JP2009269352A - Evaluation method and evaluation device for delivery pulse - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly evaluate a delivery pulse, even when a delivery frequency is made higher. <P>SOLUTION: This evaluation method for the delivery pulse has a measuring step and an evaluation step. A liquid droplet is delivered continuously using sequentially a preceding delivery pulse having a variation pattern of potential for delivering the liquid droplet, an evaluation objective delivery pulse, and a following delivery pulse, in the measuring step, to measure a flying velocity of the liquid droplet delivered by the following delivery pulse. The flying velocity of the liquid droplet is measured while differing an interval from the evaluation objective delivery pulse to the following delivery pulse. The variation pattern of the potential in the evaluation objective delivery pulse is evaluated based on a relation between the interval from the evaluation objective delivery pulse to the following delivery pulse and the flying velocity of the liquid droplet, in the evaluation step. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ejection pulse evaluation method and an evaluation apparatus.

  Some liquid ejection devices such as an ink jet printer (hereinafter also simply referred to as a printer) use ejection pulses. The ejection pulse is a potential change pattern for ejecting a liquid droplet from the nozzle, and is applied to an element that performs an operation for ejecting the liquid droplet. In this type of liquid ejection device, when ejecting the same amount of ink droplets continuously, ejection pulses having the same potential change pattern are continuously applied to the element (see, for example, Patent Document 1).

In addition, a technique for optimizing a potential change pattern based on the flight speed and weight of a liquid drop has been proposed. In this technique, when optimizing a potential change pattern in a certain ejection pulse, ejection pulses having the same potential change pattern are applied to the element at regular intervals (see, for example, Patent Document 2).
JP 2002-103619 A JP 2003-94629 A

The above technique is useful when an ejection pulse having the same potential change pattern is applied to the element at regular intervals.
However, the demand for the liquid ejection device is high, and further increase in the ejection frequency is required. In this case, since the interval between successive ejection pulses becomes shorter, the ejection characteristics of the liquid droplets ejected earlier (eg, flight speed, flight direction) and the ejection characteristics of the liquid droplets ejected later are different. There is. The above-described technique cannot take into account such a difference in ejection characteristics.
The present invention has been made in view of such circumstances, and an object thereof is to perform an appropriate evaluation of ejection pulses even when the ejection frequency is increased.

The main invention for achieving the object is as follows:
Liquid that has a potential change pattern and discharges liquid droplets, sequentially discharges liquid droplets using the preceding discharge pulse, the evaluation target discharge pulse, and the subsequent discharge pulse in this order, and is discharged by the subsequent discharge pulse. A measurement step for measuring the flight speed of the droplet, the measurement step for measuring the flight speed of the liquid droplet a plurality of times with different intervals from the evaluation target ejection pulse to the subsequent ejection pulse;
An evaluation step for evaluating a potential change pattern in the evaluation target ejection pulse based on a relationship between an interval from the evaluation target ejection pulse to the subsequent ejection pulse and a flight speed of the liquid droplet;
It is the evaluation method of the ejection pulse which has.
Other features of the present invention will become apparent from the description of this specification and the accompanying drawings.

At least the following will be made clear by the description of the present specification and the accompanying drawings.
That is, a liquid droplet is continuously discharged using a preceding discharge pulse, an evaluation target discharge pulse, and a subsequent discharge pulse in order, which has a potential change pattern and discharges the liquid droplet, and is discharged by the subsequent discharge pulse. A measuring step for measuring the flying speed of the liquid droplet, the measuring step for measuring the flying speed of the liquid drop a plurality of times with different intervals from the evaluation target ejection pulse to the subsequent ejection pulse, and the evaluation target It is possible to realize an ejection pulse evaluation method comprising: an evaluation step for evaluating a potential change pattern in the evaluation target ejection pulse based on a relationship between an interval from the ejection pulse to the subsequent ejection pulse and a flight speed of the liquid droplet. Is revealed.
According to such an evaluation method of the ejection pulse, the change in the liquid pressure in the pressure chamber after the liquid droplet is ejected by the evaluation target ejection pulse, the interval from the evaluation target ejection pulse to the subsequent ejection pulse, and the liquid droplet It can be recognized based on the flight speed relationship. For this reason, even if the discharge interval between the liquid droplet based on the preceding discharge pulse and the liquid droplet based on the evaluation target discharge pulse is short, that is, when the discharge frequency is increased, the evaluation target discharge pulse can be appropriately evaluated.

In this ejection pulse evaluation method, in the evaluation step, a potential change pattern in the evaluation target ejection pulse may be evaluated based on a difference between a minimum value and a maximum value in a fluctuation amount of a flight speed of the liquid droplet. preferable.
According to such a discharge pulse evaluation method, the evaluation target discharge pulse can be evaluated based on the degree of change in the liquid pressure in the pressure chamber after the liquid droplet is discharged by the evaluation target discharge pulse.

In this discharge pulse evaluation method, in the measurement step, the preceding discharge pulse, the evaluation target discharge pulse, and the subsequent discharge pulse are applied to an element that gives a pressure change to the liquid in the pressure chamber. It is preferable that a pressure change is caused in the liquid in the pressure chamber according to the change in the potential, and the liquid droplet is ejected from a nozzle communicated with the pressure chamber.
According to such an ejection pulse evaluation method, liquid droplets are ejected at a speed corresponding to a change in potential, so that the evaluation accuracy can be improved.

In this method of evaluating a discharge pulse, the preceding discharge pulse is generated after a first excitation element that excites a pressure vibration in the liquid in the pressure chamber, and after the first excitation element, and a liquid droplet is discharged from the nozzle. A first discharge element that causes the element to perform an operation for discharging, and the evaluation target discharge pulse includes a second excitation element that excites pressure vibration in the liquid in the pressure chamber, and a second excitation element. And a second ejection element that is generated later and causes the element to perform an operation for ejecting a liquid droplet from the nozzle. The subsequent ejection pulse excites a pressure oscillation in the liquid in the pressure chamber. It is preferable to include three excitation elements and a third ejection element that is generated after the third excitation element and causes the element to perform an operation for ejecting a liquid droplet from the nozzle.
According to such an ejection pulse evaluation method, since each ejection pulse has an excitation element and an ejection element, the pressure of the liquid is finely adjusted, and the accuracy of evaluation can be increased.

In this ejection pulse evaluation method, in the measurement step, the ejection pulse generation unit is provided with data indicating a potential change pattern in time series, whereby the preceding ejection pulse, the evaluation target ejection pulse, and the subsequent It is preferable to generate a row ejection pulse.
According to such an ejection pulse evaluation method, the potential of each ejection pulse can be accurately determined.

In this ejection pulse evaluation method, it is preferable that the potential change pattern of the subsequent ejection pulse is the same as the potential change pattern of the preceding ejection pulse.
According to such an ejection pulse evaluation method, it is possible to evaluate when a liquid droplet is ejected by alternately using the preceding ejection pulse and the evaluation target ejection pulse.

In this ejection pulse evaluation method, in the measurement step, the liquid for each of the evaluation target ejection pulses and other evaluation target ejection pulses having a potential change pattern different from the certain evaluation target pattern. It is preferable that the flight speed of the droplet is measured a plurality of times, and in the evaluation step, the evaluation result of the certain evaluation target discharge pulse is compared with the evaluation result of the other evaluation target discharge pulse.
According to such an ejection pulse evaluation method, it is possible to select which one of the evaluation target ejection pulses or another evaluation target ejection pulse is better.

It will also be clarified that an apparatus for evaluating the next ejection pulse can be realized.
That is, a pressure chamber that communicates with the nozzle, an element that performs an operation for applying a pressure change to the liquid in the pressure chamber according to a change in potential, and a discharge pulse that generates a discharge pulse in which the potential change pattern is defined The generation unit, which has a potential change pattern and discharges a liquid droplet, includes a preceding discharge pulse, an evaluation target discharge pulse, and a subsequent discharge pulse in this order, and the subsequent discharge from the evaluation target discharge pulse. A discharge pulse generation unit that repeatedly generates with different intervals up to a pulse; a speed measurement unit that measures a flight speed of a liquid droplet discharged from the nozzle by application of the subsequent discharge pulse to the element; It is also clarified that an ejection pulse evaluation apparatus having the above can be realized.

=== First Embodiment ===
<Overall Configuration of Printer 1>
FIG. 1A is a block diagram illustrating the configuration of the printer 1. FIG. 1B is a conceptual diagram illustrating a storage area of the memory 63 included in the printer-side controller 60. The printer 1 is a kind of liquid ejection device, and records an image on a medium by ejecting liquid ink. Here, the ink includes both water-based ink and oil-based ink. The medium is an object on which the ejected liquid is landed, for example, paper.

  As illustrated in FIG. 1A, the printer 1 includes a paper transport mechanism 10, a carriage movement mechanism 20, a head unit 30, a drive signal generation circuit 40, a detector group 50, and a printer-side controller 60. The sheet transport mechanism 10 corresponds to a medium transport unit that transports a medium, and transports a sheet as a medium. The carriage moving mechanism 20 moves the carriage to which the head unit 30 is attached in the carriage moving direction. The carriage movement direction is a direction that intersects the conveyance direction, for example, a paper width direction that is orthogonal to the conveyance direction. Since the head unit 30 includes the head HD, the carriage movement direction corresponds to the head movement direction.

  The head unit 30 includes a head HD and a head controller HC. The head unit 30 is attached to the carriage. The head HD ejects liquid ink in droplets. The head controller HC controls ink ejection by the head HD. The head HD will be described in detail later. The drive signal generation circuit 40 generates a drive signal used when ink droplets are ejected based on the DAC data. The DAC data is data indicating the change pattern of the potential in the drive signal in time series. In the printer 1, a first drive signal COM_A and a second drive signal COM_B (see FIG. 4) are generated. The first drive signal COM_A and the second drive signal COM_B include an ejection pulse PS2 for ejecting ink droplets. Therefore, the drive signal generation circuit 40 corresponds to an ejection pulse generation unit that generates the ejection pulse PS2. The drive signal generation circuit 40 and the generated drive signal COM will be described later.

  The detector group 50 includes a plurality of detectors that monitor the situation inside the printer 1. These detectors output detection results to the printer-side controller 60. The printer-side controller 60 controls the operation of the printer 1. That is, the printer-side controller 60 controls the paper transport mechanism 10, the carriage moving mechanism 20, the head HD, the head control unit HC, and the drive signal generation circuit 40 as control target units. The printer-side controller 60 includes an interface unit 61, a CPU 62, and a memory 63. The interface unit 61 exchanges data with the computer CP, which is an external device. The CPU 62 is an arithmetic processing unit for performing overall control of the printer 1. The memory 63 secures an area for storing the program of the CPU 62, a work area, and the like. For example, as shown in FIG. 1B, a partial area of the memory 63 includes a firmware storage area for storing firmware, a first DAC data storage area for storing first DAC data for the first drive signal COM_A, and a second drive signal. It is used as a second DAC data storage area for storing the second DAC data for COM_B.

<About Head HD>
For example, as shown in FIG. 2A, the head HD includes a case 31, a flow path unit 32, and a piezo element unit 33. The case 31 is a block-like member that accommodates the piezo element unit 33 therein, and a flow path unit 32 is joined to a front end surface facing the sheet.

  The flow path unit 32 is a member having a plurality of series of ink flow paths from the common ink chamber 321 to the nozzle 324 through the ink supply path 322 and the pressure chamber 323. This ink flow path is filled with ink when the printer 1 is used. The nozzle 324 is a portion from which droplet ink (corresponding to a liquid droplet) is ejected. For example, as shown in FIG. 2B, a plurality of nozzles 324 are provided in a state of being aligned in the paper transport direction, and constitute a nozzle row. The aforementioned ink flow path is provided for each of the plurality of nozzles 324. That is, the ink supply path 322 and the pressure chamber 323 are provided for each nozzle 324.

  The pressure chamber 323 is a portion that applies a pressure change to the ink when the ink is ejected, and communicates with the nozzle 324. The pressure chamber 323 is a space that is elongated in a direction that intersects the direction in which the nozzles 324 are arranged. A part of the pressure chamber 323 is partitioned by a diaphragm portion 325. The diaphragm portion 325 includes an elastic film 325a and an island portion 325b. The elastic film 325 a is a resin film having elasticity, and defines a part of the pressure chamber 323 on the side opposite to the nozzle 324. The island portion 325b is a portion to which the tip surface of the piezo element PZT included in the piezo element unit 33 is joined. The island portion 325b is provided on the surface of the elastic film 325a on the side opposite to the pressure chamber 323. An elastic region of only the elastic film 325a is provided around the island portion 325b. In the diaphragm portion 325, the island portion 325b can move toward the pressure chamber 323 or move in the opposite direction due to the elasticity of the elastic film 325a. The volume of the pressure chamber 323 decreases when the island portion 325b moves toward the pressure chamber 323, and increases when the island portion 325b moves to the opposite side. By such a volume change of the pressure chamber 323, a pressure change can be applied to the ink in the pressure chamber 323. Such a change in the volume of the pressure chamber 323 is made by deformation of the piezo element PZT. Therefore, the ink pressure can be accurately controlled based on the potential change pattern in the ejection pulse PS2.

  The ink supply path 322 is a portion that communicates between the common ink chamber 321 and the pressure chamber 323. The shape of the ink supply path 322 is determined so that ink is supplied to the pressure chamber 323 without excess and deficiency, and the pressure change applied to the ink in the pressure chamber 323 is efficiently used for ink discharge. It is done. The common ink chamber 321 is a part for temporarily storing ink supplied from an ink cartridge (not shown) or the like before supplying it to each ink flow path.

  In the ink flow path, the nozzle 324 and the ink supply path 322 communicate with the pressure chamber 323, respectively. Therefore, when analyzing characteristics such as ink flow, the Helmholtz resonator concept is applied. That is, when ink is ejected from the nozzle 324, a pressure change is applied to the ink in the pressure chamber 323. At this time, the pressure chamber 323, the ink supply path 322, and the nozzle 324 function like a Helmholtz resonator. For this reason, when pressure is applied to the ink in the pressure chamber 323, the magnitude of the pressure changes in a unique period called a Helmholtz period. In other words, the ink in the pressure chamber 323 undergoes pressure vibration having a natural vibration period. In the exemplified head HD, the natural vibration period is 6.7 μs. Then, the meniscus (the free surface of the ink exposed by the nozzle 324) moves with the pressure change of the ink in the pressure chamber 323. For example, when the ink pressure is increased, the meniscus moves in the nozzle 324 in the ejection direction. On the other hand, when the ink pressure is lowered, the meniscus moves in the nozzle 324 toward the pressure chamber 323.

  The piezo element unit 33 includes a piezo element group 331, an adhesion substrate 332, and a head side wiring member 333. The piezo element group 331 has a comb-teeth shape, and each comb-teeth portion is a piezo element PZT. The piezo element group 331 includes a number of piezo elements PZT corresponding to the nozzles 324. The bonding substrate 332 is a rectangular plate, and the piezoelectric element group 331 is bonded to one surface and the other surface is bonded to the case 31. The element wiring board is provided with wiring to each piezo element PZT and a head controller HC. The piezo element PZT is deformed by applying a potential difference between opposing electrodes. In this example, it expands and contracts in the longitudinal direction of the element. The amount of expansion / contraction is determined according to the potential of the piezo element PZT. The potential of the piezo element PZT is determined by the potential of the applied drive signal COM. That is, the piezo element PZT is charged and discharged by the application of the drive signal COM and expands and contracts. Since the diaphragm portion 325 is deformed as the piezo element PZT expands and contracts, a pressure change can be applied to the ink in the pressure chamber 323.

  Such a piezo element PZT is an element that is charged and discharged by the drive signal COM (ejection pulse PS2), and corresponds to an element that performs an operation for ejecting ink (liquid). When this piezo element PZT is used for ink ejection, the deformation state of the piezo element PZT can be controlled according to the potential of the drive signal COM, so that the ink ejection operation can be finely controlled.

<About the drive signal generation circuit 40>
As shown in FIG. 3, the drive signal generation circuit 40 as an ejection pulse generation unit includes a first drive signal generation circuit 40A and a second drive signal generation circuit 40B. The first drive signal generation circuit 40A generates the first drive signal COM_A based on the first DAC data (first potential information). The first drive signal generation circuit 40A includes a first waveform generation circuit 41A and a first current amplification circuit 42A. The second drive signal generation circuit 40B generates the second drive signal COM_B based on the second DAC data (second potential information). The second drive signal generation circuit 40B includes a second waveform generation circuit 41B and a second current amplification circuit 42B.

  The first waveform generation circuit 41A is a part that generates a first waveform signal corresponding to the first DAC data, and includes a first digital-analog converter 411A and a first preamplifier 412A. The first digital-analog converter 411A is an electric circuit that outputs an analog signal having a potential corresponding to the first DAC data. The first DAC data is stored in the first DAC data storage area of the memory 63 and is output from the CPU 62. The first preamplifier 412A amplifies the potential of the analog signal output from the first digital-analog converter 411A to a level suitable for the operation of the piezo element PZT, and outputs it as a first waveform signal. The first current amplification circuit 42A amplifies the current of the first waveform signal generated by the first waveform generation circuit 41A and outputs it as the first drive signal COM_A. The first current amplifying circuit 42A includes, for example, a pair (transistor pair) of a PNP transistor and an NPN transistor that are complementarily connected.

  The second waveform generation circuit 41B generates a second waveform signal corresponding to the second DAC data. The second current amplification circuit 42B amplifies the current of the second waveform signal and outputs it as the second drive signal COM_B. The configurations of the second waveform generation circuit 41B and the second current amplification circuit 42B are the same as those of the first waveform generation circuit 41A and the first current amplification circuit 42A. Briefly, the second waveform generation circuit 41B includes a second digital-analog converter 411B and a second preamplifier 412B, and the second current amplification circuit 42B includes a pair of transistors connected in a complementary manner.

  In this drive signal generation circuit 40, the first DAC data indicating the potential of the first drive signal COM_A in time series and the second DAC data indicating the potential of the second drive signal COM_B in time series are converted into analog signals, and the first drive signal COM_A and Since the second drive signal COM_B is generated, the change pattern of the potentials of the drive signals COM_A and COM_B can be finely set based on each DAC data. This makes it possible to accurately determine the amount of ink droplets to be ejected, the flight speed, and the like.

  The first drive signal COM_A generated by the first drive signal generation circuit 40A and the second drive signal COM_B generated by the second drive signal generation circuit 40B are selectively applied to each piezo element PZT. For this reason, in the head controller HC, a set of the first switch 326A and the second switch 326B is provided for each piezo element PZT. The first switch 326A is provided in the middle of the signal line that supplies the first drive signal COM_A, and applies or blocks the first drive signal COM_A to the piezo element PZT. The second switch 326B is provided in the middle of the signal line that supplies the second drive signal COM_B, and applies or blocks the second drive signal COM_B to the piezo element PZT. The head controller HC controls the first switch 326A and the second switch 326B based on the head control signal from the printer-side controller 60, and converts the necessary portions of the first drive signal COM_A and the second drive signal COM_B into piezoelectric elements. Apply to PZT.

<About the outline of the drive signal COM>
Next, the drive signal COM will be described. First, an outline of the drive signal COM will be described. The drive signal COM in the printer 1 is applied to the piezo element PZT for the purpose of suppressing the increase in ink viscosity when the ink pulse is ejected and the ejection pulse PS2 applied to the piezo element PZT when the ink drop is not ejected. And a fine vibration pulse PS1. These ejection pulse PS2 and micro-vibration pulse PS1 are potential change patterns corresponding to the operation performed by the piezo element PZT, and correspond to drive pulses for driving the piezo element PZT.

  In the printer 1, during the formation of large dots, the ejection pulse PS2 having the same target ejection amount (11 ng) of ink droplets is continuously applied to the piezo element PZT. Then, the potential change pattern in the odd-numbered ejection pulse PS2 (first ejection pulse PS2a) is different from the potential variation pattern in the even-numbered ejection pulse PS2 (second ejection pulse PS2b). ing. As will be described in detail later, in the first ejection pulse PS2a applied oddly, the pressure chamber 323 is rapidly contracted at the timing when the ink in the pressure chamber 323 reaches a predetermined pressure, and an ink droplet is ejected from the nozzle 324. Discharge. On the other hand, in the second ejection pulse PS2b applied evenly, the pressure chamber 323 is rapidly contracted at a certain timing during which the ink in the pressure chamber 323 is lower than the predetermined pressure, and the ink droplets are ejected from the nozzle 324. To discharge.

  By adopting such a configuration, even when the interval between the odd-numbered first ejection pulses PS2a and the even-numbered second ejection pulses PS2b is shortened, the ink droplets ejected by the even-numbered second ejection pulses PS2b are stabilized. Can be discharged. As a result, the ink droplet ejection frequency can be increased.

<Details of drive signal COM>
As shown in FIG. 4, the first drive signal COM_A is repeatedly generated every repetition period T, and has a first first half part generated in the first half period T1 and a first second half part generated in the second half period T2. The first first half portion includes a fine vibration pulse PS1, and the first second half portion includes an ejection pulse PS2. The second drive signal COM_B is also repeatedly generated every repetition period T, and has a second first half part generated in the first half period T1 and a second second half part generated in the second half period T2. The second first half portion includes the ejection pulse PS2, and the second second half portion is constant at the intermediate potential VB as the reference potential.

  The fine vibration pulse PS1 is a pulse applied to the piezo element PZT when ink droplets are not ejected. The illustrated micro-vibration pulse PS1 is configured by a trapezoidal wave. That is, the fine vibration pulse PS1 has a fine vibration expansion element vc, a fine vibration hold element vh, and a fine vibration contraction element vd. The minute vibration expansion element vc is a part that increases the potential with a constant gradient (potential change amount per unit time) from the intermediate potential VB to the minute vibration potential VV. When the minute vibration expansion element vc is applied to the piezo element PZT, the piezo element PZT contracts. The volume of the pressure chamber 323 expands from the reference volume corresponding to the intermediate potential VB to the minute vibration volume corresponding to the minute vibration potential VV. The fine vibration hold element vh is a constant portion at the fine vibration potential VV. When the fine vibration hold element vh is applied to the piezo element PZT, the piezo element PZT maintains a contracted state corresponding to the fine vibration potential VV, and the pressure chamber 323 maintains a fine vibration volume. The fine vibration contraction element vd is a part that lowers the potential with a constant gradient from the fine vibration potential VV to the intermediate potential VB. When this fine vibration contraction element vd is applied to the piezo element PZT, the piezo element PZT expands. Then, the volume of the pressure chamber 323 contracts to the reference volume.

  Along with the change in volume of the pressure chamber 323, the pressure in the ink in the pressure chamber 323 changes so weak that no ink droplets are ejected. As a result, the meniscus moves in a direction opposite to the direction in which the meniscus is drawn into the pressure chamber 323 side. As a result, the ink existing near the nozzle 324 is agitated and the thickening is suppressed.

  The ejection pulse PS2 is a pulse applied to the piezo element PZT when ejecting ink droplets. The ejection pulse PS2 is composed of a pair of pulses having the same target ejection amount of ink droplets. That is, the first ejection pulse PS2a and the second ejection pulse PS2b are configured. The first ejection pulse PS2a is a pulse generated first in the first second half part and the second first half part. The second ejection pulse PS2b is a pulse generated following the first ejection pulse PS2a in the first second half part and the second first half part. In the illustrated first drive signal COM_A and second drive signal COM_B, the first ejection pulse PS2a included in the first second half portion is generated after a lapse of a predetermined period W1 from the start of the generation of the fine vibration ejection pulse PS2. ing. In this example, the generation of the first ejection pulse PS2a is started after 35.5 μs has elapsed. In addition, the first ejection pulse PS2a included in the second first half portion is started to be generated at the same timing as the micro-vibration ejection pulse PS2. The second ejection pulse PS2b is generated after a predetermined period W2 has elapsed since the generation of the first ejection pulse PS2a was started. In this example, both the second ejection pulse PS2b included in the first second half part and the second ejection pulse PS2b included in the second first half part are both after 17.6 μs have elapsed from the generation start of the first ejection pulse PS2a generated earlier. Generation has started.

  When forming a large dot, the second first half portion is applied to the piezo element PZT, and then the first second half portion is applied to the piezo element PZT. In other words, all ejection pulses PS2 are applied to the piezo element PZT. In this case, the first ejection pulse PS2a included in the second first half is first applied to the piezo element PZT, and then the second ejection pulse PS2b included in the second first half is applied. Thereafter, the first ejection pulse PS2a included in the first second half is applied, and finally the second ejection pulse PS2b included in the first second half is applied. In short, the first ejection pulse PS2a and the second ejection pulse PS2b are alternately applied to the piezo element PZT.

<Discharge pulse PS2>
Next, the ejection pulse PS2 will be described. First, each element included in the ejection pulse PS2 will be described. These elements are the same for the first ejection pulse PS2a and the second ejection pulse PS2b. As shown in FIG. 5A, the ejection pulse PS2 includes the first expansion element c1, the first hold element h1, the contraction element d1, the second hold element h2, the second expansion element c2, and the third hold element h3. And a third expansion element c3.

  The first expansion element c1 is a part that increases the potential with a constant gradient from the intermediate potential VB to the maximum potential VH. When the first expansion element c1 is applied, the piezo element PZT contracts. Accordingly, the pressure chamber 323 expands from the reference volume corresponding to the intermediate potential VB to the maximum volume corresponding to the maximum potential VH. By the expansion of the pressure chamber 323, ink is supplied into the pressure chamber 323 from the ink supply path 322, and the amount of ink droplets ejected by the contraction element d1 can be increased later. At the same time, pressure vibration (forced vibration) is excited in the ink in the pressure chamber 323. The first expansion element c1 corresponds to an excitation element.

  The first hold element h1 is a part that maintains the maximum potential VH for a predetermined time. The first hold element h1 corresponds to a constant potential element that connects the end of the first expansion element c1 and the start of the contraction element d1 at a constant potential. When the first hold element h1 is applied, the piezo element PZT maintains the contracted state. Accordingly, the pressure chamber 323 maintains the maximum volume. In the application period of the first hold element h1, the ink pressure in the pressure chamber 323 changes due to residual vibration.

  The contraction element d1 is a part that lowers the potential with a constant gradient from the highest potential VH to the lowest potential VL. When the contraction element d1 is applied, the piezo element PZT expands. Along with this, the pressure chamber 323 rapidly contracts from the maximum volume to the minimum volume. As a result, the pressure of the ink in the pressure chamber 323 increases, and an ink droplet is ejected from the nozzle 324. For this reason, the contraction element d1 corresponds to an ejection element for ejecting ink droplets. In the ejection pulse PS2, since the contraction element d1 lowers the potential from the highest potential VH to the lowest potential VL, the amount of deformation of the element can be maximized. Thereby, a large pressure change of the ink in the pressure chamber 323 can be given. Note that the difference between the highest potential VH and the lowest potential VL is 31 V (25 ° C.).

  The second hold element h2 is a part that maintains the minimum potential VL for an extremely short time, and ensures a control time for shifting to the control by the second expansion element c2. The second hold element h2 constitutes a part of the return part. The second expansion element c2 is a part for increasing the potential with a constant gradient from the lowest potential VL to the damping potential VN. By applying the second expansion element c2, the piezo element PZT expands from the minimum volume to the damping volume corresponding to the damping potential VN. Here, the damping potential VN is determined between the lowest potential VL and the intermediate potential VB. As will be described later, the damping potential VN defines the degree of expansion of the pressure chamber 323 by the third expansion element c3 (damping element). Accordingly, the second expansion element c2 corresponds to a volume adjustment element for adjusting the volume of the pressure chamber 323. The second hold element h2 also constitutes a part of the return part. The third hold element h3 is a part that maintains the damping potential VN for a certain period of time, and determines the timing for starting the expansion of the pressure chamber 323 by the third expansion element c3. Therefore, the third hold element h3 corresponds to a timing adjustment element that adjusts the vibration suppression start timing. The third hold element h3 also constitutes a part of the return part.

  The third expansion element c3 is a part that increases the potential with a constant gradient from the damping potential VN to the intermediate potential VB. When the third expansion element c3 is applied, the piezo element PZT contracts. The pressure chamber 323 expands from the damping volume to the reference volume. As a result, the pressure change of the ink in the pressure chamber 323 after the ink droplet is ejected is alleviated, and the ejection of the next ink droplet can be started early. That is, the ink droplet ejection frequency can be increased. Such a third expansion element c3 corresponds to a vibration damping element. Here, the degree of expansion of the pressure chamber 323 by the third expansion element c3 is adjusted by the second expansion element c2, and the timing for starting expansion of the pressure chamber 323 is determined by the third hold element h3. Since the expansion operation of the pressure chamber 323 by the third expansion element c3 is optimized by the second expansion element c2 and the third hold element h3, the ink pressure change can be effectively suppressed. The third expansion element c3 also constitutes a part of the return part.

<About each ejection pulse PS2a, PS2b>
As described above, the first ejection pulse PS2a and the second ejection pulse PS2b have the same target ejection amount but different potential change patterns. That is, the timing for contracting the pressure chamber 323 to eject ink droplets with the second ejection pulse PS2b is higher than the timing for contracting the pressure chamber 323 to eject ink droplets with the first ejection pulse PS2a. The ink pressure in the inside is determined to be low.

  Specifically, the generation period of each element from the first expansion element c1 to the third expansion element c3 is set to the period shown in FIG. 5B. The first ejection pulse PS2a will be described. The first expansion element c1 as the first excitation element has a generation period of 2.7 μs, and the first hold element h1 as the first constant potential element has a generation period of 3.1 μs. The generation period of the contraction element d1 as the first ejection element is set to 2.5 μs. The generation periods of the second hold element h2, the second expansion element c2, the third hold element h3, and the third expansion element c3 that function as the first return portion are as follows. That is, the generation period of the second hold element h2 is 0.6 μs, the generation period of the second expansion element c2 is 1.0 μs, the generation period of the third hold element h3 is 3.0 μs, and the generation period of the third expansion element c3 is 2.5 μs.

  On the other hand, in the second ejection pulse PS2b, the generation period of the first expansion element c1 as the second excitation element is 3.4 μs, and the generation period of the first hold element h1 as the second constant potential element is 2.9 μs. In addition, the contraction element d1 as the second discharge element has a generation period of 2.3 μs. The generation periods of the second hold element h2, the second expansion element c2, the third hold element h3, and the third expansion element c3 that function as the second return part are the same as those of the first ejection pulse PS2a. That is, the generation period of the second hold element h2 is 0.6 μs, the generation period of the second expansion element c2 is 1.0 μs, the generation period of the third hold element h3 is 3.0 μs, and the generation period of the third expansion element c3 is 2.5 μs.

  When the first ejection pulse PS2a and the second ejection pulse PS2b are compared, the following can be said. The first expansion element c1 (first excitation element) of the first ejection pulse PS2a has a generation period of 2.7 μs, whereas the first expansion element c1 (second excitation element) of the second ejection pulse PS2b has a generation period. Is 3.4 μs. As can be seen from the waveform of FIG. 5A, the potential difference of the first expansion element c1 is equal between the first ejection pulse PS2a and the second ejection pulse PS2b. For this reason, when the second ejection pulse PS2b is used, the expansion speed (expansion amount per unit time) of the pressure chamber 323 is smaller than when the first ejection pulse PS2a is used. As a result, when the first expansion element c1 of the second ejection pulse PS2b is used, the amplitude of the pressure vibration excited by the ink in the pressure chamber 323 is the case where the first expansion element c1 of the second ejection pulse PS2b is used. Smaller than.

  The ink pressure in the pressure chamber 323 changes during the application period of the first hold element h1. At this time, the ink pressure in the pressure chamber 323 periodically changes, and the mode of the change is the degree of expansion and expansion speed (excitation degree) of the pressure chamber 323 by the first expansion element c1, and the pressure chamber 323. It depends on factors such as the natural vibration period of the ink. The ink pressure at the application start timing of the contraction element d1 can be adjusted by the generation period of the first hold element h1.

  Therefore, the ink pressure at the application start timing of the contraction element d1 can be adjusted by changing one or both of the length of the generation period of the first expansion element c1 and the length of the generation period of the first hold element h1. it can.

  In the present embodiment, the ink pressure at the application start timing of the contraction element d1 of the second ejection pulse PS2b is lower than the ink pressure (corresponding to a predetermined pressure) at the application start timing of the contraction element d1 of the first ejection pulse PS2a. Thus, the generation period of each first hold element h1 is determined. Specifically, while the generation period of the first hold element h1 (first constant potential element) included in the first discharge pulse PS2a is set to 3.1 μs, the first hold element included in the second discharge pulse PS2b. The generation period of h1 (second constant potential element) is set to 2.9 μs.

  With the application of the contraction element d1, the ink in the pressure chamber 323 is rapidly pressurized and ejected from the nozzle 324 as ink droplets. Here, the contraction element d1 (first ejection element) of the first ejection pulse PS2a has a generation period of 2.5 μs. In contrast, the contraction element d1 (second ejection element) of the second ejection pulse PS2b has a generation period of 2.3 μs. The potential difference between the first contraction element d1 and the second contraction element d1 is the same. For this reason, the contraction speed of the pressure chamber 323 due to the contraction element d1 of the second ejection pulse PS2b is higher than the contraction speed of the pressure chamber 323 due to the first ejection pulse PS2a. The reason for the difference in the shrinkage speed is as follows. When the second ejection pulse PS2b is used, the ink pressure in the pressure chamber 323 at the application start timing of the contraction element d1 is lower than when the first ejection pulse PS2a is used. The ink pressure at this timing affects the flight speed of the ink droplets. That is, the higher the ink pressure, the higher the flight speed. Accordingly, if the gradients of the contraction element d1 of the second ejection pulse PS2b and the contraction element d1 of the first ejection pulse PS2a are made uniform, the flight speed of the ink droplets ejected by the second ejection pulse PS2b becomes excessively slow. There is a fear. In view of such circumstances, in this printer 1, the generation period of the contraction element d1 of the second ejection pulse PS2b is set shorter than the generation period of the contraction element d1 of the first ejection pulse PS2a, and the flying speed of the ink droplets becomes slow. I try not to pass too much.

  The generation periods of the second hold element h2, the second expansion element c2, the third hold element h3, and the third expansion element c3 as the first return part and the second return part are the first discharge pulse PS2a and the second discharge part. The same applies to the pulse PS2b. This is based on the following findings. As described above, the target ejection amount of ink droplets is the same for the first ejection pulse PS2a and the second ejection pulse PS2b. The flying speed of the ink droplet is adjusted so as not to cause a large difference by adjusting the gradient of the contraction element d1. For this reason, it is considered that the change in the pressure of the ink in the pressure chamber 323 after the ink droplet is ejected is not significantly different between the case where the first ejection pulse PS2a is used and the case where the second ejection pulse PS2b is used. . For this reason, by making the potential change pattern the same in the first ejection pulse PS2a and the second ejection pulse PS2b for each element that is the first restoration portion and the second restoration portion, the ink after ejection of the ink droplets is changed. The pressure change can be converged at an early stage, and the ink droplet ejection frequency can be increased.

<About evaluation results>
Next, an evaluation result obtained by changing the potential change pattern between the second ejection pulse PS2b and the first ejection pulse PS2a will be described. 6 and 7 are diagrams for explaining the evaluation results.

  FIG. 6 is a diagram showing the amount of variation of the ink droplet from the specified flight speed. Specifically, the third ejection pulse when three ejection pulses PS2 are continuously applied to the piezo element PZT and the interval from the second ejection pulse PS2 to the third ejection pulse PS2 is changed. It is a figure which shows the fluctuation amount of the flight speed of PS2. For this reason, the vertical axis in FIG. 6 indicates the variation amount of the flying speed of the ink droplet. In addition, the horizontal axis of FIG. 6 indicates the difference between the second discharge pulse PS2 and the third discharge pulse PS2 and the interval in the drive signal COM. In FIG. 6, a line segment indicated by a series of squares is a diagram for explaining the evaluation result of this embodiment. That is, it is a diagram illustrating a case where the second ejection pulse PS2b is applied to the piezo element PZT following the first ejection pulse PS2a. On the other hand, the line segment indicated by the diamond series is a diagram showing a comparative example. Specifically, it is a diagram illustrating a case where the first ejection pulse PS2a is continuously applied to the piezo element PZT.

  FIG. 7 is a diagram for explaining the ejection pulse group used for the evaluation. That is, the upper part of FIG. 7 is a diagram for explaining an ejection pulse group for evaluating this embodiment. Further, the lower part of FIG. 7 is a diagram for explaining an ejection pulse group for evaluating a reference example. In FIG. 7, the vertical axis represents potential and the horizontal axis represents time. In both the ejection pulse group of the present embodiment and the ejection pulse group of the comparative example, the application start timing of the second ejection pulse PS2 is set to the same interval (predetermined period W2) as the drive signal COM. Further, in FIG. 7, the third ejection pulse PS2 applied to the piezo element PZT is shown by three types: a solid line, an alternate long and short dash line, and a dotted line. This means that the flying speed of the ink droplet is repeatedly measured while shifting the generation timing of the ejection pulse PS2. The application start timing of the third ejection pulse PS2 is based on the application start timing (predetermined period W1) of the first ejection pulse PS2a included in the first second half portion of the drive signal COM. The measurement is performed with a predetermined interval longer than the reference timing.

  As shown in FIG. 6, in this embodiment, the variation amount of the flying speed of the ink droplet is periodically changed. This change is considered to be caused by the pressure vibration of the ink in the pressure chamber 323 after the ejection of the second ink droplet. After ink droplets are ejected, residual vibration occurs in the ink in the pressure chamber 323. In order to suppress this residual vibration, the return portion is applied to the piezo element PZT, but even if this return portion is applied, the pressure vibration of the ink remains. Then, it is considered that the flying speed of the ink droplet by the third ejection pulse PS2 varies according to the ink pressure at the application start time of the ejection pulse PS2. That is, it can be considered that the higher the ink pressure at the start of application, the higher the flying speed of the ink drop, and the lower the pressure, the lower the flying speed of the ink drop. Therefore, as the amplitude of the residual vibration of the ink pressure after the application of the return portion is larger, the flying speed of the ink droplet by the third ejection pulse PS2 changes greatly.

  When the fluctuation width of the flight speed is compared between the ejection pulse group of this embodiment and the ejection pulse group of the comparative example, it can be seen that the fluctuation width of the ejection pulse group of this embodiment is smaller. For example, when the ejection pulse group of the present embodiment is used, the maximum fluctuation width is the size indicated by reference numeral VP1 in FIG. 6, whereas when the ejection pulse group of the comparative example is used, the maximum fluctuation width is The size is indicated by reference numeral VP2 in FIG. The fluctuation range VP1 is about 1.5 times larger than the fluctuation range VP1. Therefore, it can be said that by using the ejection pulse group of the present embodiment, pressure vibration after application of the second ejection pulse PS2b can be suppressed, and high frequency ejection of ink droplets can be realized.

  As described above, the ink pressure at the application start timing of the contraction element d1 (second ejection element) included in the second ejection pulse PS2b is used as the ink pressure at the application start timing of the contraction element d1 (first ejection element) included in the first ejection pulse PS2a. By setting the pressure lower than the ink pressure, the residual vibration of the ink pressure after the application of the second ejection pulse PS2b can be reduced. Thereby, the ejection frequency of ink droplets can be increased.

  Here, in the ejection pulse group of the present embodiment, contraction is achieved by making the generation period of the first expansion element c1 in the second ejection pulse PS2b longer than the generation period of the first expansion element c1 in the first ejection pulse PS2a. The ink pressure in the pressure chamber 323 at the application start timing of the element d1 is lowered. In other words, the liquid pressure at the application start timing of the second ejection element is reduced by making the gradient of the second excitation element (potential change amount per unit time) smaller than the gradient of the first excitation element. It is lower than the liquid pressure (predetermined pressure) at the application start timing.

  By the way, when the first expansion element c1 is applied to the piezo element PZT, pressure vibration is excited in the ink in the pressure chamber 323. In this case, the ink pressure in the pressure chamber 323 changes with time. For this reason, the ink pressure in the pressure chamber 323 at the application start timing of the contraction element d1 also changes depending on the generation period of the first hold element h1. For this reason, the same effect can be obtained even if the generation period of the first hold element h1 is adjusted. In short, by adjusting at least one of the generation period of the contraction element d1 and the generation period of the first hold element h1, the liquid pressure at the application start timing of the second discharge element is changed to the liquid pressure at the application start timing of the first discharge element. Can be lower.

<Evaluation of ejection pulse PS2>
In the drive signal COM of the present embodiment, the potential change pattern differs between the first ejection pulse PS2a and the second ejection pulse PS2b. Here, the conventional evaluation apparatus ejects ink droplets using one type of ejection pulse. For this reason, when ink droplets are ejected at a high frequency by a plurality of types of ejection pulses PS2a and PS2b having different potential change patterns as in the drive signal COM of the present embodiment, proper evaluation cannot be performed. In view of such circumstances, in this embodiment, as shown in FIG. 7, evaluation is performed using three ejection pulses PS2.

  That is, the first ejection pulse PS2a (first ejection pulse) applied first to the piezo element PZT, the second ejection pulse PS2b (evaluation target ejection pulse) applied to the piezo element PZT and secondly evaluated. Third, ink droplets are continuously ejected by a first ejection pulse PS2a (following ejection pulse) that is applied to the piezo element PZT and the flying speed of the ink droplets is measured. Then, the flying speed of the ink droplet is measured a plurality of times by changing the interval between the second second ejection pulse PS2b and the third first ejection pulse PS2a. Then, based on the relationship between the interval from the second ejection pulse PS2b to the first ejection pulse PS2a and the flight speed of the ink droplet, for example, based on the magnitude of variation in the variation amount of the flight speed, the potential at the second ejection pulse PS2b. Evaluate change patterns.

  When such an evaluation method is adopted, the change in the ink pressure in the pressure chamber 323 after the ink droplet is ejected by the second ejection pulse PS2b, the interval from the second ejection pulse PS2b to the first ejection pulse PS2a and the ink It can be recognized based on the relationship between the flight speeds of the drops. For this reason, even when the ejection frequency is increased, the second ejection pulse PS2b can be properly evaluated. This will be described in detail below.

<Ejection Pulse Evaluation Apparatus 100>
FIG. 8A is a diagram for explaining the ejection pulse evaluation apparatus 100. The illustrated evaluation apparatus 100 includes a head HD, a head control unit HC, a drive signal generation circuit 110, an ink droplet detection unit 120, an output device 130, and a controller 140. Among these, the head HD, the head controller HC, and the drive signal generation circuit 110 are the same as those included in the printer 1. That is, as described with reference to FIG. 2A, the head HD changes the pressure chamber 323 communicating with the nozzle 324 and the ink supply path 322, and changes the volume of the pressure chamber 323, thereby changing the pressure of the ink in the pressure chamber 323. It has a piezo element PZT. The drive signal generation circuit 110 functions as an ejection pulse generation unit, and generates a drive signal COM including the ejection pulse PS2. Note that a detailed description of these parts will be omitted.

  The ink droplet detection unit 120 detects ink droplets ejected from the head HD. The ink droplet detection unit 120 includes a light emitting unit 121 and a light receiving unit 122. The light emitting unit 121 is configured by a semiconductor laser, and the light receiving unit 122 is configured by a photodiode. The light emitting unit 121 outputs the laser beam toward the light receiving unit 122. The light receiving unit 122 outputs an H level signal over a period in which the laser beam from the light emitting unit 121 is received. As shown in FIG. 8B, ink droplets are ejected through a path that interrupts the laser beam halfway. Therefore, as shown in FIG. 8C, an L level signal is output from the light receiving unit 122 over a period in which the ink droplets block the laser beam. In the illustrated ink droplet detection unit 120, two sets of the light emitting unit 121 and the light receiving unit 122 are provided in the vertical direction. For this reason, the flight speed of the ink droplet can be measured by the distance between the laser beams and the light shielding time. In the example of FIGS. 8B and 8C, the distance between the upper laser beam LXu and the lower laser beam LXd is Ld, and the ink is measured by the lower light receiving unit 122 from the timing t1 when the ink droplet is measured by the upper light receiving unit 122. The period until the timing when the ink droplet is measured is Wd. For this reason, the flight speed is Ld / Wd. The ink droplet detection unit 120 is not limited to this configuration as long as it can detect ink droplets.

  The controller 140 controls the operation of the evaluation apparatus 100 and includes a CPU 141 and a memory 142. The CPU 141 controls the head HD and the drive signal generation circuit 110 based on the firmware and DAC data stored in the memory 142. Further, the flying speed of the ink droplet is obtained based on the output signal from the light receiving unit 122. Therefore, the controller 140 functions as a speed measurement unit that measures the flying speed of the ink droplets together with the ink droplet detection unit 120. The output device 130 outputs various information related to measurement. For example, the measurement condition, the potential difference and generation period of each element in the ejection pulse PS2, and the flying speed of the ink droplet are output. The output device 130 may output information on a sheet or may display the information on a display. In short, it is only necessary to output information related to evaluation.

<About evaluation results>
Next, an evaluation result when the generation period of the first hold element h1 is changed will be described with reference to FIGS. FIG. 9 is a diagram illustrating the ejection pulse group used for the evaluation. FIG. 10 shows the relationship between the variation in the flying speed of the ink droplet and the interval from the second ejection pulse (evaluation target ejection pulse PSY) to the third ejection pulse (following ejection pulse PSZ). It is a figure shown for every kind of pulse.

  First, the ejection pulse group used for evaluation will be described. As shown in FIG. 9, the ejection pulse group is composed of three ejection pulses. The first ejection pulse is the preceding ejection pulse PSX, the second ejection pulse PS2 is the evaluation target ejection pulse PSY, and the third ejection pulse PS2 is the subsequent ejection pulse PSZ. That is, other ejection pulses PSX and PSZ are generated one by one before and after the evaluation target ejection pulse PSY to be evaluated and applied to the piezo element PZT.

  Each of the preceding ejection pulse PSX, the evaluation target ejection pulse PSY, and the subsequent ejection pulse PSZ has each element shown in FIG. 5A. Therefore, the first expansion element c1 included in the preceding ejection pulse PSX corresponds to a first excitation element that excites pressure vibration in the ink in the pressure chamber 323, and the contraction element d1 ejects ink droplets from the nozzle 324. This corresponds to a first ejection element that causes the piezo element PZT to perform the above operation. Similarly, the first expansion element c1 included in the evaluation target ejection pulse PSY corresponds to a second excitation element, and the contraction element d1 corresponds to a second ejection element. The first expansion element c1 included in the subsequent ejection pulse PSZ corresponds to a third excitation element, and the contraction element d1 corresponds to a third ejection element.

  In addition, the preceding ejection pulse PSX and the subsequent ejection pulse PSZ are determined to have the same potential change pattern as the first ejection pulse PS2a. Since the potential change pattern and the generation period of each element have already been described (see FIGS. 5A and 5B), description thereof is omitted here. On the other hand, the evaluation target ejection pulse PSY has a potential change pattern defined on the basis of the first ejection pulse PS2a described above. In this example, as schematically shown in FIG. 9, a plurality of types of evaluation target ejection pulses PSY in which the generation period of the first hold element h <b> 1 is increased stepwise are set as evaluation targets. Specifically, as shown in the lower part of FIG. 10, the first hold element h1 has the same potential change pattern as the first ejection pulse PS2a, that is, the generation period of the first hold element h1 is the first hold element h1 of the first ejection pulse PS2a. 6 types of evaluations in total, from the same (ΔPwh1 = 0 μs) to the generation period of the first hold element h1 that is 1 μs longer than the first hold element h1 of the first ejection pulse PS2a (ΔPwh1 = 1 μs) The target ejection pulse PSY is an evaluation target.

  For each evaluation target ejection pulse PSY, the flying speed of the ink droplet ejected by the subsequent ejection pulse PSZ is measured. At this time, the flight speed of the ink droplet is measured a plurality of times while the interval between the evaluation target ejection pulse PSY and the subsequent ejection pulse PSZ is increased stepwise. Specifically, the case where the interval from the preceding ejection pulse PSX to the subsequent ejection pulse PSZ is the same as the drive signal COM, that is, the predetermined interval W1, is set as a reference (Delay time = 0 μs). Then, the flight speed is measured by delaying the generation start timing of the trailing ejection pulse PSZ by 1 μs by 9 μs at the maximum.

  FIG. 10 shows the evaluation results. Here, the variation in the fluctuation amount of the flight speed (difference between the maximum value and the minimum value) is used for the evaluation. As described with reference to FIG. 6, the fluctuation amount of the flight speed means a variation in ink pressure at the application start timing of the contraction element d1. For this reason, it can be said that the smaller the fluctuation amount, the more stably the ink droplet can be ejected. That is, it can be said that ink droplets can be ejected at a high frequency. In the evaluation result of FIG. 10, when the potential change patterns of the preceding ejection pulse PSX and the evaluation target ejection pulse PSY are both the same as the potential variation pattern in the first ejection pulse PS2a, in other words, the first ejection pulse PS2a is continuously applied. When applied, the variation (maximum amplitude) is 0.547. And if the production | generation period of the 1st hold element h1 is lengthened, the dispersion | variation will become small. For example, when the generation period of the first hold element h1 is increased by 0.2 μs, the variation is 0.466, and when the generation period is increased by 0.4 μs, the variation is 0.49. Similarly, if the generation period of the first hold element h1 is increased by 0.6 μs, the variation becomes 0.448, and if the generation period of the first hold element h1 is increased by 0.8 μs, the variation becomes 0.232. This is presumably because the ink pressure at the application start timing of the contraction element d1 becomes smaller as the first hold element h1 becomes longer.

  This can be seen from the graph of FIG. FIG. 11 is a diagram illustrating the flight speed of ink droplets ejected by one ejection pulse PS2, and is a diagram illustrating the flight speed of ink droplets when the generation period of the first hold element h1 is increased stepwise. is there. In the ejection pulse PS2, the first expansion element c1 (excitation element) and the contraction element d1 (ejection element) are set to the same potential difference and generation period as the first ejection pulse PS2a. Therefore, the range indicated by the symbol A in FIG. 11 corresponds to the evaluation range in FIG. As is clear from FIG. 11, in the range indicated by the symbol A, the ink pressure at the application start timing of the contraction element d1 becomes smaller as the first hold element h1 becomes longer. This means that the longer the first hold element h1, the more the ink pressure can be prevented from becoming excessively high. In other words, it means that the variation in the flying speed and flying direction of ink droplets can be suppressed and stabilized.

  FIG. 12 is a diagram schematically showing the flight state of the ink droplet by the preceding ejection pulse PSX, the ink droplet by the evaluation target ejection pulse PSY, and the ink droplet by the subsequent ejection pulse PSZ. In this figure, the upper numerical value indicates the generation period of the first hold element h1 in the evaluation target ejection pulse PSY. That is, as in FIG. 10, the difference from the generation period of the first ejection pulse PS2a is shown. Note that the intervals of the preceding ejection pulse PSX, the evaluation target ejection pulse PSY, and the subsequent ejection pulse PSZ are the same as those of the drive signal COM. In addition, black circles within the range indicated by symbol B indicate ink droplets ejected by the ejection pulses PSX, PSY, PSZ. That is, in the range B, the lowermost black circle indicates an ink droplet ejected by the preceding ejection pulse PSX, and the uppermost black circle indicates an ink droplet ejected by the subsequent ejection pulse PSZ. A black circle located between the upper and lower black circles indicates an ink droplet ejected by the evaluation target ejection pulse PSY.

  As can be seen from FIG. 12, when the generation period of the first hold element h1 in the evaluation target ejection pulse PSY is the same as that of the first ejection pulse PS2a, the flight speed of the ink droplet ejected by the evaluation target ejection pulse PSY is the leading speed. It can be seen that the ink droplets ejected by the ejection pulse PSX are sufficiently faster than the flying speed of the ink droplets. The ink droplet ejected by the evaluation target ejection pulse PSY becomes slower as the generation period of the first hold element h1 becomes longer. In this example, if 0.3 μs is added, in other words, if it is set 10% longer than the generation period (3.1 μs) of the first hold element h1 in the first ejection pulse PS2a, the flight speed and the flight direction Is stable. In the result of FIG. 12, the flight speed and the flight direction are stabilized when 0.3 μs or more is added, but from the viewpoint of high-frequency ejection of ink droplets, the addition period is 0.9 μs or less (30% or less). It can be said that it is preferable.

  Next, with reference to FIG.13 and FIG.14, the evaluation result at the time of changing the production | generation period of the 1st expansion element c1 is demonstrated. FIG. 13 is a diagram for explaining the ejection pulse group used for the evaluation. FIG. 14 shows the relationship between the variation in the flying speed of the ink droplet and the interval from the second ejection pulse (evaluation target ejection pulse PSY) to the third ejection pulse (following ejection pulse PSZ). It is a figure shown for every kind of pulse.

  First, the ejection pulse group used for evaluation will be described. As shown in FIG. 13, this ejection pulse group is also constituted by three ejection pulses including a preceding ejection pulse PSX, an evaluation target ejection pulse PSY, and a subsequent ejection pulse PSZ. Of these ejection pulses PSX, PSY, and PSZ, the preceding ejection pulse PSX and the subsequent ejection pulse PSZ are the same as those in FIG.

  The evaluation target ejection pulse PSY has a potential change pattern determined based on the first ejection pulse PS2a described above. In this example, as schematically illustrated in FIG. 13, a plurality of types of evaluation target ejection pulses PSY in which the generation period of the first expansion element c <b> 1 is increased stepwise are set as evaluation targets. Specifically, as shown in the lower part of FIG. 14, the first expansion element c1 having the same potential change pattern as the first ejection pulse PS2a, that is, the generation period of the first expansion element c1 is the first expansion element c1 of the first ejection pulse PS2a. 6 types in total, from the same (ΔPwc1 = 0 μs) to the generation period of the first expansion element c1 that is 1 μs longer than the first expansion element c1 of the first ejection pulse PS2a (ΔPwc1 = 1 μs) The target ejection pulse PSY is an evaluation target. For each evaluation target ejection pulse PSY, the flying speed of the ink droplet ejected by the subsequent ejection pulse PSZ is measured. Also in this case, the flying speed of the ink droplet is measured a plurality of times while the interval between the evaluation target ejection pulse PSY and the subsequent ejection pulse PSZ is increased stepwise.

  FIG. 14 shows the evaluation results. Again, the variation in the variation in flight speed is used for evaluation. In the evaluation result of FIG. 14, when both the potential change patterns of the preceding ejection pulse PSX and the evaluation target ejection pulse PSY are the same as the potential variation pattern in the first ejection pulse PS2a, the variation is 0.547. And if the production | generation period of the 1st expansion element c1 is lengthened, the dispersion | variation will become small. For example, when the generation period of the first expansion element c1 is increased by 0.2 μs, the variation is 0.501, and when the generation period is increased by 0.4 μs, the variation is 0.479. Similarly, when the generation period of the first expansion element c1 is increased by 0.6 μs, the variation is 0.496, and when the generation period of 0.8 μs is increased, the variation is 0.455. From this, it can be seen that the longer the first expansion element c1, the smaller the ink pressure at the application start timing of the contraction element d1.

  When the evaluation result of FIG. 14 is considered in comparison with the evaluation result of FIG. 10, the generation period of the first expansion element c1 in the evaluation target discharge pulse PSY is longer than the generation period of the first expansion element c1 in the first discharge pulse PS2a. It is considered that the ejection of ink droplets is stabilized by making the length 0.2 μs or longer. This is because, in the evaluation result of FIG. 10, the variation when the generation period of the first hold element h1 is longer than the generation period of the first hold element h1 in the first ejection pulse PS2a by 1 μs or more is 0.513. In addition, the ink droplet ejection was stable. In this example, since the generation period of the first expansion element c1 in the first ejection pulse PS2a is 2.7 μs, it is considered that the flight speed and the flight direction are stabilized by setting this generation period at least 10% longer. From the viewpoint of high-frequency ejection of ink droplets, it can be said that the addition period is preferably 0.9 μs or less (1/3 or less), similarly to the first hold element h1.

  Then, by appropriately changing the combination of the generation periods of the first expansion element c1 and the first hold element h1 in the evaluation target ejection pulse PSY, the flying speed of the ink droplet by the subsequent ejection pulse PSZ is measured, and the variation in the flying speed is small. By selecting the combination, the potential change pattern in the evaluation target ejection pulse PSY can be optimized.

<Summary>
As described above, in this embodiment, the first ejection pulse PS2a and the second ejection pulse PS2b are continuously applied to the piezo element PZT, whereby two ink droplets (first liquid droplets) having the same target ejection amount are applied. , Second liquid droplets) are continuously discharged. In other words, by applying the first expansion element c1 (first excitation element) of the first ejection pulse PS2a to the piezo element PZT, the pressure vibration is excited in the ink in the pressure chamber 323. The timing is adjusted by the first hold element h1 (first constant potential element), and the contraction element d1 (first ejection element) is applied at the timing when the ink in the pressure chamber 323 reaches a predetermined pressure. Thereafter, the first expansion element c1 (second excitation element) of the second ejection pulse PS2b is applied to the piezo element PZT to excite the pressure vibration in the ink in the pressure chamber 323, and the first hold element h1 (second constant element h1). The timing is adjusted by the potential element. Then, the contraction element d1 (second ejection element) is applied at a certain timing during the period when the ink pressure in the pressure chamber 323 is also lower than the predetermined pressure. Accordingly, it is possible to suppress the ink pressure in the pressure chamber 323 from becoming excessively high when the piezo element PZT is expanded to eject the second ink droplet. As a result, even if the discharge interval between the first ink droplet and the second ink droplet is shortened, the second ink droplet can be stably discharged, and the discharge frequency of the ink droplet can be increased.

  In this embodiment, the potential change pattern in the evaluation target ejection pulse PSY is evaluated using three ejection pulses of the preceding ejection pulse PSX, the evaluation target ejection pulse PSY, and the subsequent ejection pulse PSZ. In other words, while changing the interval from the evaluation target ejection pulse PSY to the subsequent ejection pulse PSZ, the variation amount of the flying speed of the ink droplet ejected by the subsequent ejection pulse PSZ is measured, and the magnitude of the variation in the variation amount is measured. Evaluating. By adopting such an evaluation method, it is possible to recognize a change in ink pressure in the pressure chamber 323 after ink droplets are ejected by the evaluation target ejection pulse PSY. Therefore, even if the discharge interval between the liquid droplet based on the preceding discharge pulse PSX and the ink droplet based on the evaluation target discharge pulse PSY is short, that is, when the discharge frequency is increased, the evaluation target discharge pulse PSY is properly evaluated. it can. Further, even if the evaluation target ejection pulse PSY has a different potential change pattern with respect to the preceding ejection pulse PSX having a certain potential change pattern, the potential change pattern can be optimized.

=== Other Embodiments ===
The embodiment of the invention described above is for facilitating the understanding of the present invention, and does not limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and the present invention includes the equivalents thereof.
In the above-described embodiment, a printer that ejects water-based ink or oil-based ink is taken as an example of the liquid ejecting apparatus. Here, the liquid to be ejected is not limited to liquid ink. For example, it may be a liquid other than ink (in addition to a liquid, including a liquid material in which particles of a functional material are dispersed and a fluid such as a gel).

  To give specific examples, a liquid material that discharges a liquid material in which a material such as an electrode material or a color material used in the manufacture of liquid crystal displays, EL (electroluminescence) displays, and surface-emitting displays is dispersed or dissolved. It may be a discharge device, a liquid discharge device that discharges bio-organic matter used in biochip manufacturing, or a liquid discharge device that discharges liquid as a sample used as a precision pipette. In addition, a transparent resin liquid such as UV curable resin is used to form a liquid ejection device that ejects lubricating oil pinpoint to precision machines such as watches and cameras, and micro hemispherical lenses (optical lenses) used in optical communication elements. A liquid discharge device that discharges a liquid onto the substrate, a liquid discharge device that discharges an etching solution such as acid or alkali to etch the substrate, and a fluid discharge device that discharges gel.

<Discharge pulse>
In the ejection pulse described above, the potential change pattern is that the potential is increased from the intermediate potential as the reference potential to the highest potential, then the potential is decreased from the highest potential to the lowest potential, and further the potential is increased to the intermediate potential. It was something to be made. Here, various potential change patterns in the ejection pulse can be determined. For example, an ejection pulse having a trapezoidal or rectangular wave potential change pattern may be used. In this ejection pulse, the potential is raised from the lowest potential as the reference potential to the highest potential, and then the highest potential is maintained for a predetermined time. Then, the potential is lowered to the lowest potential. In short, the ejection pulse only needs to have an element that excites pressure vibration in the liquid in the pressure chamber and an element that causes the element to perform an operation for ejecting a liquid droplet from the nozzle.

<About an element that operates to discharge liquid>
In the above-described embodiment, the piezo element PZT is exemplified as an element that operates to discharge liquid. Here, there are a piezo element PZT used for a head for ejecting liquid, one that expands the pressure chamber as the potential increases, and one that contracts the pressure chamber as the potential increases. The present invention can be applied to any piezo element PZT. When the latter piezo element is used, the waveform of the ejection pulse is inverted with respect to the potential level.
In addition, this element is not limited to the piezo element PZT. In other words, any device may be used as long as it excites the pressure vibration in the liquid in the pressure chamber with the application of the excitation element, and the liquid droplet is ejected from the nozzle with the application of the ejection element. For example, a magnetostrictive element may be used.

FIG. 1A is a block diagram illustrating the configuration of a printer. FIG. 1B is a conceptual diagram illustrating the storage area of the memory. FIG. 2A is a cross-sectional view of the head. FIG. 2B is a view of the flow path unit as viewed from the nozzle side. It is a block diagram explaining structures, such as a drive signal generation circuit. It is a figure explaining a drive signal. FIG. 5A is a diagram showing a potential change pattern in the ejection pulse. FIG. 5B is a diagram for explaining a generation period of each element constituting the ejection pulse. It is a figure explaining an evaluation result, and shows the amount of change from the regulation flight speed of an ink drop. It is a figure explaining the discharge pulse group used for evaluation. FIG. 8A is a diagram for explaining an ejection pulse evaluation apparatus. FIG. 8B is a diagram illustrating the relationship between ink droplets and laser beams. FIG. 8C is a diagram illustrating a change in the output level of the light receiving unit. It is a figure explaining the ejection pulse group used for evaluation when changing the production | generation period of a 1st hold element. It is a figure which shows the relationship between the variation | change_quantity of the flight speed of an ink drop, and the space | interval from an evaluation object discharge pulse to a subsequent discharge pulse. It is a figure which shows the flight speed of the ink drop at the time of making the production | generation period of a 1st hold element long in steps. It is a figure which shows typically the flight state of the ink droplet by a preceding discharge pulse, the ink droplet by an evaluation object discharge pulse, and the ink droplet by a subsequent discharge pulse. It is a figure explaining the discharge pulse group used for evaluation when changing the production | generation period of a 1st expansion | swelling element. It is a figure which shows the relationship between the variation | change_quantity of the flight speed of an ink drop, and the space | interval from an evaluation object discharge pulse to a subsequent discharge pulse.

Explanation of symbols

1 printer, 10 paper transport mechanism, 20 carriage movement mechanism,
30 head units, 31 cases, 32 flow path units,
321 common ink chamber, 322 ink supply path, 323 pressure chamber,
324 nozzle, 325 diaphragm, 325a elastic film,
325b island, 326A first switch, 326B second switch,
33 piezo element units, 331 piezo element groups,
332 bonding substrate, 333 head side wiring member,
40 drive signal generation circuit, 40A first drive signal generation circuit,
41A first waveform generation circuit, 411A first digital-analog converter,
412A first preamplifier, 42A first current amplifier circuit,
40B second drive signal generation circuit, 41B second waveform generation circuit,
411B second digital-analog converter, 412B second preamplifier,
42B second current amplification circuit, 50 detector groups,
60 printer-side controller, 61 interface section,
62 CPU, 63 memory, 100 evaluation device,
110 drive signal generation circuit, 120 ink droplet detection unit,
121 light emitting unit, 122 light receiving unit, 130 output device,
140 controller, 141 CPU, 142 memory,
CP computer, HD head, PZT piezo element,
HC head controller, T repetition period, T1 first half period,
T2 latter half period, COM_A first drive signal,
COM_B second drive signal, PS1 slight vibration pulse,
vc micro-vibration expansion element, vh micro-vibration hold element,
vd slight vibration contraction element, PS2 discharge pulse,
PS2a first ejection pulse, PS2b second ejection pulse,
PSX preceding discharge pulse, PSY evaluation target discharge pulse,
PSZ trailing discharge pulse, c1 first expansion element,
h1 first hold element, d1 contraction element, h2 second hold element,
c2 second expansion element, h3 third hold element, c3 third expansion element,
VH maximum potential, VV slight vibration potential, VB intermediate potential, VN damping potential,
VL lowest potential

Claims (8)

Liquid that has a potential change pattern and discharges liquid droplets, sequentially discharges liquid droplets using the preceding discharge pulse, the evaluation target discharge pulse, and the subsequent discharge pulse in this order, and is discharged by the subsequent discharge pulse. A measurement step for measuring the flight speed of the droplet, the measurement step for measuring the flight speed of the liquid droplet a plurality of times with different intervals from the evaluation target ejection pulse to the subsequent ejection pulse;
An evaluation step for evaluating a potential change pattern in the evaluation target ejection pulse based on a relationship between an interval from the evaluation target ejection pulse to the subsequent ejection pulse and a flight speed of the liquid droplet;
Evaluation method of ejection pulse having It is the evaluation method of the ejection pulse according to claim 1,
In the evaluation step,
An ejection pulse evaluation method for evaluating a potential change pattern in the evaluation target ejection pulse based on a difference between a minimum value and a maximum value in a fluctuation amount of a flight speed of the liquid droplet. A method for evaluating an ejection pulse according to claim 1 or 2, wherein
In the measurement step,
By applying the preceding ejection pulse, the evaluation target ejection pulse, and the subsequent ejection pulse to an element that changes the pressure in the liquid in the pressure chamber, the pressure in the liquid in the pressure chamber is changed according to the change in the potential. An ejection pulse evaluation method in which the liquid droplets are ejected from a nozzle communicated with the pressure chamber. A method for evaluating a discharge pulse according to claim 3,
The preceding ejection pulse is:
A first excitation element that excites pressure vibration in the liquid in the pressure chamber;
A first ejection element that is generated after the first excitation element and causes the element to perform an operation for ejecting a liquid droplet from the nozzle;
The evaluation target ejection pulse is:
A second excitation element that excites pressure vibration in the liquid in the pressure chamber;
A second ejection element that is generated after the second excitation element and causes the element to perform an operation for ejecting a liquid droplet from the nozzle;
The subsequent discharge pulse is:
A third excitation element that excites pressure vibration in the liquid in the pressure chamber;
A discharge pulse evaluation method comprising: a third discharge element that is generated after the third excitation element and causes the element to perform an operation for discharging a liquid droplet from the nozzle. A method for evaluating a discharge pulse according to any one of claims 1 to 4,
In the measurement step,
An ejection pulse evaluation method for generating the preceding ejection pulse, the evaluation target ejection pulse, and the subsequent ejection pulse by providing data representing a potential change pattern in time series to the ejection pulse generation unit. It is the evaluation method of the ejection pulse according to claim 5,
The change pattern of the potential of the subsequent ejection pulse is:
The ejection pulse evaluation method is the same as the potential change pattern of the preceding ejection pulse. The method for evaluating a discharge pulse according to any one of claims 1 to 6,
In the measurement step,
For each evaluation target ejection pulse and another evaluation target ejection pulse whose potential change pattern is different from the certain evaluation target pattern, the flight speed of the liquid droplet is measured a plurality of times,
In the evaluation step,
An ejection pulse evaluation method for comparing an evaluation result of the certain evaluation target ejection pulse with an evaluation result of the other evaluation target ejection pulse. A pressure chamber in communication with the nozzle;
An element that performs an operation of applying a pressure change to the liquid in the pressure chamber in accordance with a change in potential;
An ejection pulse generation unit for generating an ejection pulse in which the change pattern of the potential is determined,
The preceding ejection pulse, the evaluation target ejection pulse, and the subsequent ejection pulse that have a potential change pattern and eject liquid droplets in this order, and the intervals from the evaluation target ejection pulse to the subsequent ejection pulse are different. An ejection pulse generator that repeatedly generates
A speed measurement unit that measures a flight speed of a liquid droplet ejected from the nozzle by application of the subsequent ejection pulse to the element;
An apparatus for evaluating ejection pulses.

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