JP2015080945A - Inkjet device and inkjet method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet device stably discharging ink drops, and further to provide an inkjet method.SOLUTION: An inkjet device comprises: a plurality of ink jet nozzles; a plurality of pressure chambers individually communicating with the plurality of ink jet nozzles; ink supply sections for supplying ink; an ink jet head including a plurality of actuators; and a driving voltage generation section for periodically applying a driving voltage to the plurality of actuators. A driving pulse signal includes an expansion pulse for expanding volumes of the pressure chambers for expansion time D and a contraction pulse for contracting the volumes of the pressure chambers subsequent to the expansion pulse with delay time R for contraction time P. A half of a natural vibration period of the ink in each of the pressure chambers is defined as pressure propagation time Ta, the expansion time D is set to the pressure propagation time Ta, and a ratio X(=R/Ta) of the delay time R to the pressure propagation time Ta and a ratio Y(=P/Ta) of the contraction time P to the pressure propagation time Ta individually satisfy an equation of 67Y+58X-147Y-179X+74XY<-144.

Description

  Embodiments described herein relate generally to an inkjet apparatus and an inkjet method.

  In recent years, in order to operate a printer at high speed, it is required to reduce the size of the ink jet head and increase the number of nozzles. In order to meet this requirement, it is necessary to increase the nozzle density by reducing the interval between the pressure chambers adjacent to each other (that is, the thickness of the partition wall). However, since the rigidity of the partition wall is weakened by this, interference between a plurality of adjacent pressure chambers, that is, crosstalk is increased. Specifically, when an arbitrary pressure chamber is driven and ink is ejected from the ink jet nozzle corresponding to this pressure chamber, the ink ejection speed and the amount of ink ejection are driven in other adjacent pressure chambers adjacent to this pressure chamber. Depends on the. Since the difference in ink ejection speed changes the time until the ink droplet reaches the paper, it is recognized as a shift in the print position of the dots when the head moves in the scanning direction in, for example, serial printing. Also, the difference in ink discharge amount is recognized as a difference in dot print density. Therefore, the increase in crosstalk results in a print position shift and a difference in print density more prominently, resulting in deterioration of print quality.

  Further, when the drive frequency of the ink jet head is increased in order to perform high-speed printing, the meniscus formed by the ink contacting the orifice surface of the ink jet nozzle is made unstable due to the influence of residual vibration. As a result, the ink droplet ejection speed varies. In addition, when the meniscus is unstable, there is a possibility that ink may entrap bubbles at the nozzle tip. As a result, there is a possibility that an ink droplet is not ejected, an extra ink droplet is ejected after the ink droplet is ejected, or the ink is pushed out as a liquid column from the nozzle.

JP 2009-66867 A

  In order to solve the above-described problems, an inkjet apparatus and an inkjet method that eject ink droplets more stably are provided.

An inkjet apparatus according to an embodiment includes a plurality of inkjet nozzles that eject ink as ink droplets, a plurality of pressure chambers that are respectively connected to the plurality of inkjet nozzles via a partition wall, and the ink is supplied to the plurality of inkjet nozzles. An ink supply unit that supplies pressure to the pressure chamber, an inkjet head that includes a plurality of actuators that change the volume of the plurality of pressure chambers in response to an applied voltage, and a pressure vibration that ejects the ink for dot printing are applied. A drive voltage generator that periodically applies a drive voltage that is a drive pulse signal to each of the plurality of actuators, and the drive pulse signal includes an expansion pulse that expands the volume of the pressure chamber by an expansion time D; A contraction that causes the volume of the pressure chamber to contract by a contraction time P after a delay time R from the expansion pulse. The expansion time D is set to the pressure propagation time Ta when the half value of the natural vibration period of the ink in the pressure chamber is defined as the pressure propagation time Ta. The ratio X (= R / Ta) with the pressure propagation time Ta and the ratio Y (= P / Ta) between the contraction time P and the pressure propagation time Ta satisfy 67Y ² + 58X ² −147Y−179X + 74XY <−144, respectively. .

FIG. 1 is a diagram for explaining an ink jet apparatus according to an embodiment. FIG. 2 is a diagram for explaining an inkjet head according to an embodiment. FIG. 3 is a diagram for explaining a driving voltage for driving the ink jet head according to the embodiment. FIG. 4 is a diagram for explaining the influence of crosstalk in the ink jet apparatus according to the embodiment. FIG. 5 is a diagram for explaining the influence of fluctuations in the ink ejection speed ejected by the ink jet apparatus according to the embodiment. FIG. 6 is a diagram for explaining the influence of crosstalk and ink ejection speed fluctuations in the ink jet apparatus according to the embodiment.

  Hereinafter, an inkjet apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows the structure of the ink jet apparatus, and FIG. 2 shows a cross-sectional structure taken along the line II-II shown in FIG. The ink jet apparatus includes an ink jet head 1 and a drive voltage generator 2. The inkjet head 1 includes a plurality of inkjet nozzles 13 that eject ink as ink droplets, a plurality of pressure chambers (ink chambers) 11 that communicate with the inkjet nozzles 13, and a common ink chamber that supplies ink to a plurality of pressure chambers. (Common pressure chamber) 16 and a plurality of actuators 10 that change the volumes of the plurality of pressure chambers 11 corresponding to the applied voltage. The drive voltage generator 2 generates a plurality of drive voltages that are any one of a drive pulse signal for applying pressure vibration for ejecting ink for dot printing and a dummy pulse signal for applying minute pressure vibration for not ejecting ink for non-dot printing. The actuator 10 is periodically applied.

  In the inkjet head 1, a plurality of inkjet nozzles 13 are arranged as nozzle rows and are formed as orifices that penetrate the nozzle plate 3. A vibration plate 14 is disposed opposite to the nozzle plate 3. The plurality of pressure chambers 11 are adjacent to each other through the partition wall 12 between the nozzle plate and the vibration plate 14. The common ink chamber 16 is disposed behind the plurality of pressure chambers 11. A pair of ink supply ports 17 connected to an external ink tank 18 are provided on the bottom surface of the common ink chamber 16, that is, the vibration plate 14. The ink can be circulated by being sent from the ink tank 18 to one ink supply port 17 and returned from the other ink supply port 17 to the ink tank 18. When the common ink chamber 16 and the plurality of pressure chambers 11 are filled with ink, an ink meniscus is formed in contact with the orifice surfaces of the plurality of inkjet nozzles 13. A plurality of electrostrictive members (piezoelectric members) 15 are fixed to the back side of the diaphragm 14. These electrostrictive members 15 are arranged corresponding to the regions of the diaphragm 14 which are the bottom surfaces of the plurality of pressure chambers 11. Each actuator 10 includes a corresponding electrostrictive member 15 and a diaphragm 14. Each electrostrictive member 15 applies pressure vibration to the corresponding pressure chamber by deforming the diaphragm 14 in accordance with the drive voltage applied from the drive voltage generator 2 via a pair of electrodes. Ink is sucked from the common ink chamber 16 as the diaphragm 14 is deformed to the outside, and ejected as ink droplets from the inkjet nozzle 13 by the generated ink pressure wave in the pressure chamber 11 as the diaphragm 14 is deformed to the inside. Is done.

  FIG. 3 shows a drive voltage generated for dot printing from the drive voltage generator 2. This drive voltage is a drive pulse signal generated including an expansion pulse P1 for expanding the volume of the pressure chamber 11 for the expansion time D and a contraction pulse P2 for contracting the volume of the pressure chamber 11 for the contraction time P. The contraction pulse P2 is generated with a delay time R from the expansion pulse P1. Therefore, the drive time DC of the drive pulse signal is DC = D + R + P. The expansion pulse P1 and the contraction pulse P2 have the same amplitude V and different polarities. The drive pulse signal is generated again after the elapse of the pause time CD following the drive time DC. The drive pulse signal is applied at a cycle time CT of CT = DC + CD = D + R + P + CD, and drives the pressure chamber 11 at a drive frequency F = 1 / CT.

  When the expansion pulse P <b> 1 is applied, the volume of the pressure chamber 11 is sharply expanded and a negative pressure is generated in the pressure chamber 11. While this state is maintained for a certain extension time D, ink is filled from the common ink chamber 16 into the pressure chamber 11, and the meniscus at the tip of the nozzle is moved back together. Subsequently, when the expansion pulse P1 is no longer applied, the volume of the pressure chamber 11 suddenly returns to the original, thereby increasing the ink pressure in the pressure chamber 11 and ejecting the ink in the pressure chamber 11 from the nozzle 13 as ink droplets. Let When a certain delay time R elapses from the ejection, the volume of the pressure chamber 11 is sharply narrowed by applying the contraction pulse P2. This state is maintained for a certain contraction time P. Subsequently, when the contraction pulse P2 is no longer applied, the volume of the pressure chamber 11 returns to the original, and the pressure vibration in the pressure chamber 11 is canceled. As a result, the residual pressure vibration is reduced and the movement of the meniscus after ink ejection is suppressed. As a result, the occurrence of erroneous ejection and the occurrence of satellites can be suppressed, and ejection stability and print quality can be improved.

  Here, the expansion time D of the expansion pulse P1 is set to the pressure propagation time Ta in which the ink pressure wave propagates in the pressure chamber 11 from the common ink chamber 16 at the rear end toward the nozzle tip. This is because the pressure chamber 11 is instantaneously expanded to make the pressure in the pressure chamber 11 negative, and the pressure chamber 11 is returned to the original state when the pressure is reversed to positive pressure as time Ta elapses. This is for obtaining a larger discharge pressure. The delay time R from the expansion pulse P1 to the contraction pulse P2 and the contraction time P of the contraction pulse P2 are set to optimum values that effectively cancel the residual pressure oscillation in the pressure chamber 11. By effectively canceling the residual vibration, the pause time CD can be shortened and the drive frequency F can be increased to perform high-speed printing.

The crosstalk Vc indicates the magnitude of the influence of driving of the adjacent pressure chambers 11. The ink discharge speed Vai when the adjacent pressure chambers 11 are driven for dot printing is the ink discharge speed Vni when the adjacent pressure chambers 11 are not driven for dot printing. In this case, the crosstalk Vc corresponds to the average of the difference between the ink ejection speed Vai and the ink ejection speed Vni for each cycle time CT. That is, the crosstalk Vc is expressed by the following formula 1.

  The smaller the crosstalk Vc is, the smaller the difference in ink ejection speed between when the other adjacent pressure chambers 11 are driven for dot printing and when they are not driven over the entire cycle time CT.

The ink ejection speed fluctuation Vd indicates the magnitude of variation in the ejection speed of the ink droplets. The sum of squares of the difference (Vni−Vm) between the ink discharge speed Vni and the total average ink discharge speed Vm (average of ink discharge speeds Vni and Vai), which is the average of the discharge speeds of all ink droplets, and the ink discharge speed Vai And the sum of squares of the differences (Vai−Vm) between the total average ink ejection speed Vm. In this case, the ink discharge speed fluctuation Vd corresponds to the average of the sum of square sums for each cycle time CT. That is, the ink discharge speed fluctuation Vd is expressed by the following formula 2.

  The smaller the ink discharge speed fluctuation Vd, the smaller the variation in the overall ink discharge speed over the entire cycle time CT.

  A value of half of the natural vibration period of the ink in the pressure chamber 11 determined by the shape of the head, the shape of the pressure chamber 11, the material of the pressure chamber 11, the physical properties of the ink, and the like is defined as the pressure propagation time Ta. By appropriately setting the delay time R from the expansion pulse P1 to the contraction pulse P2 of the drive pulse signal and the contraction time P of the contraction pulse P2 with the pressure propagation time Ta as a reference, the crosstalk Vc and the ink ejection speed fluctuations are set. Both Vd can be kept low over the entire cycle time.

  FIG. 4 shows an example of the influence of crosstalk in the ink jet apparatus. For example, the expansion time D of the expansion pulse P1 of the drive pulse signal is set to the pressure propagation time Ta. Further, the ratio between the delay time R of the drive pulse signal and the pressure propagation time Ta is X (= R / Ta), and the ratio between the contraction time P and the pressure propagation time Ta is Y (= P / Ta). In this case, the ink droplet ejection speed is measured for each cycle time CT while varying the delay time R and the contraction time P of the drive pulse signal.

  The crosstalk Vc is calculated based on the result of this measurement and Equation 1, and the value of Vc, which is the calculation result, is plotted as contour lines by statistical analysis software such as Minitab (registered trademark) of the Structural Planning Laboratory. Thereby, a contour plot (first contour plot) 401 as shown in FIG. 4 can be generated. In the example of FIG. 4, the range where Vc is smaller than 0.8 is indicated by the innermost light-colored region 402. The numerical value “0.8” is determined by the design concept and is a value that can be arbitrarily set.

  FIG. 5 shows an example of the discharge speed fluctuation in the ink jet apparatus. The ejection speed fluctuation Vd is calculated based on the measurement result of the ink droplet ejection speed for each cycle time CT and Equation 2, and the value of Vd, which is the calculation result, is plotted as a contour line by statistical analysis software, for example. Thereby, a contour plot (second contour plot) 501 as shown in FIG. 5 can be generated. In the example of FIG. 5, the range where Vd is smaller than 0.8 is indicated by the innermost light-colored region 502. The numerical value “0.8” is determined by the design concept and is a value that can be arbitrarily set.

  FIG. 6 shows a contour map 601 in which the first contour plot 401 in FIG. 4 and the second contour plot 501 in FIG. 5 are overlaid.

  The contour map 601 has a region 602 in which Vc is smaller than 0.8 and Vd is smaller than 0.8. The approximate ellipse 603 can be extracted by approximating this region 602 to an elliptic equation. The approximate ellipse 603 is formed in a region 602 where Vc is smaller than 0.8 and Vd is smaller than 0.8. That is, when P / Ta and R / Ta corresponding to the coordinates inside the approximate ellipse 603 are set, both the crosstalk Vc and the speed fluctuation Vd are less than preset values (0.8 in this example). become.

The approximate ellipse 603 is expressed by Equation 3, for example.

  As described above, the time D of the expansion pulse P1 of the drive pulse signal is set to the pressure propagation time Ta, the ratio X (= R / Ta) between the delay time R of the drive pulse signal and the pressure propagation time Ta, and the drive pulse By setting R and P satisfying Equation 3 when the ratio of the signal contraction time P to the pressure propagation time Ta is Y (= P / Ta), the crosstalk Vc is less than 0.8 over the entire cycle time. And the ink discharge speed fluctuation Vd can be suppressed to less than 0.8.

  In this embodiment, the voltage waveform of the drive pulse signal (specifically, the drive times D, R, and P) is determined based on the pressure propagation time Ta depending on the physical properties of the ink, the shape of the head, and the like. That is, the drive pulse energization waveform (D, R, P) is optimized based on the value of the pressure propagation time Ta. As a result, crosstalk and ink ejection speed can be optimized even in a driving environment where residual pressure vibration exists as the cycle time CT is shortened, and the influence of residual pressure vibration can be reduced. When this crosstalk is reduced, there is a difference in ink discharge speed and ink discharge amount between a case where a plurality of adjacent pressure chambers 11 are driven for dot printing and a case where the adjacent pressure chambers 11 are not driven for dot printing. Get smaller. Accordingly, dot position deviation and dot diameter variation can be suppressed in the print result dot pattern, and the print quality is improved.

  Further, the meniscus instability can be eliminated by reducing the ink discharge speed fluctuation. Thereby, the fluctuation | variation of the discharge speed of an ink drop can be suppressed. Further, it is possible to prevent the ink from entraining bubbles at the nozzle tip. As a result, it is possible to prevent ink droplets from being ejected, ejection of extra ink droplets after ejection of ink droplets, or ejection of ink from a nozzle as a liquid column. As a result, it is possible to provide an inkjet apparatus and an inkjet method that eject ink droplets more stably.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Inkjet head, 2 ... Drive voltage generation part, 10 ... Actuator, 11 ... Pressure chamber, 12 ... Partition, 13 ... Nozzle, 14 ... Diaphragm, 15 ... Electrostrictive member, 16 ... Common ink chamber, 17 ... Ink supply Mouth, 18 ... ink tank, 401 ... first contour plot, 402 ... region, 501 ... second contour plot, 502 ... region, 601 ... contour map, 602 ... region, 603 ... approximate ellipse.

Claims (3)

A plurality of inkjet nozzles that eject ink as ink droplets;
A plurality of pressure chambers respectively communicating with the plurality of inkjet nozzles and adjacent to each other via a partition;
An ink supply unit for supplying the ink to the plurality of pressure chambers;
And an inkjet head including a plurality of actuators that change the volumes of the plurality of pressure chambers in response to an applied voltage;
A drive voltage generator for periodically applying a drive voltage, which is a drive pulse signal for applying pressure vibration for ejecting the ink for dot printing, to each of the plurality of actuators;
With
The drive pulse signal includes an expansion pulse that expands the volume of the pressure chamber by an expansion time D, and a contraction pulse that contracts the volume of the pressure chamber by a contraction time P after a delay time R from the expansion pulse. When the pressure propagation time Ta is a half value of the natural vibration period of the ink generated in the pressure chamber,
The extension time D is set to the pressure propagation time Ta,
The ratio X (= R / Ta) between the delay time R and the pressure propagation time Ta and the ratio Y (= P / Ta) between the contraction time P and the pressure propagation time Ta are 67Y ² + 58X ² −147Y−, respectively. Inkjet device satisfying 179X + 74XY <−144. The ratio X (= R / Ta) between the delay time R and the pressure propagation time Ta and the ratio Y (= P / Ta) between the contraction time P and the pressure propagation time Ta are influenced by driving of adjacent pressure chambers. Satisfying 67Y ² + 58X ² −147Y−179X + 74XY <−144 where the crosstalk indicating the size of the ink is less than a predetermined value and the ink discharge speed fluctuation indicating the magnitude of the variation in the ejection speed of the ink droplets is less than the predetermined value The inkjet apparatus according to claim 1, wherein the inkjet apparatus is set as follows. A plurality of ink jet nozzles that eject ink as ink droplets; a plurality of pressure chambers that are respectively connected to the plurality of ink jet nozzles through a partition wall; and an ink supply unit that supplies the ink to the plurality of pressure chambers. And an inkjet head including a plurality of actuators that change the volumes of the plurality of pressure chambers in response to an applied voltage, and a drive voltage that is a drive pulse signal that applies a pressure vibration for ejecting the ink for dot printing. A drive voltage generator that periodically applies to each of a plurality of actuators, and an inkjet method used in an inkjet device comprising:
The drive pulse signal includes an expansion pulse that expands the volume of the pressure chamber by an expansion time D, and a contraction pulse that contracts the volume of the pressure chamber by a contraction time P after a delay time R from the expansion pulse. When the pressure propagation time Ta is a half value of the natural vibration period of the ink generated in the pressure chamber,
The extension time D is set to the pressure propagation time Ta,
The ratio X (= R / Ta) between the delay time R and the pressure propagation time Ta and the ratio Y (= P / Ta) between the contraction time P and the pressure propagation time Ta are 67Y ² + 58X ² −147Y−, respectively. An ink jet method satisfying 179X + 74XY <−144.