JP7552190B2 - Inkjet head drive setting method and drive method - Google Patents

Description

This invention relates to a drive setting method and a drive method for an inkjet head.

There is an inkjet recording device that records images, thin films, wiring, three-dimensional structures, etc. by applying pressure fluctuations to ink supplied through an ink flow path (ink channel) in a pressure chamber located midway along the ink channel, and ejecting ink from a large number of nozzles that are each connected to a large number of pressure chambers. As the number of ink channels increases, it becomes more difficult to form all the nozzles and pressure chambers uniformly, and accordingly, the speed of ink ejected from nozzles tends to vary. Patent Document 1 discloses a technology that stores and holds correction data calculated in advance for each nozzle, and corrects and outputs a reference drive voltage signal based on the correction data.

JP 2013-59961 A

However, performing correction processing on all nozzles every time they are driven is time-consuming and requires complex configuration and control.

The object of this invention is to provide a method for setting and driving an inkjet head that can more simply reduce the variation in ink ejection speed between nozzles.

In order to achieve the above object, the present invention provides:
1. A drive setting method for an inkjet head comprising: a plurality of nozzles each ejecting ink droplets; a plurality of ink flow paths communicating with the plurality of nozzles; a plurality of drive elements each performing an operation of applying a pressure fluctuation to ink in the plurality of ink flow paths; and a drive control unit applying a drive pulse to the plurality of drive elements, causing the drive elements to generate a pressure fluctuation corresponding to a pulse width of the drive pulse, the method comprising the steps of:
an acquisition step of measuring an ink droplet ejection speed for each of the plurality of ink flow paths and acquiring a maximum drive pulse width at which the ink droplet ejection speed is maximized;
a setting step of setting a value based on the acquired plurality of fastest drive pulse widths to a pulse width of the drive pulse to be output to the plurality of drive elements;
Including,
In the setting step, an average value of the plurality of fastest drive pulse widths is set as the pulse width of the drive pulse.
It is characterized by:

The present invention relates to a method for setting a drive state of an inkjet head, comprising the steps of:
The obtaining step is characterized in that the fastest drive pulse width is specified by fitting a relationship between the pulse width and the ejection speed with a predetermined function.

The present invention relates to a method for setting a drive state of an inkjet head, comprising the steps of:
The acquiring step is characterized in that ink ejection velocities corresponding to at least four different pulse widths are measured.
The invention according to claim 4 is as follows:
1. A drive setting method for an inkjet head comprising: a plurality of nozzles each ejecting ink droplets; a plurality of ink flow paths communicating with the plurality of nozzles; a plurality of drive elements each performing an operation of applying a pressure fluctuation to ink in the plurality of ink flow paths; and a drive control unit applying a drive pulse to the plurality of drive elements, causing the drive elements to generate a pressure fluctuation corresponding to a pulse width of the drive pulse, the method comprising the steps of:
an acquisition step of measuring an ink droplet ejection speed for each of the plurality of ink flow paths and acquiring a maximum drive pulse width at which the ink droplet ejection speed is maximized;
a setting step of setting a value based on the acquired plurality of fastest drive pulse widths to a pulse width of the drive pulse to be output to the plurality of drive elements;
Including,
In the obtaining step, ink ejection speeds corresponding to at least four different pulse widths are measured, and the fastest drive pulse width is specified by fitting a relationship between the pulse width and the ejection speed with a predetermined function.
It is characterized by:

The present invention as set forth in claim 5 provides the inkjet head drive setting method as set forth in any one of claims 1 to 4, further comprising:
the inkjet head includes a plurality of nozzle groups each including the plurality of nozzles;
The setting step is characterized in that the pulse width is set for each of the nozzle groups.

The present invention as set forth in claim 6 is the inkjet head drive setting method as set forth in any one of claims 1 to 5, further comprising:
The processes in the obtaining step and the setting step are performed during a pre-shipment inspection of the inkjet head.

The present invention relates to a method for setting a drive state of an inkjet head, comprising:
The method further includes an evaluation step of evaluating a level of performance according to the variation in the fastest drive pulse width for each of the plurality of ink flow paths obtained in the acquisition step relative to the pulse width set in the setting step.

The invention according to claim 8 further comprises:
A method for driving an inkjet head comprising: a plurality of nozzles each ejecting an ink droplet; a plurality of ink flow paths communicating with the plurality of nozzles; a plurality of drive elements each performing an operation of applying a pressure fluctuation to ink in the plurality of ink flow paths; and a drive control unit applying a drive pulse to the plurality of drive elements, causing the drive elements to generate a pressure fluctuation corresponding to a pulse width of the drive pulse, the method comprising the steps of:
A method for driving an inkjet head, comprising: a driving step of outputting, to each of the driving elements, the driving pulses having the pulse widths determined by the driving setting method according to any one of claims 1 to 7.

The present invention provides a method for driving an ink jet head according to the present invention, comprising the steps of:
In the driving step, a plurality of ink droplets can be ejected by a plurality of successive driving pulses, and can be caused to land on the same pixel area of a recording medium;
Among the multiple output intervals of the drive pulse, the output interval of the last two drive pulses is wider than the output intervals other than the last two output intervals among three or more output intervals of the drive pulse.

According to the present invention, it is possible to drive the inkjet head more simply so as to reduce the variation in the ink ejection speed between nozzles.

1 is a block diagram showing a functional configuration of an inkjet recording apparatus having an inkjet head which is a setting target of a drive setting method of the present embodiment. 4 is a bottom view showing the ink ejection surface of the recording operation unit. FIG. FIG. 4 is a diagram illustrating an ejection pulse. FIG. 11 is a diagram showing an example of a waveform of a driving pulse in a multi-drop system. FIG. 13 is a diagram illustrating AL estimation. FIG. 13 is a diagram showing an example of AL estimation. 13 is a diagram showing the difference between the average AL and the central AL, and the difference between the ejection speed of a single ink droplet and the ejection speed of multiple drops when driven at the central AL. FIG. 2 is a block diagram showing a functional configuration of the inspection device. 10 is a flowchart showing a control procedure of a drive waveform setting process.

The following describes an embodiment of the present invention with reference to the drawings.

FIG. 1 is a block diagram showing the functional configuration of an inkjet recording apparatus 100 having an inkjet head 21 which is the target of the drive setting method of this embodiment.
The inkjet recording device 100 includes a conveying unit 10, a recording operation unit 20, a driving waveform signal generating unit 29, a memory unit 30, a control unit 40, an imaging unit 50, a communication unit 70, an operation receiving unit 81, a display unit 82, a power supply unit 90, and the like.

The transport unit 10 includes a transport belt 12 and a transport motor 14. When an appropriate drive signal is input to the transport motor 14, the transport motor 14 rotates. The transport belt 12 is endless and is stretched over rollers rotated by the transport motor 14, and moves in circles at a speed according to the rotation of the rollers. A recording medium placed on the outer circumferential surface of the transport belt 12 is moved and transported in accordance with this rotation.

The recording operation unit 20 ejects ink onto the recording medium transported by the transport unit 10 to record an image or the like. The recording operation unit 20 includes a head drive unit 25 (drive control unit) and a plurality of recording elements 20a. Each recording element 20a has a piezoelectric element 26 (drive element), a nozzle 27, and an ink flow path 28 (channel). The head drive unit 25 applies a drive signal (drive pulse) to a selected piezoelectric element 26 to deform the piezoelectric element 26. Ink is sent to each nozzle 27 from a common supply path for the plurality of nozzles 27 through an ink flow path 28 that communicates with each nozzle 27. Each ink flow path 28 includes a pressure chamber, and a pressure fluctuation is applied to the ink in the pressure chamber by a deformation operation in response to the application of a drive voltage to the piezoelectric element 26 located along the wall surface of the pressure chamber (or forming the wall surface itself). The piezoelectric element 26 applies pressure fluctuations corresponding to the drive pulses to the ink supplied to the nozzle 27, causing ink droplets to be ejected (discharged) from the nozzle 27 to record an image. The inkjet recording device 100 is provided with a number of recording operation units 20 corresponding to the number of colors and types of ink ejected in one image recording operation in the inkjet recording device 100. The recording operation unit 20 is capable of ejecting ink using a multi-drop method in which multiple ink droplets are continuously ejected, merged midway, and landed as a single droplet on a corresponding pixel range (the same pixel range), as described below, and the density gradation of each pixel range can be determined according to the number of ink droplets.

The drive waveform signal generating unit 29 generates a drive pulse that the head driving unit 25 outputs to the recording element 20a. The drive waveform signal generating unit 29 converts digital data indicating a predetermined drive waveform into analog, and outputs a signal with amplified voltage and current as a drive pulse to the head driving unit 25, although this is not particularly limited. The generated drive pulse may include a trapezoidal wave or rectangular wave shape that ejects ink, as well as a drive pulse with a waveform that causes a more gradual pressure change in the ink (such as a triangular wave. The pulse width is, for example, the half-width (the width of the part that is 50% or more of the amplitude). It may be a value other than 50%).

The control unit 40 is a processor that includes a CPU 41 (Central Processing Unit) and a RAM 42 (Random Access Memory), and controls various operations of the inkjet recording device 100. The CPU 41 performs various calculation processes to execute control operations. The RAM 42 provides the CPU 41 with working memory space and stores temporary data. The control unit 40 controls the output of drive pulses related to the ink ejection operation in the recording operation unit 20 to the recording elements 20a based on the image data to be recorded and setting data related to the recording of the image.

The storage unit 30 stores image data to be recorded, and also stores various programs and setting data. The storage unit 30 has at least a non-volatile memory, and may also have a volatile memory (RAM). The image data may be stored in the RAM. The setting data includes waveform setting data 31. The non-volatile memory is, for example, a flash memory, and may additionally or instead have a HDD (Hard Disk Drive). Note that a part of the storage unit 30 may be held by the inkjet head 21 (see FIG. 2) of the recording operation unit 20. Parameter information specific to the inkjet head 21 (head unit) and information on initially abnormal nozzles may be stored in a non-volatile memory provided in the inkjet head 21. This information may be read by the control unit 40 during initial settings after the inkjet head 21 (head unit) is attached to the inkjet recording device 100, and may be stored and managed in an integrated manner in the storage unit 30 of the inkjet recording device 100 body.

The waveform setting data 31 stores waveform pattern data of the drive pulses output to each recording element 20a. The waveform pattern data stored here 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, in particular. The pulse width information may be a parameter obtained from a non-volatile memory provided in the inkjet head 21 (the pulse width set in the drive waveform setting process (drive setting method) described below). These may be digital data that are the basis of the drive pulses generated by the drive waveform signal generation unit 29.

The imaging unit 50 captures an image of the surface of the conveyor belt 12 (medium M placed on it) downstream of the recording operation unit 20 in the direction of conveyance of the medium M on the conveyor belt 12 by the conveyor unit 10. The imaging unit 50 is, for example, a line sensor in which CCD (Charge-Coupled Device) imaging elements or CMOS (Complementary Metal Oxide Semiconductor) imaging elements are arranged in the width direction, and is capable of capturing two-dimensional images of the medium M in combination with the movement of the medium M in the conveyance direction. The imaging results are analyzed by the control unit 40 and used to detect image recording abnormalities and adjust density gradation.

The communication unit 70 executes and controls communications with external devices. The communication unit 70 is connected to an external computer based on a communication standard such as TCP/IP, for example, to acquire job data including image data to be recorded, and can output the status of the image recording operation based on the job data. The communication unit 70 may also be directly connected to a peripheral device via a USB (Universal Serial Bus) or the like to send and receive data.

The operation reception unit 81 receives input operations by a user or the like, and outputs the received contents to the control unit 40 as an input signal. The operation reception unit 81 includes, for example, a touch panel or a push button switch. The touch panel is positioned so as to overlap with the display screen of the display unit 82, and the operation contents may be specified in synchronization with the display contents on the display screen.

The display unit 82 displays status, selection menus, etc. to the user, etc. The display unit 82 has, for example, a display screen and an indicator (lamp). The display unit 82 has, for example, an LCD display, etc., and can display various characters and figures on the display screen in a dot matrix format. The indicator may be used, for example, to indicate the presence or absence of power supply or the presence or absence of operational abnormalities, etc., using an LED lamp, etc.

The power supply unit 90 supplies power at a voltage corresponding to each part of the inkjet recording device 100. A voltage corresponding to the peak voltage of each drive waveform is output to the drive board of the recording operation unit 20.

In addition to the above configurations, the inkjet recording device 100 may have a measuring unit that measures the ink ejection speed from each nozzle 27. Alternatively, the inkjet recording device 100 may have an attachment unit for an external measuring device that measures the ink ejection speed from each nozzle 27. Note that the ejection speed does not directly measure the ink flight speed, but may be determined from the landing position based on the imaging data captured by the imaging unit 50.

FIG. 2 is a bottom view showing the ink ejection surface of the recording operation unit 20. As shown in FIG.
The recording operation unit 20 has eight inkjet heads 21, and is fixed to the carriage 22 so that the ink ejection surfaces of the inkjet heads 21 are exposed in a staggered arrangement. The openings of the nozzles 27 are arranged in a predetermined arrangement pattern on the ink ejection surface of each inkjet head 21. The openings of the nozzles 27 are arranged at a predetermined interval (nozzle pitch) in the width direction that intersects (here, perpendicular to) the conveying direction of the recording medium by the conveyor belt 12 as a whole. The positions of the openings of the nozzles 27 in the conveying direction do not need to be the same. Here, each inkjet head 21 has nozzle rows in which the openings of the nozzles 27 are arranged in the width direction at four different positions in the conveying direction. The openings of the nozzles 27 in each nozzle row are arranged at intervals four times the nozzle pitch, and are shifted from each other in the width direction by ¼ of the length, so that the interval is the nozzle pitch as a whole.

Next, the ink ejection operation in the inkjet recording apparatus 100 of this embodiment will be described.
FIG. 3 is a diagram illustrating the ejection pulse.
As shown in Fig. 3A, in the inkjet recording device 100, a trapezoidal wave (or rectangular wave) driving pulse is applied to the piezoelectric element 26, and the ink flow path 28 (pressure chamber) is temporarily compressed or expanded and then returned to its original state, thereby applying a pressure fluctuation to the ink, thereby performing an ink ejection operation. Note that, for the sake of explanation, the rise and fall of the trapezoidal wave voltage from the initial voltage and to the initial voltage are shown with easy-to-understand lengths, but the rise time and fall time relative to the maintenance period of the drive voltage may be appropriately determined. Also, the rise and fall of the trapezoidal wave are not limited to a linear (first-order) voltage change. They may be exponential rises, etc.

In the case of a push shot, where the ink is compressed first, the ink flow path 28 is compressed and pushed out of the opening of the nozzle 27, and the ink in the nozzle 27 is separated from the ink inside the nozzle 27 that is pulled back as the volume of the ink flow path 28 returns to its original state, and the ink droplets are generated and then fly. In the case of a pull shot, where the ink is expanded first, the ink flow path 28 is expanded and pulled back in a direction away from the opening of the nozzle 27 (i.e., toward the back of the ink flow path), and the ink flow path 28 returns to its original state with force as the volume of the ink flow path 28 returns to its original state, and part of the ink at the tip of the ink flies out of the opening, separates, and is generated and then flies.

Here, the ink pressure fluctuation has a resonant frequency (acoustic resonant frequency) that depends on the structure of the ink flow path and the physical properties of the ink. By ejecting ink in synchronization with the vibration due to this resonant frequency, the ink ejection speed is improved efficiently, while ejecting ink in the opposite phase to the vibration due to the resonant frequency reduces the ink ejection speed. In other words, even with the same pulse voltage amplitude, the pressure wave vibration applied varies depending on the pulse width (here, the time from the start of the rise to the start of the fall of the drive pulse in the trapezoidal drive wave is taken as the pulse width Pw), and the ejection speed also varies. By applying a drive pulse with a pulse width Pw of about half the acoustic resonant frequency (Acoustic Length; AL), it is possible to eject ink most efficiently.

In reality, there is some structural variation between the ink flow paths 28 that communicate with the many nozzles 27 due to manufacturing reasons. For this reason, even if drive pulses of the same pulse width are applied to the piezoelectric elements 26 corresponding to each nozzle 27, the same ejection speed cannot be obtained. As shown in FIG. 3(b), the ink ejection speed from each nozzle 27 decreases as the applied pulse width moves away from the AL of the ink flow path 28, but the ink ejection speeds from two nozzles whose pulse widths Pwa and Pwb are equal to the AL are different values at a certain pulse width Pw1.

The structure from the ink flow path 28 to the nozzle 27 includes changes in cross-sectional area, and the end of the ink flow path 28 opposite to the end connected to the nozzle 27 is connected to a common ink supply path. Furthermore, since the AL also varies from the design value depending on manufacturing variations, it is difficult to determine the AL analytically, and in general, it can be experimentally determined as the pulse width at which the droplet ejection speed is maximized when the voltage value is kept constant and the pulse width is changed. For convenience, one representative nozzle 27 is determined, for example, a nozzle located in the center of the nozzle array is selected, and the pulse width at which the maximum ejection speed is obtained for this nozzle 27 is measured. Then, an inkjet head 21 in which the ejection speed of ink ejected from all nozzles 27 at this pulse width is within the standard range, or a head unit combining multiple inkjet heads 21, is shipped and used as a product that meets the standard (accepted product). However, if the AL of the representative nozzle 27 itself is significantly different from the AL of the other nozzles 27, the inkjet head 21 is likely to fail the inspection.

Such variations in ejection speed between nozzles 27 due to variations in AL can have a more pronounced effect in the multi-drop method, in which multiple ink droplets are ejected in succession and either merged in flight or land separately within the same pixel range to produce different density gradations.

FIG. 4 is a diagram showing an example of a waveform of a driving pulse in the multi-drop system.
Four (multiple) ink droplets are ejected in succession by a series of drive pulses (four in this embodiment), and land on the same pixel area (these droplets coalesce during flight). Here, the voltage amplitude of the subsequent drive pulse is larger than that of the preceding drive pulse so that the subsequent ink droplets can catch up with the preceding ink droplets.

Note that between the penultimate drive pulse and the final drive pulse, there is a period in which no drive pulse is ejected. In this way, by making the interval between the penultimate drive pulse (droplet ejection) and the final drive pulse (droplet ejection) (the output interval of the last two drive pulses) longer (wider) by about one period than the others (output intervals other than the last two output intervals among the output intervals of three or more drive pulses), the generation of satellites during ink droplet ejection, that is, microdroplets other than the originally intended ink droplets, is reduced. Such microdroplets are unnecessary ink droplets, and the landing position and timing are also deviated from the originally intended position, so they adhere to the recorded image and reduce the image quality. They may also adhere to the nozzle 27 that was ejected without reaching the recording medium or around the opening of other nozzles 27, and if they solidify, they may cause abnormal ink ejection.

In such continuous ejection, the pressure wave vibration of the ink in the ink flow path 28 caused by the previous drive pulse is not sufficiently attenuated when the pressure fluctuation caused by the next drive pulse is applied, so the vibration is further amplified or offset depending on the relationship between the phase of the previous pressure wave vibration and the timing of the pressure fluctuation caused by the new drive pulse. This can result in a larger difference in ejection speed overall compared to when ink is ejected in a single shot.

In the inkjet head 21 of this embodiment, the pulse width (AL) at which the ejection speed is maximum is estimated for all nozzles 27, and the average value (statistical representative value for the entire head) is determined as the pulse width of the inkjet head 21. At this time, since it is time-consuming to specify the AL of all the nozzles 27, the ejection speed is calculated for each nozzle 27 at a predetermined number of pulse widths, and the AL is estimated by fitting based on these results. Note that the average value is not limited to being calculated for all nozzles 27 of the inkjet head 21. In cases where there are a large number of nozzles, the nozzles may be divided into multiple groups (nozzle groups), and the average value may be calculated for each nozzle group, and the pulse width may be set. For example, in the case of an inkjet head 21 having multiple nozzle rows (four rows in this embodiment), the nozzle groups may be grouped by the nozzle rows, or may be divided at a predetermined number of positions in the width direction or grouped every predetermined number of nozzles. The set pulse width is stored in the waveform setting data 31, which is read by the control unit 40 and used to set the drive waveform signal generating unit 29, and a drive pulse with that pulse width is output to drive the piezoelectric element 26 (driving step).

FIG. 5 is a diagram illustrating the estimation of the AL.
The ejection speed is shown by an upwardly convex curve with respect to the deviation of the pulse width from the actual AL, and can be approximately represented by a quadratic or higher curve. Here, the measurement results of the ejection speed for seven types of pulse widths are approximated by a cubic curve, and the pulse width at which the maximum value (local maximum value) of the curve is obtained is estimated as the AL. Since it is a cubic curve, the ejection speed is measured with at least four pulse widths. The accuracy improves if the number of measured pulse widths is somewhat larger, but the effort and time also increase, and the efficiency eventually becomes the same as when the AL is specified asymptotically (if there are too many, the efficiency becomes worse), so an appropriate number, for example, 10 points or less, may be used. In addition, although not particularly limited, the intervals of the set pulse widths may be equal. In addition, the intervals may differ depending on the value of the designed AL. That is, in the case of a nozzle 27 (ink flow path 28) with a short designed AL, the intervals may be small, and in the case of a nozzle 27 (ink flow path 28) with a long designed AL, the intervals may be large.

FIG. 6 is a diagram showing an example of AL estimation.
As shown in FIG. 6A, for example, ink is ejected at nine different pulse widths for each of the 256 ink flow paths 28 for the 256 nozzles 27, and the ink ejection speed is measured. Here, the pulse width is set to be wider at both ends than at the center, but it may be evenly spaced as described above. These measurement results are fitted for each ink flow path 28 to identify the AL that is the maximum value (local maximum value). FIG. 6B shows the fitting results for two ink flow paths 28 (channel 2 and channel 128). FIG. 6C shows the distribution of AL values obtained by fitting. In addition to the difference between the fine ink flow paths 28, it can be seen that the AL is generally low in the channels before channel 160. In this way, there are cases where the AL tendency is somewhat grouped due to the structure, and by setting the pulse width to an average value for the whole rather than to be grouped according to the position of the representative nozzle, large fluctuations in the ink ejection speed in parts can be suppressed.

Figure 7 shows the difference between the ejection speed of a single ink droplet and the ejection speed of a multi-drop ejection by a drive pulse of a pulse width of a nozzle 27 selected near the center, relative to the amount of deviation (difference) in the pulse width with respect to the AL of the nozzle 27 selected near the center. The nozzle 27 selected near the center here refers to a specific nozzle 27 that is determined as a representative nozzle located in the center, and is expected to have an AL deviation of up to about ±0.05 μsec with respect to the average value (average AL) of the fastest drive pulse width (AL) of all nozzles 27. The ejection speed is the average value of the ejection speeds from each nozzle 27 in one row of the inkjet head 21.

As the pulse width deviates from the average AL, there is a tendency for the deviation (variation) between the ink droplet speed ejected in multi-drop by a drive pulse of this pulse width and the ink droplet speed during single ejection to tend to increase. In other words, if one of the nozzles 27 is simply selected as the representative nozzle, the ejection speed during multi-drop may vary greatly depending on the AL of this nozzle 27. Conversely, by setting the average AL as the pulse width and ejecting ink, it is clear that there is no large variation in droplet speed (i.e., landing position) even when ejected in multi-drop, and image quality can be stabilized.

The above-mentioned process of inspecting and setting the drive waveform (pulse width) is performed, for example, by mounting the inkjet head 21 or head unit to an inspection device during pre-shipment inspection of the inkjet head 21 or head unit.

FIG. 8 is a block diagram showing the functional configuration of the inspection device 200.
The inspection device 200 includes a transport unit 210, a head drive unit 225, a drive waveform signal generation unit 229, a memory unit 230, a control unit 240, an imaging unit 250, a communication unit 270, an operation reception unit 281, a display unit 282, and the like.

The drive waveform signal generating unit 229 generates and outputs a signal with the same drive waveform as that of the drive waveform signal generating unit 29 of the inkjet recording device 100. The head driving unit 225 outputs the signal (drive pulse) input from the drive waveform signal generating unit 229 to the attached inkjet head 21 based on the control of the control unit 240.

The transport unit 210 transports the recording medium in correspondence with the ink ejection surface of the inkjet head 21. As with the inkjet recording device 1, the transport unit 210 may be configured to move a transport belt in a circular motion to transport the recording medium placed on the outer peripheral surface of the transport belt. The imaging unit 250 captures an image of the surface of the recording medium downstream of the ink landing position in the transport direction of the transport unit 210. As with the imaging unit 50, the imaging unit 250 may be configured to obtain a two-dimensional image by combining one-dimensional imaging by a line sensor with the movement of the recording medium.

The operation reception unit 281 receives input operations from the outside, such as from a user. The operation reception unit 281 has, for example, some or all of various input devices such as a touch panel, a keyboard, a numeric keypad, and a mouse, and push button switches. The display unit 282 is not particularly limited, but is, for example, a liquid crystal display, has a display screen, and performs various displays based on the control of the control unit 240. The display unit 282 can display, for example, a test setting menu, a status related to the progress of the test, and the results of the test.

The control unit 240 has a CPU 241 and a RAM 242, and controls the operations related to the inspection. The storage unit 230 is a non-volatile memory or the like, and stores programs related to the inspection, setting data, measurement data 231, etc.

The communication unit 270 controls communication with the outside. The communication unit 270 may have, for example, a network card and be capable of communicating with an external device via a network. The communication unit 270 may also be connectable to a storage unit of the inkjet head 21 connected to the head driving unit 225, and may be capable of writing information on the set pulse width and the like to this storage unit under the control of the control unit 240.
In addition, the inspection device 200 may be a device in which the configuration related to the operation and the configuration related to the control are different and are combined.

9 is a flow chart showing a control procedure by the control unit 240 of the inspection device 200 for setting a drive waveform for the inkjet head 21. This process includes the inkjet head drive setting method of this embodiment.
When the drive waveform setting process is started, the control unit 240 (CPU 241) of the inspection device 200 sets the pulse width (step S101). The control unit 240 ejects ink from each nozzle 27 in order or in a predetermined number of nozzles at a time, and measures the ejection speed of each ink droplet (step S102). The ink ejection speed may be obtained by acquiring the movement amount of the ink droplet that flies directly, or may be calculated based on information on the position where the ink droplet lands on the test recording medium that is moved relatively.

The control unit 240 determines whether or not measurements have been completed for all (multiple) pulse widths that have been set (step S103). If it is determined that measurements have not yet been completed (step S103: NO), the control unit 240 returns to step S101 and repeats setting and measuring other pulse widths that have not been set.

When it is determined that the measurements have been completed for all pulse widths ("YES" in step S103), the control unit 240 acquires the velocity distribution for a plurality of pulse widths for each nozzle 27, and fits the relationship between the pulse width and the ejection velocity to a predetermined function (a cubic function in this case).The control unit 240 then estimates (specifies) the maximum velocity (maximum velocity) and the pulse width at that time (fastest drive pulse width), i.e., the AL for this nozzle 27, based on the parameters of the fitted function (step S104).
The processes in steps S101 to S104 constitute the acquisition step in the drive setting method of this embodiment.

The control unit 240 calculates the average value of the calculated AL (step S105). If an AL that is extremely different from the design value is calculated, it may be assumed that an ejection abnormality has occurred in the first place and ink ejection from the nozzle 27 in question may be prohibited. The control unit 240 also calculates the variation (e.g., variance, etc.) of the AL of each nozzle relative to the calculated average value, performs a performance level evaluation of the inkjet head 21 (head unit) according to the degree of the variation, and determines the evaluation level (e.g., five levels of numbers 1 to 5, five levels of letters A to E, etc.) (step S106; evaluation step). The control unit 240 sets the calculated average value as the pulse width of the inkjet head 21 (head unit) to be inspected (step S107; setting step). The setting is written, for example, in a non-volatile memory (part of the storage unit 30) provided in the inkjet head 21, and in this case, it is sufficient that the control unit 40 can read the setting after the inkjet head 21 is attached to the inkjet recording device 100. The written content may also include the evaluation level. Then, the control unit 240 ends the drive waveform setting process.

As described above, the drive setting method of this embodiment is a drive setting method for an inkjet head 21 including a plurality of nozzles 27 each ejecting an ink droplet, a plurality of ink flow paths 28 communicating with the plurality of nozzles 27, a plurality of piezoelectric elements 26 that perform an operation of applying pressure fluctuations to the ink in the plurality of ink flow paths 28, and a head drive unit 25 that outputs drive pulses to the plurality of piezoelectric elements 26 and causes the piezoelectric elements 26 to generate pressure fluctuations according to the pulse width of the drive pulses. This drive setting method includes an acquisition step of measuring the ejection speed of ink droplets for each of the plurality of ink flow paths 28 and acquiring the fastest drive pulse width at which the ejection speed is maximized, and a setting step of setting a value based on the acquired plurality of fastest drive pulse widths as the pulse width of the drive pulse to be output to the piezoelectric elements 26. In this way, by setting the pulse width of the drive pulse to a value (statistical representative value) based on the AL of multiple ink flow paths 28 rather than using the AL of the ink flow path 28 associated with a single nozzle 27 as a representative value, it is possible to reduce ink ejection from nozzles 27 associated with ink flow paths 28 whose pulse widths differ greatly from the AL, thereby reducing the variation in ink ejection speed. At the same time, since the pulse width itself can be made uniform for multiple nozzles 27 in this way, there is no need to have a configuration in which each nozzle is set and applied, and the effort, cost, size of the drive circuit, etc. can be effectively reduced.

In particular, in the setting step, the average value of the multiple fastest drive pulse widths is set as the pulse width of the drive pulse, which makes it difficult for the pulse width to deviate significantly from the AL of each ink flow path 28 (nozzle 27).

In the acquisition step, the relationship between the pulse width and the ink ejection speed is fitted with a predetermined function to identify the fastest drive pulse width. Since the ink ejection speed can be roughly approximated with a function (e.g., a cubic function) that has a maximum (local maximum) at AL for the pulse width, fitting to measurements at multiple pulse widths makes it possible to estimate the maximum pulse width without having to directly identify it by measurement, thereby reducing the amount of work required.

In addition, in the acquisition step, the ink ejection speed corresponding to at least four different pulse widths is measured. When fitting to a higher-order function, particularly a cubic function, using data from four or more points generally provides sufficient accuracy.

The inkjet head 21 also has multiple nozzle groups, each of which has multiple nozzles 27, and in the setting step, a pulse width is set for each nozzle group. In this way, depending on the situation, such as when there are a large number of nozzles or when the size is large and the AL is prone to vary from position to position due to manufacturing, it is possible to set a pulse width for each of several nozzles 27, rather than a single pulse width. This makes it possible to effectively reduce variation in the ejection speed depending on the situation, without significantly increasing the effort required for setting or the complexity of drive control.

The acquisition step and setting step are performed during the pre-shipment inspection of the inkjet head 21. By setting the steps at the same time during the pre-shipment inspection, the work can be reduced. After shipment, the processing is easy because it is only necessary to read the setting data and determine the drive pulse.

This drive setting method also includes an evaluation step of evaluating the level of performance according to the variation in the fastest drive pulse width for each ink flow path 28 obtained in the acquisition step for the pulse width set in the setting step. The average value does not reflect the degree of variation (dispersion, etc.) in AL, so uniform performance is not necessarily obtained. Therefore, by performing an evaluation according to the degree of variation, the expected accuracy can be easily obtained. In addition, by combining and using inkjet heads 21 with evaluation levels according to the image quality level required for the inkjet recording device 100, it is possible to obtain an inkjet recording device 100 having inkjet heads 21 that can obtain the desired level of image quality while suppressing increases in costs due to reduced yields, etc.

The method of driving the inkjet head 21 of this embodiment also includes a driving step of outputting to the piezoelectric elements 26 driving pulses having pulse widths determined by setting the pulse width of the driving pulses obtained by the above method.
The inkjet head 21 driven in this manner can eject ink at a stable ejection speed with less variation through simple control.

In addition, in the driving step, it is possible to eject multiple ink droplets by multiple consecutive drive pulses and land them on the same pixel range of the recording medium, and the output interval of the last two drive pulses among the output intervals of the multiple drive pulses is wider than the output intervals other than the last two output intervals among the output intervals of three or more drive pulses. In this way, when ink ejection using a multi-drop method is possible, the ink ejection speed may vary more depending on the pulse width, but even in such cases, the variation is appropriately reduced. Also, by making the penultimate ejection period (the interval from the rising edge of a pulse to the rising edge of the next pulse) longer, the occurrence of satellites (microdroplets) is reduced, and deterioration of image quality and deterioration of the ink ejection characteristics are suppressed.

The present invention is not limited to the above-described embodiment, but may be modified in various ways.
For example, in the above embodiment, the average value of the ALs for all the ink flow paths 28 (nozzles 27) is used as a statistical representative value for setting the pulse width, but this is not limited to this. Other statistical representative values include the mode and the median. The average value may also be adjusted slightly depending on the skewness, etc.

In addition, in the above embodiment, the pulse width is set for each inkjet head 21, but a unified pulse width may be set across multiple inkjet heads 21 (e.g., in a head unit).

In addition, in the above embodiment, the fastest drive pulse width is estimated by fitting a cubic function based on the ejection speed for multiple pulse widths, but this is not limited to the above. The fastest drive pulse width may be determined asymptotically within a predetermined range of accuracy. Also, other functions may be used instead of a cubic function. Furthermore, the fastest drive pulse width may be estimated by combining multiple approximation lines, rather than by a single fitting.

In addition, in the above embodiment, a performance level evaluation is described, but it is not necessary to perform the evaluation.

In the above embodiment, the pulse width is set by a dedicated inspection machine during pre-shipment inspection, but this is not limited to the above. The setting or change may be made directly in the inkjet recording device 100 after shipment. Furthermore, the inspection results may be output to an external device (such as a PC) and the pulse width setting value may be calculated.

In addition, in the above embodiment, it has been described that ink ejection can be performed using a multi-drop method, but this is not necessarily limited to this. It may also be possible to switch between single-drop ink ejection and non-drop for each pixel range.

Furthermore, the drive element that applies pressure fluctuations to the ink does not have to be the piezoelectric element 26. There are no particular limitations as long as the drive element is configured to be able to apply pressure fluctuations that correspond to the pulse width of the drive pulse.
In addition, the specific details of the setting method, driving method, and configuration of the inkjet head 21 shown in the above embodiment can be modified as appropriate without departing from the spirit of the present invention. The scope of the present invention includes the scope of the invention described in the claims and its equivalents.

REFERENCE SIGNS LIST 10 Conveying section 12 Conveying belt 14 Conveying motor 20 Recording operation section 20a Recording element 21 Inkjet head 22 Carriage 25 Head driving section 26 Piezoelectric element 27 Nozzle 28 Ink flow path 29 Driving waveform signal generating section 30 Storage section 31 Waveform setting data 40 Control section 41 CPU
42 RAM
50 Imaging section 70 Communication section 81 Operation reception section 82 Display section 90 Power supply section 100 Inkjet recording apparatus 200 Inspection device 210 Conveying section 225 Head driving section 229 Driving waveform signal generating section 230 Storage section 231 Measurement data 240 Control section 241 CPU
242 RAM
250 imaging unit 270 communication unit 281 operation reception unit 282 display unit

Claims (9)

1. A drive setting method for an inkjet head comprising: a plurality of nozzles each ejecting ink droplets; a plurality of ink flow paths communicating with the plurality of nozzles; a plurality of drive elements each performing an operation of applying a pressure fluctuation to ink in the plurality of ink flow paths; and a drive control unit applying a drive pulse to the plurality of drive elements, causing the drive elements to generate a pressure fluctuation corresponding to a pulse width of the drive pulse, the method comprising the steps of:
an acquisition step of measuring an ink droplet ejection speed for each of the plurality of ink flow paths and acquiring a maximum drive pulse width at which the ink droplet ejection speed is maximized;
a setting step of setting a value based on the acquired plurality of fastest drive pulse widths to a pulse width of the drive pulse to be output to the plurality of drive elements;
Including,
In the setting step, the average value of the plurality of fastest drive pulse widths is set to the pulse width of the drive pulse.
2. A method for setting the drive of an inkjet head, comprising: 2. The inkjet head drive setting method according to claim 1 , wherein in the obtaining step, the fastest drive pulse width is specified by fitting a relationship between the pulse width and the ejection speed with a predetermined function. 3. The inkjet head drive setting method according to claim 2 , wherein the acquiring step measures ink ejection velocities corresponding to at least four different pulse widths. 1. A drive setting method for an inkjet head comprising: a plurality of nozzles each ejecting ink droplets; a plurality of ink flow paths communicating with the plurality of nozzles; a plurality of drive elements each performing an operation of applying a pressure fluctuation to ink in the plurality of ink flow paths; and a drive control unit applying a drive pulse to the plurality of drive elements, causing the drive elements to generate a pressure fluctuation corresponding to a pulse width of the drive pulse, the method comprising the steps of:
an acquisition step of measuring an ink droplet ejection speed for each of the plurality of ink flow paths and acquiring a maximum drive pulse width at which the ink droplet ejection speed is maximized;
a setting step of setting a value based on the acquired plurality of fastest drive pulse widths to a pulse width of the drive pulse to be output to the plurality of drive elements;
Including,
In the obtaining step, ink ejection speeds corresponding to at least four different pulse widths are measured, and the fastest drive pulse width is specified by fitting a relationship between the pulse width and the ejection speed with a predetermined function.
2. A method for setting the drive of an inkjet head, comprising: the inkjet head includes a plurality of nozzle groups each including the plurality of nozzles;
5. The inkjet head drive setting method according to claim 1, wherein in the setting step, the pulse width is set for each of the nozzle groups. The inkjet head drive setting method according to any one of claims 1 to 5, characterized in that the acquisition step and the setting step are performed during a pre-shipment inspection of the inkjet head. The inkjet head drive setting method according to any one of claims 1 to 6, characterized in that it includes an evaluation step of evaluating the level of performance according to the variation in the fastest drive pulse width for each of the plurality of ink flow paths obtained in the acquisition step with respect to the pulse width set in the setting step. A method for driving an inkjet head comprising: a plurality of nozzles each ejecting an ink droplet; a plurality of ink flow paths communicating with the plurality of nozzles; a plurality of drive elements each performing an operation of applying a pressure fluctuation to ink in the plurality of ink flow paths; and a drive control unit applying a drive pulse to the plurality of drive elements, causing the drive elements to generate a pressure fluctuation corresponding to a pulse width of the drive pulse, the method comprising the steps of:
8. A method for driving an inkjet head, comprising: a driving step of outputting, to each of the driving elements, the driving pulses having the pulse widths determined by the driving setting method according to claim 1. In the driving step, a plurality of ink droplets can be ejected by a plurality of successive driving pulses, and can be caused to land on the same pixel area of a recording medium;
9. The inkjet head driving method according to claim 8, wherein, among the output intervals of the plurality of drive pulses, the output interval of the last two drive pulses is wider than the output intervals of the three or more drive pulses other than the output interval of the last two drive pulses.

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