JP6620685B2 - Inkjet head, inkjet recording apparatus, and inkjet head driving method - Google Patents

Description

  The present invention relates to an inkjet head, an inkjet recording apparatus, and an inkjet head driving method, and more particularly, to an inkjet head, an inkjet recording apparatus, and an inkjet head driving method capable of reducing the number of necessary power supplies.

  The ink jet recording apparatus includes a drive pulse generation circuit, and forms an image by supplying a drive pulse to the ink channel of the ink jet head from the drive pulse generation circuit. In recent years, there has been a demand for a recording apparatus with high definition and a high production rate, and in an ink jet recording apparatus, the density of ink channels has been increased and the driving speed has been increased.

  In Patent Document 1, in order to sequentially supply a plurality of drive pulses to one ink channel, the time interval between the drive pulses is gradually increased so that the natural period of the ink channel (AL: 1/2 of the acoustic resonance period). ), By using a simple drive signal, one dot is formed by a plurality of droplets ejected from one ink channel.

  Also, in non-grayscale binary printing, Patent Document 2 discloses that a time interval between drive pulses is made shorter than that at the time of gradation printing, thereby gradually amplifying the pressure in the ink channel, and printing speed. It is described to speed up.

  By the way, in order to simultaneously drive a large number of high-density ink channels at a high frequency, it is necessary to avoid the influence due to variation in characteristics of each ink channel. In general, to avoid the influence due to the variation in characteristics of each ink channel, the voltage level of the drive pulse is changed for each ink channel and the displacement amount of the piezoelectric element of the ink channel is adjusted.

JP 2002-46270 A JP 11-216880 A

  In the ink jet head, in order to avoid the influence due to the characteristic variation for each ink channel, it is necessary to use a plurality of power sources having different electromotive voltages in order to make the voltage level of the drive pulse different for each ink channel. Use of a plurality of power supplies is not preferable because it leads to a complicated and large device configuration.

  Therefore, an object of the present invention is to provide an inkjet head, an inkjet recording apparatus, and an inkjet head driving method that can reduce the number of necessary power supplies.

  Other problems of the present invention will become apparent from the following description.

  The above problems are solved by the following inventions.

An inkjet head reflecting one aspect of the present invention is:
A plurality of ink channels having a nozzle and a pressure generating element corresponding to the nozzle;
A drive pulse generating circuit for supplying a drive pulse to the plurality of ink channels and discharging droplets from the nozzles of each ink channel;
The drive pulse generation circuit applies a plurality of ejection pulses having the same voltage level and a pulse width of 1.0 to 1.6 AL to 1.9 AL to 2.1 AL for each ink channel within one pixel period. Are sequentially supplied at a time interval of, and a droplet is ejected by each ejection pulse, and one dot is formed by a plurality of droplets ejected from one ink channel,
The discharge pulse supplied to one ink channel and the discharge pulse supplied to another ink channel having different characteristics fall from the start of one pixel cycle for at least one discharge pulse with respect to the same drawing data. The elapsed time from the start of one pixel period to the dot formation time is different between the droplets ejected from the one ink channel and the droplets ejected from the other ink channel. It is characterized by being substantially equal.

Further, an inkjet recording apparatus reflecting one aspect of the present invention,
At least one inkjet head according to the present invention;
And a conveying unit that conveys a recording medium on which dots ejected by ink ejected from each nozzle land in a certain direction at a constant speed.

Further, an inkjet head driving method reflecting one aspect of the present invention includes:
For a plurality of ink channels having nozzles and pressure generating elements corresponding to the nozzles, the drive pulse generation circuit causes the voltage level to be equal and the pulse width to be within the range of 1.0 to 1.6 AL within one pixel period. A plurality of ejection pulses are sequentially supplied at a time interval of 1.9AL to 2.1AL, and droplets are ejected from the nozzles of each ink channel by each ejection pulse, and a plurality of droplets ejected from one ink channel. 1 dot is formed,
The discharge pulse supplied to one ink channel and the discharge pulse supplied to another ink channel having different characteristics fall for at least one discharge pulse from the start of one pixel cycle for the same drawing data. The elapsed time from the start of one pixel period to the dot formation time is different between the droplets ejected from the one ink channel and the droplets ejected from the other ink channel. It is characterized by being substantially equal.

  According to the present invention, it is possible to provide an inkjet head, an inkjet recording apparatus, and an inkjet head driving method capable of reducing the number of necessary power supplies.

Schematic diagram showing the configuration of an ink jet recording apparatus provided with a line-type head block The figure which shows the example of arrangement | positioning of the head block of a head unit Diagram showing the relationship between head block outline, discharge width and staggered arrangement Diagram showing an example of shear mode type head block The figure explaining an example of the volume change of an ink channel Block diagram illustrating an example of a drive pulse generation circuit Graph explaining an example of drive pulse Graph explaining another example of drive pulse Graph explaining yet another example of drive pulse Graph explaining yet another example of drive pulse A diagram showing an example of a so-called MEMS type head block Graph showing one discharge pulse Graph explaining an example of a conventional ejection pulse The graph explaining an example of the ejection pulse of an Example

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

<Configuration of inkjet recording apparatus>
The present invention is suitably applied to an ink jet recording apparatus including an ink jet head that discharges ink from a nozzle by raising the pressure in an ink channel filled with ink by a pressure generating element.

  The ink channel includes a space filled with ink, a nozzle that communicates the space with the outside, and a pressure generating element that corresponds to the nozzle. In order to increase the pressure in the ink channel by the pressure generating element, a driving pulse is supplied to the ink channel by the driving pulse generation circuit. In the ink channel, the supplied driving pulse is input to the pressure generating element. In the present invention, the ink jet head includes a drive pulse generation circuit and a head block including an ink channel to which drive pulses are supplied from the drive pulse generation circuit. Of the drive pulses, a pulse for ejecting ink from the ink channel is referred to as an ejection pulse, and a pulse for not ejecting ink from the ink channel is referred to as a non-ejection pulse.

  In the present invention, any of various specific configurations (arrangements) for increasing the pressure in the ink channel can be employed, regardless of the specific configuration (arrangement). The ink jet recording apparatus to which the present invention is applied may be of various known types such as a line type and a serial type. Hereinafter, the present invention will be described in detail by taking a line type ink jet recording apparatus as an example.

  FIG. 1 is a schematic diagram illustrating a configuration of an inkjet recording apparatus 1 including a line-type head block.

  The long recording medium 10 wound in a roll shape is fed out in the direction of arrow X from the unwinding roll 10A by a driving means (not shown) and conveyed. Note that the arrow X direction also indicates the conveyance direction of the recording medium 10 in all the following drawings.

  The long recording medium 10 is supported by the back roll 20 and conveyed. To this recording medium 10, ink is ejected from the head unit 30 based on the drawing data, and image formation is performed. The head unit 30 has a plurality of head blocks 31 arranged in the width direction of the recording medium 10 corresponding to the required ejection width. If the required ejection width can be secured by the single head block 31, the number of head blocks 31 may be one.

  FIG. 2 shows an arrangement example of the head block 31 of the head unit 30. In this example, all the head blocks 31 are arranged at the same height with respect to the intermediate tank 40 that temporarily stores ink. Since the discharge width that can be discharged by one head block 31 is narrower than the outer dimensions of the head block 31, a plurality of head blocks 31 are arranged in a staggered manner in the conveyance direction of the recording medium 10 in order to discharge without gaps. In the example shown in FIG. 2, a plurality of head blocks 31 corresponding to the ejection width are arranged in two rows in a staggered manner in the width direction of the recording medium 10.

  FIG. 3 shows the relationship among the outer shape, ejection width, and staggered arrangement of the head block 31. The number of head blocks 31 and the number of rows in a staggered arrangement are appropriately set according to the ejection width of the head block 31 and the like, and are not limited to the example of FIG.

  As shown in FIG. 1, the ink is supplied to each head block 31 through a plurality of ink tubes 43 from an intermediate tank 40 that adjusts the back pressure of the ink in the head block 31. In this description, the ink tube 43 in the figure is a plurality of ink tubes.

  Ink is supplied to the intermediate tank 40 from a storage tank 50 that stores ink through a supply pipe 51 by a liquid feed pump P disposed in the middle of the supply pipe 51.

  The recording medium 10 on which the image is formed is dried by the drying unit 1000 and taken up by the take-up roll 10B. The drying unit 1000 does not need to be provided if there is no problem with natural drying.

  The head block 31 performs image recording when the recording medium 10 is transported in the transport direction in a stationary state. While the recording medium 10 is being transported, a drive pulse based on the drawing data is supplied for each pixel period, and ink is ejected.

  Each head block 31 is arranged with the nozzle surface facing the recording surface of the recording medium 10, and a drive pulse generating circuit (not shown here) that generates a drive pulse via a flexible cable (not shown here). ) Is electrically connected.

[Configuration of head block]
FIG. 4 is a view showing an example of a shear mode type head block 31 provided in the ink jet recording apparatus 1. FIG. 4 (a) is a perspective view showing a cross section of the appearance, and FIG. 4 (b) is a side view. FIG. In FIG. 4, 310 is a head chip, and 22 is a nozzle plate bonded to the front surface of the head chip 310.

  In the present specification, a surface on the side where ink is ejected from the head chip 310 is referred to as a “front surface”, and a surface on the opposite side is referred to as a “rear surface”. In addition, the outer surfaces located above and below in the figure across the channels arranged in parallel in the head chip 310 are referred to as “upper surface” and “lower surface”, respectively.

  The head chip 310 has a channel row in which a plurality of ink channels 28 partitioned by a partition wall 27 are arranged in parallel. Here, the channel row has 512 ink channels 28, but the number of ink channels 28 constituting the channel row is not limited at all.

  Each partition wall 27 includes a piezoelectric element such as PZT which is an electric / mechanical conversion means as a pressure generating element. In the present embodiment, each partition wall 27 is composed of two piezoelectric materials 27a and 27b having different polarization directions. However, the piezoelectric material only needs to be in at least a part of each partition wall 27 and may be arranged so that each partition wall 27 can be deformed.

  The piezoelectric material used for the piezoelectric materials 27a and 27b is not particularly limited as long as it is deformed by applying a voltage, and a known material is used. The piezoelectric material may be a substrate made of an organic material, but a substrate made of a piezoelectric non-metallic material is preferable. Examples of the substrate made of a piezoelectric non-metallic material include a ceramic substrate formed through processes such as molding and firing, and a substrate formed through coating and lamination processes. Examples of the organic material include organic polymers and hybrid materials of organic polymers and inorganic materials.

As the ceramic substrate, there are PZT (PbZrO ₃ -PbTiO ₃ ) and third component added PZT, and the third component is Pb (Mg _1/3 Nb _2/3 ) O ₃ , Pb (Mn _1/3 Sb _{2 / 3} ) O ₃ , Pb (Co _1/3 Nb _2/3 ) O ₃ or the like, and further formed using BaTiO ₃ , ZnO, LiNbO ₃ , LiTaO ₃ or the like.

  In this embodiment, two piezoelectric materials are used by being bonded so that the polarization directions are opposite. As a result, the amount of shear deformation is doubled compared to the case of one piezoelectric material. Is advantageous in that the drive voltage can be ½ or less.

  On the front surface and the rear surface of the head chip 310, an opening on the front surface side and an opening on the rear surface side of each ink channel 28 are opened. Each ink channel 28 is a straight type whose size and shape are not substantially changed in the length direction from the opening on the rear surface side to the opening on the front surface side.

  One end of the ink channel 28 is connected to the nozzle 23 formed in the nozzle plate 22, and the other end is connected to the ink tube 43 through the common ink chamber 77 and the ink supply port 25.

  An electrode 29 made of a metal film is formed in close contact with the entire inner surface of each ink channel 28. The electrode 29 in the ink channel 28 is electrically connected to a drive pulse generation circuit (not shown here) via the connection electrode 300, the anisotropic conductive film 78 and the flexible cable 6.

When a drive pulse is supplied to the ink channel 28 from the drive pulse generation circuit, the drive pulse is applied between the electrodes 29 in the ink channel 28. Then, the partition wall 27 made of a piezoelectric element is bent and deformed at the boundary between the upper wall portion 27a and the lower wall portion 27b. Due to the bending deformation of the partition wall 27, a pressure wave is generated in the ink channel 28, and a pressure for ejecting from the nozzle 23 is applied to the ink in the ink channel 28.

  FIG. 5 is a cross-sectional view taken along the line vv in FIG. 4B and is a diagram for explaining an example of the volume change of the ink channel.

  As shown in FIG. 5A, in a state where no driving pulse is applied to any of the electrodes 29A, 29B, 29C in the ink channels 28A, 28B, 28C adjacent to each other (steady state), the partition walls 27A, 27B, Neither 27C nor 27D is deformed.

  In order to expand the volume of the ink channel 28 from the steady state, an expansion pulse (+ V) is used as a drive pulse. When the electrodes 29A and 29C of the ink channels 28A and 28C adjacent to the ink channel 28B to be expanded are grounded and the expansion pulse (+ V) from the drive pulse generation circuit is applied to the electrode 29B of the ink channel 28B to be expanded, the ink to be expanded In both the partition walls 27B and 27C of the channel 28B, slippage deformation occurs in the joint surfaces of the upper wall portion 27a and the lower wall portion 27b, respectively. As a result, as shown in FIG. 5B, both the partition walls 27B and 27C are bent and deformed toward each other to expand the volume of the ink channel 28B to be expanded. Due to this bending deformation, a negative pressure wave is generated in the ink channel 28B, and ink from the common flow path can flow into the ink channel 28B.

  On the other hand, a contraction pulse (−V) is used as a drive pulse in order to contract the volume of the ink channel 28 from the steady state. The electrodes 29A and 29C of the ink channels 28A and 28C adjacent to the ink channel 28B to be contracted are grounded, and when the contraction pulse (−V) from the drive pulse generating circuit is applied to the electrode 29B of the ink channel 28B to be contracted, the electrodes 29A and 29C are contracted. In both the partition walls 27B and 27C of the ink channel 28B, the deformation of the joint surfaces of the upper wall portion 27a and the lower wall portion 27b occurs in the direction opposite to the above-described expansion. As a result, as shown in FIG. 5C, both the partition walls 27B and 27C are bent and deformed toward each other, and the volume of the ink channel 28B to be contracted is contracted. By this bending deformation, a positive pressure wave is generated in the ink channel 28 </ b> B, and ink can be ejected from the corresponding nozzle 23.

  It should be noted that a positive pressure wave is also generated in the ink channel 28 when the volume of the ink channel 28 shown in FIG. 5B is expanded from the steady state to return to the steady state shown in FIG. Generated and ink can be ejected.

  In the ink channel 28 shown in FIG. 5, since the adjacent ink channels 28 cannot be expanded or contracted simultaneously, so-called three-cycle driving is also preferable. In the 3-cycle drive, all the ink channels are divided into three groups and the adjacent ink channels are time-division controlled.

  The present invention can also be applied to a so-called independent type ink jet head in which ejection channels and channels that do not perform ejection (dummy channels) are alternately arranged. In an independent type ink jet head, adjacent ink channels can be expanded or contracted simultaneously, so that it is not necessary to perform three-cycle driving, and independent driving can be performed.

  The embodiment described below can be similarly applied to an inkjet head driven by three cycles and an inkjet head driven independently.

<Configuration of drive pulse generation circuit>
FIG. 6 is a block diagram illustrating an example of a drive pulse generation circuit.

  In FIG. 6, reference numeral 502 denotes a memory in which drawing data that is a basis of a drive pulse is stored. Reference numeral 504 denotes a drive pulse generation circuit that generates a drive pulse based on the drawing data. Reference numeral 503 denotes a power source. Reference numerals 31a and 31b denote first and second head blocks.

  The first head block 31a and the second head block 31b have different characteristics such as piezoelectric characteristics and resonance period. Here, the sensitivity of the first head block 31a is relatively higher than that of the second head block 31b. Therefore, when only one ejection pulse having the same width is supplied, the velocity of the droplet ejected from the first head block 31a is relatively higher than the velocity of the droplet ejected from the second head block 31b. Fast.

  Based on the drawing data stored in the memory 502, the drive pulse generation circuit 504 generates a drive pulse in which the electromotive voltage value of the power source 503 is set to the drive voltage value. The drive pulse generation circuit 504 supplies each drive pulse to the plurality of ink channels 28 of the head block 31 within one pixel period. For example, using the example described above, the drive pulse generation circuit 504 passes through the flexible cable 6, the connection electrode 300, and the electrode 29 in the ink channel to each of the piezoelectric elements included in the partition wall 27 within one pixel period. Then, each drive pulse is input.

  FIG. 7 is a graph for explaining an example of the drive pulse. In the graph, the vertical axis represents voltage and the horizontal axis represents time. On the vertical axis, G is the ground potential (reference potential), and V is the power supply voltage.

  In this ink jet head, as shown in FIG. 7, within one pixel period, the drive pulse generation circuit 504 applies the same voltage level V to the ink channel 28 of each head block 31a, 31b, and the pulse width is 1.0 to. A plurality of ejection pulses P-1a, P-2a, P-1b, and P-2b within the range of 1.6AL are sequentially supplied at a time interval of 1.9AL to 2.1AL. A plurality of ejection pulses P-1a and P-2a are supplied to the first head block 31a, and a plurality of ejection pulses P-1b and P-2b are supplied to the second head block 31b.

  In each of the ejection pulses P-1a, P-2a, P-1b, and P-2b, since the electromotive voltage supplied from the power source 503 is the peak value voltage V, it is not necessary to use a plurality of voltages. Therefore, in the head blocks 31a and 31b, the number of necessary power supplies can be reduced, and unevenness in heat generation is reduced.

  Here, the pulse is a rectangular wave having a constant voltage peak value, and when the ground potential G is 0% and the peak voltage V is 100%, the rise time between 10% and 90% of the voltage, Each of the fall times refers to a waveform that is within ½, preferably within ¼ of AL (Acoustic Length). AL is an abbreviation for Acoustic Length, and is 1/2 of the acoustic resonance period of the pressure wave in the ink channel 28. AL measures the flying speed of a droplet discharged when a rectangular wave drive signal is applied to the drive electrode, and changes the pulse width of the rectangular wave while keeping the rectangular wave voltage value constant. It is determined as the pulse width that maximizes the droplet flight speed. The pulse width is defined as the time between 10% rise from the ground potential G and 10% fall from the peak voltage V. However, in the present invention, the drive pulse is not limited to a rectangular wave, and may be a trapezoidal wave or the like.

  An expansion pulse is a pulse that causes the volume of the ink channel to expand from the volume in a steady state. As shown in FIG. 7, the expansion pulse is a pulse that changes the voltage from the ground potential G to the peak voltage V, holds the peak value voltage V for a predetermined time, and then changes the voltage to the ground potential G again. A contraction pulse is a pulse that causes the volume of the ink channel to contract from the volume in a steady state. Although not shown, the contraction pulse is a pulse that changes the voltage from the ground potential G to the peak voltage -V, holds the peak value voltage -V for a predetermined time, and then changes the voltage to the ground potential G again.

  Then, at the fall of each ejection pulse P-1a, P-2a, P-1b, P-2b, a droplet is ejected from the nozzle 23 of each ink channel 28, and a plurality of inks ejected from one ink channel 28 are discharged. One dot is formed by the droplet. That is, a plurality of droplets are ejected from each ink channel 28 of the first head block 31a by a plurality of ejection pulses P-1a and P-2a. Dots are formed. In addition, a plurality of droplets are ejected from each ink channel 28 of the second head block 31b by a plurality of ejection pulses P-1b and P-2b. Dots are formed.

  Here, as an aspect in which one dot is formed, a plurality of separated liquid droplets are ejected from one ink channel 28, and they fly while separated and land on the same or close positions on the recording medium. A mode of merging or a mode in which a plurality of separated droplets are ejected from one ink channel 28, and these are united or linked while flying, and landed and united at the same or close positions on the recording medium. Or a mode in which a plurality of droplets are ejected from one ink channel 28 in a linked state, and these are united or linked while flying, and land and unite at the same or close positions on the recording medium. However, “one dot formation” in the present invention includes all these modes.

  The ejection pulses P-1a and P-2a supplied to the ink channel 28 of the first head block 31a and the ejection pulses P-1b and P- supplied to the ink channel 28 of the second head block 31b having different characteristics. In 2b, the time from the start of one pixel cycle to the fall is different for at least one ejection pulse with respect to the same drawing data.

  As a result, a dot is formed from the beginning of one pixel cycle with a droplet ejected from the ink channel 28 of the first head block 31a and a droplet ejected from the ink channel 28 of the second head block 31b. The elapsed time until time is approximately equal. Since the elapsed time from the start of one pixel period to the dot formation is substantially equal, the dot formation positions on the recording medium 10 are also aligned in the head blocks 31a and 31b. In the present invention, “the elapsed time from the start of one pixel period to the time of dot formation is substantially equal” means that the error of the dot formation position (droplet landing position) on the recording medium 10 is the set resolution. On the other hand, it means that the time difference is within a range that is within half a pixel. This time difference is relatively determined by the set resolution, the conveyance speed of the recording medium 10, and the like.

  In this ink jet head, it is not necessary to use drive pulses of different voltage levels, and therefore it is not necessary to use a plurality of power supplies. Since it is not necessary to use a plurality of power supplies, the device configuration can be simplified and downsized. In addition, since a plurality of power supplies are not used, uneven heat generation does not occur. Further, in this ink jet head, each head block 31a, 31b has a different time from the start of one pixel period to the fall of at least one ejection pulse, so that the cross between the head blocks 31a, 31b is different. The effect of talk is reduced.

  In this embodiment, the start of one pixel cycle is the rise of the discharge pulses P-1a and P-1b supplied first. However, since the start of one pixel cycle can be detected by a clock signal (not shown), it does not have to be at the rising edge of the ejection pulse.

  In FIG. 7, only the last ejection pulses P-2a and P-2b among the plurality of ejection pulses P-1a, P-2a, P-1b, and P-2b that are sequentially supplied from the start of one pixel cycle. The time until the fall is different. That is, the last ejection pulse P-2a supplied to the first head block 31a has a wider pulse width than the last ejection pulse P-2b supplied to the second head block 31b. The time from the start of the cycle to the fall is different and the discharge timing is delayed. The droplets ejected from the first head block 31a have a velocity component larger than that of the droplets ejected from the second head block 31b. Therefore, the second head block 31b catches up with the delay of the ejection timing. Dots are formed simultaneously with the discharged droplets.

  FIG. 8 is a graph for explaining another example of the drive pulse. In the graph, the vertical axis represents voltage and the horizontal axis represents time. On the vertical axis, G is the ground potential (reference potential), and V is the power supply voltage.

  In this ink jet head, as shown in FIG. 8, only the first ejection pulses P-1a and P-1b among the plurality of ejection pulses P-1a, P-2a, P-1b, and P-2b that are sequentially supplied. For the above, the pulse width may be varied to vary the time from the start of one pixel cycle to the fall. That is, the first ejection pulse P-1a supplied to the first head block 31a has a wider pulse width than the first ejection pulse P-1b supplied to the second head block 31b. The time from the start of the cycle to the fall is different, and the discharge timing is delayed. The droplets ejected from the first head block 31a have a velocity component larger than that of the droplets ejected from the second head block 31b. Therefore, the second head block 31b catches up with the delay of the ejection timing. Dots are formed simultaneously with the discharged droplets.

  FIG. 9 is a graph for explaining still another example of the drive pulse. In the graph, the vertical axis represents voltage and the horizontal axis represents time. On the vertical axis, G is the ground potential (reference potential), and V is the power supply voltage.

  In this ink jet head, as shown in FIG. 9, at least one of the plurality of discharge pulses P-1a, P-2a, P-1b, and P-2b that are sequentially supplied is only at the fall time. Instead, the time from the start of one pixel cycle may be varied at the time of rising. In this case, the start of one pixel cycle is detected by a clock signal (not shown). Also in this case, the discharge timing of the first head block 31a is later than that of the second head block 31b. The droplets ejected from the first head block 31a have a velocity component larger than that of the droplets ejected from the second head block 31b. Therefore, the second head block 31b catches up with the delay of the ejection timing. Dots are formed simultaneously with the discharged droplets.

  FIG. 10 is a graph for explaining still another example of the drive pulse. In the graph, the vertical axis represents voltage and the horizontal axis represents time. On the vertical axis, G is the ground potential (reference potential), and V is the power supply voltage.

  In this inkjet head, as shown in FIG. 10, a non-ejection pulse P-3 is supplied before or after a plurality of ejection pulses P-1a, P-2a, P-1b, P-2b that are sequentially supplied. Also good. The non-ejection pulse P-3 is not limited to the contraction pulse shown in FIG. 10, but may be an expansion pulse although not shown. When the peak voltage of this non-ejection pulse P-3 is different from the peak voltage of each ejection pulse P-1a, P-2a, P-1b, P-2b, the power supply for the non-ejection pulse P-3 Must be used separately from the power supply for each ejection pulse.

  In each of the embodiments described above, the example in which the ejection pulse supplied within one pixel period is two pulses has been described. However, the present invention is not limited to this, and the ejection pulse supplied within one pixel period is 3 There may be more than one pulse.

  In addition, each of the above-described embodiments corresponds to the difference in characteristics of the head block that occurs due to manufacturing variation or the like, but is not limited to this, and can correspond to, for example, a difference in characteristics of ink. In this application, “another ink channel having different characteristics” means not only a case where the ink channel itself has a characteristic difference, but also a difference in the characteristics of the ink channel due to the difference in the characteristics of the supplied ink. This includes cases where

  For example, a relatively high voltage is generally required for ejecting ink with high viscosity. According to the present invention, even when discharging inks having different viscosities, by changing the time from the start of one pixel cycle to the fall of the discharge pulse without changing the peak voltage of the discharge pulse, The dot formation positions can be aligned. That is, even when a plurality of types of ink are mixed in one ink jet head, the dot formation positions can be aligned without increasing the number of necessary power supplies.

  Also, when using high density ink such as white ink, the speed of pressure waves propagating through the ink is different, so the AL value is also different, and the operation for the same ejection pulse is different from when using color ink. There is. Even in such a case, according to the present invention, by changing the time from the start of one pixel cycle to the fall of the discharge pulse without changing the peak voltage of the discharge pulse, the dot formation position Can be aligned. That is, according to the present invention, it is possible to reduce the influence of variations in ink characteristics.

[Other Embodiment (1)]
FIG. 11 is a view showing an example of a so-called MEMS type head block 31c in which a plurality of ink channels are two-dimensionally arranged. FIG. 11 (a) is a cross-sectional view seen from the side, and FIG. It is the bottom view which looked at the nozzle surface from the bottom.

   As shown in FIG. 11A, the so-called MEMS type head block 31 c has an ink manifold 70 that constitutes a common ink chamber 71. The opened bottom of the ink manifold 70 is closed by the upper substrate 75. The common ink chamber 71 is filled with ink.

   A lower substrate 76 is disposed below the upper substrate 75 in parallel with the upper substrate 75. A plurality of piezoelectric elements 80 are arranged between the upper substrate 75 and the lower substrate 76. A drive pulse is applied to these piezoelectric elements 80 via a wiring pattern (not shown) formed on the lower surface of the upper substrate 75. Corresponding to each of these piezoelectric elements 80, a plurality of pressure chambers 73 are provided. These pressure chambers 73 are through holes formed in the lower substrate 76, and the upper part is closed by the corresponding piezoelectric element 80 and the bottom part is closed by the nozzle plate 79. The nozzle plate 79 is bonded to the lower surface of the lower substrate 76.

   Each pressure chamber 73 has a bottom portion through an injection hole 72 formed through the upper substrate 75 and the lower substrate 76 corresponding to each pressure chamber 73 and a groove formed in the upper surface of the nozzle plate 79. It communicates with the common ink chamber 71. The ink in the common ink chamber 71 is supplied into each pressure chamber 73 via a groove formed in the upper surface of the injection hole 72 and the nozzle plate 79. Each pressure chamber 73 communicates outward (downward) via a nozzle 74 formed in the nozzle plate 79 corresponding to each pressure chamber 73.

   In the head block 31 c, when a drive pulse is applied to the piezoelectric element 80, the volume of the corresponding pressure chamber 73 changes (shrinks), and the ink in the pressure chamber 73 moves outward (through the nozzle 74). Discharged downward).

   In the head block 31c, as shown in FIG. 11B, the nozzles 74 are two-dimensionally arranged on the lower surface of the nozzle plate 79. The piezoelectric elements 80 are also two-dimensionally arranged corresponding to the nozzles 74.

  The head block 31 c constitutes an ink jet together with a drive pulse generation circuit that supplies a drive pulse to the piezoelectric element 80. In the ink jet recording apparatus, the head blocks 31c are arranged in one or a plurality of rows and used.

  In order to apply the present invention to the head block 31c, one pixel cycle for at least one ejection pulse with respect to the same drawing data for a plurality of head blocks 31c according to the difference in characteristics of each head block 31c. Different time from the start to the fall. Alternatively, the piezoelectric elements 80 corresponding to a plurality of adjacent nozzles 74 arranged in one or a plurality of rows are taken as one set, and the first to nth sets (where n is an integer of 2 or more) A, B, C ... n. Then, the time from the start of one pixel cycle to the fall is made different for at least one ejection pulse with respect to the same drawing data in accordance with the difference in characteristics of each set of piezoelectric elements 80. In this way, the present invention can be applied in the same manner as the above-described embodiment.

[Other embodiment (2)]
In the above embodiment, the inkjet head may be configured as a droplet discharge device that discharges liquid other than ink. The liquid here may be any material that can be discharged from the droplet discharge device. For example, it may be in a state in which the substance is in a liquid phase, such as a liquid with high or low viscosity, sol, gel water, other inorganic solvents, organic solvents, solutions, liquid resins, liquid metals (metal melts ). Further, not only a liquid as one state of a substance but also a substance in which particles of a functional material made of a solid such as a pigment or a metal particle are dissolved, dispersed or mixed in a solvent is included. Typical examples of the liquid include ink and liquid crystal as described in the above embodiment. Here, the ink includes general water-based inks and oil-based inks, and various liquid compositions such as gel inks and hot melt inks.

  Specific examples of the droplet discharge device include, for example, a material such as a liquid crystal display, an EL (electroluminescence) display, a surface emitting display, and an electrode material and a color material used for manufacturing a color filter in a dispersed or dissolved form. There is a droplet discharge device that discharges liquid as droplets. Further, it may be a droplet discharge device that discharges bio-organic matter used for biochip manufacturing, a droplet discharge device that discharges a liquid that is used as a precision pipette, and serves as a sample. In addition, a transparent resin liquid such as UV curable resin is used to form a droplet ejection device that ejects lubricating oil pinpoint to precision machines such as watches and cameras, and hemispherical lenses (optical lenses) used in optical communication elements. May be a droplet discharge device that discharges the liquid onto the substrate. In addition, a droplet discharge device that discharges an etching solution such as an acid or an alkali to etch a substrate or the like may be used.

  FIG. 12 is a graph showing one ejection pulse, in which the vertical axis represents voltage and the horizontal axis represents time. On the vertical axis, G is the ground potential (reference potential), and V is the power supply voltage.

  In this embodiment, the first head block 31a and the second head block 31b are head blocks having the same configuration and AL of 4.0 μs. The first head block 31a is relatively more sensitive to the actuator than the second head block 31b due to manufacturing variations. That is, when only one ejection pulse having the same pulse width is supplied, the droplet ejected from the first head block 31a has a velocity component higher than the droplet ejected from the second head block 31b. Is big. As shown in FIG. 12, when the ejection pulse P-0 having a pulse width of 4.0 μs (1AL) is supplied, the velocity component of the droplet is 7.4 m / sec for the first head block 31a, The head block 31b was 6.9 m / sec.

  FIG. 13 is a graph for explaining an example of a conventional ejection pulse, in which the vertical axis represents voltage and the horizontal axis represents time. On the vertical axis, G is the ground potential (reference potential), and V is the power supply voltage.

  Next, an ejection pulse P-1a having a pulse width of 5.0 μs (1.25 AL) and an ejection pulse P-2a having a pulse width of 4.0 μs (1AL) shown in FIG. 13 are spaced at intervals of 3.0 μs (0.75 AL). It was opened and supplied to each of the first head block 31a and the second head block 31b. The time interval at the rise of each ejection pulse P-1a, P-2a is 8.0 μs (2AL).

  In the first head block 31a, the velocity component of the droplet ejected by the ejection pulse P-1a is 3.8 m / sec, and the velocity component of the droplet ejected by the ejection pulse P-2a is 7.4 m / sec. Thus, one droplet having a velocity of 5.6 m / sec was discharged. In this embodiment, a large droplet is formed by two droplets in a state where the liquid column communicates in the droplet discharge process.

  In the second head block 31b, the velocity component of the droplet ejected by the ejection pulse P-1a is 3.3 m / sec, and the velocity component of the droplet ejected by the ejection pulse P-2a is 6.9 m / sec. Thus, one droplet having a velocity of 5.1 m / sec was discharged.

  As described above, when the same two ejection pulses are supplied to the first and second head blocks 31a and 31b, the speed of the ejected droplets is different, and the elapsed time from the start of one pixel period to the dot formation time. Is different. Therefore, a difference occurs in the dot formation position, and the image quality is affected.

  FIG. 14 is a graph for explaining an example of the ejection pulse of the example, in which the vertical axis represents voltage and the horizontal axis represents time. On the vertical axis, G is the ground potential (reference potential), and V is the power supply voltage.

  Then, as shown in FIG. 14, the ejection pulse of this example is applied to the first and second head blocks 31a and 31b by ejection pulses P-1a having different times from the start of one pixel cycle to the fall. , P-1b. The same ejection pulses P-1a and P-2a as shown in FIG. 13 were supplied to the first head block 31a. Two droplets were ejected from the first head block 31a, and one droplet having a velocity of 5.6 m / sec was thereby ejected.

  In the second head block 31b, an ejection pulse P-1b having a pulse width of 4.5 μs (1.125 AL) and an ejection pulse P-2 b having a pulse width of 4.0 μs (1AL) are supplied to the second head block 31b at 3.5 μs (0.875 AL). Supplied at intervals. The time interval at the rise of each ejection pulse P-1b, P-2b is 8.0 μs (2AL). In the second head block 31b, the velocity component of the droplet ejected by the ejection pulse P-1a is 4.4 m / sec, and the velocity component of the droplet ejected by the ejection pulse P-2a is 6.9 m / sec. Thus, one droplet having a velocity of 5.6 m / sec was discharged.

  As described above, in the present invention, by using one power supply to supply ejection pulses having the same peak voltage, the first and second head blocks 31a and 31b having relatively different sensitivities have the same speed. Droplets could be ejected, and the elapsed time from the start of one pixel cycle to the dot formation could be made substantially equal. Therefore, the dot formation positions are aligned, and drawing with good image quality can be performed.

1: Inkjet recording apparatus 22: Nozzle plate 23: Nozzle 27: Partition wall 28: Channel 29: Electrode 30: Head unit 31: Head block 31a: First head block 31b: Second head block 31c: MEMS type head block 300: Connection electrode 310: Head chip 501: Control unit 502: Memory 503: Separation unit 504: Drive pulse generation circuit 6: Flexible cable

Claims (9)

A plurality of ink channels having nozzles and pressure generating elements corresponding to the nozzles;
A drive pulse generating circuit for supplying a drive pulse to the plurality of ink channels and discharging droplets from the nozzles of each ink channel;
The drive pulse generation circuit applies a plurality of ejection pulses having the same voltage level and a pulse width of 1.0 to 1.6 AL to 1.9 AL to 2.1 AL for each ink channel within one pixel period. Are sequentially supplied at a time interval of, and a droplet is ejected by each ejection pulse, and one dot is formed by a plurality of droplets ejected from one ink channel,
The discharge pulse supplied to one ink channel and the discharge pulse supplied to another ink channel having different characteristics fall from the start of one pixel cycle for at least one discharge pulse with respect to the same drawing data. The elapsed time from the start of one pixel period to the dot formation time is different between the droplets ejected from the one ink channel and the droplets ejected from the other ink channel. An ink jet head characterized by being substantially equal.   The drive pulse generation circuit includes, for only the last ejection pulse among a plurality of ejection pulses that are sequentially supplied, an ejection pulse that is supplied to one ink channel and an ejection pulse that is supplied to another ink channel having different characteristics. 2. The ink jet head according to claim 1, wherein the time from the start of one pixel period to the fall is varied.   The drive pulse generation circuit includes, for only the first ejection pulse among the plurality of ejection pulses sequentially supplied, an ejection pulse supplied to one ink channel and an ejection pulse supplied to another ink channel having different characteristics. 2. The ink jet head according to claim 1, wherein the time from the start of one pixel period to the fall is varied.   The inkjet head according to claim 1, wherein the drive pulse generation circuit supplies a non-ejection pulse before or after a plurality of ejection pulses to be sequentially supplied. At least one or more inkjet heads according to claim 1;
An ink jet recording apparatus comprising: a transport unit configured to transport a recording medium on which dots ejected by ink ejected from each nozzle land in a constant direction at a constant speed. For a plurality of ink channels having nozzles and pressure generating elements corresponding to the nozzles, the drive pulse generation circuit causes the voltage level to be equal and the pulse width to be within the range of 1.0 to 1.6 AL within one pixel period. A plurality of ejection pulses are sequentially supplied at a time interval of 1.9AL to 2.1AL, and droplets are ejected from the nozzles of each ink channel by each ejection pulse, and a plurality of droplets ejected from one ink channel. 1 dot is formed,
The discharge pulse supplied to one ink channel and the discharge pulse supplied to another ink channel having different characteristics fall for at least one discharge pulse from the start of one pixel cycle for the same drawing data. The elapsed time from the start of one pixel period to the dot formation time is different between the droplets ejected from the one ink channel and the droplets ejected from the other ink channel. A method for driving an ink jet head, characterized by being substantially equal.   Only the last of the plurality of discharge pulses that are sequentially supplied, the discharge pulse supplied to one ink channel and the discharge pulse supplied to another ink channel having different characteristics from the start of one pixel cycle 7. The method of driving an ink jet head according to claim 6, wherein the time until the falling time is made different.   From only the first ejection pulse among the plurality of ejection pulses that are sequentially supplied, the ejection pulse that is supplied to one ink channel and the ejection pulse that is supplied to another ink channel with different characteristics are from the start of one pixel cycle. 7. The method of driving an ink jet head according to claim 6, wherein the time until the falling time is made different.   9. The ink jet head driving method according to claim 6, wherein the non-ejection pulse is supplied before or after the plurality of ejection pulses to be sequentially supplied.

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