JP2011063010A - Liquid ejecting apparatus and control method for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid ejecting apparatus which can stably micrify liquid droplets regardless of individual difference of liquid ejection heads and to provide a control method of the same. <P>SOLUTION: An ejection driving pulse DP is a pulse waveform which includes a pressure chamber expansion component p1, a first contraction component p3 (pressure chamber contraction component), and a re-expansion component p5. The pressure chamber expansion component p1 contains the front side expansion component p1a that expands the pressure chamber by change in potential at the first potential change ratio, the rear side expansion component p1b that is generated after the front side expansion component p1a and that further expands the pressure chamber by change in potential at the second potential change ratio greater than the first potential change ratio, and an expansion maintaining component p1c that is generated between the front and the rear expansion component p1a, p1b and that maintains a potential at the completion of the front side expansion component p1a. A time T from the start of the front side expansion component p1a until the start of the rear side expansion component p1b is set in accordance with a natural vibration period Tc that is produced in a liquid in the pressure chamber. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a liquid ejection apparatus such as an ink jet printer and a method for controlling the liquid ejection apparatus, and in particular, it is possible to control liquid ejection by applying a driving pulse included in a driving signal to a pressure generating unit. The present invention relates to a liquid ejecting apparatus and a method for controlling the liquid ejecting apparatus.

  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 typical 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 a 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 exemplified. 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.

  The printer applies a discharge drive pulse to a pressure generating means (for example, a piezoelectric vibrator, a heat generating element, etc.) and drives it to give a pressure change to the liquid in the pressure chamber. Some are configured to eject droplets from nozzles communicating with the chamber. For example, in the printer disclosed in Patent Document 1, an expansion process for preparing the maximum meniscus of the nozzle toward the pressure chamber, a hold process for maintaining the state and timing of ink droplet ejection, and a pressure chamber A driving pulse (driving waveform) including a first contracting process for ejecting ink droplets by contraction of the ink and a second contracting process for reducing meniscus pull-in due to reaction of the ejecting operation is used. . That is, after the meniscus is drawn to the pressure chamber side in the expansion step, the pressure chamber side is contracted, so that ink droplets can be ejected using the reaction of the meniscus drawing.

  By the way, in the configuration in which the pressure chamber is simply expanded / contracted to eject ink as in the driving pulse described above, a liquid having a higher viscosity than a liquid such as an ink in an ink jet printer conventionally used in homes or the like (hereinafter, referred to as a drive pulse). It was difficult to discharge minute droplets when using a high viscosity liquid). That is, when the meniscus is suddenly drawn to the pressure chamber side in the expansion process, the central portion that is not easily affected by the inner peripheral surface of the nozzle moves to the pressure chamber side at a faster speed, while the portion closer to the inner peripheral surface of the nozzle (hereinafter referred to as the inner peripheral surface). This portion is called a boundary layer), and its moving speed becomes slower because it is difficult to follow the pressure change due to its viscosity. For this reason, in the conventional expansion | swelling process, the whole meniscus cannot be drawn in large including a boundary layer.

  In order to eject a few ng of fine ink droplets, it is necessary to draw the entire meniscus including the boundary layer large, push the central part of the meniscus to the ejection side by the reaction, and eject only this central part. However, if the entire meniscus cannot be drawn largely to the pressure chamber side, not only the central portion but also the surrounding portions are discharged together when the central portion of the meniscus is pushed out and discharged. For this reason, it is difficult to make ink droplets minute. In addition, the center portion is pulled by the inertial movement of the boundary layer to the pressure chamber side and pulled, and the flying speed of the ink droplet may be reduced. When the flying speed of the ink droplet is lowered, the flying direction is bent, and there is a possibility that the ink droplet is landed on a landing target such as a recording paper at a position away from the normal landing position (original target landing position). In addition, there is a possibility that the ejected ink droplet does not land on the landing target and becomes mist.

  Further, in the case of high viscosity ink, the phenomenon that the rear end of the ink in the traveling direction of the ink extends like a tail (claw) tends to become more prominent. Then, there is a possibility that the tail portion separates from the ink droplet main body and flies, and does not land on the regular 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.

  For this reason, in order to eject a small ink droplet more effectively, the expansion process is divided into two times. In the first expansion process, the pressure chamber is expanded relatively slowly, and the second expansion process. Has proposed a drive pulse configured to expand the pressure chamber at a pressure stronger than that of the first expansion step (see, for example, Patent Document 2). In this configuration, the entire meniscus can be drawn largely to the pressure chamber side in the first expansion step, and the ink droplet can be made smaller by rapidly drawing the central portion of the meniscus and then ejecting it in the second expansion step. can do.

Japanese Patent No. 3412682 JP 2003-118116 A

  However, when the same drive pulse is uniformly used for the same type of recording head, there is a problem that the ejection characteristics, specifically, the flying speed and weight of the ejected ink droplets vary between the recording heads. This is because the period of pressure vibration (natural vibration period Tc) generated in the pressure chamber differs for each recording head. That is, even with the same type of recording head, the inherent vibration period Tc differs depending on the dimensional error at the time of manufacture. This vibration period Tc can be expressed by the following equation (1).

Tc = 2π√ [[(Mn × Ms) / (Mn + Ms)] × Cc] (1)
In Equation (1), Mn is inertance at the nozzle, Ms is inertance at the ink supply port leading from the reservoir to the pressure chamber, and Cc is compliance of the pressure chamber (represents volume change per unit pressure, degree of softness). It is. In the above formula (1), inertance M indicates the ease of ink movement in the flow path, and is the mass of ink per unit cross-sectional area. Then, assuming that the density of the ink is ρ, the cross-sectional area of the surface orthogonal to the ink flow direction of the flow path is S, and the length of the flow path is L, the inertance M can be expressed by the following equation (2). it can.
Inertance M = (density ρ × length L) / cross-sectional area S (2)
Tc is not limited to the above formula (1), and may vary depending on the structure of the recording head.

  In order to efficiently move the meniscus following the expansion or contraction of the pressure chamber, it is necessary to set the expansion speed or contraction speed of the pressure chamber in consideration of the Tc. That is, for example, when the expansion speed of the pressure chamber in the pressure chamber expansion process is determined based on the natural vibration period Tcx of a certain recording head (hereinafter referred to as a reference head) so as to obtain an optimum discharge characteristic, from this Tcx In the recording head having a smaller natural vibration period Tc, the reaction at the central portion of the meniscus is large when the pressure chamber is expanded (that is, it is quickly drawn into the pressure chamber side), whereas the boundary layer is more viscous than the central portion due to viscosity. However, it tends to be drawn into the pressure chamber side later. In this recording head, ink droplets are ejected in a state where the boundary layer is not sufficiently drawn into the pressure chamber side as compared with the case of the reference head, so that the inertial force of the boundary layer toward the pressure chamber side Acts on the center of the meniscus so that the flying speed of ink droplets is insufficient. On the other hand, in the recording head having a natural vibration period Tc larger than the above Tcx, the entire meniscus tends to be slowly drawn when the pressure chamber expands, so that both the central portion and the boundary layer are sufficiently drawn to the pressure chamber side. Ink droplets are ejected in this state, but since more portions are ejected from the nozzles than in the case of the reference head, the weight of the ejected ink droplets becomes excessive.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a liquid ejecting apparatus capable of stably miniaturizing droplets regardless of individual differences of liquid ejecting heads, and An object of the present invention is to provide a method for controlling a liquid ejection apparatus.

Application Example 1 A liquid that includes a nozzle, a pressure chamber that communicates with the nozzle, and a pressure generation unit that causes a pressure fluctuation in the liquid in the pressure chamber, and discharges the liquid from the nozzle by the operation of the pressure generation unit An ejection head; and drive signal generation means for generating a drive signal including an ejection drive pulse for driving the pressure generation means to eject liquid from the nozzle, and the ejection drive pulse expands the pressure chamber. A pressure chamber expansion element that draws the meniscus in the nozzle to the pressure chamber side, a pressure chamber contraction element that contracts the pressure chamber expanded by the pressure chamber expansion element and pushes the meniscus to the discharge side, and the pressure chamber A re-expanding element that re-expands the pressure chamber, and the pressure chamber expansion element changes in potential at a first potential change rate. A front side expansion element that expands the pressure chamber and a pressure change that occurs after the front side expansion element and has a second potential change rate that is greater than the first potential change rate further expands the pressure chamber. A rear expansion element; and an expansion maintaining element that is generated between the front expansion element and the rear expansion element and maintains a potential at the end of the front expansion element, and at the start of the front expansion element The time T from the start of the expansion maintaining element to the start of the rear expansion element is determined so as to satisfy the following formula according to the natural vibration period Tc generated in the liquid in the pressure chamber, and from the start to the end of the expansion maintaining element Time t is determined so that the moving direction of the central part of the meniscus at the start of the rear expansion element and the moving direction of the boundary layer of the meniscus in the vicinity of the inner peripheral surface of the nozzle are not at least opposite to each other. A liquid discharge apparatus characterized by.
0.5Tc ≦ T ≦ Tc (1)

  According to this configuration, the pressure chamber expansion element is generated after the front expansion element that expands the pressure chamber by changing the potential at the first potential change rate, and after the front expansion element. A rear expansion element that further expands the pressure chamber by changing the potential at a large second potential change rate, and a time T from the start time of the front expansion element to the start time of the rear expansion element is It is determined according to the natural vibration period Tc generated in the liquid. Thereby, it is possible to further reduce the size of the ejected droplets while suppressing variations in the ejection characteristics of the liquid ejection head. In particular, when discharging a high-viscosity liquid having a viscosity of 10 or more mPas or more during discharge, the influence of the viscosity of the liquid can be suppressed and the droplets can be miniaturized.

  In addition, it includes an expansion maintaining element that is generated between the front expansion element and the rear expansion element and maintains the potential at the end of the front expansion element, and the time t from the start to the end of the expansion maintenance element is The moving direction of the central portion of the meniscus at the start of the side expansion element is determined so that the moving direction of the boundary layer in the vicinity of the inner peripheral surface of the meniscus is not at least opposite. Thereby, after the center part of the meniscus is mainly drawn to the pressure chamber side by the front side expansion element, the phase of vibration of the center part of the meniscus and the phase of vibration of the boundary layer of the meniscus are maintained by maintaining the expanded state. The timing to align can be measured.

Application Example 2 Liquid that has a nozzle, a pressure chamber that communicates with the nozzle, and pressure generation means that causes a pressure fluctuation in the liquid in the pressure chamber, and discharges liquid from the nozzle by the operation of the pressure generation means A method for controlling a liquid ejection apparatus comprising: an ejection head; and a drive signal generation unit that generates a drive signal including an ejection drive pulse for driving the pressure generation unit to eject liquid from the nozzle. A pressure chamber expansion step of expanding a chamber and drawing a meniscus in the nozzle toward the pressure chamber; a pressure chamber contraction step of contracting the pressure chamber expanded by the pressure chamber expansion step and pushing out the meniscus toward a discharge side; A re-expansion step for re-expanding the pressure chamber, and the pressure chamber expansion step is a front side for expanding the pressure chamber at a first expansion speed. A tensioning step, a rear expansion step that is performed after the front side expansion step, and expands the pressure chamber at a second expansion rate that is faster than the first expansion rate, and the front side expansion step and the rear side expansion step. And an expansion maintaining step that maintains a potential at the end of the front expansion step, and a time T from the start of the front expansion step to the start of the rear expansion step is According to the natural vibration period Tc generated in the liquid in the pressure chamber, it is determined so as to satisfy the following formula, and the time t from the start to the end of the expansion maintaining process is the time at the start of the rear expansion process. The liquid ejecting apparatus control method according to claim 1, wherein the moving direction of the central portion of the meniscus and the moving direction of the boundary layer in the vicinity of the inner peripheral surface of the meniscus are at least not opposite to each other.
0.5Tc ≦ T ≦ Tc (1)

  According to this configuration, the pressure chamber expansion process is performed after the front expansion process for expanding the pressure chamber at the first expansion speed and after the front expansion process, and the second expansion speed is higher than the first expansion speed. The time from the start of the front expansion process to the start of the rear expansion process is determined according to the natural vibration period Tc generated in the liquid in the pressure chamber. As a result, it is possible to further reduce the size of the ejected droplets while suppressing variations in ejection characteristics among the liquid ejection heads. In particular, when discharging a high-viscosity liquid having a viscosity of 10 or more mPas or more during discharge, the influence of the viscosity of the liquid can be suppressed and the droplets can be miniaturized.

  In addition, it includes an expansion maintaining step that is executed between the front expansion step and the rear expansion step and maintains the potential at the end of the front expansion step, and the time t from the start to the end of the expansion maintenance step is The moving direction of the central portion of the meniscus at the start of the side expansion process is determined so that the moving direction of the boundary layer in the vicinity of the inner peripheral surface of the meniscus is not at least opposite. Thereby, after the central part of the meniscus is mainly drawn to the pressure chamber side by the front side expansion process, the phase of vibration of the central part of the meniscus and the phase of vibration of the boundary layer of the meniscus are maintained by maintaining the expanded state. The timing to align can be measured.

2 is a block diagram illustrating an electrical configuration of a printer. FIG. FIG. 3 is a cross-sectional view of a main part for explaining the configuration of a recording head. It is a wave form diagram explaining the structure of an ejection drive pulse. It is a table | surface which shows the result of having observed the change of the ejection characteristic when time T is changed. (A)-(d) is a schematic diagram which shows the movement of the meniscus at the time of discharging an ink drop. (A), (b) is a schematic diagram which shows the movement of the meniscus at the time of discharging an ink drop.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described 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. The drive signal generation circuit 8 in the present embodiment discharges ink droplets (a type of liquid droplets) and forms ejection dots on recording paper (a type of landing target) or nozzles 37 (FIG. 2). The drive signal COM includes a free surface of the exposed ink (a kind of liquid), that is, a fine vibration pulse for agitating the ink by slightly vibrating the meniscus within one recording period. ing.

  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 (LS) 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 drive 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 drive pulse is supplied to the piezoelectric vibrator 20, and the waveform of this ejection drive pulse. Following this, 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 the ejection drive pulse is not 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 discharge control means, and based on the dot pattern data, the necessary discharge drive from the drive signal. A pulse is selected and applied (supplied) to the piezoelectric vibrator 20. As a result, the piezoelectric vibrator 20 expands or contracts, and the pressure chamber 35 (see FIG. 2) expands or contracts in accordance with the expansion / contraction of the piezoelectric vibrator 20, thereby depending on the gradation information constituting the dot pattern data. A sufficient amount of ink droplets are ejected from the nozzles.

  FIG. 2 is a cross-sectional view of an essential part for explaining the configuration of the recording head 10 (a kind of liquid ejection head). The recording head 10 includes a case 23, a vibrator unit 24 housed in the case 23, a flow path unit 25 joined to the bottom surface (tip surface) of the case 23, and the like. The case 23 is made of, for example, an epoxy resin, and a housing empty portion 26 for housing the vibrator unit 24 is formed therein. The vibrator unit 24 includes a piezoelectric vibrator 20 that functions as a kind of pressure generating means, a fixed plate 28 to which the piezoelectric vibrator 20 is joined, and a flexible cable 29 for supplying a drive signal and the like to the piezoelectric vibrator 20. And. The piezoelectric vibrator 20 is a laminated type produced by cutting a piezoelectric plate in which piezoelectric layers and electrode layers are alternately laminated into a comb-like shape, and can be expanded and contracted in a direction perpendicular to the lamination direction (electric field direction). This is a piezoelectric vibrator in a longitudinal vibration mode (field transverse effect type).

  The flow path unit 25 is configured by joining a nozzle plate 31 to one surface of the flow path forming substrate 30 and a diaphragm 32 to the other surface of the flow path forming substrate 30. The flow path unit 25 is provided with a reservoir 33 (common liquid chamber), an ink supply port 34, a pressure chamber 35, a nozzle communication port 36, and a nozzle 37. A series of ink flow paths from the ink supply port 34 to the nozzle 37 through the pressure chamber 35 and the nozzle communication port 36 are formed corresponding to each nozzle 37.

  The nozzle plate 31 is a thin plate made of metal such as stainless steel in which a plurality of nozzles 37 are formed in a row at a pitch (for example, 180 dpi) corresponding to the dot formation density. The nozzle plate 31 is provided with a plurality of nozzle rows (nozzle groups) by arranging nozzles 37, and one nozzle row is composed of, for example, 180 nozzles 37.

  The diaphragm 32 has a double structure in which an elastic film 39 is laminated on the surface of a support plate 38. In this embodiment, the vibration plate 32 is manufactured using a composite plate material in which a stainless steel plate, which is a kind of metal plate, is used as the support plate 38 and a resin film is laminated on the surface of the support plate 38 as an elastic film 39. The diaphragm 32 is provided with a diaphragm portion 40 that changes the volume of the pressure chamber 35. The diaphragm 32 is provided with a compliance portion 41 that seals a part of the reservoir 33.

  The diaphragm 40 is produced by partially removing the support plate 38 by etching or the like. That is, the diaphragm portion 40 includes an island portion 42 to which the distal end face of the free end portion of the piezoelectric vibrator 20 is joined, and a thin elastic portion 43 that surrounds the island portion 42. The compliance part 41 is produced by removing the support plate 38 in the region facing the opening surface of the reservoir 33 by etching or the like in the same manner as the diaphragm part 40, and the pressure fluctuation of the liquid stored in the reservoir 33 is reduced. Functions as a damper to absorb.

  Since the tip surface of the piezoelectric vibrator 20 is joined to the island portion 42, the volume of the pressure chamber 35 can be changed by expanding and contracting the free end of the piezoelectric vibrator 20. A pressure fluctuation occurs in the ink in the pressure chamber 35 along with the volume fluctuation. The recording head 10 uses this pressure fluctuation to eject ink droplets from the nozzles 37.

  FIG. 3 is a waveform diagram illustrating the configuration of the ejection drive pulse DP included in the drive signal COM generated by the drive signal generation circuit 8 having the above configuration. The exemplified ejection driving pulse DP is an ejection driving pulse (small dot ejection driving pulse) for ejecting the smallest ink droplet among the ink droplets that can be ejected by the printer according to the present embodiment. The ejection drive pulse DP has a constant pressure chamber expansion element p1 for increasing the potential from the reference potential VL to the first expansion potential VH1 to expand the pressure chamber 35 from the reference volume to the maximum expansion volume, and the expansion state of the pressure chamber 35 is constant. A first hold element p2 that is constant at a first expansion potential VH1 that is maintained for a period of time, and a first contraction element p3 (pressure chamber that contracts the pressure chamber 35 by decreasing the potential from the first expansion potential VH1 to the contraction potential VL2 with a constant gradient. Contraction element), a second hold element p4 that is constant at a contraction potential VL2 that maintains the contraction state of the pressure chamber 35, and a potential that increases from the contraction potential VL2 to the second expansion potential VH2 to re-expand the pressure chamber 35 again. The third hold element p6 that is constant at the second expansion potential VH2 that maintains the expansion state of the expansion element p5 and the pressure chamber 35 for a certain period of time, and constant from the second expansion potential VH2 to the reference potential VL Is configured to include a second contraction element p7 for returning the pressure chamber 35 potential distribution is lowered to the reference volume is contracted, the.

  Here, the pressure chamber expansion element p1 in the ejection drive pulse DP is configured to change the expansion speed in the process of expansion of the pressure chamber 35. That is, the pressure chamber expansion element p1 includes a front expansion element p1a whose potential changes at a first change rate, and a second change rate that is generated after the front expansion element p1a and is greater than the first change rate. For example, a rear expansion element p1b whose potential changes at a rate similar to the potential change rate of the pressure chamber expansion element of the conventional ejection drive pulse for minute ink, and the front expansion element p1a and the rear expansion element p1b An expansion maintaining element p1c that is generated in between and maintains the potential at the end of the front expansion element p1a for a certain period of time indicated by time t. The front expansion element p1a is a waveform element that increases in potential from the reference potential VL to the intermediate potential VM1 and expands the pressure chamber 35 relatively slowly from the reference volume (volume serving as a reference for expansion or contraction) to the first intermediate expansion volume. It is. The expansion maintaining element p1c is a waveform element that is constant at the intermediate potential VM1, and maintains the first intermediate expansion volume of the pressure chamber 35 for a certain period of time. The rear expansion element p1b is a waveform element that raises the potential from the intermediate potential VM1 to the first expansion potential VH1 to expand the pressure chamber 35 relatively steeply from the first intermediate expansion volume to the maximum expansion volume.

Further, the time T from the start end of the front expansion element p1a to the start end of the rear expansion element p1b, that is, the time T from the start of the front expansion process to the start of the rear expansion process is expressed by the following equation (A). It is determined to satisfy. The potential difference from the start end potential (reference potential VL) of the front expansion element p1a to the end potential (intermediate potential VM1) is maintained constant regardless of the natural vibration period Tc.
0.5Tc ≦ T ≦ Tc (A)
That is, the time T is determined according to the natural vibration period Tc generated in the ink in the pressure chamber.

  FIGS. 5A to 5D are schematic diagrams illustrating the movement of the meniscus when ejecting ink droplets. The arrows in the figure indicate the moving direction of the meniscus. The time T is set within the range of the above formula (A) when the meniscus is moved (withdrawn) toward the pressure chamber 35 in the straight portion 37a (see FIG. 5A) of the nozzle 37. This is to prevent pulling too fast or too slow in consideration of the reaction speed of the meniscus with respect to the pressure change. More specifically, the object is to draw the entire meniscus to the pressure chamber side while suppressing the speed difference between the central portion of the meniscus and the boundary layer. At this time T, the generation time t of the expansion maintaining element p1c is set sufficiently shorter than the generation time of the front expansion element p1a. Various known methods can be used for measuring the natural vibration period Tc.

  When the ejection drive pulse DP is applied to the piezoelectric vibrator 20, it operates as follows. First, the piezoelectric vibrator 20 is contracted by the front expansion element p1a of the pressure chamber expansion element p1, and the pressure chamber 35 is gradually reduced from the minimum volume corresponding to the reference potential VL to the first intermediate expansion volume defined by the intermediate potential VM1. Inflate (front slow expansion step). Accordingly, as shown in FIG. 5A, the meniscus is drawn into the pressure chamber 35 side at a relatively slow speed. By slowly pulling the meniscus in this way, the meniscus can be moved to the entire pressure chamber while suppressing a difference in moving speed between the central portion of the meniscus and the boundary layer in the vicinity of the nozzle inner peripheral surface.

  After this expansion, the expansion state of the pressure chamber 35 is maintained for a certain time by the expansion maintaining element p1c. This fixed time is a period in which the moving direction of the center portion of the meniscus and the moving direction of the boundary layer in the vicinity of the inner peripheral surface of the meniscus are not at least opposite at the start of the rear expansion element p1b described later. Thereby, as shown in FIG.5 (b), it can wait until the phase of the vibration of the center part of a meniscus and a boundary layer is equal.

  Subsequently, the rear side expansion of the pressure chamber expansion element p1 is performed at a timing when the meniscus is pulled to the extent that it exceeds the boundary between the straight portion 37a having a constant inner diameter and the tapered portion 37b having an inner diameter that gradually increases toward the pressure chamber 35 side. The element p1b is applied to the piezoelectric vibrator 20. By this rear side expansion element p1b, the piezoelectric vibrator 20 contracts and the pressure chamber 35 rapidly expands from the first intermediate expansion volume to the maximum expansion volume (rear side expansion step). Thereby, as shown in FIG.5 (c), the whole meniscus is drawn largely in the pressure chamber 35 side at a faster speed than a front side slow expansion process. The expansion state of the pressure chamber 35 is maintained over the supply period of the first hold element p2. Thereafter, when the first contraction element p3 is applied to the piezoelectric vibrator 20, the piezoelectric vibrator 20 rapidly expands and the volume of the pressure chamber 35 contracts from the maximum expansion volume to the contraction volume corresponding to the contraction potential VL2 ( First shrinking step, corresponding to the pressure chamber shrinking step). The ink in the pressure chamber 35 is pressurized by the rapid contraction of the pressure chamber 35, and as a result, as shown in FIG. 5D, the central portion of the meniscus that easily follows the pressure fluctuation is pushed out to the discharge side. It rises in a columnar shape (hereinafter, this portion is referred to as a columnar portion). The contracted state of the pressure chamber 35 is maintained over the supply period of the second hold element p4.

  Thereafter, the re-expansion element p5 is applied to the piezoelectric vibrator 20, whereby the piezoelectric vibrator 20 contracts and the pressure chamber 35 rapidly expands again from the contracted volume to the second expansion volume corresponding to the second expansion potential VH2. (Re-expansion step). Thereby, as shown to Fig.6 (a), the part around the columnar part in a meniscus is drawn in to the pressure chamber 35 side at a comparatively high speed. On the other hand, the columnar portion continues to move to the discharge side by the inertial force when pushed out to the discharge side in the first contraction step. At this time, the columnar portion extends to the maximum. The expansion state of the pressure chamber 35 at this time is maintained over the supply period of the third hold element p6.

  After that, as shown in FIG. 6B, the columnar part is cut off halfway, and the part separated from the meniscus is a nozzle having a small number pl (pico liter) of ink droplets having a diameter smaller than the inner diameter of the nozzle 37. 37 is discharged. Then, following the third hold element p6, the second contraction element p7 is applied to the piezoelectric vibrator 20 at the timing when the meniscus is drawn to the pressure chamber 35 side by the reaction caused by the ejection of the ink droplet, and the piezoelectric vibrator 20 is moved. When extended, the pressure chamber 35 contracts from the second expansion volume defined by the second expansion potential VH2 to the reference volume (second contraction step). As a result, the meniscus is prevented from being drawn into the pressure chamber side, the residual vibration of the meniscus is suppressed, and excess ink is absorbed by the meniscus by bringing the meniscus closer to the ejected ink droplets. , It is possible to prevent the tail of the ejected ink droplet from extending like a tail (tail).

  Here, when the meniscus is moved in the portion having the smallest inner diameter in the flow path of the recording head 10, that is, in the straight portion 37 a of the nozzle 37, a difference is easily generated between the meniscus central portion and the boundary layer. For this reason, as described above, the time T related to the step (waveform element) for moving the meniscus in the straight portion 37a is determined according to the natural vibration period Tc, while suppressing variations in ejection characteristics among the recording heads. Ink droplets can be miniaturized. This point will be described below with a specific example.

  FIG. 4 is a table showing the results of observing changes in ejection characteristics when the time T is changed when the natural vibration period Tc of the recording head 10 is 8 μs, for example. Note that the pass / fail judgment symbol indicates the influence of the ejection characteristics on the image quality of a recorded image or the like. Specifically, x is a determination indicating that there is a possibility that the image quality of a recorded image or the like may be impaired. Δ is a determination indicating that there is a possibility that the image quality of a recorded image or the like may be affected, but is acceptable. A circle indicates that an ideal image quality of the recorded image can be obtained.

  In the above table, the above formula (A) is satisfied when T is 4 to 8 (application range). In this application range, a value within the allowable range (6 to 8.7 (m / s)) was obtained for the flying speed of the ejected ink droplets. In this application range, a value within the allowable range (3.2 to 5 ng) was obtained with respect to the weight of the ejected ink droplet. When it was within the applicable range, generally good results were obtained with respect to the image quality of recorded images and the like.

  On the other hand, when T is smaller than the range defined by the above formula (A) (T <Tc / 2), the flying speed of ink droplets tends to be insufficient, and the image quality of recorded images and the like is impaired. Alternatively, the recorded image may be affected. In this case, the reaction at the central portion of the meniscus when the pressure chamber 35 is expanded is large (that is, it is quickly drawn into the pressure chamber side), whereas the boundary layer near the inner peripheral surface of the nozzle is in the center due to the influence of viscosity. It tends to be drawn into the pressure chamber side later than the part. Since the ink droplets are ejected in a state where the boundary layer is not sufficiently drawn into the pressure chamber side as compared with the case of the application range, the inertial force toward the pressure chamber side of the boundary layer acts on the center of the meniscus. As a result, the flying speed of ink droplets is insufficient.

  Further, when T is larger than the range defined by the above formula (A), the weight of ink droplets tends to be excessive, and the image quality of recorded images and the like is impaired. In this case, since the entire meniscus tends to be drawn slowly when the pressure chamber 35 expands, ink droplets are ejected in a state where both the center portion of the meniscus and the boundary layer are sufficiently drawn to the pressure chamber side. Compared to the case of the range, the portion ejected from the nozzle 37 together with the central portion is increased, so that the weight of the ejected ink droplet is increased.

  As described above, according to the present invention, the meniscus in the nozzle 37 is drawn regardless of the individual difference of the recording heads by determining the time T according to the natural vibration period Tc for each recording head 10 according to the natural vibration period Tc. At this time, since the difference in the pull-in speed between the central portion and the boundary layer can be suppressed, it is possible to miniaturize the ink droplets while suppressing the variation in the ejection characteristics for each recording head. In particular, when discharging a high-viscosity liquid having a viscosity of 10 or more mPas or more during discharge, the influence of the viscosity of the liquid can be suppressed and the droplets can be miniaturized.

  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.

  In the above embodiment, the ejection drive pulse DP shown in FIG. 3 has been described as an example of the ejection drive pulse in the present invention, but the shape of the ejection drive pulse is not limited to this. In short, at least a pressure chamber expansion element p1 for preliminarily expanding the pressure chamber, a first contraction element p3 (pressure chamber contraction element) for contracting the expanded pressure chamber and pushing out the meniscus, and then the pressure Any discharge drive pulse having a configuration including a re-expansion element p5 for expanding the chamber and the pressure chamber expansion element p1 including a front expansion element and a rear expansion element can be used.

  For example, in the ejection drive pulse, the contraction potential VL2 that is the potential at the end of the first contraction element p3 and the terminal potential of the second contraction element p7 may be lower than the reference potential VL. The potential difference of each element is determined according to the amount of ejected ink droplets, the magnitude of vibration generated in the ink in the pressure chamber 35 after ejection, and the like.

  In each of the above embodiments, the so-called longitudinal vibration type piezoelectric vibrator 20 is exemplified as the pressure generating means. However, the present invention is not limited to this, and for example, a so-called flexural vibration type piezoelectric vibrator 20 may be employed. is there. In this case, with respect to the exemplified drive signal, the waveform changes in the direction of potential change, that is, upside down.

  Furthermore, with regard to the shape of the nozzle 37, the above embodiment has exemplified the nozzle constituted by the straight portion 37a having a constant inner diameter and the tapered portion 37b having an inner diameter gradually increasing toward the pressure chamber 35 side. I can't. In short, any nozzle having a structure in which the cross-sectional area on the pressure chamber side is larger than the discharge side may be used.

  The present invention is not limited to a printer, as long as it is a liquid ejection apparatus capable of controlling the ejection of liquid using ejection drive pulses, and various ink jet recording apparatuses and recording apparatuses such as plotters, facsimile apparatuses, and copiers. The present invention can also be applied to other liquid ejecting apparatuses such as a display manufacturing apparatus, an electrode manufacturing apparatus, and a chip manufacturing apparatus.

  DESCRIPTION OF SYMBOLS 1 ... Printer controller, 2 ... Print engine, 6 ... Control part, 8 ... Drive signal generation circuit, 10 ... Recording head, 20 ... Piezoelectric vibrator, 24 ... Vibrator unit, 35 ... Pressure chamber, 37 ... Nozzle, DP ... Discharge drive pulse, p1 ... pressure chamber expansion element, p1a ... front expansion element, p1b ... rear expansion element, p1c ... expansion maintenance element, p3 ... first contraction element, p5 ... reexpansion element, T ... time, Tc ... inherent Vibration period.

Claims (2)

A nozzle, a pressure chamber communicating with the nozzle, and a pressure generating means for causing a pressure fluctuation in the liquid in the pressure chamber, and a liquid discharging head for discharging the liquid from the nozzle by the operation of the pressure generating means;
Drive signal generating means for driving the pressure generating means to generate a drive signal including an ejection drive pulse for discharging liquid from the nozzle, and
The discharge driving pulse expands the pressure chamber and discharges the meniscus by contracting the pressure chamber expansion element that draws the meniscus in the nozzle toward the pressure chamber and the pressure chamber expanded by the pressure chamber expansion element. A voltage waveform including at least a pressure chamber contraction element that pushes out to a side, and a re-expansion element that expands the pressure chamber again,
The pressure chamber expansion element has a front expansion element that expands the pressure chamber by changing a potential at a first potential change rate;
A rear expansion element that occurs after the front expansion element and further expands the pressure chamber by changing a potential at a second potential change rate larger than the first potential change rate;
An expansion maintaining element that is generated between the front expansion element and the rear expansion element and maintains a potential at the end of the front expansion element,
A time T from the start of the front expansion element to the start of the rear expansion element is determined so as to satisfy the following expression according to the natural vibration period Tc generated in the liquid in the pressure chamber, and the expansion The time t from the start to the end of the maintenance element is such that the movement direction of the central portion of the meniscus and the movement direction of the boundary layer in the vicinity of the inner peripheral surface of the meniscus at the start of the rear expansion element are at least A liquid ejection apparatus, characterized in that it is determined not to be opposite.
0.5Tc ≦ T ≦ Tc (1)
A nozzle, a pressure chamber communicating with the nozzle, and a pressure generating means for generating a pressure fluctuation in the liquid in the pressure chamber, and a liquid discharging head for discharging the liquid from the nozzle by the operation of the pressure generating means; A drive signal generating means for generating a drive signal including a discharge drive pulse for driving the pressure generating means to discharge the liquid from the nozzle,
A pressure chamber expansion step of expanding the pressure chamber and drawing a meniscus in the nozzle toward the pressure chamber;
A pressure chamber contraction step of contracting the pressure chamber expanded by the pressure chamber expansion step to push the meniscus to the discharge side;
A re-expansion step of re-expanding the pressure chamber,
The pressure chamber expansion step includes a front side expansion step of expanding the pressure chamber at a first expansion rate;
A rear side expansion step that is performed after the front side expansion step and expands the pressure chamber at a second expansion rate that is faster than the first expansion rate;
An expansion maintaining step that is performed between the front side expansion step and the rear side expansion step, and maintains a potential at the end of the front side expansion step;
A time T from the start of the front expansion step to the start of the rear expansion step is determined so as to satisfy the following equation according to the natural vibration period Tc generated in the liquid in the pressure chamber, and the expansion The time t from the start to the end of the maintenance process is such that the movement direction of the central part of the meniscus and the movement direction of the boundary layer in the vicinity of the inner peripheral surface of the meniscus at the start of the rear side expansion process are at least A control method for a liquid ejection apparatus, characterized in that it is determined not to be opposite.
0.5Tc ≦ T ≦ Tc (1)

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