurizes liquid in the pressure chamber in response to a supplied drive waveform, the drive waveform including, within one drive cycle, an ejection pulse group including one or more ejection pulses that eject droplets from the nozzle, and a voltage swing that does not eject droplets from the nozzle, three or more voltage swings are arranged after a first ejection pulse that is the last ejection pulse of the ejection pulse group, and the first ejection In this drive waveform generating method, the start of a first voltage swing, which is a voltage swing immediately after the pulse, is located at a position separated by a first time from the start of the first ejection pulse, and the start of a second voltage swing, which is a voltage swing immediately after the first voltage swing, is located at a position separated by a second time from the start of the first voltage swing, and if a period of two ejection pulses at which the speed of the ejected droplets is the fastest in the two ejection pulses is defined as a resonant pulse period, the first time is 80% to 120% of the resonant pulse period, and if a pulse width of one ejection pulse at which the speed of the ejected droplets is the fastest in one ejection pulse is defined as a resonant pulse width, the second time is 80% to 120% of the resonant pulse width. By driving the droplet ejection elements of the liquid ejection head with the drive waveform generated by this aspect, it is possible to suppress the stringing length and the occurrence of satellites.

[0019] In order to achieve the above object, a program according to an eleventh aspect of the present disclosure is a program for causing a computer to execute the driving waveform generating method of the tenth aspect. By driving the droplet ejection elements of the liquid ejection head with the driving waveform generated by executing the program of this aspect by a computer, it is possible to suppress the string length and the occurrence of satellites. A non-transitory computer-readable recording medium such as a CD-ROM (Compact Disk-Read Only Memory) storing the program according to the eleventh aspect is also included in the present disclosure. Effect of the Invention

[0020] According to the present invention, the thread length and the occurrence of satellites can be suppressed. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram showing an overall configuration of an example of an inkjet printing apparatus. [Diagram 2] FIG. 2 is a bottom view of the inkjet head as viewed from the nozzle surface side. [Diagram 3] FIG. 3 is a diagram illustrating an example of the configuration of a nozzle surface of an inkjet head. [Figure 4] FIG. 4 is a cross-sectional view showing an example of the structure of an inkjet head. [Diagram 5] FIG. 5 is a block diagram showing a schematic configuration of a control system of the inkjet printing apparatus. [Figure 6] FIG. 6 is a block diagram showing the inside of the image recording control unit. [Figure 7] FIG. 7 is a diagram for explaining the terminology of the drive waveform. [Figure 8] FIG. 8 is a diagram showing an example of a conventional driving waveform. [Figure 9] FIG. 9 shows a series of photographs taken at regular intervals using a strobe to show the flight of ink droplets ejected from a nozzle when a drive waveform is applied to an individual electrode of a piezoelectric element. [Figure 10] FIG. 10 is a diagram showing another example of a conventional driving waveform. [Figure 11] FIG. 11 is a series of photographs of ink droplets when a drive waveform is applied to the individual electrodes of a piezoelectric element. [Figure 12] FIG. 12 is a diagram showing an example of a driving waveform according to the present disclosure. [Figure 13] FIG. 13 is a diagram showing another example of the driving waveform of the present disclosure. [Figure 14] FIG. 14 is a diagram showing another example of the driving waveform of the present disclosure. [Figure 15] FIG. 15 is a photograph taken with a strobe showing the flight of ink droplets ejected from a nozzle when a drive waveform is applied to an individual electrode of a piezoelectric element. [Figure 16] FIG. 16 shows a series of photographs taken at regular intervals using a strobe to show the flight of ink droplets ejected from a nozzle when each waveform element of a drive waveform is applied to an individual electrode of a piezoelectric element. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of each embodiment, illustration and description of parts common to other embodiments will be omitted as appropriate.

[0023] <Overall configuration of the inkjet printing device> Fig. 1 is an overall configuration diagram showing an example of an inkjet printing device. The inkjet printing device 10 is a sheet-fed aqueous inkjet printer that prints an image on paper 1 (an example of a "substrate") by an inkjet method using aqueous ink (an example of a "liquid"). The inkjet printing device 10 is mainly composed of a transport drum 20 that transports the fed paper 1, an image recording unit 30 that prints an image on the printing surface of the paper 1, and a transport drum 40 that transports the paper 1 on which the image has been printed.

[0024] The image recording unit 30 prints a color image by applying ink droplets of each color ink to the printing surface of the paper 1 while transporting the paper 1. The image recording unit 30 is configured with an image recording drum 32 that transports the paper 1, a paper pressing roller 34 that presses the paper 1 transported by the image recording drum 32 to bring the paper 1 into close contact with the outer circumferential surface of the image recording drum 32, inkjet heads 36C, 36M, 36Y, and 36K (examples of "liquid ejection heads") that eject ink droplets of each color, cyan (C), magenta (M), yellow (Y), and black (K), onto the paper 1, and an imaging unit 38 that reads the image printed on the paper 1.

[0025] The image recording drum 32 is a conveying means for the paper 1 in the image recording unit 30, and is an example of a relative movement mechanism for relatively moving the inkjet heads 36C, 36M, 36Y, and 36K and the paper 1. The image recording drum 32 is formed in a cylindrical shape, and is driven by a motor (not shown) to rotate about the center of the cylinder as an axis. A gripper 32A is provided on the outer circumferential surface of the image recording drum 32. The image recording drum 32 grips the leading edge of the paper 1 with the gripper 32A, and conveys the paper 1 while wrapping it around the outer circumferential surface by rotating with the motor (not shown).

[0026] Furthermore, the image recording drum 32 has a large number of suction holes (not shown) formed in a predetermined pattern on its outer circumferential surface. The paper 1 wrapped around the outer circumferential surface of the image recording drum 32 is attracted to and held on the outer circumferential surface of the image recording drum 32 by being sucked through the suction holes. This allows the image recording drum 32 to transport the paper 1 with high smoothness. The mechanism for attracting and holding the paper 1 on the outer circumferential surface of the image recording drum 32 is not limited to a negative pressure attraction method, and an electrostatic attraction method can also be used.

[0027] The grippers 32A are disposed at two locations on the outer circumferential surface of the image recording drum 32. The image recording drum 32 can transport two sheets of paper 1 with one rotation by the two grippers 32A. The rotations of the transport drum 20 and the image recording drum 32 are controlled so that the timing of receiving and transferring the paper 1 is synchronized. Similarly, the rotations of the image recording drum 32 and the transport drum 40 are controlled so that the timing of receiving and transferring the paper 1 is synchronized. In other words, the transport drum 20, the image recording drum 32, and the transport drum 40 are driven to have the same circumferential speed and are driven so that the positions of the grippers are synchronized.

[0028] The paper pressure roller 34 is made of a rubber roller. The paper pressure roller 34 is installed in pressure contact with the outer circumferential surface of the image recording drum 32 near the paper receiving position of the image recording drum 32. The image recording drum 32 brings the paper 1 into close contact with the outer circumferential surface of the image recording drum 32 by passing the paper 1 delivered from the transport drum 20 between the outer circumferential surface and the paper pressure roller 34.

[0029] The inkjet heads 36C, 36M, 36Y, and 36K are each composed of a line head corresponding to the paper width. The inkjet heads 36C, 36M, 36Y, and 36K are arranged at regular intervals along the transport path of the paper 1 by the image recording drum 32. The inkjet heads 36C, 36M, 36Y, and 36K are each arranged such that the nozzle surface 50A faces the outer circumferential surface of the image recording drum 32. The inkjet heads 36C, 36M, 36Y, and 36K print an image on the printing surface of the paper 1 transported by the image recording drum 32 by ejecting ink droplets from a plurality of nozzles 54 (see FIG. 3) formed on the nozzle surface 50A toward the image recording drum 32.

[0030] The imaging unit 38 is an imaging means for capturing an image printed on the printing surface of the paper 1 by the inkjet heads 36C, 36M, 36Y, and 36K. The imaging unit 38 has a line sensor made of a solid-state imaging element such as a CCD (Charge-Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor), and a fixed-focus imaging optical system. The imaging unit 38 is installed downstream of the rearmost inkjet head 36K in the conveying direction of the paper 1 by the image recording drum 32.

[0031] In the image recording unit 30 configured as described above, the image recording drum 32 receives the paper 1 transported by the transport drum 20. The image recording drum 32 transports the paper 1 by rotating while gripping the leading edge of the paper 1 with a gripper 32A. The paper pressing roller 34 brings the paper 1 into close contact with the outer circumferential surface of the image recording drum 32. The image recording drum 32 sucks the paper 1 through suction holes, and adsorbs and holds the paper 1 on the outer circumferential surface of the image recording drum 32.

[0032] When the paper 1 passes through the opposing positions, the inkjet heads 36C, 36M, 36Y, and 36K deposit ink droplets of cyan, magenta, yellow, and black, respectively, onto the printing surface of the paper 1, thereby printing a color image on the printing surface.

[0033] The imaging unit 38 reads the image printed on the printing surface of the paper 1 when the paper 1 passes through the opposing position. The reading of this printed image is performed as necessary, and image defects such as streaks are detected from the read image to inspect for defective nozzles such as nozzles with poor ejection and / or nozzles with deflected ejection that caused the image defects. When reading, the image is read while being held by suction on the image recording drum 32, so reading can be performed with high accuracy. In addition, since reading is performed immediately after printing, for example, abnormalities such as nozzles with poor ejection and nozzles with deflected ejection can be detected immediately and measures can be taken promptly. This makes it possible to prevent unnecessary printing and minimize the occurrence of paper waste.

[0034] Thereafter, the image recording drum 32 transfers the paper 1 to the transport drum 40 .

[0035] <Inkjet head structure> Next, the structure of the inkjet heads will be described. Since the inkjet heads 36C, 36M, 36Y, and 36K corresponding to the respective colors have a common structure, hereinafter, the head will be represented by the reference numeral 36.

[0036] 2 is a bottom view of the inkjet head 36 as viewed from the nozzle surface 50A side. The inkjet head 36 has a structure in which a plurality of head modules 52 are connected in the longitudinal direction of the inkjet head 36. The plurality of head modules 52 have a common structure. There is no limit to the number of head modules 52, and it is determined appropriately depending on the overall length of the paper 1 in the direction perpendicular to the transport direction.

[0037] The inkjet head 36 includes a base frame 53. A plurality of head modules 52 are attached to the base frame 53. The base frame 53 includes attachment portions according to the number of attachable head modules 52. The base frame 53 includes adjustment portions that adjust the positions of the head modules 52. Note that the attachment portions and adjustment portions are omitted from FIG. 2.

[0038] 3 is a diagram illustrating an example of the configuration of a nozzle surface 50A of the inkjet head 36. The vertical position of each head module 52 is adjusted so that the nozzle surfaces 50A of the respective head modules 52 form the same plane.

[0039] In the head module 52, a plurality of nozzles 54, each of which ejects ink droplets, are arranged on the nozzle surface 50A. The nozzles 54 are arranged in a matrix at a density that achieves a specified printing resolution. A projected nozzle row in which the plurality of nozzles 54 are projected in a direction perpendicular to the transport direction of the paper 1 is equivalent to a nozzle row in which the plurality of nozzles 54 are arranged at approximately equal intervals along the direction perpendicular to the transport direction of the paper 1.

[0040] Generally equal intervals means that the ink dots formed using the inkjet head 36 are substantially equal intervals. For example, the concept of equal intervals also includes a case in which the nozzles 54 are slightly spaced apart to take into account manufacturing errors and the movement of ink dots on the paper 1 due to landing interference.

[0041] The arrangement of the nozzles 54 is not limited to a matrix arrangement. Examples of the arrangement of the nozzles 54 include a linear arrangement in one row, a V-shaped arrangement, and a W-shaped arrangement in which V-shaped arrangements are repeated.

[0042] 4 is a cross-sectional view showing an example of the structure of the inkjet head 36. The inkjet head 36 includes an ejector 70, a supply-side common branch channel 80, a vibration plate 82, and a cover plate 88.

[0043] The ejector 70 includes a nozzle 54, a pressure chamber 72, a piezoelectric element 74 (an example of a "droplet ejection element"), a nozzle flow path 76, and an individual supply path 78. The nozzle 54 communicates with the pressure chamber 72 via the nozzle flow path 76. The pressure chamber 72 communicates with a supply-side common branch flow path 80 via the individual supply path 78.

[0044] The piezoelectric element 74 includes an individual electrode 84 and a piezoelectric body 86. The diaphragm 82 that constitutes the top surface of the pressure chamber 72 includes a conductive layer (not shown) that functions as a common electrode corresponding to the lower electrode of the piezoelectric element 74. The pressure chamber 72, the walls of the other flow passage parts, and the diaphragm 82 are made of silicon. The material of the diaphragm 82 is not limited to silicon, and it is also possible to form the diaphragm 82 from a non-conductive material such as resin. The diaphragm 82 itself may be made of a metal material such as stainless steel, and may serve as a diaphragm that also serves as a common electrode.

[0045] A piezoelectric unimorph actuator is formed by stacking a piezoelectric element 74, which is made up of a piezoelectric body 86 and an individual electrode 84, on a vibration plate 82. When a drive voltage with a drive waveform is applied to the individual electrode 84, which is the upper electrode of the piezoelectric element 74, the piezoelectric body 86 deforms. When the piezoelectric body 86 deforms, the vibration plate 82 bends, and the volume of the pressure chamber 72 changes. Due to the change in the volume of the pressure chamber 72, the ink in the pressure chamber 72 is pressurized, and ink is ejected from the nozzle 54.

[0046] When the piezoelectric body 86 returns to its original state after the ink is ejected, new ink is filled into the pressure chamber 72 from the supply-side common branch channel 80 through the individual supply channel 78. The action of filling the pressure chamber 72 with ink is called refilling. The shape of the pressure chamber 72 in plan view is not particularly limited, and various shapes are possible, such as a rectangle or other polygon, a circle, or an ellipse.

[0047] The cover plate 88 is a member that maintains a movable space 90 for the piezoelectric element 74 and seals the periphery of the piezoelectric element 74. A supply-side ink chamber and a recovery-side ink chamber (not shown) are formed above the cover plate 88. The supply-side ink chamber is connected to a supply-side common main flow path (not shown) via a communication path (not shown). The recovery-side ink chamber is connected to a recovery-side common main flow path (not shown) via a communication path (not shown).

[0048] <Control system configuration> 5 is a block diagram showing a schematic configuration of a control system of the inkjet printing apparatus 10. The inkjet printing apparatus 10 includes a system controller 100, a communication unit 102, an image memory 104, a transport control unit 106, an image recording control unit 108, an inspection unit 110, an operation unit 112, and a display unit 114.

[0049] The system controller 100 functions as a control unit that controls each unit of the inkjet printing device 10, and also functions as a calculation unit that performs various calculation processes. The system controller 100 also performs required signal processing on the image data stored in the image memory 104 to generate dot data corresponding to each nozzle 54.

[0050] The system controller 100 includes a processor 100A and a memory 100B. The processor 100A executes instructions stored in the memory 100B. The hardware structure of the processor 100A is various processors as shown below. The various processors include a CPU (Central Processing Unit), which is a general-purpose processor that executes software (programs) and acts as various functional units, a GPU (Graphics Processing Unit), which is a processor specialized for image processing, a PLD (Programmable Logic Device), which is a processor whose circuit configuration can be changed after manufacture such as an FPGA (Field Programmable Gate Array), and a dedicated electric circuit, which is a processor having a circuit configuration designed specifically for executing specific processing such as an ASIC (Application Specific Integrated Circuit).

[0051] A processing unit may be configured with one of these various processors, or may be configured with two or more processors of the same or different types (for example, multiple FPGAs, or a combination of a CPU and an FPGA, or a combination of a CPU and a GPU). Also, multiple functional units may be configured with one processor. As an example of configuring multiple functional units with one processor, first, as represented by a computer such as a client or a server, there is a form in which one processor is configured with a combination of one or more CPUs and software, and this processor acts as multiple functional units. Second, as represented by a SoC (System On Chip), there is a form in which a processor is used that realizes the functions of the entire system including multiple functional units with one IC (Integrated Circuit) chip. In this way, the various functional units are configured using one or more of the above various processors as a hardware structure.

[0052] Furthermore, the hardware structure of these various processors is, more specifically, an electric circuit that combines circuit elements such as semiconductor elements.

[0053] The memory 100B stores instructions to be executed by the processor 100A. The memory 100B includes a RAM (random access memory) and a ROM (read only memory), not shown. The processor 100A uses the RAM as a working area, executes software using various programs and parameters, including a drive waveform generating program described below, stored in the ROM, and executes various processes of the inkjet printing device 10 by using the parameters stored in the ROM, etc.

[0054] The communication unit 102 includes a required communication interface, and transmits and receives data to and from the host computer 200 connected to the communication interface.

[0055] The image memory 104 functions as a temporary storage means for various data including image data, and data is read and written through the system controller 100. Image data received from the host computer 200 via the communication unit 102 is stored in the image memory 104.

[0056] The transport control unit 106 controls the driving of the transport drum 20, the image recording drum 32, and the transport drum 40, which are a transport system for the paper 1 in the inkjet printing device 10. The transport control unit 106 controls the transport system in response to commands from the system controller 100, and transports the paper 1 smoothly.

[0057] The image recording control unit 108 generates a drive waveform according to the dot data generated by the system controller 100, and supplies it to the individual electrodes 84 of each piezoelectric element 74. That is, in response to a command from the system controller 100, the image recording control unit 108 supplies the generated drive waveform to the inkjet heads 36C, 36M, 36Y, and 36K so that an image based on the dot data is printed on the paper 1 transported by the image recording drum 32. As a result, ink droplets are ejected from the nozzles 54 of the inkjet heads 36C, 36M, 36Y, and 36K, dots are formed on the printing surface of the paper 1, and the image is printed on the printing surface.

[0058] The inspection unit 110 analyzes the results of reading the test pattern by the imaging unit 38 to identify defective nozzles from the plurality of nozzles 54 of the inkjet heads 36C, 36M, 36Y, and 36K.

[0059] The inspection unit 110 identifies nozzles 54 that are defective nozzles having ejection abnormalities. The inspection unit 110 causes inkjet heads 36C, 36M, 36Y, and 36K to print a test pattern for detecting defective nozzles on paper 1 based on pre-stored data of the test pattern for detecting defective nozzles. The inspection unit 110 causes the imaging unit 38 to read the printed test pattern, and analyzes the reading result of the imaging unit 38 to identify defective nozzles from the multiple nozzles 54 of inkjet heads 36C, 36M, 36Y, and 36K.

[0060] The defective nozzles include, for example, non-ejecting nozzles that do not eject ink at all, and deflected ejection nozzles where the landing position error of ejected ink exceeds an allowable value. The inspection unit 110 stores the identified defective nozzles in a storage unit (not shown).

[0061] The image recording control unit 108 may correct the dot data so that the dot to be formed by the defective nozzle identified by the inspection unit 110 is complemented by the nozzle 54 adjacent to the defective nozzle.

[0062] The operation unit 112 is an input unit equipped with operation buttons, a keyboard, a touch panel, and the like. A user can input a print job to the inkjet printing device 10 through the operation unit 112. Here, a print job refers to a processing unit that is a set of processing to be printed based on image data. The operation unit 112 outputs the input print job to the system controller 100. The system controller 100 executes various processes according to the print job input from the operation unit 112.

[0063] The display unit 114 includes a display device such as an LCD (Liquid Crystal Display) panel, and displays required information on the display device in response to a command from the system controller 100 .

[0064] Fig. 6 is a block diagram showing the inside of the image recording control unit 108. Fig. 6 shows a portion corresponding to one individual electrode 84 of the image recording unit 30. The image recording control unit 108 and the image recording unit 30 constitute a liquid ejection device. The image recording control unit 108 includes a waveform generating unit 120, a digital-to-analog converting unit 122, a pulse selection switch 124, a switch controller 126, and a bias resistor 128.

[0065] The waveform generating unit 120 (an example of a "drive waveform generating device") executes a drive waveform generating method for generating a drive waveform W, which is a reference drive waveform, in synchronization with a drive timing signal input from the system controller 100. The digital-to-analog converting unit 122 converts the input drive waveform W, which is a digital signal, into an analog signal and outputs it. The output of the digital-to-analog converting unit 122 is input to one end of a pulse selection switch 124.

[0066] One end of the pulse selection switch 124 is connected to the output of the digital-to-analog conversion unit 122, and the other end is connected to the corresponding individual electrode 84. In addition, one terminal of a bias resistor 128 is connected to the individual electrode 84, and the other terminal of the bias resistor 128 is connected to a bias voltage that is a reference potential of the drive waveform.

[0067] The switch controller 126 controls the on and off of the pulse selection switch 124 in synchronization with the drive timing signal input from the system controller 100 based on the dot data input from the system controller 100 .

[0068] The pulse selection switch 124 is controlled to be turned on and off by a switch controller 126. When the pulse selection switch 124 is turned on, an analog driving waveform output from the digital-to-analog conversion unit 122 is supplied to the individual electrode 84. On the other hand, when the pulse selection switch 124 is turned off, the input to the individual electrode 84 is fixed (latched) to a bias voltage.

[0069] In the inkjet printing device 10 configured as above, the system controller 100 acquires image data to be printed on the paper 1 from the host computer 200 via the communication unit 102. The system controller 100 stores the acquired image data in the image memory 104.

[0070] The system controller 100 performs required signal processing on the image data stored in the image memory 104 to generate dot data corresponding to each nozzle 54. The image recording control unit 108 controls the driving of each inkjet head 36C, 36M, 36Y, and 36K of the image recording unit 30 in accordance with the generated dot data, and prints an image represented by the image data on the recording surface of the paper 1.

[0071] The dot data is generated by performing color conversion processing and halftone processing on the image data. The color conversion processing is processing for converting image data expressed in sRGB (standard Red Green Blue) or the like into ink volume data for each color of ink used in the inkjet printing device 10. The color conversion processing of this embodiment converts into ink volume data for each color of cyan, magenta, yellow, and black. The halftone processing is processing for converting the ink volume data for each color generated by the color conversion processing into dot data for each color by processing such as error diffusion. The dot data may be data having a plurality of gradations.

[0072] The system controller 100 controls the driving of the corresponding inkjet heads 36C, 36M, 36Y, and 36K in accordance with the dot data for each color thus generated, thereby printing an image represented by the image data onto the paper 1.

[0073] <Terminology> A "pulse" is a rectangular, trapezoidal, or triangular voltage change over time. For example, in the case of a so-called push-pull pulse in which the pressure chamber 72 is depressurized and then pressurized, it refers to a portion that includes, in that order, a falling slope where the voltage decreases, a portion where the voltage is held constant, and a rising slope where the voltage increases. In the case of a so-called push-pull pulse in which the pressure chamber 72 is pressurized and then depressurized, it refers to a portion that includes, in that order, a rising slope, a holding portion, and a falling slope. Note that even if there is a holding portion in the middle of the slope that is less than half the "pulse width" described below, it may be regarded as one pulse. The rising slope and falling slope of the voltage are each called a "voltage swing."

[0074] Fig. 7 is a diagram for explaining the terminology of the drive waveform. The horizontal axis of Fig. 7 indicates time (unit: μs), and the vertical axis indicates voltage (unit: V). The drive waveform W1 shown in Fig. 7 is constant at bias voltage VB from timing t0 to timing t1. The "bias voltage" is the reference potential of the substrate that constitutes the image recording control unit 108.

[0075] 7 is a falling slope in which the voltage drops from the bias voltage VB to the voltage V1 from timing t1 to timing t2. That is, the slope SL1 starts at timing t1 and ends at timing t2, and has an amplitude of the absolute value of (VB-V1), that is, a voltage swing of |VB-V1|.

[0076] A holding portion C1 shown in FIG. 7 is a portion in which the voltage is kept constant at V1 from time t2 to time t3.

[0077] 7 is a rising slope in which the voltage rises from the voltage V1 to the bias voltage VB from timing t3 to timing t4. That is, the slope SL2 starts at timing t3 and ends at timing t4, and has an amplitude of the absolute value of (V1-VB), that is, a voltage swing of |V1-VB|.

[0078] A holding portion C2 shown in FIG. 7 is a portion in which the bias voltage VB is held constant from timing t4 to timing t5.

[0079] Slope SL3 shown in Fig. 7 is a falling slope where the voltage drops from bias voltage VB to voltage V1 from timing t5 to timing t6. Hold portion C3 shown in Fig. 7 is a portion where the voltage is kept constant at V1 from timing t6 to timing t7. Slope SL4 shown in Fig. 7 is a rising slope where the voltage rises from voltage V1 to bias voltage VB from timing t7 to timing t8. Hold portion C4 shown in Fig. 7 is a portion where the voltage is kept constant at bias voltage VB from timing t8.

[0080] In such a drive waveform, the slope SL1, the hold portion C1, and the slope SL2 constitute a pulse P1. The start of the pulse P1 is timing t1, the end of the pulse P1 is timing t4, and the "pulse width" of the pulse P1 is (timing t3-timing t1). The amplitude of the pulse P1 is |VB-V1|.

[0081] Similarly, the slope SL3, the hold portion C3, and the slope SL4 configure the pulse P2. The starting edge of the pulse P2 is timing t5, the ending edge of the pulse P2 is timing t8, and the "pulse width" of the pulse P2 is (timing t7-timing t5). The amplitude of the pulse P2 is |VB-V1|. The "pulse period" of the pulse P1 and the pulse P2 is (timing t5-timing t1).

[0082] When a pulse is applied to an individual electrode 84 of the piezoelectric element 74 and an ink droplet flies away from the nozzle 54, the pulse is called an "ejection pulse." In other words, an "ejection pulse" is a pulse that ejects an ink droplet from the nozzle 54. On the other hand, when a pulse is applied to an individual electrode 84 of the piezoelectric element 74 and the ink droplet does not leave the nozzle 54, the pulse is called a "non-ejection pulse." In other words, a "non-ejection pulse" is a pulse that does not cause an ink droplet to be ejected from the nozzle 54.

[0083] The "resonant pulse width" is the pulse width of the single pulse at which the ink droplet has the fastest velocity when the ink droplet is ejected from the nozzle 54 by one ejection pulse (single pulse) with the pulse width changed. The "resonant pulse width" is generally half the Helmholtz vibration period Tc (=Tc / 2) or the acoustic length AL. The Helmholtz vibration period Tc is the natural period of the entire vibration system determined by the ink flow path system, ink, and the dimensions, materials, physical properties, etc. of the piezoelectric element. The acoustic length AL is half the time of the natural vibration period of the ink flow path system.

[0084] The "resonance pulse period" is the pulse period of the double pulse at which the ink droplets have the fastest velocity when the pulse period is changed to two ejection pulses (double pulses) and the ink droplets are ejected from the nozzle 54. The "resonance pulse period" may be the Helmholtz oscillation period Tc, or may be longer than the Helmholtz oscillation period Tc.

[0085] <Problems with conventional driving waveforms> The driving waveform is closely related to the physical properties of the ink and the structure of the inkjet head. In particular, satellites are greatly affected by the surface tension of the ink. In order to spread the ink droplets on a substrate such as paper, it is preferable for the ink to have a low surface tension. However, if the ink surface tension is low, the thread is more likely to stretch when ejected, and the droplet is more likely to split into a main droplet and a small droplet (satellite) after the thread breaks. In other words, even with the same waveform, satellites are less likely to occur if the ink surface tension is relatively high, and satellites are more likely to occur if the surface tension is relatively low.

[0086] Generally, when a drive waveform has a non-ejection waveform portion following the first ejection pulse placed at the end of an ejection pulse group, the waveform is often set with the purpose of suppressing meniscus reverberation and satellites, etc. When suppressing satellites, it is said to be effective to place two voltage swings, i.e., one non-ejection pulse, at the resonance position following the first ejection pulse.

[0087] Fig. 8 is a diagram showing an example of a conventional driving waveform, showing one driving cycle here. The horizontal axis of Fig. 8 indicates time (unit: μs), and the vertical axis indicates voltage (unit: V). The driving waveform W1 shown in Fig. 8 includes an ejection pulse P11, an ejection pulse P12, and a non-ejection pulse P13 within one driving cycle. The non-ejection pulse P13 is placed at the resonance position of the ejection pulse P12.

[0088] FIG. 9 shows a series of photographs taken at regular intervals with a strobe to show the flight of ink droplets ejected from the nozzle 54 when the driving waveform W1 is applied to the individual electrode 84 of the piezoelectric element 74. In FIG. 9, the vertical direction of the figure is the flight direction of the ink droplets, and the ink droplets fly from the top to the bottom of the figure. Also, photographs at each time are arranged in order along the horizontal direction of the figure. As a result, FIG. 9 shows the time series change of the ink droplets from the left side to the right side of the figure. As shown in FIG. 9, when the driving waveform W1 is applied, the non-ejection pulse P13 has the effect of pushing out the rear end of the liquid column, shortening the drawn thread and suppressing satellites. However, mist is generated when the drawn thread breaks. Also, a bulge occurs in the nozzle 54 after ejection due to the reverberation of the meniscus.

[0089] Fig. 10 is a diagram showing another example of a conventional driving waveform, similar to Fig. 8, for one driving cycle. The driving waveform W2 shown in Fig. 10 includes an ejection pulse P21, an ejection pulse P22, and a non-ejection pulse P23 in one driving cycle, and the non-ejection pulse P23 is arranged at a position in opposite phase to the resonance position of the ejection pulse P22.

[0090] Fig. 11 is a diagram similar to Fig. 9 showing a series of photographs of ink droplets when the driving waveform W2 is applied to the individual electrode 84 of the piezoelectric element 74. As shown in Fig. 11, when the driving waveform W2 is applied, the non-ejection pulse P23 applies a force in the opposite direction to the ink droplets being ejected, so that it is possible to break the string and suppress mist and reverberation of the meniscus. However, satellites are generated.

[0091] In this way, it was found that with only one non-ejection pulse for satellite suppression, i.e., only two voltage swings, the moment the thread breaks and the vibration of the meniscus are left to the movement of the fluid, resulting in the generation of a lot of mist and inability to suppress the reverberation of the meniscus. The generation of mist and the effects of the reverberation of the meniscus have a significant impact on stable ejection, so measures are necessary.

[0092] <Driving waveform of the present disclosure> The driving waveform of the present disclosure includes, within one driving cycle for applying ink droplets to the printing surface of the paper 1 to form one pixel, an ejection pulse group including one or more ejection pulses that cause ink droplets to be ejected from the nozzle 54, and three or more voltage swings that do not cause ink droplets to be ejected from the nozzle 54 after the ejection pulse group. In other words, an additional voltage swing is placed after the two voltage swings that do not cause ink droplets to be ejected. This suppresses mist and reverberation of the meniscus.

[0093] Fig. 12 is a diagram showing an example of a drive waveform of the present disclosure, similar to Fig. 8, for one drive cycle. The drive waveform W11 shown in Fig. 12 includes, within one drive cycle, an ejection pulse group GW1, a first voltage swing SW1, a second voltage swing SW2, a third voltage swing SW3, and a fourth voltage swing SW4.

[0094] The ejection pulse group GW1 includes a first ejection pulse PE1 that ejects ink droplets from the nozzle 54. The first ejection pulse PE1 has an amplitude of |VB-VL1| and a pulse width that is a resonant pulse width. As an example, the first ejection pulse PE1 has an amplitude of 30V and a pulse width of 2.4 μs. The pulse width of the first ejection pulse PE1 may be 80% or more and 120% or less of the resonant pulse width. The pulse width of the first ejection pulse PE1 may be 70% or more and 130% or less of the resonant pulse width, or 90% or more and 110% or less of the resonant pulse width. The first ejection pulse PE1 may be a triangular wave.

[0095] After the first ejection pulse PE1, which is the last ejection pulse of the ejection pulse group GW1, four voltage swings, namely, a first voltage swing SW1, a second voltage swing SW2, a third voltage swing SW3, and a fourth voltage swing SW4, are arranged (an example of an "arrangement of three or more"). The first voltage swing SW1, the second voltage swing SW2, the third voltage swing SW3, and the fourth voltage swing SW4 do not cause ink droplets to be ejected from the nozzle 54, respectively.

[0096] The first voltage swing SW1 is a falling slope where the voltage linearly decreases from the bias voltage VB to the voltage VL2 from timing t11 to timing t12. As an example, the time from timing t11 to timing t12 is 0.25 μs. The second voltage swing SW2 is a rising slope where the voltage linearly increases from the voltage VL2 to the bias voltage VB from timing t13 to timing t14.

[0097] The start end (timing t11) of the first voltage swing SW1 is located at a position separated by a first time T1 from the start end (timing t10) of the first ejection pulse PE1. The first time T1 is 80% or more and 120% or less of the resonant pulse period. The first time T1 may be 70% or more and 130% or less of the resonant pulse period, or 90% or more and 110% or less of the resonant pulse period.

[0098] Also, the start end (timing t13) of the second voltage swing SW2 is located at a position separated from the start end (timing t11) of the first voltage swing SW1 by the second time T2. The second time T2 is 80% or more and 120% or less of the resonant pulse width. The second time T2 may be 70% or more and 130% or less of the resonant pulse width, or 90% or more and 110% or less of the resonant pulse width. The first voltage swing SW1 and the second voltage swing SW2, together with the holding portion therebetween (timing t12 to timing t13), constitute a non-ejection pulse. The end of the first voltage swing SW1 may be the same timing t13 as the start end of the second voltage swing SW2. In this case, the first voltage swing SW1 and the second voltage swing SW2 constitute a triangular non-ejection pulse.

[0099] The third voltage swing SW3 is a falling slope where the voltage drops linearly from the bias voltage VB to the voltage VL3 from time t14 to time t15. The fourth voltage swing SW4 is a rising slope where the voltage rises linearly from the voltage VL3 to the bias voltage VB from time t16 to time t17.

[0100] The start of the third voltage swing SW3 (timing t14) is placed at a position separated by a third time T3 from the start of the first voltage swing SW1 (timing t11). The third time T3 is 80% or more and 120% or less of half the resonant pulse period. The third time T3 may be 70% or more and 130% or less of half the resonant pulse period, or 90% or more and 110% or less of half the resonant pulse period.

[0101] By locating the third voltage swing SW3 in such a position, it is possible to apply a force to cut the thread and suppress the generation of mist. The position of the third voltage swing SW3 is set to a position halfway through the resonance pulse period from the starting point of the first voltage swing SW1 as a reference, and it is preferable to locate it at a position around that position where the satellite suppression effect can be maximized while suppressing mist.

[0102] The start end (timing t16) of the fourth voltage swing SW4 is located at a position separated by a fourth time T4 from the start end (timing t11) of the first voltage swing SW1, or at a position separated by a fifth time T5 from the start end (timing t14) of the third voltage swing SW3. The fourth time T4 is 80% to 120% of an even multiple of the resonant pulse width, or 80% to 120% of an integer multiple of the resonant pulse period. The fourth time T4 may be 70% to 130% of an even multiple of the resonant pulse width, or 70% to 130% of an integer multiple of the resonant pulse period, or 90% to 110% of an even multiple of the resonant pulse width, or 90% to 110% of an integer multiple of the resonant pulse period. The fifth time T5 is 80% to 120% of an even multiple of the resonant pulse width, or 80% to 120% of an integer multiple of the resonant pulse period. The fifth time T5 may be 70% or more and 130% or less of an even multiple of the resonant pulse width, or 70% or more and 130% or less of an integer multiple of the resonant pulse period, or may be 90% or more and 110% or less of an even multiple of the resonant pulse width, or 90% or more and 110% or less of an integer multiple of the resonant pulse period.

[0103] By arranging the fourth voltage swing SW4 in such a position, it is possible to provide vibration in the opposite phase to the vibration of the meniscus, thereby suppressing the reverberation of the meniscus. It is preferable to arrange the fourth voltage swing SW4 in an effective position according to whether the reverberation of the first voltage swing SW1 and the second voltage swing SW2 or the reverberation of the third voltage swing SW3 remains.

[0104] The amplitudes of the first voltage swing SW1 and the second voltage swing SW2 are smaller than the amplitude of the first ejection pulse PE1. That is, there is a relationship of |VB-VL1|>|VB-VL2|. Here, there is a relationship of |VB-VL1|>|VB-VL2|×2.

[0105] Moreover, the amplitudes of the third voltage swing SW3 and the fourth voltage swing SW4 are smaller than the amplitudes of the first voltage swing SW1 and the second voltage swing SW2. That is, there is a relationship of |VB-VL2|>|VB-VL3|. Here, there is a relationship of |VB-VL1|>|VB-VL3|×3.

[0106] When the driving waveform W11 configured in this manner is applied to the individual electrode 84 of the piezoelectric element 74, first, the first ejection pulse PE1 ejects an ink droplet from the nozzle 54. Then, the first voltage swing SW1 and the second voltage swing SW2 cut the thread and suppress satellites.

[0107] Next, the mist is suppressed by the third voltage swing SW3, and further, the reverberation of the meniscus is suppressed by the fourth voltage swing SW4.

[0108] The ejected ink droplets land on the paper 1. As a result, one dot is formed on the printing surface of the paper 1. That is, the drive waveform W11 forms one pixel by the ejection pulse group GW1 contained in one drive cycle. Furthermore, satellites and mist are suppressed in this dot, making it possible to form a high-quality pixel. Furthermore, reverberation of the meniscus after ejection is suppressed, making it possible to improve the stability of ejection.

[0109] Fig. 13 is a diagram showing another example of the driving waveform of the present disclosure, similar to Fig. 8, for one driving cycle. The driving waveform W12 shown in Fig. 13 includes, within one driving cycle, an ejection pulse group GW2, a first voltage swing SW11, a second voltage swing SW12, a third voltage swing SW13, and a fourth voltage swing SW14.

[0110] The ejection pulse group GW2 includes a first ejection pulse PE11, a second ejection pulse PE12, a third ejection pulse PE13, and a fourth ejection pulse PE14 that eject ink droplets from the nozzle 54. The first ejection pulse PE11, the second ejection pulse PE12, the third ejection pulse PE13, and the fourth ejection pulse PE14 each have a bias voltage at the beginning and end. That is, the ejection pulse group GW2 returns to the bias voltage after all the ejection pulses are output.

[0111] The first ejection pulse PE11 is the last ejection pulse of the ejection pulse group GW2. The first ejection pulse PE11 has an amplitude of |VB-VL11| and a pulse width of the resonance pulse width.

[0112] The second ejection pulse PE12 is an ejection pulse immediately before the first ejection pulse PE11. The start end (timing t21) of the second ejection pulse PE12 is located at a position separated by a sixth time T6 from the start end (timing t23) of the first ejection pulse PE11. The sixth time T6 is 80% or more and 120% or less of the resonant pulse period. The sixth time T6 may be 70% or more and 130% or less of the resonant pulse period, or 90% or more and 110% or less of the resonant pulse period. The second ejection pulse PE12 has an amplitude of |VB-VL12| and a pulse width (timing t21 to timing t22) of a seventh time T7. The seventh time T7 is 80% or more and 120% or less of the resonant pulse width. The seventh time T7 may be 70% or more and 130% or less of the resonant pulse width, or 90% or more and 110% or less of the resonant pulse width.

[0113] The position of the starting end of the second ejection pulse PE12 is based on a position that is one resonance pulse period away from the starting end of the first ejection pulse PE11, and when that position is changed back and forth, it is preferable to place the satellite at a position where it comes closest to the main droplet when compared while keeping the speed of the main droplet the same.

[0114] The third ejection pulse PE13 is an ejection pulse immediately before the second ejection pulse PE12. The starting end of the third ejection pulse PE13 is located at a position about twice the resonance pulse period from the starting end of the second ejection pulse PE12. The third ejection pulse PE13 has an amplitude of |VB-VL11| and a pulse width of about the resonance pulse width.

[0115] In addition, between a position before the second ejection pulse PE12 and a position (timing t20) that is separated by an eighth time T8 from the start end (timing t21) of the second ejection pulse PE12, an ejection pulse that ejects ink droplets from the nozzle 54 and a non-ejection pulse that does not eject ink droplets from the nozzle 54 are not arranged. The eighth time T8 is 120% of the resonance pulse period. The eighth time T8 may be 130% of the resonance pulse period or 110% of the resonance pulse period. Here, the bias voltage VB is constant between the third ejection pulse PE13 and the second ejection pulse PE12. This makes it possible to suppress the speed of the ink droplets ejected by the second ejection pulse PE12 and to suppress satellites.

[0116] The fourth ejection pulse PE14 is an ejection pulse immediately before the third ejection pulse PE13. The starting end of the fourth ejection pulse PE14 is located at a position approximately one resonance pulse period away from the starting end of the third ejection pulse PE13. The fourth ejection pulse PE14 has an amplitude of |VB-VL11| and a pulse width of approximately the resonance pulse width.

[0117] The first voltage swing SW11, the second voltage swing SW12, the third voltage swing SW13, and the fourth voltage swing SW14 each prevent ink droplets from being ejected from the nozzle 54.

[0118] The arrangement of the first voltage swing SW11, the second voltage swing SW12, the third voltage swing SW13, and the fourth voltage swing SW14 is similar to the arrangement of the first voltage swing SW1, the second voltage swing SW2, the third voltage swing SW3, and the fourth voltage swing SW4 of the drive waveform W11, respectively.

[0119] That is, the start of the first voltage swing SW11 is located at a position separated by a first time T1 from the start of the first ejection pulse PE11, and the start of the second voltage swing SW12 is located at a position separated by a second time T2 from the start of the first voltage swing SW11. The third voltage swing SW13 is located at a position separated by a third time T3 from the start of the first voltage swing SW11. Furthermore, the start of the fourth voltage swing SW14 is located at a position separated by a fourth time T4 from the start of the first voltage swing SW11 or a position separated by a fifth time T5 from the start of the third voltage swing SW13.

[0120] Furthermore, the amplitudes of the first voltage swing SW11, the second voltage swing SW12, the third voltage swing SW13, and the fourth voltage swing SW14 are similar to the amplitudes of the first voltage swing SW1, the second voltage swing SW2, the third voltage swing SW3, and the fourth voltage swing SW4 of the drive waveform W11, respectively.

[0121] When the driving waveform W12 configured in this manner is applied to the individual electrode 84 of the piezoelectric element 74, first, four ink droplets are ejected from the nozzle 54 by each ejection pulse, which are generated by the first ejection pulse PE11, the second ejection pulse PE12, the third ejection pulse PE13, and the fourth ejection pulse PE14.

[0122] After that, the first voltage swing SW1 and the second voltage swing SW2 cut the thread and suppress the satellites. Next, the third voltage swing SW3 suppresses the mist. Furthermore, the fourth voltage swing SW4 suppresses the reverberation of the meniscus.

[0123] The four ink droplets ejected from the nozzle 54 merge before reaching the paper 1, and the merged ink droplet lands on the paper 1. As a result, one dot is formed on the printing surface of the paper 1. That is, the drive waveform W12 forms one pixel by the ejection pulse group GW2 contained in one drive cycle. This dot has suppressed satellites and mist, making it possible to form a high-quality pixel. In addition, since reverberation of the meniscus after ejection is suppressed, the stability of ejection can be improved.

[0124] Fig. 14 is a diagram showing another example of the driving waveform of the present disclosure, similar to Fig. 8, for one driving cycle. The driving waveform W13 includes an ejection pulse group GW3, a first voltage swing SW21, a second voltage swing SW22, and a third voltage swing SW23 within one driving cycle.

[0125] The ejection pulse group GW3 includes a first ejection pulse PE21, a second ejection pulse PE22, a third ejection pulse PE23, and a fourth ejection pulse PE24, which cause the nozzle 54 to eject ink droplets.

[0126] The arrangement and pulse widths of the first ejection pulse PE21, the second ejection pulse PE22, the third ejection pulse PE23, and the fourth ejection pulse PE24 are similar to those of the first ejection pulse PE11, the second ejection pulse PE12, the third ejection pulse PE13, and the fourth ejection pulse PE14 of the driving waveform W12, respectively.

[0127] The second ejection pulse PE22, the third ejection pulse PE23, and the fourth ejection pulse PE24 each have a start point and an end point VL21, and an amplitude |VL21-VL22|. In this way, the second ejection pulse PE22, the third ejection pulse PE23, and the fourth ejection pulse PE24 each have an amplitude without returning to the bias voltage. In this way, the ejection pulse group GW3 may not have the voltage of the ejection pulse return to the bias voltage.

[0128] The first ejection pulse PE21 has a starting edge VL21 and a falling slope with an amplitude of |VL21-VL22|. The first ejection pulse PE21 has a rear edge at the bias voltage VB and a rising slope with an amplitude of |VB-VL22|.

[0129] The first voltage swing SW21, the second voltage swing SW22, and the third voltage swing SW23 each prevent ink droplets from being ejected from the nozzle 54.

[0130] The first voltage swing SW21 is a falling slope where the voltage drops linearly from the bias voltage VB to the voltage VL21 from timing t31 to timing t32. The second voltage swing SW22 is a rising slope where the voltage rises linearly from the voltage VL21 to the bias voltage VB from timing t33 ​​to timing t34.

[0131] The starting edge of the first voltage swing SW21 is located at a position separated by a first time T1 from the starting edge of the first ejection pulse PE21, and the starting edge of the second voltage swing SW22 is located at a position separated by a second time T2 from the starting edge of the first voltage swing SW21. The first voltage swing SW21 and the second voltage swing SW22, together with the holding portion therebetween (timing t32 to timing t33), constitute a non-ejection pulse.

[0132] The third voltage swing SW23 has a falling slope in which the voltage linearly decreases from the bias voltage VB to the voltage VL21 from timing t35 to timing t36. The starting point of the third voltage swing SW23 is located at a position separated by a third time T3 from the starting point of the first voltage swing SW21.

[0133] A fourth voltage swing may be provided after the third voltage swing SW23. The start of the fourth voltage swing is located at a position separated by a fourth time T4 from the start of the first voltage swing SW21 or at a position separated by a fifth time T5 from the start of the third voltage swing SW23.

[0134] The fourth voltage swing may be a rising slope in which the voltage rises from the voltage VL21 to the bias voltage VB. In this case, after the fourth voltage swing, a falling slope in which the voltage drops from the bias voltage VB to the voltage VL21 may be provided.

[0135] In addition, the third voltage swing SW23 may be a falling slope in which the voltage drops from the bias voltage VB to a voltage lower than the voltage VL21 (e.g., voltage VL23), and the fourth voltage swing may be a rising slope in which the voltage increases from that voltage (e.g., voltage VL23) to the voltage VL21.

[0136] The driving waveform W13 thus configured can also achieve the same effects as the driving waveforms W11 and W12.

[0137] <Effect of driving waveform> Fig. 15 is a photograph taken with a strobe, showing the flight of ink droplets ejected from the nozzle 54 when the drive waveform W13 is applied to the individual electrode 84 of the piezoelectric element 74. F15A in Fig. 15 shows the occurrence of mist when the position of the starting end of the third voltage swing SW23 is relatively far from the reference position which is half the resonance pulse period away from the starting end of the first voltage swing SW21. Moreover, F15B in Fig. 15 shows the occurrence of mist when the position of the starting end of the third voltage swing SW23 is relatively close to the reference position.

[0138] 15, by locating the third voltage swing SW23 at a position close to the reference position, it is possible to suppress the generation of mist. The position of the start end of the third voltage swing SW23 can be adjusted within a range of 80% to 120% based on the reference position. The position of the start end of the third voltage swing SW23 may be adjusted within a range of 70% to 130% based on the reference position.

[0139] Figure 16 is a series of photographs taken with a strobe at regular intervals, showing the flight of ink droplets ejected from the nozzle 54 when each waveform element of the driving waveform W13 is applied to the individual electrode 84 of the piezoelectric element 74, and is shown in the same manner as Figure 9.

[0140] F16A in Fig. 16 shows a case where only the first ejection pulse PE21 is applied. In this case, it can be seen that the drawn thread is relatively long and not uniform.

[0141] 16 shows a case where the first ejection pulse PE21 and the second ejection pulse PE22 are applied, and the starting end of the second ejection pulse PE22 is positioned at a position separated by the resonance pulse period from the starting end of the first ejection pulse PE21. In the case of F16B, it can be seen that the ink droplets ejected by the first ejection pulse PE21 and the ink droplets ejected by the second ejection pulse PE22 are united, but the satellites are not united.

[0142] 16 shows a case where the first ejection pulse PE21 and the second ejection pulse PE22 are applied, and the position of the starting end of the second ejection pulse PE22 is shifted from that of F16B. Here, the starting end of the second ejection pulse PE22 is positioned at 80% of the resonance pulse period from the starting end of the first ejection pulse PE21. In the case of F16C, it can be seen that the ink droplets ejected by the first ejection pulse PE21 and the ink droplets ejected by the second ejection pulse PE22 are closer to the satellite main droplets than in the case of F16B.

[0143] In this way, by adjusting the position of the second ejection pulse PE22, the satellites can be better gathered. The starting end of the second ejection pulse PE22 can be adjusted in a range of 80% to 120% based on the resonance pulse period from the starting end of the first ejection pulse PE21. The starting end of the second ejection pulse PE22 may be adjusted in a range of 70% to 130% based on the resonance pulse period from the starting end of the first ejection pulse PE21. By adjusting in such a range, the flying state can be adjusted while maintaining similar properties.

[0144] 16 shows a case where the first ejection pulse PE21, the second ejection pulse PE22, the first voltage swing SW21, and the second voltage swing SW22 are applied. In the case of F16D, it can be seen that the main droplet, which is the ink droplet ejected by the first ejection pulse PE21 and the ink droplet ejected by the second ejection pulse PE22, is united with the satellite. In this way, the satellite is improved by the first voltage swing SW21 and the second voltage swing SW22.

[0145] As described above, satellites can be suppressed by the first voltage swing SW21 and the second voltage swing SW22, and mist can be suppressed by the third voltage swing SW23. Furthermore, better results can be obtained by adjusting the positions of the ejection pulse and the voltage swing.

[0146] Different surface tensions of ink result in different effects of the driving waveform of the present disclosure. Currently, the surface tension of ink that achieves a state without satellites even with a conventional driving waveform that does not apply the driving waveform of the present disclosure is 35 mN / m or more. Therefore, the effect of the driving waveform of the present disclosure is large when the surface tension of the ink is 35 mN / m or less. The surface tension of the ink used in the experiments described so far is 29 mN / m, and satellites are generated with a driving waveform that does not apply the driving waveform of the present disclosure, so the effect of the driving waveform of the present disclosure is even greater at 30 mN / m or less. Note that the surface tension of the ink is preferably 20 mN / m or more.

[0147] The surface tension of the ink can be measured at room temperature using an automatic surface tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

[0148] <Other> The technical scope of the present invention is not limited to the scope described in the above embodiments. The configurations and the like in each embodiment can be appropriately combined with each other without departing from the spirit of the present invention. [Explanation of symbols]

[0149] 1. Paper 10...Inkjet printing device 20...Transport drum 30...Image recording unit 32...Image recording drum 32A…Gripper 34...Paper pressure roller 36…Inkjet head 36C...Inkjet head 36K...Inkjet head 36M…Inkjet head 36Y…Inkjet head 38…Imaging unit 40...Transport drum 50A…Nozzle surface 52...Head module 53…Base frame 54…Nozzle 70…Ejector 72...Pressure chamber 74...Piezoelectric element 76…Nozzle flow passage 78…Individual supply route 80…Supply side common tributary channel 82…Diaphragm 84...Individual electrode 86...Piezoelectric body 88…Cover plate 90…Movable space 100...System controller 100A…Processor 100B…Memory 102…Communications Department 104…Image memory 106...Transport control unit 108...Image recording control unit 110…Inspection Department 112...Operation unit 114...Display section 120...Waveform generation section 122…Digital-to-analog conversion section 124...Pulse selection switch 126…Switch controller 128...Bias resistor 200...host computer C1…Holding part C2…Holding part C3…Holding part GW1…Ejection pulse group GW2: Ejection pulse group GW3…Ejection pulse group P1...Pulse P2...Pulse P11…Ejection pulse P12…Ejection pulse P13…Non-ejection pulse P21…Ejection pulse P22…Ejection pulse P23…Non-ejection pulse PE1: First discharge pulse PE11…First ejection pulse PE12: Second discharge pulse PE13…Third ejection pulse PE14…4th ejection pulse PE21…First ejection pulse PE22: Second discharge pulse PE23…Third ejection pulse PE24: 4th ejection pulse SL1…Slope SL2…Slope SL3…Slope SL4…Slope SW1…First voltage swing SW2: Second voltage swing SW3…Third voltage swing SW4…4th voltage swing SW11…First voltage swing SW12…Second voltage swing SW13…Third voltage swing SW14…4th voltage swing SW21…First voltage swing SW22…Second voltage swing SW23…Third voltage swing W…Drive waveform W1…Drive waveform W2…Drive waveform W11…Drive waveform W12…Drive waveform W13…Drive waveform

Claims

1. one or more processors; one or more memories storing instructions for execution by the one or more processors; Equipped with The processor, a liquid ejection head including a nozzle for ejecting liquid droplets, a pressure chamber communicating with the nozzle, and a liquid ejection element for pressurizing the liquid in the pressure chamber in response to the supplied drive waveform; The driving waveform is a voltage swing that does not cause the nozzle to eject a droplet, and a group of ejection pulses including one or more ejection pulses that cause the nozzle to eject a droplet within one drive cycle; three or more of the voltage swings are arranged after a first ejection pulse that is the last ejection pulse of the ejection pulse group; a start of a first voltage swing immediately following the first ejection pulse is positioned at a first time from the start of the first ejection pulse; a starting point of a second voltage swing immediately following the first voltage swing is disposed at a position spaced a second time from the starting point of the first voltage swing; When a period of the two ejection pulses at which the velocity of the ejected droplets is the fastest is defined as a resonance pulse period, the first time is 80% or more and 120% or less of the resonance pulse period, When a pulse width of one ejection pulse at which the velocity of the ejected droplet is the fastest is defined as a resonance pulse width, the second time period is 80% or more and 120% or less of the resonance pulse width. Driving waveform generator.

2. a starting edge of a third voltage swing, which is the voltage swing immediately after the second voltage swing of the driving waveform, is disposed at a position spaced a third time from the starting edge of the first voltage swing; The third time is 80% or more and 120% or less of half the resonant pulse period.

2. The drive waveform generating device according to claim 1.

3. a starting point of a fourth voltage swing, which is the voltage swing immediately after the third voltage swing of the drive waveform, is disposed at a position spaced a fourth time from the starting point of the first voltage swing or a position spaced a fifth time from the starting point of the third voltage swing; the fourth time period is 80% or more and 120% or less of an even multiple of the resonance pulse width, or 80% or more and 120% or less of an integer multiple of the resonance pulse period, The fifth time is 80% or more and 120% or less of an even multiple of the resonance pulse width, or 80% or more and 120% or less of an integer multiple of the resonance pulse period. The drive waveform generating device according to claim 2 .

4. a starting edge of a second ejection pulse, which is the ejection pulse immediately before the first ejection pulse of the driving waveform, is disposed at a position spaced apart from the starting edge of the first ejection pulse by a sixth time, and a pulse width of the second ejection pulse is a seventh time; the sixth time period is equal to or greater than 80% and equal to or less than 120% of the resonance pulse period, The seventh time is equal to or greater than 80% and equal to or less than 120% of the resonance pulse width.

2. The drive waveform generating device according to claim 1.

5. the drive waveform is such that the ejection pulse and a non-ejection pulse that does not cause droplets to be ejected from the nozzle are not disposed between a position before the second ejection pulse and a position that is separated by eight hours from the starting end of the second ejection pulse, The eighth time is 120% of the resonant pulse period.

5. The drive waveform generating device according to claim 4.

6. The liquid has a surface tension of 35 mN / m or less.

2. The drive waveform generating device according to claim 1.

7. The liquid has a surface tension of 30 mN / m or less.

2. The drive waveform generating device according to claim 1.

8. A drive waveform generating device according to any one of claims 1 to 7, a liquid ejection head having a nozzle for ejecting droplets, a pressure chamber communicating with the nozzle, and a droplet ejection element for pressurizing the liquid in the pressure chamber in response to a supplied drive waveform; Equipped with the processor supplies the drive waveform generated by the drive waveform generating device to the droplet ejection element to eject droplets from the nozzle; Liquid discharge device.

9. The liquid ejection device according to claim 8 ; a relative movement mechanism for moving the liquid ejection head and the substrate relative to each other; Equipped with The processor, The liquid ejection head and the substrate are moved relative to each other to eject liquid droplets from the nozzles, thereby printing an image on the substrate. Printing device.

10. A method for generating a drive waveform executed by one or more processors, comprising: the one or more processors: a nozzle for ejecting droplets, a pressure chamber communicating with the nozzle, and a droplet ejection element for pressurizing the liquid in the pressure chamber in response to the supplied drive waveform; The driving waveform is a voltage swing that does not cause the nozzle to eject a droplet, and a group of ejection pulses including one or more ejection pulses that cause the nozzle to eject a droplet within one drive cycle; three or more of the voltage swings are arranged after a first ejection pulse that is the last ejection pulse of the ejection pulse group; a start of a first voltage swing immediately following the first ejection pulse is positioned at a first time from the start of the first ejection pulse; a starting point of a second voltage swing immediately following the first voltage swing is disposed at a position spaced a second time from the starting point of the first voltage swing; When a period of the two ejection pulses at which the velocity of the ejected droplets is the fastest is defined as a resonance pulse period, the first time is 80% or more and 120% or less of the resonance pulse period, When a pulse width of one ejection pulse at which the velocity of the ejected droplet is the fastest is defined as a resonance pulse width, the second time period is 80% or more and 120% or less of the resonance pulse width. A driving waveform generation method.

11. A program for causing a computer to execute the drive waveform generating method according to claim 10.

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