JP3941823B2 - Liquid ejection apparatus and drive control method - Google Patents

Description

  The present invention relates to a liquid discharge head, a liquid discharge apparatus, and a drive control method, and more particularly, to a structure of a liquid discharge head used in an ink jet recording apparatus and the like and a discharge control technique.

  As an example of an image forming apparatus, an inkjet head (ejection head) in which a large number of nozzles (ejection elements) are arranged, and ink is ejected from the nozzles while relatively moving the inkjet head and the medium (ejection medium). An ink jet recording apparatus that forms an image on a medium by discharging is known.

  In the ink ejection method in the ink jet head of such an ink jet recording apparatus, the volume of the pressure chamber is changed by deforming a vibration plate (pressure plate) constituting a part of the pressure chamber by deformation of the piezoelectric element. When the volume is increased, ink is introduced from the ink supply path into the pressure chamber, and when the volume of the pressure chamber is decreased, the ink in the pressure chamber is discharged as a droplet from the nozzle, or the ink in the ink chamber (pressure chamber) is heated. There is known a thermal ink jet method in which bubbles are generated and ink is ejected with expansion energy when the bubbles grow.

  When a pressurizing unit that pressurizes ink ejected from a nozzle, such as a piezoelectric element or a heater, is driven using a drive signal corresponding to image data, ejection energy applied to the ink from the pressurizing unit is generated. This ejection energy acts on the ink in the pressure chamber, and the ink is ejected from each nozzle.

  Ink jet recording apparatuses affect the quality and printing efficiency of an image from which ink ejection performance can be obtained. In order to realize high-speed and stable ink ejection, various ideas have been made on the inkjet head. For example, when ink is ejected from an inkjet head by a piezoelectric method, a technique has been proposed in which a piezoelectric element driving method that pressurizes ink is devised to stably eject ink at high speed. .

  The ink jet recording apparatus described in Patent Document 1 is configured to reduce a meniscus vibration change by generating a sub-pulse having a power value smaller than or equal to the main pulse subsequent to the main pulse for ejecting ink. The vibration of the meniscus generated in the vicinity of the orifice that leads to the path can be removed, ink leakage from the jet outlet and the mixing of bubbles can be prevented when the liquid path is not driven, and a stable and good recorded image can always be obtained. .

Further, in the ink jet recording apparatus and the ink discharge control method described in Patent Document 2, after increasing the volume of the ink storage chamber in the supply stage, the volume of the ink storage chamber is decreased in the discharge stage to discharge ink from the nozzles. In the ink discharge cycle, when the volume of the ink storage chamber is increased to the first value in the supply stage and then the volume of the ink storage chamber is decreased to the second value in the discharge stage, the ink storage is performed in the latter stage of the discharge stage. After the chamber volume is maintained at a third value between the first value and the second value, the chamber volume is reduced to the second value, and ink disturbance in the ejection stage is effectively suppressed. Ink supply in the next cycle is executed promptly.
JP-A 64-26454 Japanese Patent Laid-Open No. 11-42775

  The ink jet recording apparatus described in Patent Document 1 and the ink jet recording apparatus and ink discharge control method described in Patent Document 2 are intended to suppress vibration of the meniscus surface, particularly when using low-viscosity ink. Is effective, but when the viscosity of the ink increases, the vibration attenuation of the meniscus surface increases, and the meniscus surface does not vibrate to the extent that it affects ejection, so there is no need to suppress vibration of the meniscus surface.

  However, as the viscosity of the ink increases, the refill time (ink supply time to the pressure chamber) increases significantly due to the effect of viscous resistance, and the standby time until the end of this refill becomes longer. There is concern about a decrease in (discharge frequency).

  The present invention has been made in view of such circumstances, and maintains a discharge frequency without reducing the refill speed even when a high-viscosity liquid is used, and is particularly suitable when using a high-viscosity liquid. An object of the present invention is to provide a liquid ejection device and a drive control method.

で表される前記ノズルの開口部の液体の体積速度ｖ（ｔ）、次式

で表されるα、次式

で表されるβ、次式

で表され、ｔ＝０のときに−Ｆとなる前記ノズルの開口部の液体の変位体積ｘ（ｔ）、１回にリフィルされる液体の体積Ａ＋Ｂに対する次の吐出に必要な液体の体積の比Ａ／（Ａ＋Ｂ）を用いて表される、次式

及び次式

の関係を満たすように前記加圧手段を制御することを特徴とする。 In order to achieve the object, the invention according to claim 1 is characterized in that a nozzle that discharges a liquid, a pressure chamber that stores a liquid that is discharged from the nozzle, and a pressure that pressurizes the liquid stored in the pressure chamber. A pressurizing means for changing the volume of the chamber; and a supply port for supplying a liquid to the pressure chamber. The inertance Mn of the nozzle, the fluid resistance Rn of the nozzle, and the compliance Cn due to the surface tension of the liquid in the nozzle inertance Ms of the supply port, which has the supply port of the fluid resistance Rn is {4 × (Mn + Ms) } / Cn ≦ (Rn + Rs) structure that meet the ^second relationship, 5.5 × ¹⁰ -3 (Pa · a liquid discharge head using a liquid having a viscosity of s) above, the refill time at which charging liquid to the pressure chamber through the supply port after the liquid has been ejected from the nozzle , During the period ts after the liquid is ejected from the nozzle, the increase from the initial state before the discharge operation starts the volume of the pressure chamber by applying a driving signal to the pressure means by the volume B Rutotomoni, the nozzle and a drive control means for the driving the pressurizing means such that the period ts has elapsed since the discharged liquid return the volume of the pressure chamber to the volume of the first period state from said control means, said drive signal Between the period ts in which the volume of the pressure chamber is increased from the initial state by applying the pressure and the period tA until the liquid A having the same volume as the volume A discharged in one discharge operation is refilled in the pressure chamber Satisfies the relationship of tA = ts, and the period tA until the liquid having the same volume as the volume A discharged in one discharge operation is refilled into the pressure chamber is expressed by the following equation:

The volume velocity v (t) of the liquid at the opening of the nozzle represented by

Α represented by

Β represented by

The displacement volume x (t) of the liquid at the opening of the nozzle that becomes −F when t = 0, and the volume of the liquid necessary for the next discharge with respect to the volume A + B of the liquid refilled at one time Expressed using the ratio A / (A + B),

And the following formula

The pressurizing means is controlled to satisfy the relationship .

That is, when refilling the liquid into the pressure chamber through the supply port after the liquid is discharged from the nozzle, the nozzle inertance M _n and the nozzle fluid are controlled so as to suppress the vibration of the meniscus located near the nozzle. resistor R _n, compliance C _n by the surface tension of the liquid in the _nozzle, the inertance M _s of the supply _port, since the relationship between the fluid resistance R _n of the supply port is determined, without increasing the refilling time, the predetermined ejection frequency Can be maintained. Also, when refilling the pressure chamber through the supply port after the liquid is discharged from the nozzle, the pressurizing means is controlled so that the volume of the pressure chamber is larger than at the time of discharge and the initial state. The refill speed can be increased by using the force generated by the pressurizing means during the refill. In particular, the present invention is effective when a high-viscosity liquid having a large fluid resistance is used, and refilling in a short time becomes possible. Furthermore, the vibration of the meniscus can be suppressed using the force generated by the pressurizing means, and the refill speed can be further increased. When a high-viscosity liquid having a higher viscosity than that of a generally used liquid is used, the refill time may be significantly increased due to the influence of the viscous resistance. The present invention is particularly effective when such a high viscosity liquid is used.

  The nozzle referred to here includes an opening, a pipe line part communicating with the opening part, and a throttle part, and the pipe part may have a structure including a plurality of pipe lines.

  As a configuration example of the ejection head, a full-line head having a nozzle row in which a plurality of nozzles for ejecting ink are arranged over a length corresponding to the entire width of the ejection target medium can be used.

  In this case, a combination of a plurality of relatively short ejection head blocks having nozzle rows less than the length corresponding to the entire width of the medium to be ejected, and connecting them together, the length corresponding to the entire width of the medium to be ejected. There is a mode that constitutes the nozzle row.

  A full-line type head is usually arranged along a direction orthogonal to the relative feed direction (relative transport direction) of the medium to be ejected, but at a certain angle with respect to the direction orthogonal to the transport direction. There may also be a mode in which the inkjet head is arranged along an oblique direction with a gap.

  The “ejection head” may include what can be called an inkjet head, a print head, or the like used in an image forming apparatus such as an inkjet recording apparatus.

  The pressurizing means includes an electromechanical conversion element that converts an electric signal into pressure, and the electromechanical conversion element includes an actuator that generates a displacement corresponding to the drive signal. In addition, the actuator includes a configuration including an electrostrictive element that generates a strain according to a drive signal and a diaphragm that is displaced according to the strain of the electrostrictive element.

  Examples of the liquid ejected from the nozzle include an ink used for an ink jet recording apparatus, a treatment liquid ejected on a medium by a coating device such as a dispenser, a chemical liquid, and water.

  The drive control means may include a drive signal generating means for generating a drive signal to be given to the pressurizing means.

  Since the discharge cycle becomes longer as the period of expanding the size of the pressure chamber becomes longer, the period of expanding the volume of the pressure chamber from the initial state (that is, the predetermined period) is approximately the same amount as the amount of liquid discharged. It is preferable that the period is the same as the period until the liquid is supplied to the pressure chamber through the supply port.

According to a second aspect of the invention relates to an aspect of the liquid discharge apparatus according to claim 1, wherein the volume increases from the initial state before the discharge operation starts the volume of the pressure chamber after the liquid has been ejected from the nozzle B Is characterized by satisfying B ≦ (2 × π × r ³ ) / 3, where r is the radius of the nozzle.

In other words, the volume change amount B to expand the pressure chamber after the liquid ejection, said volume variation B so is not ejected liquid from the nozzle when the pressure means is driven when returning the volume of the pressure chamber to the volume of the initial state The upper limit of is determined.

で表される前記ノズルの開口部の液体の体積速度ｖ（ｔ）、次式

で表されるα、次式

で表されるβ、次式

で表され、ｔ＝０のときに−Ｆとなる前記ノズルの開口部の液体の変位体積ｘ（ｔ）、１回にリフィルされる液体の体積Ａ＋Ｂに対する次の吐出に必要な液体の体積の比Ａ／（Ａ＋Ｂ）を用いて表される、次式

及び次式

の関係を満たすように前記加圧手段を制御することを特徴とする。 The present invention also provides a method invention for achieving the above object. That is, the drive control method according to the third aspect of the invention includes a nozzle that discharges a liquid, a pressure chamber that stores a liquid that is discharged from the nozzle, and a pressure that pressurizes the liquid stored in the pressure chamber. A pressurizing means for changing the volume of the chamber; and a supply port for supplying a liquid to the pressure chamber. The inertance Mn of the nozzle, the fluid resistance Rn of the nozzle, and the compliance Cn due to the surface tension of the liquid in the nozzle The pressure unit is driven using a liquid discharge head having a structure in which the inertance Ms of the supply port and the fluid resistance Rn of the supply port satisfy a relationship of {4 × (Mn + Ms)} / Cn ≦ (Rn + Rs) ² discharging Engineering a liquid having a volume viscosity of more than 5.5 × accommodated in the pressure chamber 10 -3 ^(Pa · s) by changing the pressure chamber to eject from the nozzle by When refilling the liquid into the pressure chamber through the supply port after the liquid is discharged from the nozzle, the pressure unit is driven for a period ts after the liquid is discharged from the nozzle. Applying a signal to increase the volume of the pressure chamber by a volume B from the initial state before the start of the discharge process, and at the time of refill , a period ts has elapsed since the liquid was discharged from the nozzle. then, it looks including a pressure chamber restoring step of returning to the volume of the first period state the volume of said pressure chamber which is increased by the volume B in the pressure chamber expanding step, in the pressure chamber expanding step, by applying the driving signal The relationship between the period ts during which the volume of the pressure chamber is increased from the initial state and the period tA until the liquid having the same volume as the volume A discharged by one discharge operation is refilled into the pressure chamber is tA = ts. Fulfills the relation, time tA until the liquid volume A and the same volume ejected by the ejection operation once the pressure chamber is refilled, the following equation

The volume velocity v (t) of the liquid at the opening of the nozzle represented by

Α represented by

Β represented by

The displacement volume x (t) of the liquid at the opening of the nozzle that becomes −F when t = 0, and the volume of the liquid necessary for the next discharge with respect to the volume A + B of the liquid refilled at one time Expressed using the ratio A / (A + B),

And the following formula

The pressurizing means is controlled to satisfy the relationship .

  The driving signal used in the discharge process includes a mode in which the pressurizing unit is driven in either the pushing direction or the pulling direction to discharge the liquid, and the pressurizing unit such as push-pull driving in the pushing direction and the pulling direction. There is a mode in which the liquid is discharged by continuously driving.

According to the present invention, the inertance M _{n of} the nozzle and the fluid resistance R _n of the nozzle are prevented so that the meniscus surface located in the vicinity of the nozzle does not vibrate during refilling when the liquid is supplied to the pressure chamber through the supply port after the liquid is discharged. Since the relationship between the compliance C _n due to the surface tension of the liquid in the nozzle, the inertance M _{s of} the supply port, and the fluid resistance R _n of the supply port can be determined, a stable high discharge frequency can be maintained without increasing the refill time. can do.

  Further, at the time of refilling, the pressure chamber is controlled so that the volume of the pressure chamber is increased from the initial state before the discharge operation and the volume of the pressure chamber is returned to the initial volume after a predetermined time has elapsed. In the case of using, the refill time is not significantly increased due to the influence of the viscous resistance, and a predetermined discharge cycle can be secured.

 Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Overall configuration of inkjet recording apparatus]
FIG. 1 is an overall configuration diagram of an ink jet recording apparatus according to an embodiment of the present invention. As shown in the figure, the inkjet recording apparatus 10 includes a print unit 12 having a plurality of print heads 12K, 12C, 12M, and 12Y provided for each ink color, and each print head 12K, 12C, 12M, An ink storage / loading unit 14 for storing ink to be supplied to 12Y, a paper feeding unit 18 for supplying recording paper (discharged medium) 16, a decurling unit 20 for removing curl of the recording paper 16, and An adsorption belt conveyance unit 22 that is arranged to face the nozzle surface (ink ejection surface) of the printing unit 12 and conveys the recording paper 16 while maintaining the flatness of the recording paper 16, and printing that reads a printing result by the printing unit 12 A detection unit 24 and a paper discharge unit 26 that discharges printed recording paper (printed matter) to the outside are provided.

  In FIG. 1, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit 18, but a plurality of magazines having different paper widths, paper quality, and the like may be provided side by side. Further, instead of the roll paper magazine or in combination therewith, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  When multiple types of recording paper are used, an information recording body such as a barcode or wireless tag that records paper type information is attached to the magazine, and the information on the information recording body is read by a predetermined reader. Therefore, it is preferable to automatically determine the type of paper to be used and perform ink ejection control so as to realize appropriate ink ejection according to the type of paper.

  The recording paper 16 delivered from the paper supply unit 18 retains curl due to having been loaded in the magazine. In order to remove this curl, heat is applied to the recording paper 16 by the heating drum 30 in the direction opposite to the curl direction of the magazine in the decurling unit 20. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

  In the case of an apparatus configuration that uses roll paper, a cutter (first cutter) 28 is provided as shown in FIG. 1, and the roll paper is cut into a desired size by the cutter 28. The cutter 28 includes a fixed blade 28A having a length equal to or greater than the conveyance path width of the recording paper 16, and a round blade 28B that moves along the fixed blade 28A. The fixed blade 28A is provided on the back side of the print. The round blade 28B is disposed on the printing surface side with the conveyance path interposed therebetween. Note that the cutter 28 is not necessary when cut paper is used.

  After the decurling process, the cut recording paper 16 is sent to the suction belt conveyance unit 22. The suction belt conveyance unit 22 has a structure in which an endless belt 33 is wound between rollers 31 and 32, and at least portions facing the nozzle surface of the printing unit 12 and the sensor surface of the printing detection unit 24 are horizontal ( Flat surface).

  The belt 33 has a width that is wider than the width of the recording paper 16, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 1, a suction chamber 34 is provided at a position facing the nozzle surface of the print unit 12 and the sensor surface of the print detection unit 24 inside the belt 33 spanned between the rollers 31 and 32. Then, the suction chamber 34 is sucked by the fan 35 to be a negative pressure, whereby the recording paper 16 on the belt 33 is sucked and held.

  When the power of a motor (not shown in FIG. 1, described as reference numeral 88 in FIG. 7) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, the belt 33 rotates in the clockwise direction in FIG. , And the recording paper 16 held on the belt 33 is conveyed from left to right in FIG.

  Since ink adheres to the belt 33 when a borderless print or the like is printed, the belt cleaning unit 36 is provided at a predetermined position outside the belt 33 (an appropriate position other than the print area). Although details of the configuration of the belt cleaning unit 36 are not shown, for example, there are a method of niping a brush roll, a water absorbing roll, etc., an air blow method of blowing clean air, or a combination thereof. In the case where the cleaning roll is nipped, the cleaning effect is great if the belt linear velocity and the roller linear velocity are changed.

  Although a mode using a roller / nip conveyance mechanism instead of the suction belt conveyance unit 22 is also conceivable, if the roller / nip conveyance is performed in the print area, the image easily spreads because the roller contacts the printing surface of the sheet immediately after printing. There is a problem. Therefore, as in this example, suction belt conveyance that does not bring the image surface into contact with each other in the print region is preferable.

  A heating fan 40 is provided on the upstream side of the printing unit 12 on the paper conveyance path formed by the suction belt conveyance unit 22. The heating fan 40 blows heated air on the recording paper 16 before printing to heat the recording paper 16. Heating the recording paper 16 immediately before printing makes it easier for the ink to dry after landing.

  The printing unit 12 is a so-called full line type head in which line type heads having a length corresponding to the maximum paper width are arranged in a direction (main scanning direction) orthogonal to the paper feed direction (see FIG. 2). Although a detailed structural example will be described later (FIGS. 3 to 5), each of the print heads 12K, 12C, 12M, and 12Y is a recording paper of the maximum size targeted by the inkjet recording apparatus 10 as shown in FIG. The line head includes a plurality of ink discharge ports (nozzles) arranged over a length exceeding at least one side of 16.

  A print head 12K corresponding to each color ink in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction of the recording paper 16 (hereinafter referred to as the sub-scanning direction). , 12C, 12M, 12Y are arranged. A color image can be formed on the recording paper 16 by discharging the color inks from the print heads 12K, 12C, 12M, and 12Y while the recording paper 16 is conveyed.

  Thus, according to the printing unit 12 in which the full line head that covers the entire area of the paper width is provided for each ink color, the operation of relatively moving the recording paper 16 and the printing unit 12 in the sub-scanning direction is performed once. An image can be recorded on the entire surface of the recording paper 16 only by performing it (that is, by one sub-scan). Thereby, it is possible to perform high-speed printing as compared with a shuttle type head in which the print head reciprocates in the main scanning direction, and productivity can be improved.

  In this example, the configuration of KCMY standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink and dark ink are added as necessary. May be. For example, it is possible to add a print head that discharges light ink such as light cyan and light magenta.

  As shown in FIG. 1, the ink storage / loading unit 14 has tanks that store inks of colors corresponding to the print heads 12K, 12C, 12M, and 12Y, and each tank is connected via a conduit (not shown). The print heads 12K, 12C, 12M, and 12Y communicate with each other. Further, the ink storage / loading unit 14 includes notifying means (display means, warning sound generating means) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. ing.

  The print detection unit 24 includes an image sensor for imaging the print result of the print unit 12, and functions as a unit for checking nozzle clogging and other ejection defects from an image read by the image sensor.

  The print detection unit 24 of this example is composed of a line sensor having a light receiving element array that is wider than at least the ink ejection width (image recording width) by the print heads 12K, 12C, 12M, and 12Y. The line sensor includes an R sensor row in which photoelectric conversion elements (pixels) provided with red (R) color filters are arranged in a line, a G sensor row provided with green (G) color filters, The color separation line CCD sensor is composed of a B sensor array provided with a blue (B) color filter. Instead of the line sensor, an area sensor in which the light receiving elements are two-dimensionally arranged can be used.

  The print detection unit 24 reads the test pattern printed by the print heads 12K, 12C, 12M, and 12Y for each color, and detects the ejection of each head. The ejection determination includes the presence / absence of ejection, measurement of dot size, measurement of dot landing position, and the like.

  A post-drying unit 42 is provided following the print detection unit 24. The post-drying unit 42 is means for drying the printed image surface, and for example, a heating fan is used. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.

  When printing on porous paper with dye-based ink, the weather resistance of the image is improved by preventing contact with ozone or other things that cause dye molecules to break by pressurizing the paper holes with pressure. There is an effect to.

  A heating / pressurizing unit 44 is provided following the post-drying unit 42. The heating / pressurizing unit 44 is a means for controlling the glossiness of the image surface, and pressurizes with a pressure roller 45 having a predetermined surface uneven shape while heating the image surface to transfer the uneven shape to the image surface. To do.

  The printed matter generated in this manner is outputted from the paper output unit 26. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. The ink jet recording apparatus 10 is provided with a sorting means (not shown) that switches the paper discharge path so as to select the print product of the main image and the print product of the test print and send them to the discharge units 26A and 26B. Yes. Note that when the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is separated by a cutter (second cutter) 48. The cutter 48 is provided immediately before the paper discharge unit 26, and cuts the main image and the test print unit when the test print is performed on the image margin. The structure of the cutter 48 is the same as that of the first cutter 28 described above, and includes a fixed blade 48A and a round blade 48B.

  Although not shown in FIG. 1, the paper output unit 26A for the target prints is provided with a sorter for collecting prints according to print orders.

[Head structure]
Next, the structure of the print head will be described. Since the structures of the print heads 12K, 12C, 12M, and 12Y provided for the respective ink colors are common, the print heads are represented by reference numeral 50 in the following.

  FIG. 3 (a) is a plan perspective view showing an example of the structure of the print head 50, and FIG. 3 (b) is an enlarged view of a part thereof. 3C is a perspective plan view showing another example of the structure of the print head 50, and FIG. 4 is a cross-sectional view showing the three-dimensional configuration of the ink chamber unit (along line 4-4 in FIG. 3A). FIG. In order to increase the dot pitch printed on the recording paper surface, it is necessary to increase the nozzle pitch in the print head 50. As shown in FIGS. 3A to 3C and FIG. 4, the print head 50 of this example includes a plurality of inks including nozzles 51 from which ink droplets are ejected and pressure chambers 52 corresponding to the nozzles 51. The chamber units 53 have a structure in which the chamber units 53 are arranged in a staggered matrix, thereby achieving an increase in the apparent nozzle pitch density.

  That is, the print head 50 according to the present embodiment prints a plurality of nozzles 51 for ejecting ink in a direction substantially perpendicular to the print medium (recording paper 16) feed direction, as shown in FIGS. 3 (a) and 3 (b). A full line head having one or more nozzle rows arranged over a length corresponding to the entire width of the medium.

  Further, as shown in FIG. 3 (c), short two-dimensionally arranged print heads 50 'may be arranged in a staggered manner and connected to form a length corresponding to the entire width of the print medium.

  The pressure chamber 52 provided corresponding to each nozzle 51 has a substantially square planar shape, and the nozzle 51 and the supply port 54 are provided at both corners on the diagonal line. Each pressure chamber 52 communicates with a common flow channel 55 through a supply port 54.

  An actuator (pressurizing means) 58 having individual electrodes 57 is joined to a pressurizing plate (vibrating plate that also serves as a common electrode) 56 constituting the top surface of the pressure chamber 52. By applying a driving voltage to the individual electrode 57, the actuator 58 is deformed to change the volume of the pressure chamber 52, and ink is ejected from the nozzle 51 due to the pressure change accompanying this. For the actuator 58, a piezoelectric body such as a piezoelectric element is preferably used. After ink discharge, new ink is supplied from the common channel 55 to the pressure chamber 52 through the supply port 54.

  Although the details will be described later, the ink chamber unit 53 also has a nozzle 51 and a supply port 54 so that the refill time is not significantly increased even when a high-viscosity ink having a higher viscosity than a commonly used ink is used. The shape, size, etc. are optimized.

  As shown in FIG. 4, the nozzle 51 of this example includes a nozzle narrow tube portion 51 </ b> B located near the opening 51 </ b> A and having a narrow pipe diameter, and a nozzle narrow tube portion having a larger diameter than the nozzle thin tube portion 51 </ b> B. A nozzle thick pipe portion 51 </ b> C positioned between the pressure chamber 52 </ b> B and the pressure chamber 52.

4, L _n1 represents the pipe length of the nozzle large pipe section 51 </ b> C, L _n2 represents the pipe length of the nozzle thin pipe section 51 </ b> B, and L _s represents the pipe length of the supply port 54. _{Further, D n1} is the diameter of the nozzle thick tube portion 51C _{(Kanro径), D n2} is the diameter of the nozzle tube portion 51B, _{D s} represents the diameter of the supply port 54.

In this example, the pipe diameter of the nozzle capillary 51B is uniform, but the nozzle diameter of the nozzle capillary 51B has a tapered shape that decreases at a constant rate from the pressure chamber 52 side toward the opening 51A. You may do it. In this case, the pipe diameter D _n2 of the nozzle thin tube portion 51B may be an average value of the tapered portion. Further, the pipe diameters of the nozzle thin tube portion 51B and the nozzle thick tube portion 51C may be the same. Furthermore, you may provide the pipe line which has a pipe diameter different from the pipe line diameter which the nozzle thin tube part 51B and the nozzle large pipe part 51C have.

  In the present embodiment, the term “nozzle (51)” may represent the opening 51 or the opening 51A or the thin tube 51B. It may be described as “nozzle (51)” including the opening 51A to the thick tube 51C.

  Further, the supply port 54 in this example includes not only an opening on the supply system side of the pressure chamber 52 but also a flow path (pipe) on the ink supply side having a throttling function.

  That is, the nozzle 51 and the supply port 54 mean a flow path serving as a basis for calculating fluid resistance and inertance, such as an opening, a pipe, and a groove each having a throttle function on the discharge side and the supply side. The flow path having the throttle function may be composed of a plurality of flow paths, or may be a part of one flow path.

  As shown in FIG. 5, a large number of ink chamber units 53 having such a structure are arranged in a row direction along the main scanning direction and an oblique column direction having a constant angle θ that is not orthogonal to the main scanning direction. The structure is arranged in a lattice pattern. With a structure in which a plurality of ink chamber units 53 are arranged at a constant pitch d along a certain angle θ with respect to the main scanning direction, the pitch P of the nozzles projected so as to be aligned in the main scanning direction is d × cos θ. .

  That is, in the main scanning direction, each nozzle 51 can be handled equivalently as a linear arrangement with a constant pitch P. With such a configuration, it is possible to realize a high-density nozzle configuration in which 2400 nozzle rows are projected per inch (2400 nozzles / inch) so as to be aligned in the main scanning direction. Hereinafter, for convenience of explanation, it is assumed that the nozzles 51 are linearly arranged at a constant interval (pitch P) along the longitudinal direction (main scanning direction) of the head.

  When the nozzles are driven by a full line head having a nozzle row corresponding to the full width of the paper, (1) all the nozzles are driven simultaneously, (2) the nozzles are sequentially driven from one side to the other (3) ) The nozzle is divided into blocks, and each block is sequentially driven from one side to the other. One line is formed in the width direction of the paper (direction perpendicular to the paper conveyance direction). Or, repeated printing of a line consisting of a plurality of rows of dots is defined as main scanning.

  In particular, when driving the nozzles 51 arranged in a matrix as shown in FIG. 5, the main scanning as described in (3) above is preferable. That is, the nozzles 51-11, 51-12, 51-13, 51-14, 51-15, 51-16 are made into one block (other nozzles 51-21,..., 51-26 are made into one block, Nozzles 51-31,..., 51-36 as one block,...), And the nozzles 51-11, 51-12,. One line is printed in 16 width directions.

  On the other hand, by relatively moving the above-mentioned full line head and the paper, printing of one line (a line formed by one line of dots or a line composed of a plurality of lines) formed by the above-described main scanning is repeatedly performed. This is defined as sub-scanning.

  In implementing the present invention, the nozzle arrangement structure is not limited to the illustrated example, and various nozzle arrangement structures such as an arrangement structure in which nozzles are arranged in the row direction along the main scanning direction and the column direction along the sub-scanning direction can be applied.

  In the present embodiment, a full line head having one or more nozzle rows arranged over a length corresponding to the entire width of the print medium in a direction substantially orthogonal to the print medium feed direction is shown. The serial type (which forms a dot row along the width direction of the print medium while moving a short head having a length shorter than the entire width of the print medium in the main operation direction orthogonal to the feed direction of the print medium) It can also be applied to a shuttle scan type head.

  In the present embodiment, a single-layer piezoelectric element having one piezoelectric layer is shown. However, the present invention may be applied to a multilayer piezoelectric element in which two or more piezoelectric layers are laminated.

  In the present embodiment, the aspect in which the pressure plate 56 and the common electrode are used together is shown, but the pressure plate 56 and the common electrode may be provided separately. In an aspect in which the pressure plate 56 and the common electrode are separately provided, an insulating layer is provided between the pressure plate 56 and the common electrode when a conductive material such as a metal material is used for the pressure plate 56.

[Configuration of ink supply system]
FIG. 6 is a schematic diagram showing the configuration of the ink supply system in the inkjet recording apparatus 10.

  The ink supply tank 60 is a base tank for supplying ink, and is installed in the ink storage / loading unit 14 described with reference to FIG. There are two types of ink supply tank 60: a system that replenishes ink from a replenishment port (not shown) and a cartridge system that replaces the entire tank when the remaining amount of ink is low. A cartridge system is suitable for changing the ink type according to the intended use. In this case, it is preferable that the ink type information is identified by a barcode or the like, and ejection control is performed according to the ink type. The ink supply tank 60 in FIG. 6 is equivalent to the ink storage / loading unit 14 in FIG. 1 described above.

  As shown in FIG. 6, a filter 62 is provided between the ink supply tank 60 and the print head 50 in order to remove foreign substances and bubbles. The filter mesh size is preferably equal to or smaller than the nozzle diameter (generally about 20 μm).

  Although not shown in FIG. 6, a configuration in which a sub tank is provided in the vicinity of the print head 50 or integrally with the print head 50 is also preferable. The sub-tank has a function of improving a damper effect and refill that prevents fluctuations in the internal pressure of the head.

  Further, the inkjet recording apparatus 10 is provided with a cap 64 as a means for preventing the nozzle 51 from drying or preventing an increase in ink viscosity near the nozzle, and a cleaning blade 66 as a nozzle surface cleaning means.

  The maintenance unit including the cap 64 and the cleaning blade 66 can be moved relative to the print head 50 by a moving mechanism (not shown), and is moved from a predetermined retracted position to a maintenance position below the print head 50 as necessary. The

  The cap 64 is displaced up and down relatively with respect to the print head 50 by an elevator mechanism (not shown). The cap 64 is raised to a predetermined raised position when the power is turned off or during printing standby, and is brought into close contact with the print head 50, thereby covering the nozzle surface with the cap 64.

  During printing or standby, if the frequency of use of a specific nozzle 51 is reduced and ink is not ejected for a certain period of time, the ink solvent near the nozzle evaporates and the ink viscosity increases. In such a state, ink cannot be ejected from the nozzle 51 even if the actuator 58 operates.

  Before such a state is reached (within the range of the viscosity that can be discharged by the operation of the actuator 58), the actuator 58 is operated, and the cap 64 (ink near the nozzle whose viscosity has increased) is discharged. Preliminary ejection (purging, idle ejection, collar ejection, dummy ejection) is performed toward the ink receiver.

  Further, when air bubbles are mixed into the ink in the print head 50 (in the pressure chamber 52), the ink cannot be ejected from the nozzle even if the actuator 58 is operated. In such a case, the cap 64 is applied to the print head 50, the ink in the pressure chamber 52 (ink mixed with bubbles) is removed by suction with the suction pump 67, and the suctioned and removed ink is sent to the collection tank 68. .

  In this suction operation, the deteriorated ink with increased viscosity (solidified) is sucked out when the ink is initially loaded into the head or when the ink is used after being stopped for a long time. Since the suction operation is performed on the entire ink in the pressure chamber 52, the amount of ink consumption increases. Therefore, it is preferable to perform preliminary ejection when the increase in ink viscosity is small.

  The cleaning blade 66 is made of an elastic member such as rubber, and can slide on the ink discharge surface (surface of the nozzle plate) of the print head 50 by a blade moving mechanism (wiper) (not shown). When ink droplets or foreign substances adhere to the nozzle plate, the nozzle plate surface is wiped by sliding the cleaning blade 66 on the nozzle plate to clean the nozzle plate surface. It should be noted that when the ink ejection surface is cleaned by the blade mechanism, preliminary ejection is performed in order to prevent foreign matter from being mixed into the nozzle 51 by the blade.

[Explanation of control system]
FIG. 7 is a principal block diagram showing the system configuration of the inkjet recording apparatus 10. The inkjet recording apparatus 10 includes a communication interface 70, a system controller 72, an image memory 74, a motor driver 76, a heater driver 78, a print control unit (drive control means) 80, an image buffer memory 82, a head driver 84, and the like.

  The communication interface 70 is an interface unit that receives image data sent from the host computer 86. As the communication interface 70, a serial interface such as IEEE1394, USB (Universal serial Bus), Ethernet (registered trademark), or a wireless network, or a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted. Image data sent from the host computer 86 is taken into the inkjet recording apparatus 10 via the communication interface 70 and temporarily stored in the image memory 74.

  The image memory 74 is a storage unit that temporarily stores an image input via the communication interface 70, and data is read and written through the system controller 72. The image memory 74 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The system controller 72 includes a central processing unit (CPU) and its peripheral circuits, and functions as a control device that controls the entire inkjet recording apparatus 10 according to a predetermined program, and also functions as an arithmetic device that performs various calculations. . That is, the system controller 72 controls each part such as the communication interface 70, the image memory 74, the motor driver 76, the heater driver 78, etc., performs communication control with the host computer 86, read / write control of the image memory 74, etc. A control signal for controlling the motor 88 and the heater 89 of the transport system is generated.

  The image memory 74 stores programs executed by the CPU of the system controller 72 and various data necessary for control. Note that the image memory 74 may be a non-rewritable storage means, or may be a rewritable storage means such as an EEPROM. The image memory 74 is used as a temporary storage area for image data, and is also used as a program development area and a calculation work area for the CPU.

  The motor driver 76 is a driver (drive circuit) that drives the motor 88 in accordance with an instruction from the system controller 72. The heater driver 78 is a driver that drives the heater 89 such as the post-drying unit 42 in accordance with an instruction from the system controller 72.

  The print control unit 80 has a signal processing function for performing various processes such as processing and correction for generating a print control signal (drive signal) from the image data in the image memory 74 in accordance with the control of the system controller 72. The control unit supplies the generated print data (dot data) to the head driver 84. Necessary signal processing is performed in the print controller 80, and the ejection amount and ejection timing of the ink droplets of the print head 50 are controlled via the head driver 84 based on the image data. Thereby, a desired dot size and dot arrangement are realized.

  The print control unit 80 includes an image buffer memory 82, and image data, parameters, and other data are temporarily stored in the image buffer memory 82 when image data is processed in the print control unit 80. In FIG. 7, the image buffer memory 82 is shown in a mode associated with the print control unit 80, but it can also be used as the image memory 74. Also possible is an aspect in which the print controller 80 and the system controller 72 are integrated and configured with one processor.

  The head driver 84 drives the piezoelectric elements of the heads 12K, 12C, 12M, and 12Y of the respective colors based on the print data provided from the print control unit 80. The head driver 84 may include a feedback control system for keeping the head driving conditions constant.

  Image data to be printed is input from the outside via the communication interface 70 and stored in the image memory 74. At this stage, RGB image data is stored in the image memory 74.

  The image data stored in the image memory 74 is sent to the print controller 80 via the system controller 72, and is converted into dot data for each ink color by the print controller 80. That is, the print control unit 80 performs processing for converting the input RGB image data into dot data of four colors of KCMY. The dot data generated by the print controller 80 is stored in the image buffer memory 82.

  The head driver 84 drives the actuators of the print heads 12K, 12C, 12M, and 12Y for each color based on the print data given from the print control unit 80. The head driver 84 may include a feedback control system for keeping the head driving conditions constant.

  Various control programs are stored in a program storage unit (not shown), and the control programs are read and executed in accordance with commands from the system controller 72. The program storage unit may be a semiconductor memory such as a ROM or EEPROM, or a magnetic disk. An external interface may be provided and a memory card or PC card may be used. Of course, you may provide several recording media among these recording media.

  The program storage unit may also be used as a recording unit (not shown) for operating parameters.

  As described with reference to FIG. 1, the print detection unit 24 is a block including a line sensor. The print detection unit 24 reads an image printed on the recording paper 16, performs necessary signal processing, and the like to perform a printing situation (whether ejection is performed, printing is performed). Variation), and the detection result is provided to the print controller 80.

  The print control unit 80 performs various corrections on the print head 50 based on information obtained from the print detection unit 24 as necessary.

  In the example shown in FIG. 1, the print detection unit 24 is provided on the print surface side, and the print surface is illuminated by a light source (not shown) such as a cold cathode tube disposed in the vicinity of the line sensor. Although the configuration is such that the reflected light is read by the line sensor, other configurations may be used in the implementation of the present invention.

[Actuator drive control]
Next, drive control of the actuator 58 used in the inkjet recording apparatus 10 will be described in detail.

  FIG. 8A shows an example (reference numeral 100) of a drive signal (drive waveform) applied to the actuator 58. FIGS. 8B and 8C show the drive signal shown in FIG. 100 modification examples (reference numerals 102 and 104) are shown.

  8A to 8C, the horizontal axis represents time, and the vertical axis represents the voltage of the drive signal. Further, the upward direction (pushing direction) of the vertical axis indicates the direction in which the volume of the pressure chamber 52 shown in FIG. 4 is contracted, and the downward direction (pulling direction) indicates the direction in which the volume of the pressure chamber 52 is expanded (expanded). Show.

  When the drive signal is 0 V, the pressure chamber 52 is not contracted or expanded, and is in an initial state (meniscus stabilization state). Of course, the drive signal may be offset so that the initial state is obtained when a voltage other than 0V is applied.

In the inkjet recording apparatus 10, after the ink is ejected using the drive signal (ejection drive signal) 100 </ b> A for ejecting ink (ejection process), before the ejection operation of the size (volume) of the pressure chamber 52 is started. state spread than in the initial state (i.e., volume increased state) and (pressure chamber expansion step), to restore the initial state before the discharge operation after a predetermined time t _s has elapsed is started (the pressure chamber The refill drive signal 100B for operating the actuator 58 is controlled to be applied as in the restoring step).

  The drive signals for ejecting ink here indicate the portions (reference numerals 100A, 102A, 104A) surrounded by broken lines in FIGS. 8A to 8C, eject ink, and eject ink. This means a drive signal for operating the actuator 58 until the vibration of the meniscus surface caused by the resonance between the nozzle 51 and the pressure chamber 52 after being performed is almost stabilized.

  The refill drive signals 100B, 102B, and 104B are drive signals that operate the actuator 58 so that the meniscus does not vibrate during refill in order to shorten the refill time. Details of the refill drive signal will be described later.

That is, in the mode shown in FIG. 8A, the ejection drive signal 100A is applied to the actuator 58 during the period from timing t ₀ (operation start timing of the actuator 58) to timing t ₁ (ink ejection timing), and after ink ejection. of the refill period of filling the ink into the pressure chamber 52 from the ink supply tank and the supply system consisting of a supply channel (not shown) shown in FIG. 6, between the timing t ₁ of the refill driving voltage application time t _s, The refill drive signal 100B is applied to the actuator 58 so as to operate the actuator 58 in the direction of expanding the pressure chamber 52.

  In addition, after applying the refill drive signal and expanding the pressure chamber 52, the actuator 58 when the pressure chamber 52 is returned to the original state so that ink is not discharged when the pressure chamber 52 is returned to the original initial state. Smaller moving speed is better. This is achieved by reducing the amount of voltage change per unit time of the refill drive signal (decreasing the slope of the voltage waveform).

Accordingly, the refill drive signal, shown at reference numeral 102B in FIG. 8 (b), and aspects its voltage gradually decreases, indicated by the reference numeral 104B in FIG. 8 (c), after maintaining a short period constant voltage than t _s A mode in which the voltage gradually decreases is preferable.

  8A to 8C, the ejection drive signals 100A, 102A, and 104A having trapezoidal waveforms (here, the ejection drive signals 100A, 102A, and 104A have the same waveform) are used to pull from the initial state. The drive signals 100, 102, and 104 for ejecting ink by operating the actuator 58 in the order of the push direction (pull-push operation) are shown. The drive signals as shown in FIGS. 9 (a) to 9 (d) are shown. You may apply. 9A to 9D, the same or similar parts as those in FIGS. 8A to 8C are denoted by the same reference numerals, and the description thereof is omitted.

FIG. 9A shows a drive signal 110 for ejecting ink by operating the actuator 58 in the pushing direction with respect to the initial state. Drive signal 110 includes a discharge drive signal 110A and refill drive signal 110B, upon application of a drive signal 110 to the actuator 58, the period of time _{t 1} from the timing _{t 0,} the actuator 58 is operated in the pushing direction from the initial state ink is ejected by, between the timing t ₁ of the period t _s, greater than when the volume of the pressure chamber 52 is discharged, and the actuator 58 to be greater than the initial state in the pulling direction with respect to the initial state Operate.

Similarly, in FIG. 9 (b) shows a driving signal 112 for ink discharge by operating the actuator 58 in the pull direction, upon application of a drive signal 112 to the actuator 58, the period of time t ₁ from the timing t ₀ is the actuator 58 operates to pull direction, operates in a direction (pulling direction with respect to initial state) press at timing t ₁ with respect to the state of timing t ₁ to eject ink. Furthermore, between the timing t ₁ of the period t _s, such that the pressure chamber 52 to maintain a greater state than the initial state, the actuator 58 is to press the direction (initial state with respect to state of the drive signal 112A is applied In the pulling direction).

FIG. 9C shows a drive signal 114 for ejecting ink by pull-pushing the actuator 58 in the order of the pulling direction and the pushing direction. When applying a drive signal 114 to the actuator 58, the period of time t ₁ from the timing t _0, the actuator 58 ejects ink pulling direction, operate in the order of pushing direction with respect to the initial state, the period from the timing t ₁ t _{During s} , the actuator 58 operates in the pulling direction with respect to the initial state so as to widen the pressure chamber 52. The drive signal 114 shown in FIG. 9 (c) is obtained by changing the ejection drive signal 100A of the drive signal 100 shown in FIG. 8 (a) from a trapezoidal waveform to a rectangular waveform.

  FIG. 9 (d) shows still another aspect of the drive signals shown in FIGS. 9 (a) to 9 (c). When the drive signal 116 shown in FIG. 9 (d) is used, the actuator 58 is first moved in the pulling direction with respect to the initial state, and then the pushing direction is gradually applied to this state (the pulling direction with respect to the initial state). To work.

  That is, the drive signal 116 first expands the pressure chamber 52 by operating the actuator 58 in the pulling direction with respect to the initial state, so that the displacement volume of the pressure chamber 52 becomes smaller than that during the previous pulling direction driving from this state. The ejection drive signal 116A for ejecting ink by operating the actuator 58 relatively in the pushing direction, and the displacement of the actuator 58 between the displacement at the time of ink ejection and the initial state (no displacement). And a refill drive signal 116B for operating the actuator 58 in the pushing direction (the pulling direction with respect to the initial state) with respect to the state of the actuator 58 during the previous pulling direction driving.

  In this way, by operating the actuator 58 so that the pressure chamber 52 expands during refilling, the ink supply speed during refilling can be increased. In addition, a predetermined supply speed can be maintained even when high viscosity ink having a large fluid resistance is used.

  On the other hand, the operation of the actuator 58 may cause the meniscus to vibrate even when high viscosity ink is used, and the refill time may be prolonged due to such vibration of the meniscus. Therefore, it is necessary to suppress meniscus vibration.

[Ink chamber unit structure]
Next, the condition that the meniscus surface does not vibrate during the refill described above will be described in detail.

  FIG. 10 shows a lumped constant model (lumped constant circuit) 200 when the function of the ink chamber unit 53 shown in FIG. 4 is replaced with an electric circuit.

The lumped model shown in FIG. 10, the inertance of the _{M n} is the nozzle 51, resistance _{R n} is the nozzle 51, the inertance of _{C n} compliance due to the surface tension of the nozzle portion, _{M s} is the supply port 54, _{R s} is the supply port 54 resistances are represented.

  The lumped constant model 200 at the time of refilling is expressed by the following equation.

Here, the density of the ink is ρ, the viscosity of the ink is ν, the surface tension of the ink is σ, the length of the nozzle large tube portion 51C is L _n1 , the area of the nozzle large tube portion 51C is A _n1 , and the nozzle large tube portion 51C. the radius _{r n1 (= D n1 / 2} ), the length _{L n2} of the nozzle tube portion 51B, the area of _{a n2} of the nozzle tube portion 51B, the radius of the nozzle tube portion _{51B r n2 (D n2 / 2} ), the length of the supply port 54 _{L s,} and the area of the supply port 54 and _{a s,} the inertance _{M n,} resistor _{R n,} compliance _{C n} due to the surface tension of the nozzles 51 of the nozzle 51 of the nozzle 51, the inertance of the supply port 54 M _s, the resistance _{R s} of the supply port 54 is expressed by the following equation.

In the lumped constant model shown in FIG. 10, the condition that the meniscus does not vibrate at the time of refilling is expressed by the following equation using the above (2) to ( 6 ).

  The condition shown in the above (7) indicates a case where the solution of the differential equation shown in (1) is not a damped vibration solution.

The condition shown in (7) above is that when the values of the right side ({4 × (M _n + M _s )} / C _n ) and the left side ((R _n + R _s ) ² ) are close (that is, the inequality sign approaches the equal sign). And refilling is further accelerated, which is preferable. More preferably, as shown in the following formula, the left side and the right side are equal.

  The conditions shown in the above (7) and (8) are conditions established for a high-viscosity ink having a viscosity of 5.5 cP or more in a general print head used in an ink jet recording apparatus.

As an example of the general conditions of the print head described above, the size of the pressure chamber 52 is 700 μm × 700 μm × 150 μm, the diameter of the nozzle 51 (diameter D _n2 of the nozzle thin tube portion 51B) is 30 μm, the nozzle 51 pipe length (nozzle The pipe length L _n2 ) of the narrow pipe portion 51B is 40 μm, the pipe size of the supply port 54 is 40 μm × 40 μm square, the pipe length L _s of the supply port 54 is 100 μm (however, the flow path resistance and inertance of the supply port 54 are This is substantially the same as the flow path resistance and compliance of the nozzle.

  Therefore, if the viscosity of the ink is 5.5 cP and the general print head shown above, it can be said that the conditions (7) and (8) are satisfied.

[Explanation of refill time]
Next, will be described in detail refill drive signal application time t _s as described above.

10, based on the lumped model 200 of the ink chamber unit 53, in order to determine the time required to refill (refill drive signal application time) t _s, using (1). (However, v represents the volume velocity of the ink on the nozzle surface (nozzle opening 51A).)
When the differential equation shown in the above (1) is solved for v and the condition of v = 0 is used at t = 0 (initial state), the ink volume velocity v on the nozzle surface is as follows: .

However, v ₀ represents the constant, the α and β are expressed by the following equations.

このようにして求められたノズル面のインクの体積速度ｖをもとに、リフィルが終了したときの（即ち、圧力室５２内へインクの充填が完了し、次の吐出されるインクが収容されている状態の）インクの体積を０とし、ノズル面のインクの変位体積ｘ（吐出方向が正、リフィル方向が負）を求めると、以下の式で表される。

Based on the volume velocity v of the ink on the nozzle surface thus obtained, when the refilling is completed (that is, the ink filling into the pressure chamber 52 is completed, the next ejected ink is accommodated). When the volume of the ink in the state of 0 is 0 and the displacement volume x of the ink on the nozzle surface (the ejection direction is positive and the refill direction is negative) is obtained, the following equation is obtained.

なお、リフィル時に圧力室５２に充填されるインクの量（体積）をＦとすると、ｔ＝０のときに、ｘ＝−Ｆとなる。

If the amount (volume) of ink filled in the pressure chamber 52 during refilling is F, then x = −F when t = 0.

  Here, A represents the amount of ink ejected in one ejection operation, and B represents the volume in which the pressure chamber 52 is expanded from the original state after ink ejection (volume of the pressure chamber 52 when the refill drive signal is applied). In this case, the amount of ink refilled at one time is A + B, and the time until refilling the ink amount A necessary for the next ejection (refill time) tA satisfies the condition expressed by the following equation.

即ち、上記（１３）は以下の式で表される。

That is, the above (13) is expressed by the following equation.

上記（１４）を満たすリフィル時間ｔＡよりも長い時間だけ圧力室５２を広げた状態を保持すれば、その後、圧力室５２を元の状態に戻したときに、次の吐出に必要なインク量Ａを圧力室５２に充填され、リフィルが完了した状態になっている。

If the state in which the pressure chamber 52 is expanded for a time longer than the refill time tA satisfying the above (14) is maintained, then the ink amount A required for the next ejection when the pressure chamber 52 is returned to the original state. Is filled in the pressure chamber 52 and the refill is completed.

That is, to satisfy the conditions shown in the following equation, refill drive signal application time t _s is set.

リフィル駆動信号印加時間ｔ_ｓを上記（１４）の条件を満たすリフィル時間ｔＡより も長くすることで、次の吐出に必要なインク量を圧力室５２内に充填することができる。但し、リフィル駆動信号印加時間ｔ_ｓを長くすると吐出周期が長くなるので、リフィル 駆動信号印加時間ｔ_ｓはできるだけ短くすることが好ましい。したがって、リフィル駆動信号印加時間ｔ_ｓとリフィル時間ｔＡとの関係は、以下の式を満たす態様が更に好ましい。

Refill drive signal application time t _s by longer than satisfying refill time tA of (14), can be filled with ink amount required for the next discharge into the pressure chamber 52. However, since the discharge period longer refill drive signal application time t _s is increased, refill drive signal application time t _s is preferably as short as possible. Therefore, the relationship between the refill drive signal application time t _s and refill time tA is the more preferred embodiment to satisfy the following expression.

一方、リフィル後にアクチュエータ５８を押し方向に動作させて圧力室５２の容積を元の初期状態に戻す際にインクが吐出されないよう、駆動信号印加時に圧力室５２の容積が広げられる量を制限する必要がある。

On the other hand, it is necessary to limit the amount by which the volume of the pressure chamber 52 is expanded when the drive signal is applied so that the ink is not ejected when the actuator 58 is moved in the pushing direction after refilling to return the volume of the pressure chamber 52 to the original initial state. There is.

The allowable range of the volumetric change of the refill drive signal application time of the pressure chamber 52 is smaller than half the volume of the droplet having the same radius and the radius r _n2 of the nozzle tube portion 51B.

  That is, the volume change amount ΔV of the pressure chamber 52 when the refill drive signal is applied satisfies the following expression.

上記（１７）の条件を満たすリフィル駆動信号印加時の圧力室５２の容積変化量ΔＶの一例を挙げると、ノズル細管部５１Ｂの直径Ｄ_ｎ２が３０μm のとき、ΔＶは略７plとなる。

An example of the volume change amount ΔV of the pressure chamber 52 when the refill drive signal satisfying the condition (17) is given. When the diameter D _n2 of the nozzle capillary 51B is 30 μm, ΔV is approximately 7pl.

That is, when the meniscus surface is formed on the nozzle opening 51A formation surface during refilling, the ink that appears outside the nozzle opening formation surface 51A when the volume of the pressure chamber 52 is returned to the initial volume. If it is less than or equal to ½ of a droplet having the same diameter as the diameter D _n2 of the nozzle capillary 51B, it indicates that the nozzle is not discharged to the outside.

The print head 50 provided in the inkjet recording apparatus 10 having the composition described above, after the discharge operation, the pressure chamber 52 and spread from the initial state before the ink discharge operation, refill drive signal application time t _s pressure chamber after Since the actuator 58 is operated so as to return 52 to the original initial state, the refill speed can be increased by using the force generated by the actuator 58 during the refill.

  Further, since the ink chamber unit 53 of the print head 50 is configured so that the meniscus surface does not vibrate during refilling, the meniscus surface does not vibrate during refilling, and the degree of freedom of the waveform of the drive signal of the actuator used for refilling can be increased. it can.

  In the above description, the ink jet recording apparatus is illustrated as an example of the liquid discharge apparatus. However, the scope of application of the present invention is not limited to this, and the liquid is discharged onto the discharge medium to form a three-dimensional shape on the discharge medium. The present invention can be applied to various image forming apparatuses and liquid ejection apparatuses.

1 is an overall configuration diagram of an ink jet recording apparatus using an image processing apparatus according to an embodiment of the present invention. FIG. 1 is a plan view of a main part around a printing unit of the ink jet recording apparatus shown in FIG. Plane perspective view showing the configuration of the head of the ink jet recording apparatus shown in FIG. The figure which shows the three-dimensional structure of the head shown in FIG. FIG. 3 is an enlarged view showing the nozzle arrangement of the head shown in FIG. Schematic diagram showing the configuration of the ink supply system in the inkjet recording apparatus of this example Main block diagram showing the system configuration of the inkjet recording apparatus of this example The figure explaining the drive signal of the head shown in FIG. The figure which shows the other aspect of the drive signal shown in FIG. The figure which shows the lumped constant model of the head shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device 50 ... Head, 51, 51A, 51B, 51C ... Nozzle, 52 ... Pressure chamber, 54 ... Supply port, 56 ... Diaphragm, 57 ... Individual electrode, 58 ... Actuator, 80 ... Print control part, 84: Head driver, 100, 102, 104, 110, 112, 114, 116: Drive signal, 200: Lumped constant model of pressure chamber

Claims (3)

A nozzle for discharging a liquid, a pressure chamber for storing the liquid discharged from the nozzle, a pressurizing means for changing the volume of the pressure chamber by pressurizing the liquid stored in the pressure chamber, and the pressure chamber A supply port for supplying liquid,
Inertance Mn of the nozzle, fluid resistance Rn of the nozzle, compliance Cn due to surface tension of the liquid in the nozzle, inertance Ms of the supply port, and fluid resistance Rn of the supply port are { 4 × (Mn + Ms)} / Cn ≦ (Rn + ^Rs) and having a structure that meets the ^second relationship, and the liquid discharge head using a liquid having ^{5.5 × 10 -3 (Pa · s} ) or more viscosity,
When refilling the liquid into the pressure chamber via the supply port after the liquid is discharged from the nozzle, a drive signal is sent to the pressurizing unit for a period ts after the liquid is discharged from the nozzle. applied to Rutotomoni is increased by the volume B from the initial state before the discharge operation starts the volume of the pressure chamber, the volume of the first period state the volume of the pressure chamber and the liquid from the nozzles is time ts elapses after discharged Drive control means for driving the pressurizing means to return to
Equipped with a,
The control means refills a liquid having the same volume as the volume A discharged in one discharge operation in a period ts during which the drive signal is applied to increase the volume of the pressure chamber from the initial state. The period tA until the liquid having the same volume as the volume A discharged by one discharge operation is refilled in the pressure chamber is expressed by the following equation.

The volume velocity v (t) of the liquid at the opening of the nozzle represented by

Α represented by

Β represented by

The displacement volume x (t) of the liquid at the opening of the nozzle that becomes −F when t = 0, and the volume of the liquid necessary for the next discharge with respect to the volume A + B of the liquid refilled at one time Expressed using the ratio A / (A + B),

And the following formula

The liquid ejecting apparatus , wherein the pressurizing unit is controlled to satisfy the relationship . Volume B to increase from the initial state of discharge operation before starting the volume of the pressure chamber after the liquid has been ejected from the nozzles, the radius of the nozzle when the r, B ≦ (2 × π × r 3 3) The liquid ejecting apparatus according to claim 1, wherein: A nozzle for discharging a liquid, a pressure chamber for storing the liquid discharged from the nozzle, a pressurizing means for changing the volume of the pressure chamber by pressurizing the liquid stored in the pressure chamber, and the pressure chamber A supply port for supplying liquid,
Inertance Mn of the nozzle, fluid resistance Rn of the nozzle, compliance Cn due to surface tension of liquid in the nozzle, inertance Ms of the supply port, and fluid resistance Rn of the supply port are {4 × (Mn + Ms)} / Cn ≦ Using a liquid discharge head having a structure satisfying the relationship of (Rn + Rs) ² , the pressure means is driven to change the volume of the pressure chamber to be accommodated in the pressure chamber 5.5 × 10 ⁻³ ( a discharge step of discharging the liquid from the nozzle having a Pa · s) or more viscosity,
When refilling the liquid into the pressure chamber via the supply port after the liquid is discharged from the nozzle , a drive signal is sent to the pressurizing unit for a period ts after the liquid is discharged from the nozzle. a pressure chamber extension step of increasing the volume of the pressure chamber by the volume B from the initial state before starting the discharge process is applied to,
During the refilling, the period ts after the liquid is ejected from said nozzle passes, the pressure chamber restoring step of returning the volume of the pressure chamber which is increased by the volume B in the pressure chamber expanding step the volume of the first period state,
Only including,
In the pressure chamber expansion step, a liquid having the same volume as the volume A discharged by one discharge operation in the pressure chamber and the period ts during which the drive signal is applied to increase the volume of the pressure chamber from the initial state. While the relationship with the period tA until refill satisfies the relationship of tA = ts, the period tA until the liquid having the same volume as the volume A discharged in one discharge operation is refilled into the pressure chamber is: Next formula

The volume velocity v (t) of the liquid at the opening of the nozzle represented by

Α represented by

Β represented by

The displacement volume x (t) of the liquid at the opening of the nozzle that becomes −F when t = 0, and the volume of the liquid necessary for the next discharge with respect to the volume A + B of the liquid refilled at one time Expressed using the ratio A / (A + B),

And the following formula

And controlling the pressurizing means so as to satisfy the relationship .

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