JP5605457B2 - Liquid ejecting apparatus and control method thereof - Google Patents

Description

  The present invention relates to a liquid ejection apparatus such as an ink jet printer and a control method thereof, and in particular, discharges liquid from the nozzle opening by applying pressure fluctuation to the pressure generation chamber communicating with the nozzle opening. The present invention relates to a liquid discharge apparatus including a liquid discharge head to be controlled, and a control method thereof.

  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. As a representative example of this liquid ejection apparatus, for example, an ink jet recording head (hereinafter simply referred to as a recording head) as a liquid ejection head is provided, and liquid ink is ejected from the nozzle of this recording head to a recording medium such as recording paper. An image recording apparatus such as an ink jet printer (hereinafter simply referred to as a printer) that records an image or the like by discharging and landing on a (landing target) can be given. In recent years, liquid ejecting apparatuses have been applied not only to the image recording apparatus but also to various manufacturing apparatuses such as a manufacturing apparatus for a color filter such as a liquid crystal display.

  In the liquid ejection device, a drive pulse (ejection pulse) is applied to a pressure generating element (for example, a piezoelectric vibrator or a heating element) and driven to change the pressure in the liquid in the pressure generating chamber. There is one configured to discharge liquid from a nozzle communicating with a pressure generation chamber using a pressure change. In such a liquid ejecting apparatus, the amount of ejected liquid can be increased by increasing the amplitude of pressure vibration applied to the liquid in the pressure generating chamber. In other words, it is possible to increase the amount of liquid ejected by increasing the drive voltage of the ejection drive pulse (see, for example, Patent Document 1).

JP 2003-94656 A

  In recent years, attempts have been made to discharge a liquid (hereinafter also referred to as a high-viscosity liquid) having a higher viscosity than a conventionally treated liquid such as UV ink (ultraviolet curable ink), for example. That is, in the past, liquids having a low viscosity such as water were targeted, but in recent years, attempts have been made to eject high viscosity liquids of 8 millipascal seconds or more. In order to obtain a sufficient discharge amount when discharging the high-viscosity liquid, it is necessary to give the liquid in the pressure generation chamber a pressure change having a magnitude corresponding to the discharge amount. However, when the pressure change is increased, the flying speed of the liquid also increases, and a phenomenon in which the rear end portion of the liquid extends like a tail tends to occur. Then, there is a possibility that the tail portion separates from the droplet main body and flies and does not land on the regular position (desired position) on the landing target. For example, an ink jet printer has a problem in that the tail part becomes a mist and is displaced from a normal position and landed to separate dots, thereby causing deterioration in image quality. In particular, in a high-viscosity liquid, the tail part is separated into several parts, and these separated parts (satellite ink droplets or mist) cause a significant deterioration in image quality.

  On the other hand, when the tail portion of the high-viscosity liquid in the nozzle opening begins to separate from the meniscus, if a pressure change that is smaller than the first pressure change is applied to the liquid in the pressure generation chamber, the liquid is discharged. Instead, the tail portion remaining on the meniscus side is drawn into the pressure generating chamber side, and a phenomenon occurs in which the length of the tail portion cut off from the meniscus is shortened. At this time, since the tail portion is broken while the tail portion is extending, the residual vibration of the meniscus may be excited by the broken reaction. As a result, when the tail portions remaining on the meniscus side are rounded together and separated, there is a problem that the separated portions are accompanied and discharged.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a liquid ejection device capable of preventing the separation of dots by suppressing the generation of mist and the like when ejecting a highly viscous liquid. And providing a control method thereof.

The present invention has been proposed to achieve the above object, and includes a pressure generation chamber communicating with the nozzle opening, and a pressure generation element that causes a pressure fluctuation in the liquid of the pressure generation chamber. A liquid discharge head capable of discharging liquid from the nozzle opening by the operation of the generating element;
Drive signal generating means for generating a series of drive signals including a drive pulse for driving the pressure generating element;
A liquid ejection device comprising:
The liquid has a viscosity of 8 millipascal seconds or more;
The drive pulse generated by the drive signal generating means includes an expansion element that expands the pressure generation chamber to draw a meniscus, a contraction element that changes a voltage to contract the expanded pressure generation chamber, and the contraction element A re-expansion element that re-expands the pressure generation chamber after contraction by the above and draws in a meniscus, and a re-contraction element that changes a voltage so as to contract the pressure expansion chamber expanded again,
The re-contraction element includes a first re-contraction element and a second re-contraction element that contracts the pressure generating chamber that has been expanded again at a voltage change rate different from that of the first re-contraction element.
A voltage change rate of the second re-shrink element is set smaller than a voltage change rate of the first re-shrink element;
Wherein during the re-expansion element and the first re-contraction element, it viewed including the re-expansion hold element for maintaining the rear end a fixed time the voltage at the re-expansion element,
The voltage change amount of the re-expansion element is set to 30% or more of the potential difference from the lowest voltage to the highest voltage of the drive pulse .

  According to this configuration, the drive pulse generated by the drive signal generating means includes an expansion element that expands the pressure generation chamber and draws in the meniscus, and a droplet by changing the voltage to contract the expanded pressure generation chamber. A contraction element to be discharged, a re-expansion element that re-expands the pressure generation chamber after the contraction element and draws in the meniscus, and a re-contraction element that changes a voltage so as to contract the pressure expansion chamber again expanded, The re-shrink element includes a first re-shrink element and a second re-shrink element that contracts the pressure generating chamber that has been expanded again at a voltage change rate different from that of the first re-shrink element. When discharging high-viscosity liquid), it is possible to suppress the phenomenon that the rear end of the discharged liquid stretches like a tail compared to the case where the recontraction element is supplied at a constant voltage change rate. Almost spherical It can be. Further, by suppressing the residual vibration of the meniscus after the ink droplet is discharged, the columnar portion remaining on the meniscus side is rounded, and this portion can be suppressed from being excessively discharged as a small amount of ink droplet. As a result, it is possible to prevent the liquid from being separated and landing on the landing target.

In addition, since the voltage change rate of the second recontraction element is set to be smaller than the voltage change rate of the first recontraction element, the pressure generating chamber is abruptly contracted by the first recontraction element, and the meniscus is rapidly pressurized. By drawing in the generation chamber side, it is possible to suppress a phenomenon in which the rear end portion of the discharged liquid extends like a tail. Then, the pressure generating chamber is gently contracted by the second recontraction element, and the tail portion remaining on the meniscus side from the meniscus after the liquid is discharged can be suppressed from being discharged.

Furthermore , since the voltage change amount of the re-expansion element is set to 30% or more of the potential difference from the lowest voltage to the highest voltage of the drive pulse, the meniscus is moved to the pressure generation chamber side when the contracted pressure generation chamber is expanded again. By reliably pulling in, tail growth associated with the liquid to be discharged can be suppressed, and when high-viscosity liquid is discharged, generation of mist or the like can be suppressed and dot separation can be prevented.

In the above configuration, the re-expansion element includes a first re-expansion element and a second re-expansion element that expands the pressure generating chamber again at a voltage change rate different from that of the first re-expansion element ,
It is desirable that at least the voltage change amount of the second re-expansion element is set to 30% or more of the potential difference from the lowest voltage to the highest voltage of the drive pulse.

  According to this configuration, the re-expansion element includes the first re-expansion element and the second re-expansion element that re-expands the pressure generation chamber at a voltage change rate different from that of the first re-contraction element, and at least the second re-expansion element. Since the voltage change amount of the expansion element is set to 30% or more of the potential difference from the lowest voltage to the highest voltage of the drive pulse, compared with the case where the re-expansion element is supplied at a constant voltage change rate, The rear end portion can be drawn into the pressure generating chamber side, and the phenomenon that the rear end portion of the discharged liquid extends like a tail can be suppressed.

  In the above configuration, it is desirable that the supply time of the second recontraction element is set to be equal to or less than the natural vibration period Tc of the liquid filled in the pressure generating chamber.

  According to the above configuration, since the supply time of the second recontraction element is set to be equal to or less than the natural vibration period Tc of the liquid filled in the pressure generating chamber, it is possible to suppress excitation of the meniscus due to liquid discharge. The phenomenon that the rear end of the discharged liquid extends like a tail can be further suppressed.

  In the above-described configuration, it is preferable that a reshrinkage hold element that maintains a voltage for a certain time at a rear end of the first reshrinkage element is preferably provided between the first reshrinkage element and the second reshrinkage element.

  According to the above configuration, the first re-shrink element includes the re-shrink hold element that maintains the voltage for a certain time at the rear end of the first re-shrink element between the first re-shrink element and the second re-shrink element. The residual vibration of the meniscus can be suppressed.

Further, the control method of the liquid ejection apparatus of the present invention includes a pressure generation chamber communicating with the nozzle opening, and a pressure generation element that causes a pressure fluctuation in the liquid in the pressure generation chamber, and the operation of the pressure generation element A liquid discharge head capable of discharging liquid from the nozzle opening;
Drive signal generating means for generating a series of drive signals including a drive pulse for driving the pressure generating element;
A method for controlling a liquid ejection apparatus comprising:
An expansion step of expanding the pressure generation chamber to draw a meniscus, a contraction step of changing a voltage so as to contract the pressure generation chamber expanded in the expansion step, and expanding the pressure generation chamber again after the contraction step A re-expansion step for drawing in the meniscus, and a re-contraction element for changing the voltage so as to contract the pressure generating chamber expanded again in the re-expansion step,
Wherein the re-contraction process, a first re-contraction step, seen including a second re-contraction process for contracting a pressure generating chamber which is again expanded in a voltage variation ratio different from that of the first re-contraction process,
The amount of voltage change in the re-expansion step is set to 30% or more of the potential difference from the lowest voltage to the highest voltage of the drive pulse .

2 is a block diagram illustrating an electrical configuration of a printer. FIG. FIG. 3 is a cross-sectional view of a main part illustrating the configuration of a recording head. It is a wave form diagram explaining the structure of a middle dot discharge pulse. (A)-(d) is a figure which shows the motion of the meniscus at the time of discharging an ink drop. It is a table | surface which shows the result of the experiment which observes the stability of discharge of an ink drop. It is a table | surface which shows the result of the other experiment which observes the stability of discharge of an ink drop. It is a wave form diagram explaining the structure of a small dot discharge pulse. It is a wave form diagram explaining the modification of a small dot discharge pulse. It is a wave form diagram explaining the structure of the middle dot discharge pulse in 2nd Embodiment.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. In the embodiments described below, various limitations are made as preferred specific examples of the present invention. However, the scope of the present invention is not limited to the following description unless otherwise specified. However, the present invention is not limited to these embodiments. In the following, an ink jet recording apparatus (hereinafter referred to as a printer) will be described as an example of the liquid ejection apparatus of the present invention.

  FIG. 1 is a block diagram showing the electrical configuration of the printer. This printer is schematically composed of a printer controller 1 and a print engine 2. The printer controller 1 includes an external interface (external I / F) 3 that exchanges data with an external device such as a host computer, a RAM 4 that stores various data, a control routine for various data processing, and the like. ROM 5 stored, control unit 6 that controls each unit, oscillation circuit 7 that generates a clock signal, drive signal generation circuit 8 that generates a drive signal to be supplied to the recording head 10, dot pattern data, drive signals, and the like And an internal interface (internal I / F) 9 for outputting to the recording head 10.

  The control unit 6 controls each unit, converts print data received from the external device through the external I / F 3 into dot pattern data, and outputs the dot pattern data to the recording head 10 side through the internal I / F 9. . This dot pattern data is constituted by print data obtained by decoding (translating) gradation data. The control unit 6 supplies a latch signal, a channel signal, and the like to the recording head 10 based on the clock signal from the oscillation circuit 7. The latch pulses and channel pulses included in these latch signals and channel signals define the supply timing of each pulse constituting the drive signal.

  The drive signal generation circuit 8 is controlled by the control unit 6 and generates a drive signal for driving the piezoelectric vibrator 20 (see FIG. 2). The drive signal generation circuit 8 in the present embodiment discharges ink droplets (a type of liquid droplets), and discharge pulses for forming dots on recording paper as a type of discharge target, or nozzle openings 32 (FIG. 2). The free surface of the ink (a kind of liquid) exposed to the reference), that is, a drive signal COM including a fine vibration pulse for stirring the ink by slightly vibrating the meniscus within one recording period is generated. Yes.

  Next, the configuration on the print engine 2 side will be described. The print engine 2 includes a recording head 10, a carriage moving mechanism 12, a paper feed mechanism 13, and a linear encoder 14. The recording head 10 includes a shift register (SR) 15, a latch 16, a decoder 17, a level shifter 18, a switch 19, and a piezoelectric vibrator 20. The dot pattern data (SI) from the printer controller 1 is serially transmitted to the shift register 15 in synchronization with the clock signal (CK) from the oscillation circuit 7. This dot pattern data is 2-bit data, for example, by gradation information representing four recording gradations (ejection gradations) composed of non-recording (microvibration), small dots, medium dots, and large dots. It is configured. Specifically, non-printing is represented by gradation information “00”, small dots are represented by gradation information “01”, medium dots are represented by gradation information “10”, and large dots are represented by gradation information “11”.

  A latch 16 is electrically connected to the shift register 15. When a latch signal (LAT) from the printer controller 1 is input to the latch 16, the dot pattern data in the shift register 15 is latched. The dot pattern data latched by the latch 16 is input to the decoder 17. The decoder 17 translates 2-bit dot pattern data to generate pulse selection data. This pulse selection data is constituted by associating each bit with each pulse constituting the drive signal COM. Then, supply or non-supply of the ejection pulse to the piezoelectric vibrator 20 is selected according to the contents of each bit, for example, “0” and “1”.

  Then, the decoder 17 outputs pulse selection data to the level shifter 18 when receiving the latch signal (LAT) or the channel signal (CH). In this case, the pulse selection data is input to the level shifter 18 in order from the upper bit. The level shifter 18 functions as a voltage amplifier. When the pulse selection data is “1”, the level shifter 18 outputs an electric signal boosted to a voltage capable of driving the switch 19, for example, a voltage of about several tens of volts. The pulse selection data “1” boosted by the level shifter 18 is supplied to the switch 19. The drive signal COM from the drive signal generation circuit 8 is supplied to the input side of the switch 19, and the piezoelectric vibrator 20 is connected to the output side of the switch 19.

  The pulse selection data controls the operation of the switch 19, that is, the supply of the drive pulse in the drive signal to the piezoelectric vibrator 20. For example, during a period in which the pulse selection data input to the switch 19 is “1”, the switch 19 is in a connected state, and the corresponding ejection pulse is supplied to the piezoelectric vibrator 20 and follows the waveform of the ejection pulse. As a result, the potential level of the piezoelectric vibrator 20 changes. On the other hand, during the period when the pulse selection data is “0”, the level shifter 18 does not output an electrical signal for operating the switch 19. For this reason, the switch 19 is in a disconnected state, and no ejection pulse is supplied to the piezoelectric vibrator 20.

  The decoder 17, level shifter 18, switch 19, control unit 6, and drive signal generation circuit 8 that perform such operations function as drive means in the present invention, and are necessary from drive signals based on the dot pattern data. An ejection pulse is selected and applied (supplied) to the piezoelectric vibrator 20. As a result, the piezoelectric vibrator 20 expands or contracts, and the pressure generating chamber 35 (see FIG. 2) expands or contracts as the piezoelectric vibrator 20 expands or contracts, so that gradation information constituting the dot pattern data is obtained. A corresponding amount of ink droplet is ejected from the nozzle opening 32.

  FIG. 2 is a cross-sectional view of the main part of the recording head 10 described above. The recording head 10 according to the present embodiment is common to a vibrator unit 25 in which a piezoelectric vibrator group 22, a fixing plate 23, a flexible cable 24, and the like are unitized, and a head case 26 that can store the vibrator unit 25. And a flow path unit 27 that forms a series of ink flow paths (liquid flow paths) from the ink chamber (common liquid chamber) through the pressure generation chamber 35 to the nozzle opening 32.

  First, the vibrator unit 25 will be described. The piezoelectric vibrator 20 (a kind of pressure generating element in the present invention) constituting the piezoelectric vibrator group 22 is formed in a comb-like shape elongated in the vertical direction, and is cut into an extremely narrow width of about several tens of μm. . The piezoelectric vibrator 20 is configured as a longitudinal vibration type piezoelectric vibrator that can expand and contract in the vertical direction. Each piezoelectric vibrator 20 is fixed in a so-called cantilever state in which a fixed end portion is joined to a fixing plate 23 so that a free end portion protrudes outward from the tip edge of the fixing plate 23. The distal end of the free end portion of each piezoelectric vibrator 20 is joined to an island portion 40 that constitutes the diaphragm portion 38 of the flow path unit 27, as will be described later. The flexible cable 24 is electrically connected to the piezoelectric vibrator 20 on the side surface of the fixed end opposite to the fixed plate 23. In addition, the fixing plate 23 that supports each piezoelectric vibrator 20 is configured by a metal plate material having rigidity capable of receiving a reaction force from the piezoelectric vibrator 20.

  Next, the flow path unit 27 will be described. The flow path unit 27 includes a nozzle plate 29, a flow path forming substrate 30, and a vibration plate 31. The nozzle plate 29 is on one surface of the flow path forming substrate 30, and the vibration plate 31 is opposite to the nozzle plate 29. Each of the flow path forming substrates 30 is arranged and laminated on the other surface and integrated by bonding or the like. The nozzle plate 29 is a thin plate made of stainless steel in which a plurality of nozzle openings 32 are opened in a row at a pitch corresponding to the dot formation density. In the present embodiment, for example, 180 nozzle openings 32 are formed in a row, and the nozzle rows (nozzle group) are configured by these nozzle openings 32. And this nozzle row is provided two rows side by side. In addition, the nozzle opening 32 of the present embodiment includes a straight portion disposed on the opposite side (discharge surface side) to the pressure generating chamber 35 in the nozzle plate 29 joined to the flow path forming substrate 30, and pressure from the straight portion. It is comprised from the enlarged diameter part expanded to the generation chamber 35 side.

  The flow path forming substrate 30 is a plate-like member that forms a series of ink flow paths (a type of liquid flow path) including a reservoir 33, an ink supply port 34, and a pressure generation chamber 35. More specifically, the flow path forming substrate 30 is formed with a plurality of vacant portions to be the pressure generating chambers 35 corresponding to the respective nozzle openings 32 in a state of being partitioned by the partition walls, and becomes the ink supply port 34 and the reservoir 33. It is a plate-like member in which a void is formed. The flow path forming substrate 30 of this embodiment is manufactured by etching a silicon wafer. The pressure generation chamber 35 is formed as an elongated chamber in a direction orthogonal to the direction in which the nozzle openings 32 are arranged (nozzle row direction), and the ink supply port 34 is provided between the pressure generation chamber 35 and the reservoir 33. It is formed as a narrowed portion with a narrow channel width that communicates. The reservoir 33 is a chamber for supplying ink stored in an ink cartridge (not shown) to each pressure generating chamber 35 and communicates with the corresponding pressure generating chamber 35 through the ink supply port 34. .

  The diaphragm 31 is a composite plate material having a double structure in which a resin film 37 such as PPS (polyphenylene sulfide) is laminated on a metal support plate 36 such as stainless steel, and one opening surface of the pressure generating chamber 35 is formed on the diaphragm 31. This is a member having a diaphragm portion 38 for sealing and changing the volume of the pressure generating chamber 25 and a compliance portion 39 for sealing one opening surface of the reservoir 33. The diaphragm portion 38 is an island portion for etching the portion of the support plate 36 corresponding to the pressure generating chamber 35 and removing the portion in an annular shape to join the tip of the free end of the piezoelectric vibrator 20. 40 is formed. Similar to the planar shape of the pressure generating chamber 35, the island portion 40 has an elongated block shape in a direction perpendicular to the direction in which the nozzle openings 32 are arranged, and the resin film 37 around the island portion 40 serves as an elastic film. Function. Further, the portion functioning as the compliance portion 39, that is, the portion corresponding to the reservoir 33 is formed of only the resin film 37 by removing the support plate 36 by etching according to the opening shape of the reservoir 33.

  In the recording head 10 having the above-described configuration, the corresponding pressure generation chamber 35 contracts or expands by deforming the piezoelectric vibrator 20, and pressure fluctuation occurs in the ink in the pressure generation chamber 35. By controlling the ink pressure, ink (ink droplets) can be ejected from the nozzle openings 32. If the pressure generating chamber 35 having a constant volume is preliminarily expanded prior to discharging ink, ink is supplied into the pressure generating chamber 35 from the reservoir 33 side through the ink supply port 34. Further, when the pressure generating chamber 35 is rapidly contracted after the preliminary expansion, ink is ejected from the nozzle opening 32.

  FIG. 3 is a waveform diagram illustrating the configuration of the ejection pulse DP1 included in the drive signal COM generated by the drive signal generation circuit 8 having the above configuration. The illustrated ejection pulse DP1 is for ejecting an ink droplet (medium dot) having an intermediate size between the smallest ink droplet and the largest ink droplet among the ink droplets that can be ejected by the printer according to the present embodiment. This is a middle dot discharge pulse. The middle dot ejection pulse DP1 includes a first expansion element p1 (corresponding to an expansion element in the present invention) that increases the potential with a constant gradient (voltage change rate) θ1 from the reference potential (lowest potential) VHB to the maximum potential VH. A first hold element p2 that maintains the maximum potential VH, which is the rear end potential of one expansion element p1, for a short time, and a first contraction element that drops the potential with a constant gradient θ2 (θ1≈θ2) from the maximum potential VH to the reference potential VHB. p3 (corresponding to the contraction element in the present invention), the second hold element p4 that maintains the reference potential VHB for a short time, and the potential is increased from the reference potential VHB to the first intermediate potential VM1 with a constant gradient (voltage change rate) θ3. The re-expansion element p5 and the re-expansion hold element p6 that maintains the first intermediate potential VM1 that is the rear end potential of the re-expansion element p5 for a certain period of time are compared to the second intermediate potential VM2. A first recontraction element p7 that drops the potential with a constant steep constant gradient θ4, a recontraction hold element p8 that maintains the second intermediate potential VM2 for a short time, and a constant gradient θ5 (from the second intermediate potential VM2 to the reference potential VHB). and a second recontraction element p9 that lowers the potential when θ5 <θ4). Note that the gradient θ2 of the first contraction element p3 may not be equal to the gradient θ1 of the first expansion element p1.

  When the middle dot ejection pulse DP1 is supplied to the piezoelectric vibrator 20, it operates as follows. First, when the first expansion element p1 is supplied to the piezoelectric vibrator 20, the piezoelectric vibrator 20 contracts in the longitudinal direction of the element, thereby corresponding to the maximum potential VH from the reference volume corresponding to the reference potential VHB. The pressure generation chamber 35 expands to the volume (expansion process). By this expansion step, the meniscus in the state shown in FIG. 4A is largely drawn into the pressure generating chamber 35 side as shown in FIG. 4B, and the pressure generating chamber 35 is inserted into the pressure generating chamber 35 from the reservoir 33 side. Ink is supplied through the ink supply port 34. And the expansion state of the pressure generation chamber 35 in this expansion process is maintained constant over the supply period t2 of the 1st hold element p2 (expansion maintenance process).

  Thereafter, when the first contraction element p3 is supplied to the piezoelectric vibrator 20, the piezoelectric vibrator 20 expands and the pressure generating chamber 35 contracts from the volume corresponding to the highest potential VH to the volume corresponding to the reference potential VHB. (Shrink process). The ink in the pressure generation chamber 35 is pressurized by the contraction of the pressure generation chamber 35, and as shown in FIG. 4C, the central portion of the meniscus is pushed out to the discharge side (opposite side of the pressure generation chamber). This is because the center portion of the meniscus is easier to move than the peripheral portion of the meniscus (the side closer to the inner periphery of the nozzle opening 32) and more easily follows pressure fluctuations. Subsequently, the second hold element p4 is supplied, and the discharge volume is maintained at t4 for a short time. Subsequently, when the piezoelectric vibrator 20 is contracted by the reexpansion element p5, the pressure generation chamber 35 is expanded again from the volume corresponding to the reference potential VHB to the volume corresponding to the first intermediate potential VM1 (reexpansion step). The re-expansion state of the pressure generation chamber 35 in this re-expansion step is kept constant over the supply time t6 of the re-expansion hold element p6 (re-expansion maintaining step). The voltage change amount Vh1 of the re-expansion element p5 is set smaller than the potential difference from the reference potential VHB to the maximum voltage VH, that is, the drive voltage Vd of the middle dot ejection pulse DP1. As a result, even during the period t7 to t9 during which the second recontraction element p9 is supplied from the first recontraction element p7 that contracts the pressure generation chamber 35 that has expanded again, the pressure fluctuation when the pressure generation chamber 35 is recontracted. Excitation by the meniscus is suppressed, and ink droplets are prevented from separating from the meniscus that vibrates residually after the ink droplets are ejected and ejected as mist or the like.

  Thereafter, when the first re-contraction element p7 is supplied to the piezoelectric vibrator 20, the piezoelectric vibrator 20 expands again, and the pressure is increased from the volume corresponding to the first intermediate potential VM1 to the volume corresponding to the second intermediate potential VM2. The generation chamber 35 contracts rapidly (first recontraction step). The ink in the pressure generating chamber 35 is pressurized by the rapid contraction of the pressure generating chamber 35, whereby the central portion of the meniscus in the enlarged diameter portion of the nozzle opening 32 rises in a columnar shape.

  Subsequently, the reshrinkage hold element p8 is supplied to the piezoelectric vibrator 20, and the second intermediate potential VM2 is maintained for a predetermined time t8 (reshrinkage maintaining step). And the contraction state of this pressure generation chamber 35 is maintained for a fixed time over the supply period of the recontraction hold element p8. During the supply period of the reshrinkage hold element p8, as shown in FIG. 4 (d), the columnar central portion of the meniscus is cut off halfway, and the tip side portion is formed as several pl ink droplets corresponding to the middle dots. It is discharged from the nozzle opening 32. Further, by supplying this reshrinkage hold element p8, the phase difference between the center side and the outer peripheral edge side of the meniscus can be suppressed, and the portion remaining on the meniscus side of the columnar center portion becomes round, and a small amount of ink droplets ( Mist ink) can be prevented from being discharged.

  After that, the second re-contraction element p9 is supplied to the piezoelectric vibrator 20, whereby the piezoelectric vibrator 20 is further expanded to perform the first re-reduction from the volume corresponding to the second intermediate potential VM2 to the volume corresponding to the reference potential VHB. The pressure generation chamber 35 contracts and returns more slowly than the contraction process (second recontraction process). Here, the gradient θ5 from the second intermediate potential VM2 to the reference potential VHB is set smaller (slower) than the gradient θ4 from the first intermediate potential VM1 to the second intermediate potential VM2. As a result, the pressure generating chamber 35 is rapidly contracted by the first re-shrinking element p7, and the meniscus is rapidly drawn toward the pressure generating chamber, whereby the rear end portion of the ejected columnar ink extends like a tail. Can be suppressed. Then, the pressure generation chamber 35 can be gently contracted by the second re-contraction element p9, and the residual vibration of the meniscus after the ink is ejected can be suppressed.

  Further, in the present embodiment, by optimizing the waveform element of the middle dot ejection pulse DP1, residual vibration after ejection of the ink droplet is suppressed, and the ink droplet is ejected stably. Specifically, in the middle dot ejection pulse DP1, the voltage change amount Vh1 of the reexpansion element p5 is set to 30% or more of the potential difference from the reference potential VHB to the maximum voltage VH of the middle dot ejection pulse DP1, and The supply time t6 + t7 of the re-expansion hold element p6 and the first re-contraction element p7 is set to 1/3 or more of the natural vibration period Tc of the ink filled in the pressure generation chamber 35.

  As described above, the voltage change amount Vh1 of the re-expansion element p5 is set to be smaller than the potential difference from the reference potential VHB of the middle dot ejection pulse DP1 to the maximum voltage VH, so that the pressure when the pressure generating chamber 35 is re-contracted. The fluctuation is suppressed from being excited by the meniscus. On the other hand, when the voltage change amount Vh1 is reduced as much as possible, the rear end of the columnar ink droplet rising from the meniscus continues to extend like a tail, and the tail portion is separated from the ink droplet main body. There is a risk of flying. Therefore, in order to maintain the ejection stability of the ink droplets, it is necessary to set the voltage change amount Vh1 within a certain range.

  FIG. 5 is a table showing the results of an experiment in which the stability of ink droplet ejection is observed by changing the supply time t6 + t7 from the reexpansion hold element p6 to the first recontraction element p7 in the middle dot ejection pulse DP1. In this experiment, the voltage change amount Vh1 of the re-expansion element p5 is set to 25% of the potential difference from the reference potential VHB of the middle dot ejection pulse DP1 to the maximum voltage VH and from the reference potential VHB of the middle dot ejection pulse DP1 to the maximum voltage. It is set to 30% of the potential difference up to VH and 50% of the potential difference from the reference potential VHB of the middle dot ejection pulse DP1 to the maximum voltage VH. On the other hand, the stability of ink droplet ejection varies depending on the state of the meniscus at the ejection timing, specifically, the position and moving speed of the meniscus. The period of the pressure vibration generated by expanding the pressure generating chamber 26 by the first expansion element p1 that excites the pressure vibration in the ink in the pressure generating chamber 26 is the natural vibration period of the pressure generating chamber 26 determined for each recording head 2. Called Tc, the state of the meniscus depends on the pressure vibration excited by the ink in the pressure generation chamber 26. That is, the meniscus vibrates according to the natural vibration period Tc, and the flying speed of the ink changes. As for the ejection stability of the ink droplets, the mist inks that fly accompanying the actually ejected ink droplets or the meniscus that vibrates after the ink droplets are ejected are observed. The case is marked with “x”, the case where tailing of ink droplets is reduced is marked with “Δ”, the case where ejection stability that can withstand use can be secured is marked with “◯”, and the case where stability is good are marked with “◎”.

  First, when the voltage change amount Vh1 of the reexpansion element p5 is set to 25% of the potential difference from the reference potential VHB of the middle dot ejection pulse DP1 to the maximum voltage VH, the reexpansion hold element p6 and the first recontraction It can be seen that stable discharge is not possible unless the supply time t6 + t7 of the element p7 is equal to or greater than ½ of the natural vibration period Tc. On the other hand, when the voltage change amount Vh1 of the reexpansion element p5 is set to 30% of the potential difference from the reference potential VHB of the middle dot ejection pulse DP1 to the maximum voltage VH, the reexpansion hold element p6 and the first recontraction element It can be seen that discharge stability can be obtained if the supply time t6 + t7 of p7 is set to be at least larger than 1/3 of the natural vibration period Tc. Similarly, when the voltage change amount Vh1 of the reexpansion element p5 is set to 50% of the potential difference from the reference potential VHB to the maximum voltage VH of the middle dot ejection pulse DP1, the reexpansion hold element p6 and the first recontraction element p7. If the supply time t6 + t7 is set to 1/3 or more of the natural vibration period Tc, it can be seen that ejection stability can be obtained.

  From the above, the voltage change amount Vh1 of the reexpansion element p5 is 30% or more of the potential difference from the reference potential VHB to the maximum voltage VH of the middle dot ejection pulse DP1, and the reexpansion hold element p6 and the first By setting the supply time t6 + t7 of the re-shrink element p7 to 1/3 or more of the natural vibration period Tc, the ink droplet tailing can be reduced while minimizing the time width of the entire waveform of the middle dot ejection pulse DP1. It was found that discharge stability can be obtained.

FIG. 6 is a table showing the results of an experiment in which the stability of ink droplet ejection is observed by changing the supply time t9 of the second recontraction element p9 in the middle dot ejection pulse DP1.
As described above, during the period in which the second re-shrink element p9 is supplied, the ejected ink droplets are separated from the ink meniscus in the nozzle opening 32, and residual vibration occurs in the meniscus as a result of this ejection. It is in an excited state. Therefore, in order to suppress the residual vibration of the meniscus, it is necessary to contract the pressure generation chamber 35 further than the contraction of the pressure generation chamber 35 by the first recontraction element p7 by supplying the second recontraction element p9. is there. In FIG. 6, the case where ink droplet tailing is reduced is indicated by Δ, the case where ejection stability that can withstand use can be secured is indicated by ○, and the case where stability is good is indicated by ◎. .

  From the results shown in FIG. 6, it can be seen that the residual vibration of the meniscus can be suppressed when the supply time t9 of the second recontraction element p9 in the middle dot ejection pulse DP1 is set shorter than the natural vibration period Tc. Therefore, by setting the natural vibration period Tc or less, the pressure generation chamber 35 can be gently contracted by the second recontraction element p9, and the residual vibration of the meniscus after ink is ejected can be suppressed. understood.

  By adopting the configuration described above, for example, when ejecting ink (high viscosity liquid) having a higher viscosity than conventional ink, such as a photocurable ink that is cured by irradiation with light energy such as ultraviolet rays. Further, when the pressure generating chamber 35 expanded again is re-contracted, the first re-contraction element p7 set to the change rate of the gradient θ4 and the gradient having a change rate smaller than the gradient θ4 of the first re-contraction element p7. By supplying the first recontraction element p9 set to θ5, the rear end portion of the ejected ink droplet has a tail as compared with the case where the recontraction element is supplied at a constant voltage change rate. The phenomenon of stretching can be suppressed, and the shape can be made as close to a sphere as possible. In addition, by suppressing the residual vibration after ink droplet ejection, the remaining part of the columnar central portion remaining on the meniscus side is rounded, preventing further ejection as a small amount of ink droplets (mist ink). it can. As a result, it is possible to prevent the liquid from being separated and landing on the landing target.

  By the way, the present invention is not limited to the above-described embodiment, and various modifications can be made based on the description of the scope of claims.

  FIG. 7 is a waveform diagram showing the small dot discharge pulse DP2. In the above embodiment, the middle dot ejection pulse DP1 has been described as an example of the ejection pulse in the present invention, but the shape of the ejection pulse is not limited thereto. For example, the small dot discharge pulse DP2 shown in FIG. 7 includes the first expansion element p1, the first hold element p2, and the first pulse in this pulse that drops the potential with a constant gradient θ2 from the highest potential VH to the fourth intermediate potential VM4. The contraction element p10, the second hold element p11 in this pulse for maintaining the fourth intermediate potential VM4, which is the rear end potential of the first contraction element p10, for a predetermined time, and a constant gradient from the fourth intermediate potential VM4 to the fifth intermediate potential VM5 (Voltage change rate) Re-expansion element p12 that raises the potential at θ6, re-expansion hold element p13 that maintains the fifth intermediate potential VM5 that is the rear end potential of the re-expansion element p12 for a certain time, and the sixth intermediate potential VM6 A first recontraction element p14 for lowering the potential with a relatively steep constant gradient θ7; and a recontraction hold element p15 for maintaining the sixth intermediate potential VM6 for a short time; And a second re-contraction element p16 Metropolitan lowering the potential at a constant gradient θ8 (θ8 <θ7) from the sixth intermediate potential VM6 to the reference potential VHB.

  When the small dot discharge pulse DP2 is supplied to the piezoelectric vibrator 20, the columnar central portion of the meniscus becomes thinner than when the middle dot discharge pulse DP1 is supplied, and the columnar central portion is cut off in the middle. The front end portion is ejected from the nozzle opening 32 as several pl ink droplets corresponding to the small dot.

  FIG. 8 is a waveform diagram showing a modification of the small dot discharge pulse. The small dot discharge pulse DP2 ′ is a first voltage in which the re-expansion element p12 of the small dot discharge pulse DP2 increases in potential at a constant gradient (voltage change rate) θ9 from the fourth intermediate potential VM4 to the eighth intermediate potential VM8. The re-expansion element p17, the re-expansion intermediate hold element p18 that maintains the eighth intermediate potential VM8 that is the rear end potential of the first re-expansion element p17 for a predetermined time, and the constant gradient from the eighth intermediate potential VM8 to the fifth intermediate potential VM5 The second re-expansion element p19 increases the potential with θ10 (θ10 <θ9). Then, the sum (Vh8 + Vh9) of the voltage change amount Vh8 of the first re-expansion element p17 and the voltage change amount Vh9 of the second re-expansion element p19 is calculated as the potential difference from the reference potential VHB of the small dot discharge pulse DP2 ′ to the maximum voltage VH. It is set to 30% or more.

  When the small dot discharge pulse DP2 ′ is supplied to the piezoelectric vibrator 20, the phase difference between the center side and the outer peripheral edge side of the meniscus can be suppressed as compared with the case where the small dot discharge pulse DP2 is supplied. The portion remaining on the meniscus side becomes round, and this portion can be prevented from being excessively ejected as a small amount of ink droplets.

The ejection pulse DP may be an ejection pulse having a configuration including at least the first recontraction elements p7 and p14 and the second recontraction elements p9 and p16 having different rates of change from the first recontraction elements p7 and p14. For example, an arbitrary waveform can be used.
For example, with respect to the middle dot ejection pulse DP1, as in the second embodiment shown in FIG. 9, a driving pulse having an intermediate potential VC corresponding to the intermediate volume of the pressure generation chamber 35 as a start potential and a termination potential may be employed. it can. The middle dot discharge pulse DP3 of the present embodiment increases the potential with a constant gradient θ11 from the intermediate potential VC (reference potential) corresponding to the intermediate volume of the pressure generating chamber 35 (volume serving as a reference for expansion or contraction) to the expansion potential VH. A first expansion element p21 that causes the expansion potential VH to be maintained for a short time, a first contraction element p23 that drops the potential from the expansion potential VH to the contraction potential VHB with a steep slope θ12 (θ12> θ11), A second hold element p24 that maintains the contraction potential VHB for a short time, a reexpansion element p25 that increases the potential from the contraction potential VHB to the eleventh intermediate potential VM11 with a steep slope θ13 (θ12≈θ13), and an eleventh intermediate potential VM11. And a constant re-expansion hold element p26, and a relatively steep constant gradient θ1 that does not eject ink up to the twelfth intermediate potential VM12. 4, the first re-shrink element p 27 that drops the potential, the re-shrink hold element p 28 that maintains the twelfth intermediate potential VM 12 for a short time, and the constant gradient θ 15 that does not eject ink from the second intermediate potential VM 12 to the intermediate potential VC. And a second recontraction element p29 that restores the potential at (θ15 <θ14).

  Also in the second embodiment, when the pressure generation chamber 35 expanded again is re-contracted, the first re-contraction element p27 set to the change rate of the gradient θ14 and the gradient θ14 of the first re-contraction element p27. By supplying the first re-shrinking element p29 set to the gradient θ15 having a smaller change rate than the case where the re-shrinking element is supplied at a constant voltage change rate, the after-discharged ink droplet is reduced. It is possible to suppress the phenomenon that the end portion extends like a tail. For this reason, when high-viscosity ink is ejected, it is possible to suppress the generation of mist and the like, thereby preventing dot separation.

  In the above embodiment, the piezoelectric vibrator 20 in the so-called longitudinal vibration mode is exemplified as the pressure generating means, but is not limited thereto. For example, the present invention can also be applied when using a so-called flexural vibration mode piezoelectric vibrator. When this flexural vibration mode piezoelectric vibrator is employed, the waveforms of the ejection pulses DP1, DP2, DP2 'and DP3 shown in FIGS.

  The present invention is not limited to a printer as long as it is a liquid ejection device that can perform ejection control using a plurality of drive signals, and other than various ink jet recording devices such as plotters, facsimile devices, copiers, and recording devices. The present invention can also be applied to a liquid ejecting apparatus such as a display manufacturing apparatus, an electrode manufacturing apparatus, and a chip manufacturing apparatus.

DESCRIPTION OF SYMBOLS 8 ... Drive signal generation circuit, 10 ... Recording head, 20 ... Piezoelectric vibrator, 32 ... Nozzle opening, 35 ... Pressure generation chamber

Claims (5)

A pressure generating chamber communicating with the nozzle opening, and a pressure generating element that causes a pressure fluctuation in the liquid in the pressure generating chamber, and a liquid discharging head capable of discharging the liquid from the nozzle opening by the operation of the pressure generating element; ,
Drive signal generating means for generating a series of drive signals including a drive pulse for driving the pressure generating element;
A liquid ejection device comprising:
The liquid has a viscosity of 8 millipascal seconds or more;
The drive pulse generated by the drive signal generating means includes an expansion element that expands the pressure generation chamber to draw a meniscus, a contraction element that changes a voltage to contract the expanded pressure generation chamber, and the contraction element A re-expansion element that re-expands the pressure generation chamber after contraction by the above and draws in a meniscus, and a re-contraction element that changes a voltage so as to contract the pressure expansion chamber expanded again,
The re-contraction element includes a first re-contraction element and a second re-contraction element that contracts the pressure generating chamber that has been expanded again at a voltage change rate different from that of the first re-contraction element.
A voltage change rate of the second re-shrink element is set smaller than a voltage change rate of the first re-shrink element;
Wherein during the re-expansion element and the first re-contraction element, it viewed including the re-expansion hold element for maintaining the rear end a fixed time the voltage at the re-expansion element,
The liquid ejecting apparatus according to claim 1, wherein a voltage change amount of the re-expansion element is set to 30% or more of a potential difference from the lowest voltage to the highest voltage of the drive pulse . The re-expansion element includes a first re-expansion element and a second re-expansion element that re-expands the pressure generating chamber at a voltage change rate different from that of the first re-expansion element,
2. The liquid ejection apparatus according to claim 1 , wherein at least a voltage change amount of the second re-expansion element is set to 30% or more of a potential difference from the lowest voltage to the highest voltage of the drive pulse . 3. The liquid ejection apparatus according to claim 1 , wherein a supply time of the second recontraction element is set to be equal to or less than a natural vibration period Tc of the liquid filled in the pressure generation chamber . The re-shrinkage hold element that maintains a voltage for a certain period of time at a rear end of the first re-shrink element is disposed between the first re-shrink element and the second re-shrink element. Item 4. The liquid ejection device according to any one of Items 3 to 3. A pressure generating chamber communicating with the nozzle opening, and a pressure generating element that causes a pressure fluctuation in the liquid in the pressure generating chamber, and a liquid discharging head capable of discharging the liquid from the nozzle opening by the operation of the pressure generating element; ,
  Drive signal generating means for generating a series of drive signals including a drive pulse for driving the pressure generating element;
  A method for controlling a liquid ejection apparatus comprising:
  The liquid has a viscosity of 8 millipascal seconds or more;
  An expansion step of expanding the pressure generation chamber to draw a meniscus, a contraction step of changing a voltage so as to contract the pressure generation chamber expanded in the expansion step, and expanding the pressure generation chamber again after the contraction step A re-expansion step for drawing in the meniscus, and a re-contraction element for changing the voltage so as to contract the pressure generating chamber expanded again in the re-expansion step,
  The re-shrinking step includes a first re-shrinking step and a second re-shrinking step of shrinking the pressure generating chamber expanded again at a voltage change rate different from that of the first re-shrinking step,
  The voltage change rate in the second reshrinking step is set smaller than the voltage change rate in the first reshrinking step,
  A re-expansion maintaining step of maintaining a voltage at a rear end in the re-expansion step for a certain period between the re-expansion step and the first re-contraction step;
  A method for controlling a liquid ejection apparatus, wherein the voltage change amount in the re-expansion step is set to 30% or more of a potential difference from the lowest voltage to the highest voltage of the drive pulse.

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