Inkjet head drive control method and inkjet recording device

Abstract

The present invention provides a drive control method for an inkjet head and an inkjet recording device, capable of obtaining an inkjet head that can be utilized by more widely reducing the variation in discharge characteristics. The drive control method for an inkjet head includes a plurality of recording elements, each of which includes a nozzle and a drive element that applies pressure fluctuations to ink in the nozzle in response to a drive pulse. A reference pulse width, at which a predetermined characteristic value associated with ink droplets discharged from each recording element in response to the drive pulse reaches a maximum relative to a variation in pulse width, has a deviation greater than a predetermined reference. The drive control method for the inkjet head includes a pulse width setting step. In the pulse width setting step, a first drive pulse having a longer pulse width than the reference pulse width and a second drive pulse having a shorter pulse width than the reference pulse width are combined for each of the plurality of recording elements, while ensuring that ink droplets discharged in response to two or more drive pulses land within the same pixel range. The combined pulses are output to the plurality of recording elements.

Description

Technical Field

[0001] The present invention relates to a drive control method for an inkjet head and an inkjet recording device. Background Art

[0002] Inkjet recording devices, which discharge ink droplets from nozzles to form desired images, structures, thin films, and the like on media, employ techniques that vary the density and grayscale of each pixel by causing multiple continuously discharged ink droplets to merge midway or land within the same pixel area. Inkjet recording devices exhibit variations in ink discharge characteristics between nozzles. In particular, when multiple ink droplets are continuously discharged, the effects of previous discharges can easily affect subsequent discharges, resulting in significant variations and complexity.

[0003] To reduce the impact of this variation, there is a technology that adjusts the electrical signal (drive pulse) used to drive each drive element, causing the pressure fluctuations in the ink within the nozzle. Patent Document 1 also discloses a technology that aligns the ink droplet volume and landing timing by adjusting the falling timing of the drive waveform within the drive pulse of each drive element.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-226201 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] However, conventionally, inkjet heads with ink ejection characteristics exceeding the standard were treated as substandard products. The increase in the number of nozzles and the higher requirements for ink ejection characteristics have led to reduced inkjet head yields and increased costs.

[0009] An object of the present invention is to provide a drive control method for an inkjet head and an inkjet recording apparatus, which can provide an inkjet head that can be used more widely while reducing variations in discharge characteristics.

[0010] Solutions to Problems

[0011] In order to achieve the above-mentioned purpose, the invention described in Technical Solution 1 is:

[0012] A method for controlling the driving of an inkjet head, wherein the inkjet head includes a plurality of recording elements, each of which includes a nozzle for discharging ink and a driving element for applying pressure fluctuations to the ink supplied to the nozzle according to an applied driving pulse, wherein:

[0013] A predetermined characteristic value associated with each ink droplet ejected from the recording element in response to a driving pulse applied to the driving element becomes maximum with respect to a change in the pulse width of the driving pulse, and a reference pulse width of the driving pulse has a deviation greater than a predetermined reference.

[0014] The drive control method of the inkjet head includes a pulse width setting step. In the pulse width setting step, when the specified number of ink droplets discharged according to more than two specified numbers of drive pulses are caused to fall within the same pixel range, for each of the multiple recording elements, a first drive pulse having a pulse width longer than the reference pulse width and a second drive pulse having a pulse width shorter than the reference pulse width are combined into the specified number and output to each of the multiple recording elements.

[0015] In addition, the invention described in claim 2 is the drive control method described in claim 1,

[0016] In the pulse width setting step, the first drive pulse having a pulse width longer than any of the reference pulse widths associated with each of the plurality of recording elements and the second drive pulse having a pulse width shorter than any of the reference pulse widths are determined.

[0017] In addition, the invention described in claim 3 is the drive control method described in claim 2,

[0018] In the pulse width setting step, the pulse width of the first drive pulse and the pulse width of the second drive pulse are determined commonly for the plurality of recording elements.

[0019] Furthermore, the invention according to claim 4 is the drive control method according to any one of claims 1 to 3.

[0020] In the pulse width setting step, the order of the first drive pulse and the second drive pulse is determined so that the pulse width closer to the reference pulse width corresponding to the smallest characteristic value among the maximum characteristic values ​​involved in the plurality of recording elements becomes the last drive pulse.

[0021] Furthermore, the invention according to claim 5 is the drive control method according to any one of claims 1 to 4 , wherein the predetermined characteristic value is a velocity of a droplet of discharged ink.

[0022] Furthermore, the invention according to claim 6 is the drive control method according to any one of claims 1 to 4 , wherein the predetermined characteristic value is the amount of discharged ink droplets.

[0023] Furthermore, the invention according to claim 7 is the drive control method according to any one of claims 1 to 6 , wherein the predetermined reference related to the deviation is 3%.

[0024] In addition, the invention described in claim 8 is the drive control method according to any one of claims 1 to 7.

[0025] The prescribed number is an even number,

[0026] In the pulse width setting step, the first drive pulse and the second drive pulse are determined to be output alternately.

[0027] In addition, the invention described in technical solution 9 is as follows:

[0028] An inkjet recording device, wherein the inkjet recording device comprises:

[0029] an inkjet head having a plurality of recording elements including nozzles for discharging ink and drive elements for applying pressure fluctuations to the ink supplied to the nozzles in response to applied drive pulses; and

[0030] a control unit that controls output of the drive pulse applied to the drive element to the recording element,

[0031] A predetermined characteristic value associated with each ink droplet ejected from the recording element in response to a driving pulse applied to the driving element becomes maximum with respect to a change in the pulse width of the driving pulse, and a reference pulse width of the driving pulse has a deviation greater than a predetermined reference.

[0032] When making the specified number of ink droplets discharged respectively according to more than two specified numbers of driving pulses fall within the same pixel range, the control unit combines the specified number of first driving pulses having a pulse width longer than the reference pulse width and second driving pulses having a pulse width shorter than the reference pulse width for each of the multiple recording elements, and outputs the combined combination to each of the multiple recording elements.

[0033] The predetermined characteristic value associated with each ink droplet ejected from the recording element in response to the driving pulse applied to the driving element becomes maximum with respect to the change in the pulse width of the driving pulse, and the reference pulse width of the driving pulse has a deviation greater than a predetermined reference.

[0034] According to the present invention, there is an effect of being able to more easily reduce variations in discharge characteristics among nozzles. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1It is a perspective view showing a schematic structure of an inkjet recording device.

[0036] Figure 2 It is a bottom view showing the bottom surface of the head unit facing the conveyor belt.

[0037] Figure 3 This is a block diagram showing the functional structure of an inkjet recording device.

[0038] Figure 4A This is a diagram for explaining the discharge pulse.

[0039] Figure 4B This is a diagram for explaining the discharge pulse.

[0040] Figure 5A This is a diagram showing an example of a driving waveform when ink is discharged a plurality of times continuously.

[0041] Figure 5B This is a diagram showing an example of a driving waveform when ink is discharged a plurality of times continuously.

[0042] Figure 6A This is a diagram showing an example of the distribution of discharge speeds of a plurality of nozzles in an inkjet head.

[0043] Figure 6B This is a diagram showing an example of the distribution of discharge speeds of a plurality of nozzles in an inkjet head.

[0044] Figure 7A This is a diagram showing an example of the discharge speed distribution when the amount of change in the pulse width is varied.

[0045] Figure 7B This is a diagram showing an example of the discharge speed distribution when the amount of change in the pulse width is varied.

[0046] Figure 8A This is a diagram explaining the variation in sensitivity between nozzles.

[0047] Figure 8B This is a diagram explaining the variation in sensitivity between nozzles.

[0048] Figure 9 This is a diagram showing an example of the distribution of discharge speeds according to the order of pulse widths in a case where nozzles having different sensitivities are included.

[0049] Figure 10 This is a flowchart showing the control procedure of the drive waveform setting process executed by the inkjet recording apparatus. DETAILED DESCRIPTION

[0050] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0051] Figure 1 It is a perspective view showing a schematic configuration of the inkjet recording apparatus 1 according to this embodiment.

[0052] The inkjet recording apparatus 1 includes a transport unit 10 , a recording operation unit 20 , a control unit 40 , an imaging unit 50 , and the like.

[0053] The transport unit 10 moves the medium M on which an image is to be recorded and discharges the medium M through the image recording position. The transport unit 10 includes a driving roller 11, a transport belt 12, a driven roller 13, a transport motor 14, a pressing roller 15, and the like.

[0054] Here, the conveyor belt 12 is annular and is mounted between a driving roller 11 and a driven roller 13. It moves according to the rotation of the driving roller 11. The driving roller 11 rotates at a speed corresponding to the rotation of the conveying motor 14. The driven roller 13 rotates at a speed corresponding to the movement of the conveyor belt 12. On the outer peripheral surface of the conveyor belt 12, a medium M is placed at a predetermined position, and an image is recorded while the medium moves. After the image is recorded, the medium is discharged at a predetermined position. The pressing roller 15 presses the medium M placed on the conveyor belt 12 against the conveyor belt 12, thereby removing any warping of the medium M caused by wrinkles, etc. The pressing roller 15 can press the medium M against the conveyor belt 12 by its own weight and rotate according to the movement of the medium M and the conveyor belt 12.

[0055] The recording unit 20 has multiple nozzles that discharge ink onto the medium M on the conveyor belt 12, recording an image based on the timing and amount of ink discharged from each nozzle. While not particularly limited, here, the recording unit 20 includes a head unit 21C that discharges cyan ink, a head unit 21M that discharges magenta ink, a head unit 21Y that discharges yellow ink, and a head unit 21K that discharges black ink, enabling it to discharge ink in four colors. Hereinafter, some or all of these units will be referred to as head units 21.

[0056] The control unit 40 comprehensively controls the entire operation of the inkjet recording apparatus 1. The control unit 40 will be described later.

[0057] The imaging unit 50 images the surface of the conveyor belt 12 (the medium M placed thereon) downstream of the recording unit 20 in the direction in which the medium M is conveyed on the conveyor belt 12 by the conveyor unit 10. The imaging unit 50 is, for example, a line sensor comprising CCD (Charge-Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) imaging elements arranged in the width direction. This imaging unit 50 is capable of capturing two-dimensional images of the medium M in combination with the movement of the medium M in the conveyance direction.

[0058] Figure 2It is a bottom view showing the surface (bottom surface) of the head unit 21 facing the conveyor belt 12. In addition, since the head units 21C, 21M, 21Y, and 21K have the same structure, any one of them will be described here.

[0059] The head unit 21 is fixed to the carriage 210. The nozzle surfaces of the 16 inkjet heads 211 included in each head unit 21 are exposed on the bottom surface of the head unit 21. Multiple nozzle openings 27a are arranged on the nozzle surface. The openings 27a are arranged at predetermined intervals (nozzle pitch) in the width direction, and the discharged ink is sprayed onto various positions in the width direction of the medium M being transported.

[0060] Figure 3 1 is a block diagram showing the functional configuration of the inkjet recording apparatus 1 .

[0061] The inkjet recording device 1 includes, in addition to the above-mentioned transport unit 10, recording operation unit 20, control unit 40 and imaging unit 50, a drive waveform signal generating unit 29, a storage unit 30, a communication unit 70, an operation receiving unit 81, a display unit 82 and a power supply unit 90.

[0062] As described above, the transport unit 10 includes the transport motor 14 , and the transport motor 14 is rotated by outputting an appropriate drive signal to the transport motor 14 .

[0063] The recording unit 20 includes a head drive unit 25 and a piezoelectric element 26 (driving element). The head drive unit 25 applies a driving signal (driving pulse) to a selected piezoelectric element 26, causing the piezoelectric element 26 to deform. Consequently, the piezoelectric element 26 applies a pressure change corresponding to the driving pulse to the ink supplied to the nozzle 27, causing the ink to be ejected from the nozzle 27, thereby recording an image. The piezoelectric element 26 and the nozzle 27 constitute the recording element 200 of this embodiment. The recording unit 20 has a plurality of recording elements 200 corresponding to the number of nozzles 27.

[0064] The drive waveform signal generating unit 29 generates drive pulses that the head driving unit 25 outputs to the recording element 200. Although not particularly limited, the drive waveform signal generating unit 29 performs analog conversion on digital data representing a predetermined drive waveform, amplifies the voltage and current, and outputs the resulting signal as a drive pulse to the head driving unit 25.

[0065] The control unit 40, comprising a CPU 41 (Central Processing Unit) and a RAM 42 (Random Access Memory), is a processor that comprehensively controls various operations of the inkjet recording device 1. The CPU 41 performs various calculations to execute control operations. The RAM 42 provides the CPU 41 with operating memory and temporarily stores data. The control unit 40 controls the output of drive pulses for ink ejection from the inkjet head 211 to the recording element 200 based on the image data of the recording target and setting data related to image recording.

[0066] The storage unit 30 stores image data of the recording object, as well as various programs and setting data. The storage unit 30 includes at least non-volatile memory and may also include volatile memory (RAM). Image data may also be stored in RAM. The setting data includes AL (Acoustic Length) measurement data 31 and waveform setting data 32. Non-volatile memory may be, for example, flash memory, and may also include an HDD (Hard Disk Drive) or the like in addition to or instead of flash memory.

[0067] The AL measurement data 31 stores the measured value of the actual AL (reference pulse width) involved in the ink in each nozzle 27 (including the ink flow path connected to the nozzle 27). AL is half of the resonance period (acoustic resonance period) of the pressure vibration generated by the ink (fluid) in the nozzle 27. This AL depends on the structure of the nozzle 27, that is, the length, width, etc. In addition, since the nozzle and the ink flow path are connected to the common ink supply path further upstream, it is sometimes slightly deviated from the theoretically correct value. In addition, there are slight deviations in the structure during manufacturing, and AL also deviates slightly according to the deviation. The AL measurement data 31 may not include the AL of all nozzles 27, and it is sufficient to store the AL obtained by sampling at a specified interval, etc., and also by locally reducing the interval as needed.

[0068] The waveform setting data 32 stores waveform pattern data for the drive pulses output to each recording element 200. The waveform pattern data stored here specifically includes information on the start timing, pulse width, and voltage amplitude of the drive pulses corresponding to each ink ejection when multiple ink ejections are performed continuously. This information can be digital data that forms the basis for the drive pulses generated by the drive waveform signal generator 29.

[0069] The communication unit 70 controls communications with external devices. For example, the communication unit 70 can connect to an external computer based on a communication standard such as TCP / IP, acquire job data including the image data to be recorded, and output the status of the image recording operation based on the job data. Alternatively, the communication unit 70 can directly connect to peripheral devices via a USB (Universal Serial Bus) or other means to transmit and receive data.

[0070] The operation receiving unit 81 receives input operations from a user or the like and outputs the received information as an input signal to the control unit 40. The operation receiving unit 81 includes, for example, a touch panel, a push button switch, etc. The touch panel may be located at a position overlapping the display screen of the display unit 82, and the operation content may be determined synchronously with the content displayed on the display screen.

[0071] The display unit 82 displays information such as status and menu selections to the user. The display unit 82 includes, for example, a display screen and indicators (lights). The display unit 82 includes, for example, a liquid crystal display (LCD), capable of displaying various text and graphics in a dot matrix format on the display screen. The indicators can also be used to indicate, for example, the presence of power supply or the presence of operational abnormalities using LED lights.

[0072] The power supply unit 90 supplies power at voltages corresponding to the various components of the inkjet recording device 1. It outputs voltages corresponding to the peak voltages of the various drive waveforms to the drive substrate 212 of the recording operation unit 20. Alternatively, it may output only the maximum peak voltage, generating multiple voltage signals on the drive substrate 212.

[0073] In addition to the above-described configurations, the inkjet recording apparatus 1 may also include a measuring unit for measuring the ink discharge speed from each nozzle 27. Alternatively, a mounting unit for the measuring unit may be externally mounted to the inkjet recording apparatus 1 to measure the ink discharge speed from each nozzle 27. It should be noted that the discharge speed may be determined based on the landing position based on the image data captured by the image capturing unit 50, rather than directly measuring the ink flight speed.

[0074] Next, the drive settings related to the ink ejection operation in the inkjet recording apparatus 1 of this embodiment will be described.

[0075] Figure 4A as well as Figure 4B This is a diagram for explaining the discharge pulse.

[0076] like Figure 4AAs shown, here, by applying a trapezoidal (or rectangular) wave drive pulse to the piezoelectric element 26, the ink supplied to the nozzle 27 is temporarily compressed or expanded in the ink flow path (ink chamber) immediately before the nozzle 27, and then returns, imparting pressure fluctuations to the ink, thereby performing the ink discharge operation. It should be noted that for ease of explanation, the rise and fall of the trapezoidal wave voltage from the initial voltage and back to the initial voltage are represented with easily understandable lengths. However, the rise and fall times compared to the maintenance period of the drive voltage can also be appropriately determined.

[0077] When ink is discharged from the nozzle 27, the ink that is squeezed out of the opening 27a by the push action that compresses the ink flow path is separated from the ink that is pulled back into the ink flow path by the action of volume recovery of the ink flow path, causing it to fly. When the ink is pulled out of the nozzle 27 by the pull action that expands the ink flow path, the ink that was pulled back into the flow path from the opening 27a of the nozzle 27 by the action of volume recovery of the ink flow path is violently returned toward the opening 27a of the nozzle 27. As a result, a portion of the ink at the leading end flies out of the opening 27a, separates, and flies.

[0078] During this pressure fluctuation, the ink experiences a periodic vibration component corresponding to the aforementioned ΔL. By applying a drive pulse with a pulse width of ΔL (here, the time from the rise to the fall of the drive pulse in the trapezoidal drive wave is referred to as pulse width Pw), the kinetic energy of the ink can be efficiently extracted from the drive pulse.

[0079] like Figure 4B As shown, depending on the applied pulse width, in particular, the greater the deviation of the pulse width from the actual AL involved in the nozzle 27, the lower (changed) the discharge speed (characteristic value). The deviation of the discharge speed from the actual AL relative to the pulse width can be approximated by, for example, a quadratic to cubic curve (or a function of higher order). Depending on the deviation of AL between the multiple nozzles 27 (here, two types are illustrated by thick and thin lines), an offset also occurs in the position of the approximate curve. Generally, if the discharge speed of the ink under a specified representative value Pw0 does not produce a deviation above the baseline between the nozzles 27, the inkjet head 211 having the nozzle 27 can be used. As the representative value Pw0, for example, the AL of the nozzle located in the center of the arrangement of the nozzles 27 is selected.

[0080] Figure 5A as well as Figure 5B This is a diagram showing an example of a driving waveform when ink is discharged a plurality of times continuously.

[0081] like Figure 5AAs shown, in the inkjet recording device 1, the ink concentration (grayscale) of each pixel range is determined in multiple stages by merging ink (multiple droplets of ink) ejected multiple times (a predetermined number greater than two) in flight or by causing them to land separately within a predetermined pixel range on the medium M. When multiple ejection operations are performed with a discharge period Pe1 twice as long as the pulse width Pw1 and AL, the vibrations of the ink from the previous ejection operation are amplified (resonated) during the second and subsequent ejections due to the reverberation of the amplitude of the ink from the previous ejection operation, thereby increasing the ejection speed. On the other hand, if the pulse width Pw1 and AL are not equal, or if the discharge period Pe1 is not twice the pulse width Pw1 or AL, the ejection speed may not increase after the second and subsequent ejection operations, resulting in a decrease in the vibrations and a decrease in the ejection speed. In other words, compared to a single ejection, the variation in ejection speed can be increased in multiple consecutive ejections due to the relationship between the set pulse width and the actual AL of each nozzle.

[0082] In the inkjet recording device 1 of the present embodiment, for example, the deviation of the reference pulse width (actual AL) in which the ink droplet velocity (predetermined characteristic value related to the ink droplet) takes a maximum value relative to the change in pulse width, that is, the inkjet head 211 in which the ink droplet velocity (predetermined characteristic value related to the ink droplet) under the actual AL is large enough to be non-negligible in terms of image quality (above the prescribed reference corresponding to the image quality) can also be used. In addition, a reference in which the droplet discharge speed under the driving pulse having the pulse width of the above-mentioned representative value Pw0 (AL of the center nozzle) increases above the prescribed reference can also be simply used. In the inkjet recording device 1, in the case of continuous discharge and landing of the same pixel range multiple times (especially an even number of times) (including the case of merging in the middle), as Figure 5BAs shown, the first pulse width Pw1 and the second pulse width Pw2 are made different. Image quality issues caused by variations in discharge velocity manifest, for example, as shifts in the ink landing position, instability in ink droplet flight caused by excessively low ink velocity, and variations in ink penetration, diffusion, and fixation on the medium M during landing. Because the amount of ink landing position shift depends on factors such as the moving speed (conveying speed) of the flying medium M, a predetermined reference is not uniformly defined. For example, a reference can be determined based on the maximum medium M travel speed achievable by the inkjet recording apparatus 1. In current inkjet recording apparatuses 1, a reference for such a shift in landing position (droplet velocity) can be set to, for example, 3%. Furthermore, if the number of consecutive ejections, the conveying speed, and the like (collectively referred to as the operating conditions) may result in a mixture of situations where the predetermined criteria are met and situations where the predetermined criteria are not met, the inkjet head 211 can be controlled so that the first pulse width Pw1 and the second pulse width Pw2 are always different, regardless of the operating conditions. In other words, there is no need to switch the settings of the individual drive pulses depending on the operating conditions.

[0083] As described above, when the pulse width of the applied drive pulse significantly deviates from the actual AL, the vibration associated with the previous ejection tends to weaken the vibration associated with the subsequent ejection, significantly reducing the ejection speed. If the subsequent ejection is slower than the previous ejection, ink droplets that should be aligned may not align during flight. Furthermore, if the speed difference is too large, not only can the ink landing position be offset, but the shape and form of the ink droplets during landing may also be affected (i.e., image quality may be degraded). Therefore, multiple ink droplets must be within an appropriate speed range.

[0084] In the inkjet recording device 1 of the present embodiment, the pulse width and the like are set by combining two driving pulses that are subsequently performed. Here, one of the two driving pulses is set to a driving pulse (first driving pulse) having a pulse width Pw1 that is longer than the AL of all nozzles in a head unit 21 of the adjustment object (including the AL of the nozzle itself that discharges ink), and the other is set to a driving pulse (second driving pulse) having a pulse width Pw2 that is shorter than the AL of all nozzles in the head unit 21 (including the AL of the nozzle itself that discharges ink). That is, all driving pulses are not set to a length that is the same as the AL involved in any nozzle. On the other hand, by making the lengths of the two times different, there will not be a nozzle that is supplied with a second pulse with a smaller length difference from the AL and a nozzle that is supplied with a second pulse with a larger length difference from the AL. The combination of the driving pulses can be determined jointly as the driving pulse involved in all nozzles.

[0085] Figure 6A as well as Figure 6B This diagram shows an example of the distribution of ejection velocities from multiple nozzles (here, 100 nozzles) in the inkjet head 211. Hereinafter, ejection velocity refers to the velocity of multiple consecutively ejected ink droplets combined. However, when calculating velocity based on the image capture results of the imaging unit 50, the average velocity from the ejection timing of any ink droplet (for example, the last one) until it lands on the medium M can also be calculated.

[0086] like Figure 6A As shown by line Lk1, when a discharge operation (here, two discharges) is performed for one pixel with a fixed pulse width Pwm (e.g., 8.6% shorter than the representative value Pw0), the discharge speed (after multiple droplets merge into one) is high for nozzles numbered 55 and above, while the discharge speed is low for nozzles numbered 45 and above. On the other hand, as shown by line Lk2, when the same discharge operation is performed with a fixed pulse width Pwp (>Pwm, e.g., 8.6% longer than the representative value Pw0), the discharge speed is high for nozzles numbered 45 and above compared to the case with the pulse width Pwm, while the discharge speed is low for nozzles numbered 55 and above compared to the case with the pulse width Pwm. In other words, it is estimated that for nozzles numbered 45 and above, AL is close to the pulse width Pwp, while for nozzles numbered 55 and above, AL is close to the pulse width Pwm.

[0087] Lines Lj1 and Lj2 respectively represent the discharge speed of each nozzle when the pulse width Pw1 is set to be sufficiently shorter than the pulse width Pwm in the first of the two discharge actions, and when the pulse width Pw2 is set to be sufficiently longer than the pulse width Pwp in the second. Sufficient here means that the shorter it is than the AL of all nozzles, the shorter it is, and the longer it is than the A of all nozzles. If there is no clear abnormality in the nozzle, even if the AL of all nozzles is not necessarily actually measured and obtained, the range of deviation of AL can be roughly assumed based on some measurement results and manufacturing characteristics. Therefore, it is sufficient to determine the pulse widths Pw1 and Pw2 within a range larger than the assumed range (here, ±15.2% of the representative value Pw0). The pulse width satisfies the relationship Pwm+Pwp=Pw1+Pw2. In addition, on line Lj1, the discharge period is twice the pulse width Pwm, and on line Lj2, the discharge period is twice the pulse width Pwp. In any case, compared with the case of a constant pulse width, the variation in discharge speed is smaller than the variation in AL of each nozzle.

[0088] Although not particularly limited, for example, the ejection period Pe1 is 2 times or less the pulse width Pw2 and 2 times or more the pulse width Pw1. The ejection period Pe1 can be, for example, about twice the average AL of all nozzles, or twice the pulse width Pw1 or the pulse width Pw2. [[ID= (2]]

[0089] Such a combination of pulse widths is not limited to the case of 2 ejections. For example, it can also be the case of 4 ejections. When performing ink ejection 4 times or more continuously, it is only necessary to set the 2 drive pulses that are repeated 2 times or more. By alternately outputting drive pulses with long and short pulse widths, the deviation of the overall ejection speed is reduced for a nozzle array having portions with different ALs.

[0090] In addition, not only in the case of performing continuous ejection 4 times or more for a single pixel range, but also in the case of high-frequency ejection such as starting ink ejection for the next pixel range during a period when the reverberation related to ink ejection for the previous pixel range has not disappeared, similarly, the influence of the vibration of the ink related to the previous ejection affects the vibration of the ink related to the subsequent ejection, and the deviation of the ejection speed tends to increase.

[0091] In Fig. 6(b), lines Li1 and Li2 respectively represent the amounts of ink ejection speeds of the first pixel and the tenth pixel when 4 ink ejections are performed for each pixel with a pulse width Pwc (Pwp > Pwc > Pwm, here the pulse width Pwc is 5.7% shorter than the representative value Pw0). The recording period for each pixel (pixel range) is about 5.22 times the ejection period. In this case, among the nozzles (nozzle numbers 55 and later) close to AL in the ink ejection speed at the time of recording the tenth pixel, due to the reverberation of the waveforms between pixels, it is weakened, and the ink ejection speed of the first pixel is reduced. That is, according to the situation of continuous operation, the ejection speed changes.

[0092] Lines Lv1 and Lv2 are respectively the distributions of the ink ejection speeds of the first pixel and the tenth pixel when the waveforms of pulse widths P1a and P2a (P1a (=0.686×Pw0) < Pwc < P2a (=1.286×Pw0)) are alternately switched in the odd-numbered and even-numbered ejections. It can be seen that not only is the deviation in the first pixel smaller than the deviation shown by line Li1, but also the difference between the ink ejection speed distributions in the ejection of the tenth pixel and the ink ejection speed distribution in the first pixel is smaller than in the case where the pulse width Pwc is fixed. Thus, a drive signal combining a long pulse width and a short pulse width also has an effect in terms of stability during continuous operation.

[0093] It should be noted that the pulse width combination that reduces the relative deviation in discharge speed does not necessarily convert kinetic energy (discharge speed) to the most efficient one. Therefore, the desired discharge speed (absolute value) can be achieved by adjusting the amplitude (voltage) of the drive waveform.

[0094] Adjustments from the representative pulse width value Pw0 based on differences in AL between nozzles are necessary when, as described above, variations in AL between nozzles have a significant impact on image quality that cannot be ignored. This can also occur when, for example, variations in discharge speed or ink droplet volume of 3% or more occur, depending on the maximum transport speed of the medium M or the highest level of required image quality. As described above, pulse widths Pw1 and Pw2 are set to intervals greater than the interval between the maximum and minimum values ​​of the AL variation corresponding to the variation in discharge speed (e.g., approximately 10%). Thus, for example, pulse widths Pw1 and Pw2 can be adjusted by approximately ±20% (40% overall) relative to the previously set representative pulse width value Pw0, or even by a larger increase or decrease.

[0095] Figure 7A as well as Figure 7B This is a diagram showing an example of the discharge speed distribution when the amount of change in the pulse width is varied.

[0096] exist Figure 7A In Figure 1, the ejection speed distribution (lines Lra and Lrb) is compared with the ejection speed distribution (lines Laa and Lab) when the second and fourth pulse widths are extended by approximately 9% with respect to the ejection speed distribution when the pulse width Pwc is fixed. On lines Lra and Laa, the ejection cycle is twice the pulse width Pwc, while on lines Lrb and Lab, the ejection cycle is twice the second and fourth pulse widths. While this amplitude difference does not result in significant variation, it does show a slight decrease in variation compared to the case with a fixed pulse width.

[0097] exist Figure 7B In the example, the first and third pulse widths are shortened by approximately 18% compared to pulse width Pwc, while the second and fourth pulse widths are extended by approximately 27% compared to pulse width Pwc. The ejection cycles for lines Lba and Lbb are the same as for lines Laa and Lab. In these cases, variations in ejection speed between nozzles are more effectively reduced.

[0098] Here, there is also a variation in sensitivity among the piezoelectric elements 26 corresponding to the respective nozzles.

[0099] Figure 8A as well as Figure 8BThis is a diagram explaining the variation in sensitivity between nozzles.

[0100] For example, Figure 8A As shown, there are nozzles with a maximum discharge speed at pulse width Pwa and nozzles with a maximum discharge speed at pulse width Pwb. These maximum discharge speeds Va and Vb are different. In other words, even if drive pulses with a pulse width equal to the actual AL are applied to both nozzles, the same discharge speed may not be achieved.

[0101] exist Figure 8B In the example shown, when the discharge speeds from multiple nozzles within the inkjet head 211 are measured using a representative pulse width Pw0, as shown by line Lt, the discharge speeds for nozzles numbers 0 to 25 and those after 50 appear relatively high. However, when the discharge speeds of these multiple nozzles are measured using a pulse width Pwm shorter than the representative value Pw0, as shown by line Ls, the discharge speeds for nozzles numbered 60 and above increase further, while the discharge speeds for nozzles numbered 50 and above decrease. On the other hand, when the discharge speeds of these multiple nozzles are measured using a pulse width Pwp longer than the representative value Pw0, as shown by line Lu, the discharge speeds for nozzles numbered 55 and above decrease, while the discharge speeds for nozzles numbered less than 50 increase. In other words, the AL for nozzles numbered 55 and above is shorter than the representative value Pw0, while the AL for nozzles numbered 50 and above is longer than Ps. However, even when the nozzles with nozzle numbers 25 to 45 are driven with a pulse width Pwp close to AL, the ejection speed does not differ significantly from the ejection speed of the nozzles with nozzle numbers 50 and later. In other words, it can be seen that the sensitivity of the piezoelectric elements 26 of the nozzles with nozzle numbers 25 to 45 is relatively low.

[0102] In this case, the order of the pulse widths is determined so that the pulse width of the second (final) drive pulse is closer to the AL (reference pulse width) of the nozzle with the lowest sensitivity (the smallest characteristic value among the maximum characteristic values ​​(discharge speed)). In a situation where sensitivity is low and speed tends to slow, by relatively increasing the speed of the later-emitted ink, the later-emitted ink catches up with the earlier-emitted ink, thereby facilitating proper discharge overall.

[0103] Figure 9 This diagram shows an example of the distribution of ejection speeds according to the order of pulse widths when nozzles with different sensitivities are included. Nozzles (piezoelectric elements 26) with nozzle numbers before 50 have relatively low sensitivities, while nozzles (piezoelectric elements 26) with nozzle numbers after 50 have relatively high sensitivities.

[0104] Line Lh represents the difference between the discharge speed and the reference discharge speed when the first pulse width is closer to the actual AL for nozzles prior to nozzle number 50, and the second pulse width is closer to the actual AL for nozzles subsequent to nozzle number 50. Line L1 represents the difference between the discharge speed and the reference discharge speed when the first pulse width is closer to the actual AL for nozzles subsequent to nozzle number 50, and the second pulse width is closer to the actual AL for nozzles subsequent to nozzle number 50. It can be seen that the discharge speed difference represented by line L1 is smaller than the discharge speed difference represented by line Lh.

[0105] Next, the pulse width setting operation in the inkjet recording apparatus 1 of this embodiment will be described.

[0106] As described above, if the AL deviation within the head unit 21 is sufficiently small, pulse width setting is unnecessary. However, if the AL deviation is large, the head unit 21 is discarded and pulse width setting is performed instead. Because the AL in each nozzle 27 deviates from the theoretical value, the discharge speed is measured while the pulse width is shifted and fitted. This fitting determines a value equal to the pulse width (reference pulse width) at which the discharge speed reaches its maximum. As described above, the AL distribution within the head unit 21 (inkjet head 211) can be estimated based on a predetermined amount of measurement data.

[0107] Figure 10 This is a flowchart showing the control steps of the control unit 40 in the drive waveform setting process executed by the inkjet recording apparatus 1 of this embodiment. The drive waveform setting process is activated by an inspector's input operation to the operation receiving unit 81 during pre-shipment inspection, for example.

[0108] When the drive waveform setting process begins, the control unit 40 (CPU 41) determines multiple (e.g., three) pulse widths and multiple nozzles 27 for ink ejection speed measurement. The control unit 40 sets all combinations of pulse widths and nozzle positions, and the recording operation unit 20 ejects ink using the set nozzles 27 and pulse widths. Furthermore, the measurement unit measures the ink ejection speed (step S101).

[0109] The control unit 40 fits the obtained velocity distribution (for example, using a quadratic or cubic curve, as described above) for each nozzle 27 whose ink ejection velocity is to be measured, and estimates the maximum (maximum) velocity and the pulse width (reference pulse width) at that maximum (maximum) velocity (step S102). The maximum (maximum) velocity can be converted into sensitivity information of the piezoelectric element 26 of the nozzle 27. The reference pulse width corresponds to the AL (actual AL) associated with that nozzle 27.

[0110] The control unit 40 estimates the maximum and minimum values ​​of the actual AL based on the distribution of the actual AL in the nozzle arrangement direction (step S103). The maximum and minimum values ​​do not need to be exact and can be estimated using a wider interval (increasing the maximum value and decreasing the minimum value). To perform this estimation, the control unit 40 can also obtain measurement data of the ink ejection speed at the aforementioned multiple pulse widths for several nozzles 27. Furthermore, the control unit 40 can use fitting, etc., to estimate the maximum and minimum values.

[0111] The control unit 40 sets a fixed pulse width and a discharge period Pe based on the estimated AL of each nozzle (step S104). The fixed pulse width can be the representative value Pw0 set in the past, but is not limited thereto. The discharge period Pe can also be twice the fixed pulse width.

[0112] The control unit 40 determines whether the variation in ink ejection speed from all nozzles 27 at the set fixed pulse width is within a predetermined reference (step S105). For example, the control unit 40 calculates the extent to which the ink ejection speed from the nozzle 27 that is furthest from the fixed pulse width by AL (either the maximum or minimum value of AL, or both values ​​may be mechanically selected) is slower than the ink ejection speed at AL. If it is determined that the variation is within the predetermined reference ("YES" in step S105), the control unit 40 confirms the set fixed pulse width and ejection period Pe, and terminates the drive waveform setting process.

[0113] If it is determined that the pulse width is not within the specified reference ("No" in step S105), the control unit 40 sets the pulse widths Pw1 and Pw2 and the discharge periods Pe1 and Pe2 based on the estimated maximum and minimum values ​​of AL (step S106). Pulse widths Pw1 and Pw2 can be obtained by, for example, multiplying the median (average) of the maximum and minimum values ​​of AL by a specified multiple (e.g., 1.2 or 0.8). Discharge period Pe1 can also be, for example, twice the obtained pulse widths Pw1 and Pw2. Discharge period Pe2 can also be the same as discharge period Pe1.

[0114] The control unit 40 compares the sensitivity distribution in the arrangement direction (width direction) of the nozzles 27 with the distribution of AL. The control unit 40 determines the order of which pulse width Pw1 or Pw2 is output first (step S107). The control unit 40 determines the range of relatively low sensitivity among all the nozzles 27, and obtains the value of the representative AL within the range. The control unit 40 determines which of the pulse widths Pw1 or Pw2 is close to the representative AL, and determines the order of discharge in such a way that the closer one is output later. The processing of steps S106 and S107 constitutes the pulse width setting step in the drive control method of this embodiment. Then, the control unit 40 ends the drive waveform setting processing.

[0115] As described above, the inkjet head 211 of this embodiment includes a plurality of recording elements 200, each of which includes nozzles 27 for discharging ink and piezoelectric elements 26 for applying pressure fluctuations to the ink supplied to the nozzles 27 in response to applied drive pulses. Ink droplets discharged from each of the recording elements 200 in response to a drive pulse applied to each of the plurality of piezoelectric elements 26 have a droplet velocity that deviates from a predetermined reference pulse width (actual AL) at least relative to a reference pulse width (where the change in the pulse width of the drive pulse is maximized) at which the droplet velocity is maximized. The drive control method of such an inkjet head 211 of the present embodiment includes the following pulse width setting step (i.e., the processing of steps S106 and S107 in the drive waveform setting processing): when the specified number of ink droplets discharged respectively according to two or more specified numbers of drive pulses are sprayed within the same pixel range, for each of the multiple recording elements 200, a first drive pulse with a pulse width Pw1 longer than the reference pulse width (actual AL) and a second drive pulse with a pulse width Pw2 shorter than the reference pulse width (actual AL) are combined in total to the above-mentioned specified number and output to each of the multiple recording elements 200.

[0116] This drive control method effectively reduces the adverse effects of variations in the inkjet recording device 1 that continuously ejects multiple droplets and lands them within the same pixel range, even when the characteristics of the nozzles 27 vary significantly, a particularly significant effect during continuous, multiple-shot ejection, and the inkjet head 211 previously did not meet the standards. Consequently, it is possible to reuse previously discarded inkjet heads 211, thereby improving manufacturing yields and reducing manufacturing costs.

[0117] Furthermore, in the pulse width setting step, a first drive pulse having a pulse width Pw1 that is longer than any of the reference pulse widths associated with each of the plurality of recording elements 200 and a second drive pulse having a pulse width Pw2 that is shorter than any of the reference pulse widths are determined. In other words, rather than setting pulse widths Pw1 and Pw2 based on the respective reference pulse widths for each nozzle, a longer pulse width Pw1 and a shorter pulse width Pw2 are set for the AL of all nozzles. This allows for a moderately large difference in the pulse widths Pw1 and Pw2, ensuring a stable ejection speed for each nozzle.

[0118] Furthermore, in the pulse width setting step, pulse widths Pw1 and Pw2 are determined commonly for multiple recording elements 200. By determining pulse widths Pw1 and Pw2 that satisfy the conditions commonly for all nozzles 27, pulse width setting can be easily performed. Furthermore, since the pulse width does not need to be changed for each piezoelectric element 26, driving operation is also simplified.

[0119] Furthermore, during the pulse width setting step, the order of the first and second drive pulses is determined so that the pulse width closest to the reference pulse width (ΔL) corresponding to the smallest ink ejection speed among the maximum ink ejection speeds of the plurality of recording elements 200 becomes the final drive pulse. In other words, a drive pulse close to ΔL is output to the piezoelectric element 26, which has low sensitivity, so that the desired ejection speed can be achieved as easily as possible with the final drive pulse. This ensures stable ink ejection and operational efficiency relative to the drive voltage without excessively reducing the ejection speed.

[0120] The predetermined characteristic value is the velocity of discharged ink droplets. Since the velocity of ink droplets can significantly affect image quality variations, adjusting the velocity as a characteristic value to align the nozzles 27 can easily reduce image quality variations.

[0121] Alternatively, the predetermined characteristic value may be the amount of discharged ink droplets. Depending on the content of the image being recorded or the requirements of the image recorder, the overall ink density (grayscale) unevenness may be more important than the ink landing position. Therefore, the present invention is also effective when using droplet volume as a characteristic value to reduce image quality variations.

[0122] The allowable range of characteristic value deviation is based on a predetermined standard of 3%. The impact of the deviation also depends on the transport speed of the medium M and the required image quality, but an appropriate value can be uniquely determined based on generally required average image quality, etc. This allows users of the inkjet recording apparatus 1 to be provided with an inkjet head 211 that simplifies inspection and setup time and allows for easy and stable production of appropriate image quality.

[0123] Furthermore, the predetermined number of ink droplets continuously ejected into a single pixel range is an even number, and is determined by alternating the output of the first drive pulse and the second drive pulse in the pulse width setting step. This facilitates achieving a more balanced final ink ejection speed for each nozzle.

[0124] The inkjet recording device 1 of this embodiment includes an inkjet head 211 having a plurality of recording elements 200, each of which includes nozzles 27 for discharging ink and piezoelectric elements 26 for applying a driving pulse to the ink supplied to the nozzles 27, and a control unit 40 for controlling the output of the driving pulse applied to the piezoelectric element 26 to the recording element 200. In the inkjet recording device 1, the droplet velocity of ink droplets discharged from each of the recording elements 200 in response to the driving pulse applied to each of the plurality of piezoelectric elements 26 deviates by a predetermined reference or greater relative to a reference pulse width (actual AL) at which a change in the pulse width of the driving pulse is maximized. In a case where a specified number of ink droplets respectively discharged according to a specified number of driving pulses of more than two specified numbers are sprayed into the same pixel range, the control unit 40 combines a first driving pulse having a pulse width Pw1 longer than a reference pulse width (AL) and a second driving pulse having a pulse width Pw2 shorter than the reference pulse width (AL) for each of the multiple recording elements 200, a specified number of combinations, and outputs them to each of the multiple recording elements 200.

[0125] According to such an inkjet recording apparatus 1, ink can be discharged at a stable ink discharge speed using the conventionally discarded non-standard inkjet head 211. Therefore, the inkjet recording apparatus 1 can reduce manufacturing and maintenance costs while performing stable image recording operations.

[0126] It should be noted that the present invention is not limited to the above-described embodiment, and various modifications are possible.

[0127] For example, in the above embodiment, a common drive signal is output to all recording elements 200 of the inkjet head 211. However, drive signals may be set individually or for each of several groups of recording elements 200 within the inkjet head 211. In this case, a pulse width Pw1 longer than any of the ALs of the recording elements 200 and a pulse width Pw2 shorter than any of the ALs may be set for each recording element 200 outputting a certain drive signal.

[0128] In addition, in the above embodiment, the following situation is described: when the deviation of the discharge speed caused by the driving signal with a pulse width of the representative value Pw0 exceeds the reference under at least any one action condition, for each pixel in the corresponding inkjet head 211, more than two consecutive ink discharges are always output, and the driving signal based on the combination of the first driving pulse and the second driving pulse is output. However, it is also possible to switch to the action of outputting the driving signal based on the combination of the first driving pulse and the second driving pulse only when the condition exceeds the reference.

[0129] In the above embodiment, the case where the ejection speed of ink droplets is used as the characteristic value is described, but the present invention is not limited thereto. For example, the amount of ink droplets can also be used as the characteristic value.

[0130] In the above embodiment, the discharge speeds measured at multiple pulse widths are fitted using a quadratic or cubic function to determine the maximum value as the reference pulse width (AL). However, the reference pulse width (AL) may be directly determined by measuring at sufficiently narrow intervals near the maximum value.

[0131] Furthermore, the order of discharge according to the sensitivity of the piezoelectric element 26 may be disregarded, and one of the longer drive pulse and the shorter drive pulse may always be placed first and the other may always be placed last.

[0132] Furthermore, the specific configurations, processing operations, and steps described in the above embodiments may be modified as appropriate without departing from the spirit of the present invention. The scope of the present invention encompasses the scope of the invention described in the claims and their equivalents.

[0133] Industrial Applicability

[0134] The present invention can be used for a drive control method of an inkjet head and an inkjet recording device.

[0135] Description of Reference Numerals

[0136] 1 Inkjet recording device

[0137] 10. Conveying unit

[0138] 11 driving roller

[0139] 12 Conveyor belt

[0140] 13 driven roller

[0141] 14 Conveyor motor

[0142] 15 rollers

[0143] 20 Recording Action Section

[0144] 21, 21C, 21M, 21Y, 21K head units

[0145] 25 Head drive unit

[0146] 26 Piezoelectric element

[0147] 27 Nozzle

[0148] 27a Opening

[0149] 29 Driving waveform signal generation unit

[0150] 30 Storage

[0151] 31 AL measurement data

[0152] 32 Waveform setting data

[0153] 40 Control Unit

[0154] 41 CPU

[0155] 42 RAM

[0156] 50 Filming Department

[0157] 70 Ministry of Communications

[0158] 81 Operation Reception Department

[0159] 82 Display unit

[0160] 90 Power Supply Department

[0161] 200 Recording Elements

[0162] 210 Slide

[0163] 211 inkjet head

Claims

1. A method for controlling the driving of an inkjet head, wherein the inkjet head comprises a plurality of recording elements, each of the recording elements including nozzles for discharging ink and a driving element for applying pressure fluctuations to the ink supplied to the nozzles in response to an applied driving pulse, wherein: A predetermined characteristic value associated with each ink droplet ejected from the recording element in response to a driving pulse applied to the driving element becomes maximum with respect to a change in the pulse width of the driving pulse, and a reference pulse width of the driving pulse has a deviation greater than a predetermined reference. The drive control method of the inkjet head includes a pulse width setting step. In the pulse width setting step, when the predetermined number of ink droplets respectively discharged according to two or more predetermined numbers of drive pulses are caused to land within the same pixel range, for each of the plurality of recording elements, a first drive pulse with a pulse width longer than the reference pulse width and a second drive pulse with a pulse width shorter than the reference pulse width are combined by the predetermined number and output to each of the plurality of recording elements. In the pulse width setting step, the order of the first drive pulse and the second drive pulse is determined so that the pulse width closer to the reference pulse width corresponding to the smallest characteristic value among the maximum characteristic values ​​involved in the plurality of recording elements becomes the last drive pulse.

2. The drive control method according to claim 1, wherein: In the pulse width setting step, the first drive pulse having a pulse width longer than any of the reference pulse widths associated with each of the plurality of recording elements and the second drive pulse having a pulse width shorter than any of the reference pulse widths are determined.

3. The drive control method according to claim 2, wherein: In the pulse width setting step, the pulse width of the first drive pulse and the pulse width of the second drive pulse are determined commonly for the plurality of recording elements.

4. The drive control method according to any one of claims 1 to 3, wherein: The predetermined characteristic value is the velocity of discharged ink droplets.

5. The drive control method according to any one of claims 1 to 3, wherein: The predetermined characteristic value is the amount of discharged ink droplets.

6. The drive control method according to any one of claims 1 to 3, wherein: The predetermined standard related to the deviation is 3%.

7. The drive control method according to any one of claims 1 to 3, wherein: The prescribed number is an even number, In the pulse width setting step, the first drive pulse and the second drive pulse are determined to be output alternately.

8. An inkjet recording device, wherein: The inkjet recording device comprises: an inkjet head having a plurality of recording elements including nozzles for discharging ink and a driving element for applying pressure fluctuations to the ink supplied to the nozzles in response to an applied driving pulse; as well as a control unit that controls output of the drive pulse applied to the drive element to the recording element, A predetermined characteristic value associated with each ink droplet ejected from the recording element in response to a driving pulse applied to the driving element becomes maximum with respect to a change in the pulse width of the driving pulse, and a reference pulse width of the driving pulse has a deviation greater than a predetermined reference. In a case where the predetermined number of ink droplets ejected in response to two or more predetermined number of driving pulses land within the same pixel range, the control unit combines the predetermined number of first driving pulses having a pulse width longer than the reference pulse width and second driving pulses having a pulse width shorter than the reference pulse width for each of the plurality of recording elements, and outputs the combined combined number to each of the plurality of recording elements. The order of the first drive pulse and the second drive pulse is determined so that a pulse width closer to the reference pulse width corresponding to the smallest characteristic value among the maximum characteristic values ​​associated with the plurality of recording elements becomes the last drive pulse.

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