JP2015112825A - Liquid discharge device, head unit, and liquid discharge method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow printing of a high quality image in which generation of variation of ink impact positions is suppressed when high speed printing is executed.SOLUTION: A liquid discharge device has: a piezoelectric element which deforms by application of a first drive signal or a second drive signal; a cavity the inside of which liquid is filled, and the internal pressure of which is increased and decreased by deformation of the piezoelectric element; a nozzle which discharges the liquid as droplets by increase and decrease of the pressure in the cavity; and a drive signal generation part which generates the first drive signal and the second drive signal, in which the first drive signal includes: a first micro vibration waveform for deforming the piezoelectric element so as not to discharge the liquid from the nozzle; and a drive waveform for deforming the piezoelectric element so as to discharge the liquid from the nozzle, the second drive signal includes; a second micro vibration waveform and a drive waveform for deforming the piezoelectric element so as not to discharge the liquid from the nozzle, and discharge amounts of a first droplet to be discharged from the nozzle by the application of the first drive signal and a second droplet to be discharged from the nozzle by the application of the second drive signal are almost equal to each other.

Description

  The present invention relates to a liquid ejection apparatus, a head unit, and a liquid ejection method.

  The liquid ejection apparatus is an apparatus that includes a liquid ejection head capable of ejecting liquid and ejects various liquids from the liquid ejection head. A typical example of this liquid ejecting apparatus is an ink jet printer that records an image or the like by ejecting liquid ink from a nozzle of a liquid ejecting head onto a recording medium such as recording paper and landing on the recording medium. be able to.

In the liquid ejection device, when liquid is ejected from a plurality of nozzles or when liquid is ejected from the same nozzle multiple times, ejection characteristics such as the flying speed (ejection speed) of the liquid to be ejected and the weight of the liquid It is important to reduce the variation in the quality of products such as images.
For example, in Patent Document 1, when liquid is ejected from a plurality of nozzles, a waveform of a signal for driving a pressure generating element corresponding to a nozzle located at an end portion and a pressure generation corresponding to a nozzle located at a central portion are disclosed. By making the waveform of the signal for driving the element into a waveform having a different shape, the ejection characteristics of the liquid ejected from the nozzle located at the end, and the ejection characteristics of the liquid ejected from the nozzle located at the center A technique for reducing the variation between the two is disclosed.

JP 2010-188695 A

  By the way, when discharging the same amount of liquid from the same nozzle multiple times, the residual vibration after the first discharge affects the second and subsequent discharges, and the first and second droplets are discharged. Discharge speed may be different. When the discharge speed for the first drop and the discharge speed for the second and subsequent drops are different, the interval between the landing positions may vary, and the quality of the image generated in the printing process may deteriorate. In particular, when high-speed printing or high-resolution printing is performed, it is difficult to secure a discharge interval with a length of time that can sufficiently suppress residual vibration. In some cases, the influence on the discharge becomes large, and the quality of the image generated in the printing process is greatly deteriorated.

  The present invention has been made in view of the above-described circumstances, and one of its purposes is to suppress the occurrence of variations in the landing positions of ink droplets even when high-speed printing or high-resolution printing is performed. An object of the present invention is to provide a liquid ejecting apparatus, a head unit, and a liquid ejecting method capable of printing a high-quality image.

  In order to solve the above problems, a liquid ejection apparatus according to the present invention includes a piezoelectric element that is deformed by application of a first drive signal or a second drive signal, a liquid filled therein, and the piezoelectric element A cavity whose internal pressure is increased or decreased by deformation, a nozzle which communicates with the cavity and discharges the liquid as droplets by increasing or decreasing the pressure in the cavity, and generates the first drive signal and the second drive signal A first fine vibration waveform for deforming the piezoelectric element so that the liquid is not ejected from the nozzle when applied to the piezoelectric element, A drive waveform that deforms the piezoelectric element so that the liquid is ejected from the nozzle when applied to the piezoelectric element, and the second drive signal includes the first micro-vibration waveform and A first waveform that includes a second fine vibration waveform that deforms the piezoelectric element so that the liquid is not discharged from the nozzle when applied to the piezoelectric element, and the drive waveform. When a signal is applied to the piezoelectric element, the discharge amount of the first droplet discharged from the nozzle, and when the second drive signal is applied to the piezoelectric element, the first droplet discharged from the nozzle. The discharge amount of the two droplets is approximately equal.

In the case where the same amount of liquid is discharged from the nozzle multiple times, the residual vibration generated in the piezoelectric element after the first discharge affects the second and subsequent discharges, so that the droplet discharge speed in the first discharge In some cases, the discharge speed of the droplets in the second discharge may be different. Especially in high-speed and high-resolution printing where the discharge interval cannot be secured sufficiently, the residual vibration generated by the first discharge has a great influence on the second discharge, and between the first discharge and the second and subsequent discharges. As a result, the variation in the discharge speed of the droplets increases. When variations occur in the ejection speed of the droplets, the interval between the landing positions of the droplets varies, so that the quality of an image formed by the ejected droplets is also lowered.
According to the present invention, in addition to the drive waveform for discharging the liquid, fine vibration waveforms having different waveforms for the first discharge and the second discharge are applied to the piezoelectric elements, respectively, and discharged in the first discharge. The discharge amount of the first droplet and the discharge amount of the second droplet discharged in the second discharge are made substantially equal. When the discharge amounts of the droplets discharged from the nozzle are substantially equal, the discharge speed is also substantially equal. For this reason, compared with the case where the waveform of the 1st minute vibration waveform and the 2nd minute vibration waveform is the same, the degree of variation of the interval of the landing positions of the droplets can be reduced, and the discharged droplets As a result, the quality of the image formed can be increased.
Note that “the discharge amounts are substantially equal” is considered to be equal in addition to the case where the discharge amounts are exactly the same, in consideration of mixing of noise with respect to the drive signal, manufacturing error of the liquid discharge device, and the like (that is, removing the error). When you can do it.

  In addition, the liquid ejection device according to the present invention includes a piezoelectric element that is deformed by applying the first drive signal or the second drive signal, and a liquid that fills the inside. A cavity that communicates with the cavity and discharges the liquid as droplets by increasing or decreasing the pressure in the cavity, and a drive signal generator that generates the first drive signal and the second drive signal, And the first drive signal includes a drive waveform that deforms the piezoelectric element so that the liquid is ejected from the nozzle when applied to the piezoelectric element, and the second drive signal includes A second micro-vibration waveform that deforms the piezoelectric element so that the liquid is not discharged from the nozzle when applied to the piezoelectric element; and the drive waveform, wherein the first drive signal is When applied to the piezoelectric element, the second liquid ejected from the nozzle when the ejection amount of the first droplet ejected from the nozzle and the second drive signal are applied to the piezoelectric element. The droplet discharge amount may be substantially equal.

In the above-described liquid ejecting apparatus, it is preferable that the second droplet is a droplet ejected after the first droplet is ejected from the nozzle.
According to this aspect, the first droplet is ejected by the first drive signal, and the second droplet ejected after the first droplet is ejected by the second drive signal having a waveform different from that of the first drive signal. To do. For this reason, even when the ejection of the first droplet is not affected by the residual vibration and the ejection of the second droplet is affected by the residual vibration, the ejection speed of the first droplet and the second droplet The discharge speed of the liquid droplets can be made substantially equal, and the degree of variation in the interval between the landing positions of the droplets can be kept low, so that a high-quality image can be formed by the liquid discharge apparatus.

In the above-described liquid ejection apparatus, it is preferable that the liquid droplets ejected from the nozzle are not ejected at the ejection timing immediately before the first liquid droplet is ejected.
According to this aspect, in the discharge of the first droplet that is not affected by the residual vibration and the discharge of the second droplet that is affected by the residual vibration, the discharge amount of the discharged droplet can be made substantially equal. Therefore, the degree of variation in the interval between droplet landing positions can be kept low, and a high-quality image can be formed by the liquid ejection device.

In the above-described liquid ejecting apparatus, the droplet ejected from the nozzle includes a third droplet, and the ejection amount of the first droplet and the ejection amount of the second droplet are the third droplet. It is preferable that the discharge amount is larger than the discharge amount.
The size of the first droplet and the second droplet is larger than the size of the third droplet, as in the case where the liquid ejecting apparatus forms a plurality of types of dots such as large dots, medium dots, and small dots. If it is larger, the dot formed by the first droplet or the second droplet is more conspicuous than the dot formed by the third droplet, and therefore an image due to variations in the ejection speed of the first droplet and the second droplet. The influence on the quality of the image is greater than the influence on the quality of the image due to the variation in the ejection speed of the third droplet.
According to this aspect, the discharge amounts of the first droplet and the second droplet are made substantially equal, thereby reducing variations in the landing positions of the first droplet and the second droplet. The influence on the quality of the image to be performed can be minimized, and even if the ejection speed of the third droplet is not accurate, the deterioration of the image quality of the entire image can be minimized.

  In addition, it is preferable that the above-described liquid ejection apparatus can perform printing at a resolution of 720 × 720 dpi or more and a printing speed of 220 m / min or more.

In the above-described liquid ejecting apparatus, it is preferable that the first fine vibration waveform and the second fine vibration waveform have different potential directions.
According to this aspect, for example, the first fine vibration waveform is a waveform that causes residual vibration, and the second fine vibration waveform is a waveform that attenuates the residual vibration, thereby reducing the influence of the residual vibration. It is possible to forcibly generate residual vibration in the discharge of the first droplet that is not affected, and to attenuate the residual vibration in the discharge of the second droplet that is affected by the residual vibration. The discharge speed of the second droplet can be made substantially equal. As a result, the degree of variation in the interval between droplet landing positions can be suppressed to a low level, and a high-quality image can be formed by the liquid ejection device.

The head unit according to the present invention includes a piezoelectric element that is deformed by application of the first drive signal or the second drive signal, and a liquid filled therein, and the internal pressure is increased or decreased by the deformation of the piezoelectric element. A cavity that communicates with the cavity and discharges the liquid as droplets by increasing or decreasing the pressure in the cavity; and a drive signal generator that generates the first drive signal and the second drive signal. And the first drive signal is applied to the piezoelectric element, and when applied to the piezoelectric element, the first fine vibration waveform for deforming the piezoelectric element so that the liquid is not discharged from the nozzle. And a drive waveform for deforming the piezoelectric element so that the liquid is ejected from the nozzle, and the second drive signal is a waveform different from the first fine vibration waveform. A second micro-vibration waveform that deforms the piezoelectric element so that the liquid is not ejected from the nozzle when applied to the piezoelectric element, and the drive waveform, and the first drive signal is applied to the piezoelectric element. When applied, the discharge amount of the first droplet discharged from the nozzle and the discharge amount of the second droplet discharged from the nozzle when the second drive signal is applied to the piezoelectric element. Is substantially equal.
According to the present invention, in addition to the drive waveform for discharging the liquid, fine vibration waveforms having different waveforms for the first discharge and the second discharge are applied to the piezoelectric elements, respectively, and discharged in the first discharge. The discharge amount of the first droplet and the discharge amount of the second droplet discharged in the second discharge are made substantially equal. When the discharge amounts of the droplets discharged from the nozzle are substantially equal, the discharge speeds are also approximately equal, so that the droplets of the droplets are compared with the case where the waveforms of the first and second fine vibration waveforms are the same. The degree of variation in the landing position interval can be reduced, and the quality of the image formed by the discharged droplets can be increased.

The liquid ejection method according to the present invention includes a piezoelectric element that is deformed by applying the first drive signal or the second drive signal, and a liquid that fills the inside, and the internal pressure is increased or decreased by the deformation of the piezoelectric element. A liquid ejecting method for a liquid ejecting apparatus, comprising: a cavity that communicates with the cavity; and a nozzle that ejects the liquid as droplets by increasing or decreasing the pressure in the cavity, the first droplet, The step of selecting which one of the first droplet and the second droplet having substantially the same discharge amount is to be ejected from the nozzle, and when ejecting the first droplet, causes the piezoelectric element to perform the first drive. A step of applying a signal, and a step of applying the second drive signal to the piezoelectric element when the second droplet is ejected, wherein the first drive signal is applied to the piezoelectric element. A first micro-vibration waveform that deforms the piezoelectric element so that the liquid is not discharged from the nozzle, and the piezoelectric element is deformed so that the liquid is discharged from the nozzle when applied to the piezoelectric element. The second drive signal is a waveform different from the first micro-vibration waveform, and the piezoelectric element is configured not to discharge the liquid from the nozzle when applied to the piezoelectric element. Including a second micro-vibration waveform that deforms and the drive waveform.
According to the present invention, in addition to the drive waveform for discharging the liquid, fine vibration waveforms having different waveforms for the first discharge and the second discharge are applied to the piezoelectric elements, respectively, and discharged in the first discharge. The discharge amount of the first droplet and the discharge amount of the second droplet discharged in the second discharge are made substantially equal. When the discharge amounts of the droplets discharged from the nozzle are substantially equal, the discharge speeds are also approximately equal, so that the droplets of the droplets are compared with the case where the waveforms of the first and second fine vibration waveforms are the same. The degree of variation in the landing position interval can be reduced, and the quality of the image formed by the discharged droplets can be increased.

The liquid ejection device according to the present invention includes a piezoelectric element that is deformed in response to a drive signal, a cavity in which an internal pressure is increased or decreased by deformation of the piezoelectric element based on the drive signal, and the cavity that communicates with the cavity. A discharge unit including a nozzle capable of discharging a liquid filled in the cavity by increasing or decreasing a pressure inside the cavity; and generating the drive signal and supplying the generated drive signal to the piezoelectric element. A drive signal generation unit that drives the piezoelectric element, and the drive signal generation unit deforms the piezoelectric element so that the liquid is not discharged from the nozzle when the discharge unit is driven so that the liquid is not discharged from the nozzle. To supply a non-ejection drive signal having a first micro-vibration waveform that causes residual vibration in the cavity to the piezoelectric element, and supply liquid from the nozzle. When driving the ejection unit to eject, a drive waveform for deforming the piezoelectric element so that liquid is ejected from the nozzle, and residual vibration generated in the cavity after the drive waveform is supplied to the piezoelectric element A discharge drive signal having a second fine vibration waveform that deforms the piezoelectric element so as to attenuate the piezoelectric element may be supplied to the piezoelectric element.
In this aspect, the drive signal generation unit supplies the drive signal to the piezoelectric element in each of one unit period and another unit period subsequent to the one unit period. Driving, and after the drive signal generator supplies the ejection drive signal to the piezoelectric element in the one unit period, the ejection drive signal is supplied to the piezoelectric element in the other unit period. When supplied, the flying speed of the liquid ejected from the nozzle in the other unit period is set as the first speed, and the drive signal generation unit outputs the non-ejection drive signal in the one unit period. When the ejection drive signal is supplied to the piezoelectric element in the other unit period after being supplied to the piezoelectric element, the liquid ejected from the nozzle in the other unit period is discharged. A speed is set to a second speed, and the drive signal generation unit applies a drive signal having a waveform obtained by removing the second micro-vibration waveform from the waveform of the ejection drive signal to the piezoelectric element in the one unit period. After supplying, when the ejection drive signal is supplied to the piezoelectric element in the other unit period, the flying speed of the liquid ejected from the nozzle in the other unit period is set as the third speed, The drive signal generation unit supplies the piezoelectric element with a drive signal having a waveform obtained by removing the first micro-vibration waveform from the waveform of the non-ejection drive signal in the one unit period. In the unit period, when the ejection drive signal is supplied to the piezoelectric element, the flying speed of the liquid ejected from the nozzle in the other unit period is set to the fourth speed. 1 rate and the difference value of the second speed, the smaller than the difference value of the third speed and the fourth speed may be characterized in that.
In this aspect, the drive signal generation unit may execute a printing process in which the liquid ejection device forms an image on the recording medium by ejecting liquid from the nozzles as droplets onto the recording medium. In the printing process, the non-ejection drive signal is supplied to the piezoelectric element of the ejection section having the nozzle before the ejection drive signal is first supplied. May be.
Further, in this aspect, the drive signal generation unit supplies the drive signal to the piezoelectric element in a unit period, thereby driving the ejection unit in the unit period, and the drive signal for ejection in the unit period. In the case of supplying the non-ejection drive signal in the unit period, the time length from the start of the supply of the second micro-vibration waveform to the end of the unit period is the first length in the case of supplying the non-ejection drive signal in the unit period. The time length from the time when the supply of the minute vibration waveform is started to the end of the unit period may be equal to or longer.

1 is a block diagram illustrating a configuration of an inkjet printer 1 according to a first embodiment of the present invention. 1 is a schematic cross-sectional view of an essential part of an inkjet printer 1. 4 is an explanatory diagram for explaining a positional relationship between a head unit 3 and a recording medium P. FIG. 3 is a schematic cross-sectional view of a main part of a head unit 3. It is explanatory drawing for demonstrating the change of the cross-sectional shape of the discharge part 35 at the time of supply of the drive signal Vin. 3 is a block diagram showing a configuration of a drive signal generation unit 5. FIG. It is explanatory drawing which shows the decoding content of decoder DC. It is a timing chart which shows operation | movement of the drive signal generation part 5 in the unit period Tu. It is a timing chart which shows the drive waveform signal ComT which concerns on proportionality. FIG. 6 is an explanatory diagram for explaining residual vibration that occurs when a drive waveform signal ComT related to the proportionality is supplied to the ejection unit 35; It is explanatory drawing for demonstrating the ink discharged from the discharge part 35 driven by the drive waveform signal ComT which concerns on proportionality. FIG. 6 is an explanatory diagram for explaining residual vibration that occurs when a drive waveform signal Com is supplied to the ejection unit 35; FIG. 6 is an explanatory diagram for explaining ink ejected from an ejection unit 35 driven by a drive waveform signal Com. It is explanatory drawing for demonstrating a 1st drive signal and a 2nd drive vibration. It is a block diagram which shows the structure of 5 A of drive signal generation parts which concern on 2nd Embodiment. It is explanatory drawing which shows the decoding content of decoder DC which concerns on 2nd Embodiment. It is a timing chart which shows drive waveform signal Com2. It is explanatory drawing for demonstrating a 1st drive signal and a 2nd drive vibration. It is a flowchart for demonstrating the printing process of the inkjet printer which concerns on 2nd Embodiment. It is a timing chart which shows drive waveform signal Com2. It is a timing chart which shows drive waveform signal Com3. It is explanatory drawing which shows the decoding content of decoder DC which concerns on the modification 2 of this invention. It is a timing chart which shows drive waveform signal Com4. It is a schematic principal part sectional drawing of 3 A of head parts which concern on the modification 3 of this invention.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, in each figure, the size and scale of each part are appropriately changed from the actual ones. Further, since the embodiments described below are preferable specific examples of the present invention, various technically preferable limitations are attached thereto. However, the scope of the present invention is particularly limited in the following description. Unless otherwise stated, the present invention is not limited to these forms.

<A. First Embodiment>
In the present embodiment, an example of an ink jet line printer that ejects ink (an example of “liquid”) and forms an image on a recording medium P such as paper, cloth, or film will be described as an example of the liquid ejecting apparatus.

<1. Configuration of inkjet printer>
Hereinafter, the configuration of the inkjet printer 1 according to the present embodiment will be described with reference to FIGS. 1 to 3.

FIG. 1 is a functional block diagram illustrating an example of the configuration of the inkjet printer 1 according to the present embodiment. FIG. 2 is a cross-sectional view illustrating the outline of the internal configuration of the inkjet printer 1.
As shown in FIG. 1, the inkjet printer 1 includes a head unit 3 (an example of a “head unit”) that includes M ejection units 35 and a drive signal generation that generates a drive signal Vin for driving the head unit 3. A control unit 6 that controls the operation of each unit of the inkjet printer 1 such as the head unit 3 and the drive signal generation unit 5, a conveyance mechanism 7 for changing the relative position of the recording medium P with respect to the unit 5, and the head unit 3. (M is a natural number of 4 or more). In the following description, in order to distinguish each of the M ejection units 35, they may be referred to as “first stage, second stage,..., M stage” in order.
The ink jet printer 1 is configured by, for example, a liquid crystal display, an organic EL display, an LED lamp, and the like, and includes an operation panel (illustrated) that includes a display unit that displays an error message and an operation unit that includes various switches. (Omitted).

  As shown in FIG. 1, the transport mechanism 7 includes a transport motor 71 serving as a drive source for transporting the recording medium P, and a motor driver 72 for driving the transport motor 71. Further, as shown in FIG. 2, the transport mechanism 7 includes a platen 77 provided on the lower side of the head unit 3 (−Z direction in FIG. 2), transport rollers 73 and 74 that are rotated by the operation of the transport motor 71, And guide rollers 75 and 76 that follow the rotation of the transport roller 73 or 74. The recording medium P is conveyed in the + X direction (from the upstream side to the downstream side) in the drawing along the conveyance path defined by the conveyance roller 73, the guide roller 75, the platen 77, the guide roller 76, and the conveyance roller 74. Is done.

As shown in FIG. 2, the inkjet printer 1 includes a carriage 32 that houses a head unit 3 including M ejection units 35.
In addition to the head unit 3, the carriage 32 stores a drive signal generation unit 5 (not shown in FIG. 2) and four ink cartridges 31. The carriage 32 is disposed on the opposite side of the platen 77 across the conveyance path of the recording medium P, that is, on the upper side (+ Z direction) of the platen 77.

The four ink cartridges 31 are provided in a one-to-one correspondence with the four colors of yellow, cyan, magenta, and black, and each ink cartridge 31 corresponds to the ink cartridge 31. Filled with colored ink. Each of the M ejection units 35 receives ink from any one of the four ink cartridges 31.
Each discharge unit 35 can fill the ink supplied from the ink cartridge 31 and discharge the filled ink from a nozzle N (see FIGS. 3 and 4 to be described later).
Each ejection unit 35 forms an image on the recording medium P by ejecting ink to the recording medium P at a timing when the transport mechanism 7 transports the recording medium P onto the platen 77.
As a result, it is possible to eject four colors of ink from the M ejection portions 35 as a whole, thereby realizing full-color printing.

  Note that the inkjet printer 1 according to the present embodiment includes four ink cartridges 31 corresponding to the four colors of ink, but the present invention is not limited to such an aspect, and three or less colors or five It may be provided with three or less or five or more ink cartridges 31 corresponding to inks of colors or more. In addition, an ink cartridge 31 filled with ink of a color different from the four colors may be provided, or only an ink cartridge 31 corresponding to a part of the four colors may be provided. Also good. That is, the ink jet printer according to the present invention may be any printer that can eject one or more colors of ink from the ejection unit 35. Further, each ink cartridge 31 may be provided in another place of the ink jet printer 1 instead of being mounted on the carriage 32.

As shown in FIG. 1, the control unit 6 controls the drive signal generation unit 5, the transport mechanism 7 and the like based on image data Img input from a host computer 9 such as a personal computer or a digital camera. Then, a printing process for forming an image corresponding to the image data Img on the recording medium P is executed.
Specifically, the control unit 6 drives the transport motor 71 to intermittently feed the recording medium P one by one in the transport direction (+ X direction) one by one under the control of the motor driver 72, and generates a drive signal. Through the control of the unit 5, the presence / absence of ink ejection from each ejection unit 35 and the ink ejection timing are controlled. Thereby, the control unit 6 adjusts the dot arrangement formed by the ink ejected on the recording medium P, and executes a printing process for forming an image corresponding to the image data Img on the recording medium P.
Note that the control unit 6 may execute a process of transferring information such as an error message or ejection abnormality to the host computer 9 as necessary.

As shown in FIG. 1, the control unit 6 includes a CPU 61 and a storage unit 62.
The storage unit 62 is an EEPROM (Electrically Erasable Programmable Read-Only Memory) that is a kind of nonvolatile semiconductor memory that stores image data Img supplied from the host computer 9 through an interface unit (not shown) in a data storage area, RAM (Random Access Memory) that temporarily stores data necessary for executing various processes such as print processing, or temporarily develops a control program for executing various processes such as print processing, and inkjet And a PROM which is a kind of nonvolatile semiconductor memory that stores a control program for controlling each unit of the printer 1.

The CPU 61 stores the image data Img supplied from the host computer 9 in the storage unit 62.
Further, the CPU 61 controls the operation of the drive signal generation unit 5 based on various data stored in the storage unit 62 such as the image data Img, and the print signal SI for driving each ejection unit 35, and In addition to generating signals such as the drive waveform signal Com, various signals such as a control signal for controlling the operation of the motor driver 72 are generated based on various data stored in the storage unit 62. Output a signal.
As described above, the control unit 6 (CPU 61) generates various signals such as the print signal SI and the drive waveform signal Com and supplies them to each unit of the inkjet printer 1, thereby controlling the operation of each unit of the inkjet printer 1. Thereby, the control unit 6 (CPU 61) executes various processes such as a printing process.

  The drive signal generation unit 5 generates a drive signal Vin for driving each of the M ejection units 35 included in the head unit 3 based on the print signal SI and the drive waveform signal Com supplied from the control unit 6. . Although details will be described later, in the present embodiment, the drive waveform signal Com includes drive waveform signals Com-A and Com-B.

  FIG. 3 is an explanatory diagram exemplarily showing a positional relationship between the recording medium P and the head unit 3 when the inkjet printer 1 is viewed in plan (that is, when the inkjet printer 1 is viewed from the + Z direction).

As described above, in the inkjet printer 1 according to this embodiment, the width of the head unit 3 in the Y-axis direction (that is, the width in the direction intersecting the conveyance direction of the recording medium P) is the same as that of the recording medium P in the Y-axis direction. A line printer having a width equal to or greater than the width.
As illustrated in this figure, the head unit 3 includes four nozzle rows each including a plurality of nozzles N extending in the lateral direction (Y-axis direction). Of the four nozzle rows, yellow (Y) ink is ejected from each nozzle N included in the first nozzle row, and magenta (from m each nozzle N included in the second nozzle row). M) ink is ejected, cyan (C) ink is ejected from each nozzle N included in the third nozzle row, and black (K) is ejected from each nozzle N included in the fourth nozzle row. Ink is ejected. The pitch between the nozzles N included in each of these nozzle rows can be appropriately set according to the printing resolution (dpi: dot per inch). As the ink jet printer 1 according to the present embodiment, a printer having a print resolution of “720 × 720 dpi” or more is assumed.

  In the present embodiment, the plurality of nozzles N constituting each nozzle row are arranged so as to be aligned in one row in the Y-axis direction, but the present invention is not limited to such an aspect. For example, among the plurality of nozzles N constituting each nozzle row, the positions of the even-numbered nozzles N and the odd-numbered nozzles N from the left in the drawing are arranged so as to be shifted in the X-axis direction (so-called staggered pattern). Arranged).

When the inkjet printer 1 is executing the printing process, the recording medium P is transported by the transport mechanism 7 in the downward direction (+ X direction) in FIG. 3 at a predetermined transport speed Mv. Hereinafter, the position in the X-axis direction on the recording medium P is referred to as an on-medium position Xp. The medium position Xp represents the distance in the X-axis direction from a predetermined location on the recording medium P (for example, the end of the recording medium P).
As the ink jet printer 1 according to the present embodiment, a printer having a conveyance speed Mv (printing speed) of “220 m / min” or higher is assumed.

<2. Configuration of head>
Next, the structure of the head unit 3 including the ejection unit 35 and the ink ejection operation in the ejection unit 35 will be described with reference to FIGS. 4 and 5.
FIG. 4 is an example of a schematic cross-sectional view of the head unit 3 and the ink cartridge 31. In this figure, for convenience of illustration, one of the M ejection units 35 included in the head unit 3 and a reservoir that communicates with the ejection unit 35 via the ink supply port 247. H.246.

  As shown in FIG. 4, the ejection unit 35 includes a laminated piezoelectric element 201 formed by laminating a plurality of piezoelectric elements 200, a cavity 245 filled with ink, a nozzle N communicating with the cavity 245, and vibrations. A plate 243. The ejection unit 35 ejects ink in the cavity 245 from the nozzle N when the piezoelectric element 200 is driven by the drive signal Vin.

  As shown in FIG. 4, the cavity 245 of the discharge unit 35 is partitioned by a cavity plate 242 formed in a predetermined shape having a recess, a nozzle plate 240 on which a nozzle N is formed, and a vibration plate 243. Space. The cavity 245 communicates with a reservoir 246 that is a space defined by the cavity plate 242 and the nozzle plate 240 via an ink supply port 247. The reservoir 246 communicates with the ink cartridge 31 through the ink supply tube 311.

  In FIG. 4, the lower end of the laminated piezoelectric element 201 is joined to the diaphragm 243 through the intermediate layer 244. A plurality of external electrodes 248 and internal electrodes 249 are joined to the laminated piezoelectric element 201. That is, the external electrode 248 is bonded to the outer surface of the laminated piezoelectric element 201, and the internal electrode 249 is installed between the piezoelectric elements 200 constituting the laminated piezoelectric element 201 (or inside each piezoelectric element). ing. More specifically, the external electrode 248 and a part of the internal electrode 249 are alternately arranged so as to overlap in the thickness direction of the piezoelectric element 200.

Then, by supplying the drive signal Vin from the drive signal generator 5 between the external electrode 248 and the internal electrode 249, the laminated piezoelectric element 201 is deformed as shown by the arrows in FIG. The diaphragm 243 vibrates by expanding and contracting in the direction. The volume of the cavity 245 (pressure in the cavity 245) is changed by the vibration of the vibration plate 243, and the ink filled in the cavity 245 is ejected from the nozzle N.
Ink is supplied from the reservoir 246 when the ink in the cavity 245 decreases due to ink ejection. Ink is supplied to the reservoir 246 from the ink cartridge 31 via the ink supply tube 311.

Next, the ink ejection operation in the ejection unit 35 will be described with reference to FIG.
When the drive signal Vin is supplied from the drive signal generation unit 5 to the piezoelectric element 200, distortion proportional to the voltage applied between the electrodes (electric field generated between the electrodes) is generated, and the diaphragm 243 is shown in FIG. 4), the volume of the cavity 245 is expanded as shown in FIG. 5B. In this state, when the voltage indicated by the drive signal Vin is changed by the control of the drive signal generation unit 5, the diaphragm 243 is restored by its elastic restoring force and goes downward beyond the position of the diaphragm 243 in the initial state. The volume of the cavity 245 contracts rapidly as shown in FIG. At this time, due to the compression pressure generated in the cavity 245, a part of the ink filling the cavity 245 is ejected as an ink droplet from the nozzle N communicating with the cavity 245.

  On the vibration plate 243 of each cavity 245, after this series of ink ejection operations is completed, a damping vibration, that is, a residual vibration is generated until the next ink ejection operation is started. The residual vibration of the vibration plate 243 is a natural vibration determined by the shape of the nozzle N and the ink supply port 247, the acoustic resistance due to the ink viscosity, the inertance due to the ink weight in the flow path, and the compliance of the vibration plate 243. It is assumed to have a frequency.

<3. Configuration and Operation of Drive Unit>
Next, the configuration and operation of the drive signal generation unit 5 will be described with reference to FIGS.
FIG. 6 is a block diagram illustrating a configuration of the drive signal generation unit 5. As shown in FIG. 6, the drive signal generation unit 5 has a one-to-one correspondence with a set of the shift register SR, the latch circuit LT, the decoder DC, and the transmission gates TGa and TGb to the M ejection units 35. So that it has M. Hereinafter, each element constituting the M sets may be referred to as a first stage, a second stage,...

The drive signal generator 5 is supplied with a clock signal CL, a latch signal LAT, a print signal SI, and a drive waveform signal Com (Com-A, Com-B) from the controller 6.
Here, the print signal SI is a 1-bit signal that defines whether or not ink is ejected from each ejection unit 35 (each nozzle N) when one dot of an image is formed. The print signal SI is serially supplied from the control unit 6 to the drive signal generation unit 5 in synchronization with the clock signal CL.
By controlling the presence / absence of ink ejection from each ejection unit 35 based on this print signal SI, it is possible to express two gradations of recording or non-recording in each dot of the recording medium P.

  Each of the shift registers SR temporarily holds the print signal SI for each bit corresponding to each ejection unit 35. More specifically, M shift registers SR corresponding to the M ejection units 35 are connected in cascade to each other, and the serially supplied print signal SI is sequentially transferred to the subsequent stage according to the clock signal CL. Transferred. When the print signal SI is transferred to all of the M shift registers SR, the supply of the clock signal CL is stopped, and each of the M shift registers SR corresponds to one bit of the print signal SI. Keep the minute data.

  Each of the M latch circuits LT simultaneously latches the print signal SI for one bit corresponding to each stage held in each of the M shift registers SR at the timing when the latch signal LAT rises. In FIG. 6, SI [1], SI [2],..., SI [M] are respectively latched by the latch circuits LT corresponding to the 1-stage, 2-stage,. A 1-bit print signal SI is shown.

By the way, the operation period, which is a period during which the inkjet printer 1 executes the printing process, includes a plurality of unit periods Tu.
The control unit 6 supplies the print signal SI to the drive signal generation unit 5 every unit period Tu, and the latch circuit LT prints the print signals SI [1], SI [2],. The drive signal generator 5 is controlled to latch [M]. In other words, the control unit 6 controls the drive signal generation unit 5 so that the drive signal Vin is supplied to the M ejection units 35 every unit period Tu.

The decoder DC decodes the 1-bit print signal SI latched by the latch circuit LT, and outputs selection signals Sa and Sb in each unit period Tu.
FIG. 7 is an explanatory diagram (table) showing the contents of decoding performed by the decoder DC. As shown in this figure, when the content indicated by the print signal SI [m] corresponding to m stages (m is a natural number satisfying 1 ≦ m ≦ M) is “1”, the m-stage decoder DC In the period Tu, the selection signal Sa is set to the high level H, and the selection signal Sb is set to the low level L. When the content indicated by the print signal SI [m] is “0”, the m-stage decoder DC sets the selection signal Sb to the high level H and sets the selection signal Sa to the low level L in the unit period Tu. Set.

Returning to FIG.
As shown in FIG. 6, the drive signal generator 5 includes M sets of transmission gates TGa and TGb. These sets of M transmission gates TGa and TGb are provided so as to correspond to the M ejection portions 35 on a one-to-one basis. The transmission gate TGa is turned on when the selection signal Sa is at the H level and turned off when the selection signal Sa is at the L level. The transmission gate TGb is turned on when the selection signal Sb is at the H level and turned off when the selection signal Sb is at the L level. That is, in each unit period Tu, the transmission gates TGa and TGb are exclusively turned on.

  The drive waveform signal Com-A is supplied to one end of the transmission gate TGa, and the drive waveform signal Com-B is supplied to one end of the transmission gate TGb. The other ends of the transmission gates TGa and TGb are commonly connected to the output end OTN to the discharge unit 35. Therefore, in each unit period Tu, one of the drive waveform signals Com-A and Com-B selected by the m-stage transmission gates TGa and TGb is supplied to the m-stage output terminal OTN. A drive signal Vin [m] is output to the output end OTN, and the drive signal Vin [m] is supplied to the piezoelectric element 200 of the m-stage ejection unit 35.

  FIG. 8 is an example of a timing chart for explaining the operation of the drive signal generator 5 in each unit period Tu. As shown in FIG. 8, the unit period Tu is defined by a latch signal LAT output from the control unit 6. The print signals SI [1], SI [2],..., SI [M] are output from the M latch circuits LT at the rising timing of the latch signal LAT, that is, the timing at which the unit period Tu is started. Is done.

As shown in FIG. 8, the drive waveform signal Com-A (an example of “ejection drive signal”) supplied from the control unit 6 in the unit period Tu is a unit waveform PA (an example of “drive waveform”). , A waveform having a fine vibration waveform PlsA (an example of a “second fine vibration waveform”).
When the drive waveform signal Com-A is supplied to the piezoelectric element 200 and the discharge unit 35 is driven by the unit waveform PA of the drive waveform signal Com-A, the unit waveform PA is a predetermined amount from the nozzle N of the discharge unit 35. The waveform is determined such that ink is ejected. For example, the potential difference dV between the highest potential Va11 and the lowest potential Va12 of the unit waveform PA is such that a predetermined amount of ink is ejected from the nozzle N provided in the ejection unit 35 when the ejection unit 35 is driven by the unit waveform PA. It is determined as follows.

As described with reference to FIG. 5, the pressure inside the discharge section 35 (cavity 245) increases or decreases according to the voltage applied to the piezoelectric element 200. In other words, the magnitude of the increase / decrease in the pressure inside the ejection unit 35 depends on the magnitude of fluctuation in the voltage applied to the piezoelectric element 200. For this reason, the ejection speed W of the ink ejected from the ejection unit 35, the amount of ejected ink, and the like are determined based on the potential difference dV. More specifically, as the potential difference dV increases, the ejection speed W of ink ejected from the ejection section 35 increases, and the amount of ink ejected also increases.
The discharge speed W and the discharge amount of the ink discharged from the discharge unit 35 do not depend only on the potential difference dV. For example, the waveform shape when changing from the highest potential Va11 to the lowest potential Va12 (for example, It also depends on the shape of the unit waveform PA other than the potential difference dV, such as the shape of the waveform such as whether or not the waveform of the change is a straight line, and the slope of the change. However, in this specification, in order to simplify the explanation, a simple waveform as shown in FIG. 8 is illustrated as the unit waveform PA, and the ejection speed W of the ink ejected from the ejection unit 35 is A potential difference dV will be described as an example of an element that changes the discharge amount.

  As shown in FIG. 8, the fine vibration waveform PlsA has such a waveform that ink is not discharged from the nozzle N provided in the discharge unit 35 when the piezoelectric element 200 included in the discharge unit 35 is driven by the fine vibration waveform PlsA. It has been established. Further, the potential at the start timing of the unit waveform PA and the potential at the end timing of the fine vibration waveform PlsA are both set to the reference potential V0.

The drive waveform signal Com-B (an example of “non-ejection drive signal”) supplied from the control unit 6 in the unit period Tu has a waveform having a fine vibration waveform PlsB (an example of “first fine vibration waveform”). Show.
The fine vibration waveform PlsB is determined to be a waveform such that ink is not ejected from the nozzles N provided in the ejection unit 35 when the piezoelectric element 200 provided in the ejection unit 35 is driven by the micro vibration waveform PlsB.

In the present embodiment, the time length Ta from the start of the supply of the fine vibration waveform PlsA to the end of the unit period Tu in which the drive waveform signal Com-A including the fine vibration waveform PlsA is supplied, and the fine vibration The drive waveform is set so that the time length Tb from the start of the supply of the waveform PlsB to the end of the unit period Tu in which the drive waveform signal Com-B including the fine vibration waveform PlsB is supplied ends. The waveforms of the signals Com-A and Com-B are determined.
In the present specification, “substantially the same” is a concept including a case where they can be regarded as the same if an error is taken into consideration, in addition to a case where they completely match. For example, if the inkjet printer 1 is designed to operate so that the time lengths Ta and Tb are the same, noise in the drive waveform signals Com-A and Com-B and the inkjet printer 1 Even when the time lengths Ta and Tb have different time lengths due to the manufacturing error, they are regarded as being equal and expressed as “substantially the same”.
In the present embodiment, the polarity (potential change direction) of the fine vibration waveform PlsA with reference to the reference potential V0 is opposite to the polarity (potential change direction) of the fine vibration waveform PlsB with reference to the reference potential V0. is there.

  As described above, the drive waveform signals (Com-A, Com-B) according to the present embodiment include the fine vibration waveforms (PlsA, PlsB), and the effects of having these fine vibration waveforms will be described. Therefore, hereinafter, a case where a drive waveform signal having no micro vibration waveform is supplied (hereinafter referred to as “proportional”) will be described.

<4. Drive waveform signal in proportion>
FIG. 9 is a timing chart showing the waveform of the drive waveform signal ComT according to the proportionality.
The drive waveform signal ComT according to the proportionality is a signal including drive waveform signals ComT-A and ComT-B according to the proportionality instead of the drive waveform signals Com-A and Com-B.
As shown in FIG. 9, the drive waveform signal ComT-A is a signal having a waveform obtained by removing the fine vibration waveform PlsA from the drive waveform signal Com-A, and the drive waveform signal except for the point that does not have the fine vibration waveform PlsA. It is a signal having the same waveform as Com-A. The drive waveform signal ComT-B is a signal having a waveform obtained by removing the fine vibration waveform PlsB from the drive waveform signal Com-B and is the same as the drive waveform signal Com-B except that the fine vibration waveform PlsB is not provided. It is a signal which has the following waveform.

  FIG. 10 shows the residual vibration Z generated in the discharge unit 35 in one unit period Tu when the proportional drive waveform signal ComT is supplied as the drive signal Vin to the discharge unit 35 over a plurality of unit periods Tu. FIG. 9 is an explanatory diagram for explaining an influence on driving of the ejection unit 35 in another unit period Tu subsequent to the one unit period Tu.

10A, the drive waveform signal ComT-B is supplied to the ejection unit 35 in the unit period Tu0, and the drive waveform signal ComT-A is supplied to the unit period Tu1 subsequent to the unit period Tu0. In this case, the drive waveform signal ComT-B supplied in the unit period Tu0 is an explanatory diagram showing the influence on the drive of the ejection section 35 in the unit period Tu1.
As described above, since the drive waveform signal ComT-B has a flat waveform that does not include the unit waveform PA and the fine vibration waveform, even if the drive waveform signal ComT-B is supplied to the ejection unit 35, the ejection unit 35. No residual vibration Z occurs in FIG. For this reason, in the case shown in FIG. 10A, the magnitude of the pressure increase / decrease in the discharge section 35 resulting from the drive by the drive waveform signal ComT-A in the unit period Tu1 is the drive waveform signal ComT-A. The unit waveform PA is determined based only on the waveform (potential difference dV, etc.). In other words, when the drive waveform signal ComT-B is supplied to the ejection unit 35 in the unit period Tu0, the ejection of ink ejected from the ejection unit 35 driven by the drive waveform signal ComT-A in the unit period Tu1. The speed and the discharge amount are determined based on the shape of the unit waveform PA.
In the following, as shown in FIG. 10A, the ejection unit 35 to which the drive waveform signal ComT-B is supplied in one unit period Tu is in another unit period Tu following the one unit period Tu. When driven by the drive waveform signal ComT-A, the ejection speed of the ink droplets ejected from the ejection section 35 in the other unit period Tu is referred to as ejection speed WTp (an example of “fourth speed”), The discharge amount of the ink droplet is referred to as discharge amount QTp (an example of “fourth discharge amount”).

FIG. 10B shows the case where the drive waveform signal ComT-A is supplied to the ejection unit 35 in the unit period Tu1 and the drive waveform signal ComT-A is supplied in the unit period Tu2 subsequent to the unit period Tu1. FIG. 10 is an explanatory diagram showing the influence of the residual vibration Z generated by the drive waveform signal ComT-A supplied in the unit period Tu1 on the drive of the discharge section 35 in the unit period Tu2.
When the drive waveform signal ComT-A is supplied to the discharge unit 35, the residual vibration Z is generated in the discharge unit 35 (hereinafter, the waveform of the residual vibration Z is referred to as a waveform PZt).
As in the present embodiment, in an inkjet printer that performs printing processing at high speed and with high resolution, the interval between the unit periods Tu is short, and therefore, the residual vibration Z that occurs in the unit period Tu1 remains in the unit period Tu2. To do. Therefore, the magnitude of the increase / decrease in the pressure inside the discharge section 35 that occurs in the unit period Tu2 depends on the shape (potential difference dV, etc.) of the unit waveform PA of the drive waveform signal ComT-A supplied in the unit period Tu2. It is determined based on the shape of the waveform PZt of the residual vibration Z that occurs in Tu1.
In the following, as shown in FIG. 10B, the ejection unit 35 to which the drive waveform signal ComT-A is supplied in one unit period Tu is in another unit period Tu following the one unit period Tu. When driven by the drive waveform signal ComT-A, the ejection speed of the ink droplets ejected from the ejection section 35 in the other unit period Tu is referred to as ejection speed WTs (an example of “third speed”). The discharge amount of the ink droplet is referred to as discharge amount QTs (an example of “third discharge amount”).

  When the unit waveform PA is supplied to the discharge unit 35 in which the residual vibration Z having the waveform PZt is generated, the discharge unit 35 generates a waveform of a virtual drive signal that causes the residual vibration Z of the waveform PZt ( That is, it is driven by a virtual drive signal waveform PAt obtained by superimposing, for example, a physical waveform generated in the discharge section 35 with a unit waveform PA when replaced with an electrical drive signal. Can be considered. Generally, the potential difference dVt between the maximum potential and the minimum potential of the waveform PAt of the virtual drive signal is larger than the potential difference dV of the unit waveform PA of the actual drive signal Vin. For this reason, the discharge speed WTs becomes faster than the discharge speed WTp, and the discharge amount QTs becomes larger than the discharge amount QTp.

  FIG. 11 is an explanatory diagram illustrating an image formed on the recording medium P when the ejection unit 35 is driven by the drive waveform signal ComT that is proportional. In the example shown in FIG. 11, in the unit period Tu0, the drive waveform signal ComT-B is supplied to each ejection unit 35 of one nozzle row (not shown in FIG. 11), and the unit periods Tu1, Tu2, Tu3, and Tu4 are supplied. In each of the above, it is assumed that the drive waveform signal ComT-A is supplied to each ejection unit 35 of the one nozzle row. In the present embodiment, when the printing process is executed, the position of the ejection unit 35 (head unit 3) in the X-axis direction is fixed and the recording medium P is transported in the + X direction. For convenience, the ejection unit 35 is described so as to move relative to the recording medium P in the −X direction.

As described above, an image corresponding to the image data Img is formed on the recording medium P by forming the dots Dt on the recording medium P by the ink ejected from each ejection unit 35. However, when the ejection amount QTp is smaller than the ejection amount QTs, as shown in FIG. 11, the size of each dot Dt formed in the unit period Tu1 is the size of each dot formed in the unit period Tu2, Tu3, or Tu4. It becomes smaller than the size of Dt.
In addition, since the ink ejection speed relative to the recording medium P is the sum (vector sum) of the ejection speed W and the transport speed Mv, when the ejection speed W is different, the relative speed viewed from the recording medium P is used. The ink discharge angle θ is also different.
That is, as shown in FIG. 11, in the case of “discharge speed WTp <discharge speed WTs”, “θTP <θTS”. Therefore, when the on-medium positions Xp where the dots Dt are formed in the unit periods Tu1 to Tu4 are Xp1 to Xp4, the distance dXt between the positions Xp1 and Xp2 is the distance dX in the X axis direction between the other dots Dt. (For example, an interval between the position Xp2 and the position Xp3) becomes narrower.
As described above, when the proportional drive waveform signal ComT is supplied to the ejection unit 35, the dot Dt size varies and the interval between the dots Dt varies, and as a result, formed on the recording medium P. There has been a problem that the image quality deteriorates at the edge of the image.

<5. Residual vibration generated in the discharge section according to the first embodiment>
On the other hand, the drive waveform signal (Com-A, Com-B) according to the present embodiment includes a fine vibration waveform (PlsA, PlsB). For this reason, it is possible to form a high-quality image in which the degree of variation in the dot Dt size and the variation in the interval between the dots Dt is reduced as compared with the case of proportionality.
FIG. 12 shows the residual vibration generated in the ejection unit 35 in one unit period Tu when the drive waveform signal Com according to this embodiment is supplied as the drive signal Vin to the ejection unit 35 over a plurality of unit periods Tu. It is explanatory drawing for demonstrating the influence which Z has on the drive of the discharge part 35 in the other unit period Tu following the said one unit period Tu.

12A shows the unit period when the drive waveform signal Com-B is supplied to the ejection unit 35 in the unit period Tu0 and the drive waveform signal Com-A is supplied in the unit period Tu1. It is explanatory drawing which shows the influence which the residual vibration Z produced by the drive waveform signal Com-B supplied to Tu0 has with respect to the drive of the discharge part 35 in unit period Tu1.
As described above, the drive waveform signal Com-B has a waveform including the fine vibration waveform PlsB. Therefore, when the drive waveform signal Com-B is supplied to the ejection unit 35, the residual vibration Z is generated in the ejection unit 35 (hereinafter, the waveform of the residual vibration Z is referred to as a waveform PZp). In this case, the magnitude of the increase / decrease in the pressure inside the discharge section 35 that occurs in the unit period Tu1 depends on the shape of the unit waveform PA of the drive waveform signal Com-A supplied in the unit period Tu1 and the residual that occurs in the unit period Tu0. It is determined based on the shape of the waveform PZp of the vibration Z.
In the following, as shown in FIG. 12A, the ejection unit 35 to which the drive waveform signal Com-B is supplied in one unit period Tu is in another unit period Tu following the one unit period Tu. When driven by the drive waveform signal Com-A, the ejection speed of the ink droplet (an example of “first droplet”) ejected from the ejection section 35 in the other unit period Tu is determined as the ejection speed Wp (“ An example of “second speed”), and the discharge amount of the ink droplet is referred to as discharge amount Qp (an example of “second discharge amount”).

  When the unit waveform PA is supplied to the ejection unit 35 in which the residual vibration Z having the waveform PZp is generated, the ejection unit 35 has a virtual drive signal waveform that causes the residual vibration Z having the waveform PZp. For example, it can be regarded as being driven by a waveform PAp of a virtual drive signal obtained by superimposing the unit waveform PA. The potential difference dVp between the highest potential and the lowest potential of the virtual drive signal waveform PAp is larger than the potential difference dV of the unit waveform PA of the actual drive signal Vin, and the potential difference dVt of the virtual drive signal waveform PAt. Smaller than. For this reason, the discharge speed Wp is faster than the discharge speed WTp and lower than the discharge speed WTs. Further, the discharge amount Qp is larger than the discharge amount QTp and smaller than the discharge amount QTs.

FIG. 12B shows a case where the drive waveform signal Com-A is supplied to the ejection unit 35 in the unit period Tu1 and the drive waveform signal Com-A is supplied in the unit period Tu2 subsequent to the unit period Tu1. FIG. 11 is an explanatory diagram showing the influence of the residual vibration Z generated by the drive waveform signal Com-A supplied during the unit period Tu1 on the drive of the discharge section 35 during the unit period Tu2.
As described above, the drive waveform signal Com-A has a waveform including the unit waveform PA that precedes on the time axis and the fine vibration waveform PlsA that is arranged after the unit waveform PA. Among these, the fine vibration waveform PlsA is a waveform that attenuates the residual vibration Z of the waveform PZt generated when the unit waveform PA is supplied to the discharge unit 35 to obtain the waveform PZs. That is, when the drive waveform signal Com-A is supplied to the ejection unit 35, the waveform of the residual vibration Z generated after the unit waveform PA is supplied becomes the waveform PZt, but after that, when the fine vibration waveform PlsA is supplied, The residual vibration Z becomes a damped waveform PZs. For this reason, the magnitude of the increase / decrease in the pressure inside the discharge section 35 that occurs in the unit period Tu2 depends on the shape of the unit waveform PA of the drive waveform signal Com-A supplied in the unit period Tu2 and the residual that occurs in the unit period Tu1. It is determined based on the shape of the waveform PZs of the vibration Z.
In the following, as shown in FIG. 12B, the ejection unit 35 to which the drive waveform signal Com-A is supplied in one unit period Tu is in another unit period Tu following the one unit period Tu. When driven by the drive waveform signal Com-A, the ejection speed of an ink droplet (an example of a “second droplet”) ejected from the ejection section 35 in the other unit period Tu is determined as the ejection speed Ws (“ An example of “first velocity”), and the ejection amount of the ink droplet is referred to as ejection amount Qs (an example of “first ejection amount”).

  When the unit waveform PA is supplied to the discharge unit 35 in which the residual vibration Z having the waveform PZs is generated, the discharge unit 35 has a virtual drive signal waveform that generates the residual vibration Z having the waveform PZs. For example, it can be considered that the unit waveform PA is driven by a waveform PAs of a virtual drive signal obtained by superimposing the unit waveform PA. The potential difference dVs between the highest potential and the lowest potential of the virtual drive signal waveform PAs is larger than the potential difference dV of the unit waveform PA of the actual drive signal Vin, and the potential difference dVt of the virtual drive signal waveform PAt. Smaller than. For this reason, the discharge speed Ws is faster than the discharge speed WTp and lower than the discharge speed WTs. Further, the discharge amount Qs is larger than the discharge amount QTp and smaller than the discharge amount QTs.

In the present embodiment, the waveforms of the fine vibration waveforms PlsA and PlsB are determined so that the discharge speed Wp is “substantially equal” to the discharge speed Ws or the discharge amount Qp is “substantially equal” to the discharge amount Qs.
However, the present invention is not limited to such an embodiment, and the discharge speed Wp, the discharge speed Ws, the discharge speed WTp, and the discharge speed WTs satisfy the following discharge speed conditions (1) to (3). Either of satisfying all, or satisfying all of the following conditions (4) to (6) relating to the discharge amount Qp, discharge amount Qs, discharge amount QTp, and discharge amount QTs: It only needs to be satisfactory.
<Conditions related to discharge speed>
(1) WTp <Wp <WTs
(2) WTp <Ws <WTs
(3) | Ws−Wp | <| WTs−WTp |
<Conditions related to discharge volume>
(4) QTp <Qp <QTs
(5) QTp <Qs <QTs
(6) | Qs−Qp | <| QTs−QTp |

  FIG. 13 is an explanatory diagram showing an image formed on the recording medium P when the ejection unit 35 is driven by the drive waveform signal Com. In the example shown in FIG. 13, in the unit period Tu0, the drive waveform signal Com-B is supplied to each ejection unit 35 of one nozzle row (not shown in FIG. 13), and the unit periods Tu1, Tu2, Tu3, and Tu4. In each of the above, it is assumed that the drive waveform signal Com-A is supplied to each ejection unit 35 of the one nozzle row. In FIG. 13, for convenience of illustration, the ejection unit 35 is described so as to move relative to the recording medium P in the −X direction as in FIG. 11.

As described above, the discharge amount Qp is substantially the same as the discharge amount Qs. Therefore, the size of each dot Dt formed in the unit period Tu1 is substantially the same as the size of each dot Dt formed in the unit period Tu2, Tu3, or Tu4.
Further, as described above, the discharge speed Wp is substantially the same as the discharge speed Ws. Therefore, with respect to the relative ink ejection angle θ viewed from the recording medium P, the relative ejection angle θP in the unit period Tu1 is substantially the same as the relative ejection angle θS in the unit periods Tu2 to Tu4. In this case, a relationship of “θTP <θP≈θS <θTS” is established between the proportional discharge angles.
For this reason, when the on-medium position Xp where the dot Dt is formed in the unit periods Tu1 to Tu4 is Xp1s to Xp4s, the position Xp1s is a position shifted in the + X direction from the position Xp1 related to the proportionality.
Since each of the positions Xp2s to Xp4s is shifted in the −X direction from each of the proportional positions Xp2 to Xp4, the interval between the adjacent dots Dt in the X-axis direction is substantially the same as the interval dX. Can be unified to the interval.

<6. Conclusion of First Embodiment>
As described above, in this embodiment, since the drive waveform signal Com has the fine vibration waveforms PlsA and PlsB, the dot Dt size variation in the image formed in the printing process is smaller than that in the case of the proportionality. And variations in the spacing between the dots Dt can be reduced. As a result, in the inkjet printer 1 that performs high-speed and high-resolution printing, it is possible to realize high-quality printing including the edge of the image formed on the recording medium P.

  In this embodiment, in each unit period Tu, the drive waveform signal Com-A having the unit waveform PA and the minute vibration waveform PlsA or the drive waveform signal Com-B having the minute vibration waveform PlsB shown in FIG. The drive signal Vin is supplied to the ejection unit 35. Such an aspect can also be considered as follows.

That is, the drive waveform signal Com-B is supplied to the ejection unit 35 in one unit period Tu, and the drive waveform signal Com-A is supplied in another unit period Tu subsequent to the one unit period Tu. In this case, the fine vibration waveform PlsB included in the drive waveform signal Com-B supplied in one unit period Tu and the unit waveform PA included in the drive waveform signal Com-A supplied in another unit period Tu are obtained. The included signal is referred to as a “first drive signal”.
Further, the drive waveform signal Com-A is supplied to the ejection unit 35 in one unit period Tu, and the drive waveform signal Com-A is supplied in another unit period Tu subsequent to the one unit period Tu. In this case, the micro-vibration waveform PlsA included in the drive waveform signal Com-A supplied in one unit period Tu and the unit waveform PA included in the drive waveform signal Com-A supplied in another unit period Tu. The included signal is referred to as a “second drive signal”.

  For example, as shown in FIG. 14, the drive waveform signal Com-B is supplied to the ejection unit 35 as the drive signal Vin in the unit period Tu0, and the drive waveform signal Com in the unit periods Tu1 to Tu3 subsequent to the unit period Tu0. -A is supplied, the fine vibration waveform PlsB included in the drive waveform signal Com-B supplied in the unit period Tu0, and the unit waveform PA included in the drive waveform signal Com-A supplied in the unit period Tu1. Corresponds to the “first drive signal”, the fine vibration waveform PlsA included in the drive waveform signal Com-A supplied in the unit period Tu1, and the unit included in the drive waveform signal Com-A supplied in the unit period Tu2. The waveform PA corresponds to the “second drive signal”.

In this case, when the ejection unit 35 is driven by the first drive signal having the fine vibration waveform PlsB and the unit waveform PA, the ejection amount of the ink droplet (first droplet) ejected from the ejection unit 35 is “ Qp ”, and the ejection amount of the ink droplet (second droplet) ejected from the ejection unit 35 when the ejection unit 35 is driven by the second drive signal having the fine vibration waveform PlsA and the unit waveform PA. Since “Qs”, both are substantially the same.
In this case, when the ejection unit 35 is driven by the first drive signal, the ejection speed of the ink ejected from the ejection unit 35 is “Wp”, and the ejection unit 35 is driven by the second drive signal. In this case, since the ejection speed of the ink ejected from the ejection section 35 is “Ws”, both are substantially the same.

<B. Second Embodiment>
In the first embodiment described above, by setting the drive waveform signal Com to a waveform having the fine vibration waveform PlsA or the fine vibration waveform PlsB, the discharge amount Qp when the discharge unit 35 discharges ink first, and the discharge The ejection amount Qs when the ink is ejected again after the part 35 ejects ink is substantially the same.
On the other hand, in the second embodiment, the CPU 61 selectively (dynamically) the fine vibration waveform PlsA or the fine vibration waveform PlsB based on the data included in the image data Img to the ejection unit 35. By supplying, the discharge amount when the discharge unit 35 discharges ink for the first time and the discharge amount when discharging the ink again after the discharge unit 35 discharges the ink are substantially the same. It is different from the embodiment.
The ink jet printer according to the second embodiment is different from the first embodiment except that the signal supplied from the control unit 6 to the drive signal generation unit 5 is different from the operation of the drive signal generation unit 5. It is comprised similarly to the inkjet printer 1 which concerns on this.
In the second embodiment exemplified below, elements having the same functions and functions as those of the first embodiment are diverted using the reference numerals referred to in the above description, and detailed descriptions thereof are appropriately omitted (described below). The same applies to the embodiment and the modified example).

FIG. 15 is a block diagram illustrating a configuration of a drive signal generation unit 5A provided in the inkjet printer according to the second embodiment.
As shown in this figure, the drive signal generator 5A receives a clock signal CL, a print signal SI2, a latch signal LAT, a change signal CH, and a drive waveform signal Com2 (Com2-A, Com2-B) from the controller 6. ), Is supplied. That is, in the second embodiment, the signal supplied from the control unit 6 to the drive signal generation unit 5A includes the print signal SI2 instead of the print signal SI, and the drive waveform signal Com2 instead of the drive waveform signal Com. Except for the points included and the change signal CH, the signal is the same as the signal supplied from the control unit 6 to the drive signal generation unit 5 in the first embodiment.

  Here, the print signal SI2 is a signal that defines whether or not ink is ejected from each ejection unit 35 (each nozzle N) by 2 bits (upper bit b1 and lower bit b2), and is synchronized with the clock signal CL. Then, serially supplied from the control unit 6. Each of the shift registers SR holds the print signal SI2 supplied from the control unit 6 for every 2 bits corresponding to each ejection unit 35. The latch circuit LT at each stage latches the print signal SI2 for 2 bits corresponding to each stage held in the shift register SR at each stage at the timing when the latch signal LAT rises. In FIG. 15, SI2 [1], SI2 [2],..., SI2 [M] are respectively latched by the latch circuits LT corresponding to the shift registers SR of the first stage, the second stage,. A 2-bit print signal SI2 is shown.

In the present embodiment, each unit period Tu is divided into a control period Ts1 and a subsequent control period Ts2. In the present embodiment, the decoder DC decodes the 2-bit print signal SI2 latched by the latch circuit LT and outputs selection signals Sa and Sb in the control periods Ts1 and Ts2.
FIG. 16 is an explanatory diagram showing the contents of decoding performed by the decoder DC according to the present embodiment. As shown in this figure, when the content indicated by the print signal SI2 [m] corresponding to m stages is, for example, (b1, b2) = (0, 1), the m-stage decoder DC is in the control period Ts1. The selection signal Sa is set to the low level L, the selection signal Sb is set to the high level H, the selection signal Sa is set to the high level H, and the selection signal Sb is set to the low level L in the control period Ts2. To do.
Therefore, when the content indicated by the print signal SI2 [m] corresponding to m stages is (b1, b2) = (0, 1), the drive waveform signal is used as the drive signal Vin [m] in the control period Ts1. In the control period Ts2, the drive waveform signal Com2-A is supplied to the m-stage ejection unit 35.
When the contents indicated by the print signal SI2 [m] corresponding to m stages are (b1, b2) = (1, 1), the drive waveform signal Com2 is used as the drive signal Vin [m] in the control period Ts1. In the control period Ts2, -A is supplied with the drive waveform signal Com2-A to the m-stage ejection units 35.
When the contents indicated by the print signal SI2 [m] corresponding to m stages are (b1, b2) = (1, 0), the drive waveform signal Com2 is used as the drive signal Vin [m] in the control period Ts1. In the control period Ts2, -A is supplied with the drive waveform signal Com2-B to the m-stage ejection units 35.

FIG. 17 is a timing chart for explaining the operation of the drive signal generator 5A in the unit period Tu. As shown in FIG. 17, the control periods Ts1 and Ts2 included in the unit period Tu are defined by the latch signal LAT and the change signal CH output from the control unit 6.
As shown in FIG. 17, the drive waveform signal Com2-A has a waveform having a fine vibration waveform PlsA arranged in the control period Ts1 in the unit period Tu and a unit waveform PA arranged in the control period Ts2. Show. The drive waveform signal Com2-B has a fine vibration waveform PlsB arranged in the control period Ts1 in the unit period Tu. In FIG. 17, the time length Ta is from the start of the minute vibration waveform PlsA to the end of the control period Ts1, and the time length Tb is from the start of the minute vibration waveform PlsB to the end of the control period Ts1.

FIG. 18 is a timing chart showing the waveform of the drive signal Vin according to the second embodiment.
As shown in this figure, when the content indicated by the print signal SI2 [m] corresponding to m stages is (b1, b2) = (0, 1), the drive signal Vin [m] is the fine vibration waveform PlsB. And a waveform Dp1 including the unit waveform PA. The drive signal Vin having the waveform Dp1 corresponds to a “first drive signal”.
When the contents indicated by the print signal SI2 [m] corresponding to m stages are (b1, b2) = (1, 1), the drive signal Vin [m] includes the fine vibration waveform PlsA and the unit waveform PA. A waveform Dp2 including
The drive signal Vin having the waveform Dp2 corresponds to a “second drive signal”.
When the contents indicated by the print signal SI2 [m] corresponding to m stages are (b1, b2) = (1, 0), the drive signal Vin [m] is a waveform Dp3 including the minute vibration waveform PlsA. Become.

FIG. 19 is a flowchart illustrating an example of the operation of the inkjet printer in the printing process according to the second embodiment.
When the printing process is started and the control unit 6 receives the image data Img (S100), the CPU 61 of the control unit 6 generates a print signal SI2 in each unit period Tu.
Specifically, in each unit period Tu, the CPU 61 first selects m stages (here, m = 1) of the ejection sections 35 from among the M stages of ejection sections 35 (S102), and the m stages of ejection. It is determined by referring to the image data Img, for example, whether or not the unit 35 is an ejection unit that should eject ink in the unit period Tu (S104).
If the determination result in step S104 is affirmative, the CPU 61 determines whether the m-stage ejection unit 35 selected in step S102 has not ejected ink in the previous unit period Tu, for example, the image data Img. The determination is made by referring to it (S106).
If the determination result in step S106 is affirmative, the print signal SI2 [m] is set to (0, 1), and the drive signal is supplied so that the waveform Dp1 is supplied to the m-stage ejection unit 35. The generation unit 5A is controlled (S108). On the other hand, if the determination result in step S106 is negative, the print signal SI2 [m] is set to (1, 1) so that the waveform Dp2 is supplied to the m-stage ejection unit 35. The drive signal generator 5A is controlled (S110).
If the determination result in step S104 is negative, the CPU 61 sets the print signal SI2 [m] to (1, 0) so that the waveform Dp3 is supplied to the m-stage ejection unit 35. The drive signal generator 5A is controlled (S112).

Thereafter, the CPU 61 determines whether or not the print signal SI2 [m] corresponding to all of the first to M-th ejection units 35 has been generated (S114). If the determination result of step S114 is negative, the CPU 61 adds the value of m by 1 and advances the process to step S104 (S116). If the determination result in step S114 is affirmative, it is determined whether or not the printing process is terminated in the current unit period Tu. If the determination result is affirmative, the printing process is terminated while the determination result is If negative, the process proceeds to step S102 (S118).
In this manner, the CPU 61 executes the printing process by repeating steps S102 to S118 for each unit period Tu.

As described above, the CPU 61 refers to the image data Img, and when the ejection unit 35 does not eject ink in one unit period Tu, in another unit period Tu subsequent to the one unit period Tu. Then, the drive signal generator 5A is controlled so that the waveform Dp1 including the fine vibration waveform PlsB and the unit waveform PA is supplied to the ejection unit 35. In this case, as described above, the ejection amount of the ink ejected from the ejection section 35 in the other unit period Tu is “Qp”.
In addition, when the ejection unit 35 ejects ink in one unit period Tu, the CPU 61 includes a fine vibration waveform PlsA and a unit waveform PA for the ejection unit 35 in another unit period Tu. The drive signal generator 5A is controlled so that the waveform Dp2 is supplied. In this case, as described above, the ejection amount of the ink ejected from the ejection section 35 in the other unit period Tu is “Qs”.

  In other words, in the present embodiment, the CPU 61 determines whether or not ink is ejected from the ejection unit 35 in one unit period Tu, so that the drive signal supplied to the ejection unit 35 in another unit period Tu. In order to determine the waveform of Vin, the ejection unit 35 that has not ejected ink in one unit period Tu ejects ink in another unit period Tu, and the ejection unit that ejects ink in one unit period Tu 35 can be made substantially the same as the amount of ink discharged in the other unit period Tu. Thereby, it is possible to reduce the variation of the dot Dt size in the image formed in the printing process and to reduce the variation of the interval between the dots Dt. As a result, it is possible to maintain high image quality even at the edge of the image formed on the recording medium P.

In the present embodiment, the drive waveform signal Com2-B has a waveform including the fine vibration waveform PlsB. However, the drive waveform signal Com2-B is flat and does not include the fine vibration waveform PlsB as shown in FIG. It may have a waveform. That is, the waveform Dp1 (first drive signal) may be a waveform including the unit waveform PA, and the waveform Dp2 (second drive signal) may be a waveform including the micro vibration waveform PlsA and the unit waveform PA.
In this case, the fine vibration waveform PlsA is ejected by the ejection unit 35 in another unit period Tu following the one unit period Tu when the ejection unit 35 is not ejecting ink in the one unit period Tu. A waveform in which the ejection amount of ink and the ejection amount of ink ejected by the ejection unit 35 in the other unit period Tu when the ejection unit 35 ejects ink in one unit period Tu are substantially the same. What is stipulated in is acceptable. Even in this case, it is possible to reduce the variation of the dot Dt size in the image formed in the printing process, and to reduce the variation of the interval between the dots Dt.
20 illustrates a case where the drive waveform signals Com2-A and Com2-B are supplied to the drive signal generation unit 5A as the drive waveform signal Com2, but the drive waveform signal Com2-B is flat (constant). The drive waveform signal Com2 may include only the drive waveform signal Com2-A without including the drive waveform signal Com2-B. Even in this case, for example, by turning off both of the transmission gates TGa and TGb, the reference potential V0 at the timing at which each unit period Tu is started is held by the capacitance of the piezoelectric element 200, and so on. The same operation as when the signal Com2-B is supplied can be performed.

<C. Modification>
Each of the above forms can be variously modified. Specific modifications are exemplified below. Two or more aspects arbitrarily selected from the following examples can be appropriately combined within a range that does not contradict each other.

<Modification 1>
In the above-described embodiment, as shown in FIG. 8 or FIG. 17, the time length Ta from the start of the minute vibration waveform PlsA to the end of the unit period Tu (or the control period Ts1) and the start of the minute vibration waveform PlsB to the unit period. The time length Tb until the end of Tu (or the control period Ts1) is substantially the same, but the present invention is not limited to such a mode, and the relationship of “time length Ta ≧ time length Tb” is established. It may satisfy.
In this case, since the fine vibration waveform PlsA that attenuates the residual vibration Z is promptly applied after the residual vibration Z occurs, the operation of the discharge unit 35 can be stabilized.

<Modification 2>
In the embodiment and the modification described above, the ink jet printer displays each dot Dt formed on the recording medium P with two gradations of “recording” or “non-recording”. It is not limited to such an embodiment, and each dot Dt may be expressed by two or more gradations. For example, each dot Dt may be expressed by four gradations of “large dot”, “medium dot”, “small dot”, and “non-recording”.
Hereinafter, in each of the first embodiment and the second embodiment described above, a specific mode in the case where each dot Dt is expressed by four gradations will be described.

FIG. 21 is an example of a timing chart showing the waveform of the drive waveform signal Com3 that the CPU 61 supplies to the drive signal generation unit 5 when each dot Dt is expressed by four gradations in the inkjet printer 1 according to the first embodiment. FIG. 22 is an explanatory diagram showing the operation of the decoder DC in this case.
21 and 22, the CPU 61 supplies the change signal CH to the drive signal generation unit 5, thereby dividing each unit period Tu into control periods Ts1 and Ts2. 21 and 22, the CPU 61 supplies the drive signal generator 5 with the print signal SI3 instead of the print signal SI and supplies the drive waveform signal Com3 instead of the drive waveform signal Com. To do.

As shown in FIG. 21, the drive waveform signal Com3 includes a drive waveform signal Com3-A and a drive waveform signal Com3-B.
Among them, the drive waveform signal Com3-A has a unit waveform PA for ejecting ink of an ejection amount corresponding to a medium dot in the control period Ts1, and a fine vibration for damping residual vibration caused by the unit waveform PA. Including a waveform PlsA, and a unit waveform PC for ejecting ink of an ejection amount corresponding to a small dot in a control period Ts2, and a fine vibration waveform PlsC for damping residual vibration caused by the unit waveform PC. Signal.
The drive waveform signal Com3-B is a signal including a fine vibration waveform PlsB for generating residual vibration in each of the control periods Ts1 and Ts2.
The fine vibration waveform PlsA, the fine vibration waveform PlsB, and the fine vibration waveform PlsC are the residual vibration Z at the end of the control period Ts1 in the discharge unit 35 to which the drive waveform signal Com3-A is supplied in the control period Ts1. The residual vibration Z at the end of the control period Ts2 in the discharge unit 35 to which the drive waveform signal Com3-A is supplied in the control period Ts2, and the discharge unit 35 to which the drive waveform signal Com3-B is supplied in each control period Ts. The residual vibration Z at the end of the control period Ts is determined to have a waveform that is substantially the same.

The print signal SI3 is a signal that defines whether or not ink is ejected from each ejection unit 35 (each nozzle N) and the ejection amount when ink is ejected by 2 bits (upper bit b1 and lower bit b2).
When the CPU 61 forms a large dot Dt by ejecting ink from the m-stage ejection unit 35,
(B1, b2) = (1, 1) is set in the print signal SI3. In this case, the m-stage ejection unit 35 is supplied with the drive waveform signal Com3-A in the control period Ts1 and the drive waveform signal Com3-A in the control period Ts2 as the drive signal Vin [m] (FIG. 5). 6 and FIG. 22).
The CPU 61 sets (b1, b2) = (1, 0) in the print signal SI3 when the medium dot Dt is formed by ejecting ink from the m-stage ejection unit 35. Thus, the drive waveform signal Com3-A is supplied in the control period Ts1, and the drive waveform signal Com3-B is supplied in the control period Ts2.
When the CPU 61 forms a small dot Dt by ejecting ink from the m-stage ejection unit 35, the CPU 61 sets (b1, b2) = (0, 1) in the print signal SI3 to the ejection unit 35. Then, the drive waveform signal Com3-B is supplied in the control period Ts1, and the drive waveform signal Com3-A is supplied in the control period Ts2.
The CPU 61 sets (b1, b2) = (0, 0) in the print signal SI3 so that the ink from the m-stage ejection unit 35 is not ejected and is not recorded, so The drive waveform signal Com3-B is supplied in the control period Ts1, and the drive waveform signal Com3-B is supplied in the control period Ts2.

  Thus, in the case shown in FIGS. 21 and 22, since the drive waveform signal Com3 includes the micro-vibration waveforms PlsA, PlsB, and PlsC, the discharge unit 35 at the end of each control period Ts (Ts1, Ts2). Since the residual vibration Z generated in the first and second dots can be made substantially the same, variations in the dot Dt size and variations in the interval between the dots Dt can be suppressed, and high-quality printing can be performed.

  FIG. 23 is an example of a timing chart showing the waveform of the drive waveform signal Com4 that the CPU 61 supplies to the drive signal generation unit 5 in the case where each dot Dt is expressed in 4 gradations in the inkjet printer according to the second embodiment. is there. In the example shown in FIG. 23, each unit period Tu is divided into three control periods Ts of control periods Ts1, Ts2, and Ts3 by a change signal CH (not shown).

As shown in FIG. 23, the drive waveform signal Com4 includes a drive waveform signal Com4-A and a drive waveform signal Com4-B.
Among these, the drive waveform signal Com4-A is provided in the control period Ts1, and is provided in the control period Ts2 and the unit waveform for ejecting ink corresponding to a small dot is provided in the control period Ts2. PC and a unit waveform PA which is provided in the control period Ts3 and discharges ink corresponding to a medium dot.
The drive waveform signal Com4-B includes a fine vibration waveform PlsB provided in the control period Ts1 for causing residual vibration, and is maintained at the reference potential V0 in the control periods Ts2 and Ts3.

In the example illustrated in FIG. 23, when the CPU 61 forms a large dot Dt by ejecting ink from the m-stage ejection unit 35, the CPU 61 outputs the drive signal Vin [m to the ejection unit 35 during the control periods Ts2 and Ts3. ] Is supplied with the drive waveform signal Com4-A.
Further, when forming the middle dot Dt by ejecting ink from the m-stage ejection unit 35, the CPU 61 supplies the drive waveform signal Com4-B to the ejection unit 35 in the control period Ts2 and the control period Ts3. The driving waveform signal Com4-A is supplied at.
When the CPU 61 forms a small dot Dt by ejecting ink from the m-stage ejection unit 35, the CPU 61 supplies the drive waveform signal Com4-A to the ejection unit 35 in the control period Ts2 and the control period Ts3. The drive waveform signal Com4-B is supplied at.
Further, when the ink from the m-stage ejection unit 35 is not ejected and is not printed, the CPU 61 supplies the drive waveform signal Com3-B to the ejection unit 35 in the control periods Ts2 and Ts3.

Further, in the example shown in FIG. 23, when the CPU 61 supplies the drive waveform signal Com4-A (unit waveform PA) to the ejection unit 35 in the control period Ts3 of one unit period Tu, during the one unit period Tu. In the control period Ts1 of another subsequent unit period Tu, the drive waveform signal Com4-A (fine vibration waveform PlsA) is supplied to the ejection unit 35.
When the CPU 61 supplies the drive waveform signal Com4-B to the ejection unit 35 in the control period Ts3 of one unit period Tu, the CPU 61 drives the ejection unit 35 in the control period Ts1 of the other unit period Tu. A waveform signal Com4-B (fine vibration waveform PlsB) is supplied.
For this reason, when the drive waveform signal Com4-A is supplied to the ejection unit 35 in the control period Ts3 of one unit period Tu, the residual generated in the ejection unit 35 at the end of the control period Ts1 of the other unit period Tu. In the control period Ts3 of the vibration Z and one unit period Tu, when the drive waveform signal Com4-B is supplied to the discharge unit 35, it occurs in the discharge unit 35 at the end of the control period Ts1 of another unit period Tu. The residual vibration Z can be made substantially the same.
This suppresses the variation in the dot Dt size and the variation in the interval between the dots Dt,
High-quality printing is possible.

In this modification, the ink liquid ejected by the ejection unit 35 that has not ejected in one unit period Tu to form a large dot Dt in another unit period Tu subsequent to the one unit period Tu. The droplet corresponds to the “first droplet”.
In addition, an ink droplet ejected by the ejection unit 35 that ejects ink to form a large dot Dt in one unit period Tu to form a large dot Dt in another unit period Tu is “second droplet”. Is equivalent to.
Further, the ink droplets ejected by the ejection unit 35 to form the medium dots Dt or the small dots Dt correspond to “third droplets”.

<Modification 3>
In the embodiment and the modification described above, the inkjet printer 1 has the head portion 3 shown in FIG. 4, but the present invention is not limited to such a form, and the head portion shown in FIG. 4. Instead of 3, a head unit 3A shown in FIG.
The head unit 3A shown in FIG. 24 is different from the head unit 3 shown in FIG. 4 in that a discharge unit 35A is provided instead of the discharge unit 35, and a reservoir 246A is provided instead of the reservoir 246. Further, the head portion 3A is different from the head portion 3 in that it includes a nozzle plate 240A instead of the nozzle plate 240 and a cavity plate 242A instead of the cavity plate 242.

  24 is different from the discharge unit 35 shown in FIG. 4 in that it includes a single piezoelectric element 200A instead of the plurality of piezoelectric elements 200 and a cavity 245A instead of the cavity 245. The ejection unit 35A ejects ink in the cavity 245A from the nozzles N when the diaphragm 243A vibrates by driving the piezoelectric element 200A.

  The cavity plate 242A includes a first plate 271, an adhesive film 272, a second plate 273, and a third plate 274. A first plate 271 is bonded to the stainless steel nozzle plate 240A on which the nozzle N is formed via an adhesive film 272, and a similar stainless steel first plate 271 is further formed thereon on the adhesive film 272. It is joined via. A second plate 273 and a third plate 274 are sequentially joined thereon. The nozzle plate 240A, the first plate 271, the adhesive film 272, the second plate 273, and the third plate 274 are each formed into a predetermined shape (a shape in which a recess is formed), and by stacking these, A cavity 245A and a reservoir 246A are formed. The cavity 245A and the reservoir 246A communicate with each other via the ink supply port 247A. The reservoir 246 </ b> A communicates with the ink intake 261.

  A diaphragm 243A is installed in the upper surface opening of the third plate 274, and the piezoelectric element 200A is joined to the diaphragm 243A via the lower electrode 263. An upper electrode 264 is bonded to the opposite side of the piezoelectric element 200A from the lower electrode 263. The drive signal generator 5 supplies the drive signal Vin between the upper electrode 264 and the lower electrode 263, thereby vibrating the piezoelectric element 200A and vibrating the diaphragm 243A bonded thereto. The volume of the cavity 245A (pressure in the cavity) is changed by the vibration of the vibration plate 243A, and the ink filled in the cavity 245A is ejected from the nozzle N. When ink is ejected and the amount of ink in the cavity 245A decreases, ink is supplied from the reservoir 246A. Ink is supplied from the ink cartridge 31 to the reservoir 246A via the ink intake port 261.

<Modification 4>
In the embodiment and the modification described above, the line printer is exemplified as the ink jet printer. However, the serial printer is different in the main scanning direction of the head unit 3 and the sub scanning direction in which the recording medium P is conveyed. Also good.

DESCRIPTION OF SYMBOLS 1 ... Inkjet printer, 3 ... Head part, 5 ... Drive signal generation part, 6 ... Control part, 7 ... Conveyance mechanism, 9 ... Host computer, 31 ... Ink cartridge, 32 ... Carriage, 35 ...... Discharge unit, 61 ... CPU, 62 ... storage unit, 71 ... conveyance motor, 72 ... motor driver, 77 ... platen, P ... recording medium, N ... nozzle, 200 ... piezoelectric element, 243 ... diaphragm, 245 ... cavity.

Claims (9)

A piezoelectric element that is deformed by applying the first drive signal or the second drive signal;
A cavity that is filled with liquid and whose internal pressure is increased or decreased by deformation of the piezoelectric element;
A nozzle that communicates with the cavity and discharges the liquid as droplets by increasing or decreasing the pressure in the cavity;
A drive signal generator for generating the first drive signal and the second drive signal;
Have
The first drive signal is:
A first micro-vibration waveform that deforms the piezoelectric element so that the liquid is not discharged from the nozzle when applied to the piezoelectric element;
A driving waveform for deforming the piezoelectric element so that the liquid is ejected from the nozzle when applied to the piezoelectric element;
Including
The second drive signal is:
A second micro-vibration waveform that is different from the first micro-vibration waveform and that deforms the piezoelectric element so that the liquid is not discharged from the nozzle when applied to the piezoelectric element;
The drive waveform;
Including
When the first drive signal is applied to the piezoelectric element, the discharge amount of the first droplet discharged from the nozzle;
When the second drive signal is applied to the piezoelectric element, the ejection amount of the second droplet ejected from the nozzle is:
Almost equal,
A liquid discharge apparatus characterized by that. A piezoelectric element that is deformed by applying the first drive signal or the second drive signal;
A cavity that is filled with liquid and whose internal pressure is increased or decreased by deformation of the piezoelectric element;
A nozzle that communicates with the cavity and discharges the liquid as droplets by increasing or decreasing the pressure in the cavity;
A drive signal generator for generating the first drive signal and the second drive signal;
Have
The first drive signal is:
When applied to the piezoelectric element, including a drive waveform for deforming the piezoelectric element to discharge the liquid from the nozzle,
The second drive signal is:
A second micro-vibration waveform that deforms the piezoelectric element so as not to eject the liquid from the nozzle when applied to the piezoelectric element;
The drive waveform;
Including
When the first drive signal is applied to the piezoelectric element, the discharge amount of the first droplet discharged from the nozzle;
When the second drive signal is applied to the piezoelectric element, the ejection amount of the second droplet ejected from the nozzle is:
Almost equal,
A liquid discharge apparatus characterized by that. The second droplet is
The liquid droplets are ejected after the first liquid droplets are ejected from the nozzle.
The liquid ejecting apparatus according to claim 1, wherein the liquid ejecting apparatus is a liquid ejecting apparatus. The droplets discharged from the nozzle are
It is not discharged at the discharge timing immediately before discharging the first droplet.
The liquid ejection apparatus according to claim 1, wherein the liquid ejection apparatus is a liquid ejection apparatus according to claim 1. The droplets discharged from the nozzle are
Including a third droplet,
The discharge amount of the first droplet and the discharge amount of the second droplet are:
More than the discharge amount of the third droplet,
The liquid ejection apparatus according to claim 1, wherein the liquid ejection apparatus is a liquid ejection apparatus according to claim 1. The liquid ejection device includes:
720 × 720 dpi or higher resolution, and
It is possible to print at a printing speed of 220 m / min or more.
The liquid ejection apparatus according to claim 1, wherein the liquid ejection apparatus is a liquid ejection apparatus according to claim 1. The first micro-vibration waveform and the second micro-vibration waveform are different in the direction of the changing potential.
The liquid ejection apparatus according to claim 1, wherein the liquid ejection apparatus is a liquid ejection apparatus according to claim 1. A piezoelectric element that is deformed by applying the first drive signal or the second drive signal;
A cavity that is filled with liquid and whose internal pressure is increased or decreased by deformation of the piezoelectric element;
A nozzle that communicates with the cavity and discharges the liquid as droplets by increasing or decreasing the pressure in the cavity;
A drive signal generator for generating the first drive signal and the second drive signal;
Have
The first drive signal is:
A first micro-vibration waveform that deforms the piezoelectric element so that the liquid is not discharged from the nozzle when applied to the piezoelectric element;
A driving waveform for deforming the piezoelectric element so that the liquid is ejected from the nozzle when applied to the piezoelectric element;
Including
The second drive signal is:
A second micro-vibration waveform that is different from the first micro-vibration waveform and that deforms the piezoelectric element so that the liquid is not discharged from the nozzle when applied to the piezoelectric element;
The drive waveform;
Including
When the first drive signal is applied to the piezoelectric element, the discharge amount of the first droplet discharged from the nozzle;
When the second drive signal is applied to the piezoelectric element, the ejection amount of the second droplet ejected from the nozzle is:
Almost equal,
A head unit characterized by that. A piezoelectric element that is deformed by applying the first drive signal or the second drive signal;
A cavity that is filled with liquid and whose internal pressure is increased or decreased by deformation of the piezoelectric element;
A nozzle that communicates with the cavity and discharges the liquid as droplets by increasing or decreasing the pressure in the cavity;
A liquid discharge method for a liquid discharge apparatus comprising:
Selecting which one of the first droplet and the second droplet having a discharge amount substantially equal to that of the first droplet is to be discharged from the nozzle;
Applying the first drive signal to the piezoelectric element when discharging the first droplet;
Applying the second drive signal to the piezoelectric element when discharging the second droplet;
Including
The first drive signal is:
A first micro-vibration waveform that deforms the piezoelectric element so that the liquid is not discharged from the nozzle when applied to the piezoelectric element;
A driving waveform for deforming the piezoelectric element so that the liquid is ejected from the nozzle when applied to the piezoelectric element;
Including
The second drive signal is:
A second micro-vibration waveform that is different from the first micro-vibration waveform and that deforms the piezoelectric element so that the liquid is not discharged from the nozzle when applied to the piezoelectric element;
The drive waveform;
including,
A liquid discharge method.

Images