JP2004168054A - Inkjet print head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a print head in which cavities are arranged in a matrix form, with good cross-talk from surrounding cavities and good image quality in which dot displacement is not felt.
SOLUTION: The number of layers of the piezoelectric element is N, the number of active layers of the piezoelectric element is A, an angle of 90 ° or less among internal angles in the virtual lattice including the cavity is α [°], and the occupied area of the virtual lattice is Spin [mm]. ² ], when the occupied area of the cavity is Scav [mm ² ], and the occupied area of the active portion in the piezoelectric element provided in the cavity is Spzt [mm ² ], the relational expression (1) shown below is satisfied. Set the angles and dimensions of each part.
K0 ・ N ^a0・ A ^b0・ α ^c0・ Spin ^d0・ (Scav / Spin) ^e0・ (Spzt / Scav) ^f0 ≤ 0.1 (1)
However, a0 = 1.87686, b0 = 0.31786, c0 = -0.18649, d0 = -1.09273, e0 = 3.97019, f0 = 0.93332, and K0 = 0.05307.
[Selection diagram] FIG.

Description

  The present invention relates to an inkjet printhead that discharges ink onto a recording medium, and more particularly, to an inkjet printhead in which a plurality of cavities that hold ink are arranged in a matrix.

  An ink jet type print head (hereinafter simply referred to as a print head) supplies ink to a plurality of cavities (pressure chambers) from an ink tank containing the ink via a manifold (supply path), and is provided in each of the cavities. By selectively applying pressure to each cavity by the provided piezoelectric element, ink is ejected from an ejection nozzle formed in communication with each cavity. In a print head, since it is required to improve the image quality and definition of an image to be printed, it is necessary to narrow the arrangement pitch of the ejection nozzles.

  Along with this, in a print head, it is required that components such as a piezoelectric element and a cavity associated with a discharge nozzle are also densely arranged. When the components are densely arranged as described above, when a specific cavity is pressurized and ink droplets are ejected, the pressing force propagates also to the cavity adjacent to the cavity to be pressurized, and the pressure is applied to the adjacent cavity. However, there is a problem that the ejection characteristics of the cavity are affected, that is, crosstalk occurs.

  In order to solve this problem, Patent Literature 1 discloses a print head including a diaphragm that forms at least one surface of a liquid chamber to which a discharge nozzle communicates, wherein the diaphragm is a laminate of a resin film and a SUS (Steel Use Stainless) material. It is disclosed that crosstalk is reduced by setting the thickness T of the resin film within the range of 0.035 * W <T <0.065 * W with respect to the width W of the liquid chamber in the width direction. ing.

JP 2000-334946 A

  However, although the technique disclosed in Patent Document 1 is considered to be effective in a print head in which the ejection nozzles are arranged in a line, the cavities are arranged in a matrix in order to arrange the ejection nozzles at a higher density. The validity of the printheads located in this area is questionable. In a print head in which cavities are arranged in a matrix, crosstalk is affected not only by cavities adjacent in one direction but also by all adjacent cavities, so that the influence of crosstalk on image quality is further increased. growing. Therefore, the technique disclosed in Patent Document 1 is considered to be less effective for a print head in which cavities are arranged in a matrix.

  The present invention has been made in view of the above-described problems, and in a print head in which cavities are arranged in a matrix, crosstalk from neighboring cavities is reduced, and misalignment of printed pixels (dots) is performed. It is an object of the present invention to provide an ink-jet printhead capable of obtaining a high-quality output result that does not make the user feel the image.

An ink jet print head according to claim 1 of the present invention is an ink jet print head that ejects ink to a recording medium, and is provided in each of the plurality of cavities holding the ink and each of the cavities. A plurality of piezoelectric elements that press each of the cavities, and discharge nozzles that are arranged in a matrix on the ink discharge surface and that communicate with each of the cavities, wherein the number of layers of the piezoelectric element is N, The number of active layers of the piezoelectric element is A, the angle of 90 ° or less among the internal angles in the virtual lattice including the cavity is α [°], the occupied area of each virtual lattice is Spin [mm ² ], and each of the cavities is of the area occupied Scav [mm ^2], the occupied area of the active portion of the piezoelectric element provided in each of the cavities when the Spzt [mm ^2], a relational expression shown below (9 And it is characterized in that it satisfies the.

K0 ・ N ^a0・ A ^b0・ α ^c0・ Spin ^d0・ (Scav / Spin) ^e0・ (Spzt / Scav) ^f0 ≤ 0.1 （9）
However, [a0 = 1.87686, b0 = 0.31786, c0 = -0.18649,
d0 = -1.09273, e0 = 3.97019, f0 = 0.93332, K0 = 0.05307].

An ink jet print head according to a seventh aspect of the present invention is an ink jet print head that ejects ink to a recording medium, wherein a plurality of cavities holding the ink and a plurality of cavities are provided. A plurality of piezoelectric elements that press each of the cavities, and discharge nozzles that are arranged in a matrix on the discharge surface of the ink and that communicate with each of the cavities. N, the number of active layers of the piezoelectric element is A, the angle of 90 ° or less among the internal angles in the virtual lattice including the cavity is α [°], the occupied area of each virtual lattice is Spin [mm ² ], and the cavity is each Scav area occupied by the [mm ^2], the occupied area of the active portion of the piezoelectric element provided in each of the cavities when the Spzt [mm ^2], the relationship shown below And it is characterized in that it satisfies (10).

^{K0 '· N a0' · A} b0 '· α c0' · Spin d0 '· (Scav / Spin) e0' · (Spzt / Scav) f0 '≦ 0.1 (10)
However, [a0 '= 1.55486, b0' = 0.27907, c0 '= 1.03986
d0 '=-0.97015, e0' = 4.24397, f0 '= 1.03880, K0' = 0.00013].

  In the ink jet print head according to the present invention, since the angles and dimensions of the respective parts are set so as to satisfy the predetermined relational expression, for all the cavities adjacent to the predetermined cavity, the reason will be described later in detail. , It is possible to obtain a high-quality output result in which the positional deviation of printed pixels (dots) is not felt.

  Hereinafter, examples showing embodiments of the present invention will be described with reference to the drawings. Hereinafter, a print head 1 according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a plan view of the print head 1 as viewed from a bottom surface serving as an ink ejection surface, and FIG. 2 is an enlarged view of a region surrounded by a chain line drawn in FIG. FIG. 3 is an enlarged view of a region surrounded by a chain line drawn in FIG. 2, and FIG. 4 is a sectional view of a main part of the print head shown in FIG.

  The print head 1 is used for moving and scanning the print head itself, which has been widely used in the past, with respect to a recording medium, or a print head for a so-called line printer having one or several rows of discharge nozzles for discharging ink. Unlike this, a structure in which a large number of ejection nozzles are arranged in a matrix on the ejection surface of the ink is adopted. The print head 1 is fixed without moving and scanning, and discharges ink from each of a large number of discharge nozzles to a recording medium passing at a very high speed, thereby forming a high-definition and high-quality image. It has the ability to print very fast.

  In the following, the direction in which the recording medium passes through the print head 1 is referred to as “sub-scanning direction”, and the direction orthogonal to the sub-scanning direction is defined as “main scanning direction”.

  As shown in FIG. 1, the print head 1 according to the present embodiment has a rectangular shape extending in one direction (main scanning direction), and is arranged in two rows in a staggered manner on the bottom surface. In addition, a plurality of trapezoidal ink ejection areas 2 are provided. That is, each ink ejection area 2 is arranged at a position shifted by a predetermined amount from the adjacent ink ejection area 2.

  A large number of ejection nozzles 8 (see FIGS. 2 and 3) are arranged on the surface of the ink ejection area 2 as described later. An ink reservoir 3 is formed inside the print head 1 along the longitudinal direction. The ink reservoir 3 communicates with an ink tank (not shown) for accommodating ink through an opening 3a provided at one end thereof, and is filled with ink when the print head 1 is used. In the ink reservoir 3, two openings 3 b are provided in a staggered manner along the extending direction of the ink reservoir 3 in a region where the ink ejection region 2 is not provided.

  As shown in FIGS. 1 and 2, the ink reservoir 3 is connected to a manifold 5 as an ink supply path disposed in a lower layer (an inner side of the print head 1 with respect to the ink ejection surface) through an opening 3 b. Communicating. The opening 3b may be provided with a filter for capturing dust and the like contained in the ink. The manifold 5 has a structure in which a tip end branches into two sub-manifolds 5a. Two sub-manifolds 5a are connected to the upper portion of one ink ejection region 2 from two openings 3b located on both sides of the ink ejection region 2 in the longitudinal direction (main scanning direction) of the print head 1 respectively. That is, a total of four sub-manifolds 5 a extend along the longitudinal direction of the print head 1 in each ink ejection area 2. Each sub-manifold 5a is filled with ink supplied from the ink reservoir 3.

  Further, on the surface of the ink ejection area 2, as shown in FIGS. 2 and 3, a number of ejection nozzles 8 are arranged. As shown in FIG. 4, each of the discharge nozzles 8 has a tapered shape on the ink discharge surface side, and communicates with the sub-manifold 5a via a cavity (pressure chamber) 10 and an aperture 12 each having a substantially rhombic planar shape. are doing.

  In the print head 1, the above-described structure allows the ink tank (not shown) to reach the cavity 10 via the ink reservoir 3, the manifold 5, the sub-manifold 5 a, and the aperture 12, and further, to form the ink flow path 32. An ink flow path to the discharge nozzle 8 through the ink passage is formed. The central axis of the ink flow path 32 extends inside the print head 1 so as to intersect perpendicularly with the plane including the cavity 10.

  In FIGS. 2 and 3, for convenience of illustration, the cavities 10 and the apertures 12 provided inside the ink ejection region 2 are indicated by solid lines, but these cavities 10 and the apertures 12 are actually It is not visible from the ink ejection surface.

  Further, as shown in FIG. 3, the print head 1 is disposed in the ink ejection area 2 in a state where the aperture 12 communicating with one cavity 10 overlaps with the cavity 10 adjacent to the cavity 10. The cavities 10 are arranged in a very dense state. Such a structure has a structure in which the print head 1 has a laminated structure including a plurality of plate members 21 to 30, and the cavity 10 and the aperture 12 are disposed on different planes of the plate members, as shown in FIG. It is possible.

  Here, the laminated structure of the print head 1 will be described. That is, as shown in FIG. 4, the print head 1 has a trapezoidal actuator unit 21 as a whole having piezoelectric elements provided corresponding to each of the cavities 10, and a through hole serving as the cavity 10. A cavity plate 22, a base plate 23 provided with communication holes corresponding to both ends of the cavity 10, an aperture plate 24 formed with another communication hole communicating with the communication hole of the base plate 23 and the aperture 12, A communication hole that forms a wall of the sub-manifold 5a and communicates with another communication hole to form a part of the ink flow path 32, and a communication hole that connects one end of the aperture 12 and the sub-manifold 5a are provided. Supply plate 25, a through hole forming the sub-manifold 5 a, and a substantially circular through hole forming the ink flow path 32. And three cover plates 29, 27, and 28 each having a hole, and a cover plate 29 that forms another wall of the sub-manifold 5a and has a through hole that connects the ink flow path 32 to the discharge nozzle 8. And a discharge nozzle plate 30 on which the discharge nozzles 8 are formed.

  A large number of cavities 10 are arranged in a matrix form (lattice form) in a dense form. In each cavity 10, an ink flow path 32 is extended to the discharge nozzle 8 while displacing in the direction of ink flowing in the cavity 10.

  The sub-manifolds 5a extend inside the print head 1 along the rows formed by the cavities 10 arranged in a matrix in the main scanning direction of the print head 1. The cavities 10 in the row adjacent to the sub-manifold 5a are arranged so as to overlap a part of the sub-manifold 5a in the thickness direction (depth direction) of the print head 1.

  As described above, the print head 1 can arrange the cavities 10 at an extremely high density by densely arranging the three elements such as the cavity 10 and the aperture 12 constituting one ink jet. Thus, a high-resolution image can be formed on a recording medium by the print head 1 having a relatively small exclusive area.

  Each of the cavities 10 is located in the ink ejection area 2 on the plane shown in FIGS. 2 and 3 and is a main scanning direction in which the print head 1 extends (hereinafter, also referred to as a “first arrangement direction”). .) And a direction slightly inclined from the width direction (sub-scanning direction) of the print head 1 (hereinafter, referred to as a “second arrangement direction”). The discharge nozzles 8 are arranged at an interval corresponding to 37.5 dpi (that is, 37.5 nozzles per inch) in the first arrangement direction. In the present embodiment, when the nozzle rows formed by disposing the discharge nozzles 8 in this manner are viewed in the second arrangement direction (substantially in the sub-scanning direction), 16 nozzle rows are arranged adjacent to each other. Is established. That is, the cavities 10 are arranged so as to include a maximum of 16 cavities in two adjacent ink ejection areas 2 in the second arrangement direction. Further, since the sixteen cavities 10 are arranged in the second arrangement direction, the displacement between the cavities 10 located at both ends in the second arrangement direction corresponds to one width of the cavities 10 in the first arrangement direction. ing. As a result, the print head 1 has 16 discharge nozzles 8 in a range separated by a distance between two discharge nozzles 8 adjacent in the first arrangement direction within the entire width (length in the sub-scanning direction). Is set to In addition, at both ends of each ink ejection region 2 in the first arrangement direction, the structure is such that the above-described setting is satisfied by being complementary with the ink ejection region 2 facing the print head 1 in the main scanning direction. ing.

  The print head 1 configured as described above, when printing on a recording medium, has a large number of recording heads arranged in the first arrangement direction and the second arrangement direction with respect to the recording medium moved at a high speed in the sub-scanning direction. By sequentially ejecting ink droplets from the ejection nozzles 8, printing can be performed at 600 dpi in the main scanning direction, and a high-definition image can be printed.

  In the print head 1, since a large number of cavities 10 are arranged in a matrix as described above, in order to obtain a high-quality output result in which the positional displacement of printed pixels (dots) is not felt, It is necessary to consider the influence of the talk. Here, “crosstalk” means that when a specific cavity 10 is pressurized and an ink droplet is ejected, a pressing force propagates also to the cavity 10 adjacent to the cavity 10 to be pressurized. This is a phenomenon in which the ejection characteristics of the adjacent cavities 10 are affected.

  In addition, as the “crosstalk” to be considered, for example, there can be mentioned several types of crosstalk such as acoustic fluid crosstalk. By setting the angles and dimensions of the respective components constituting the head 1 so as to satisfy predetermined conditions, it is possible to reduce the crosstalk of the rigid body.

  Therefore, in the following, the angles and dimensions to be set for each part of the print head 1 will be described based on the results of analysis using the physical model shown in FIGS.

  First, a physical model in a case where printing is performed on a recording medium (paper) using the print head 1 is shown in FIG. As shown in FIG. 5, the ejection speed of the ink droplet ejected from the predetermined ejection nozzle 8 of interest in the print head 1 as the analysis target is v1, and the ejection speed of the ink droplet ejected from the neighboring ejection nozzle 8 adjacent to the analysis target ejection nozzle 8 is v1. It is assumed that the ejected ink droplet has a velocity of v2.

  At this time, when the ejection speed of the ink droplets ejected from the two ejection nozzles 8 is the same (v1 = v2), the position of each ejection nozzle in the print head 1 and the position of the ink droplet landed on the paper 41 are determined. The relative positional relationship is the same. That is, in this case, each ink droplet ejected from the two ejection nozzles is shifted by a position corresponding to the transport amount of the paper 41 moving within the arrival time from the landing position at rest when the paper 41 is stationary. Will land.

  However, when the ejection speeds of the ink droplets ejected from the two ejection nozzles 8 are different (v1 ≠ v2), the ink droplets having a low ejection speed are required to reach the paper surface in comparison with the ink droplets having a high ejection speed. Since a long time is required, the paper 41 moves by the lengthened arrival time and deviates from the normal landing position. That is, due to the difference in the ejection speed of each ink droplet, a deviation occurs between the landing position when the paper 41 is stationary and the actual landing position in each ink droplet.

  From the above, assuming that the transport speed of the paper 41 as the recording medium is vp and the distance (gap) between the print head 1 and the paper 41 is G, the difference Δt in the arrival time of the ink droplet ejected from each ejection nozzle 8 is Δt. Can be represented by the following relational expression.

Δt = G ・ (1 / v2-1 / v1)
Assuming that the difference between the deviation amount of the ink droplets ejected from the ejection nozzle 8 of interest and the surrounding ejection nozzles from the normal impact position is the impact accuracy q, and the paper transport speed is vp, the impact accuracy q Can be represented by the following relational expression.

q ≧ Δt ・ vp = G ・ (1 / v2-1 / v1) ・ vp = G ・ vp / v1 ・ (v1 / v2-1)
By modifying the above relational expression, the following relational expression (A) can be obtained.

v2 / v1 ≧ G ・ vp / (q ・ v1 + G ・ vp)… (A)
Here, the volume change amount of the piezoelectric element of the actuator unit 21 corresponding to the discharge nozzle 8 of interest is dVc, and the volume change amount of the piezoelectric element corresponding to the surrounding discharge nozzle 8 with respect to the volume change amount of the piezoelectric element corresponding to the discharge nozzle 8 of interest. Assuming that the difference between the volume changes is the volume change difference dVs, there is a relationship shown in FIG. 7 between the volume change dVc and the volume change difference dVs. In FIG. 7, the relationship between the voltage V applied to the piezoelectric element of the actuator unit 21 and the discharge speed of ink from the discharge nozzle 8 and the volume change (PZT volume change) dV of the piezoelectric element is also shown. . Since the voltage V and the volume change dV are substantially proportional, the following relational expression can be obtained based on the relation shown in FIG.

v2 / v1 = (dVc-dVs) / dVc = 1-dVs / dVc
Therefore, when the above relational expression is substituted into the relational expression (A), the following relational expression can be obtained.

dVs / dVc ≤ 1-G ・ vp / (q ・ v1 + G ・ vp) = q ・ v1 / (q ・ v1 + G ・ vp)
Here, when the values of the above variables are vp = 846.7 mm / s, G = 1 mm, v1 = 9 m / s, for example, in order to suppress the landing accuracy q to 5 μm, it is necessary to set dVs / dVc ≦ 5.0%. For example, a result is obtained in which it is necessary to satisfy dVs / dVc ≦ 9.6% in order to suppress the landing accuracy q to 10 μm. In other words, by setting the landing accuracy within the above range, it is possible to suppress a shift in the landing position of each ink droplet.

  In the description of the present example, the above dVs / dVc is defined as the crosstalk received by the cavity from the surrounding cavity adjacent to the cavity of interest, that is, the surrounding crosstalk F0.

  The cavities 10 adjacent to each other in the first arrangement direction, which is a direction orthogonal to the paper conveyance direction, are often driven to eject ink droplets at the same time. For this reason, when focusing on the specific cavity 10, the crosstalk component received from the cavity adjacent to the noted cavity 10 in the first arrangement direction is higher than the crosstalk component received from the cavity adjacent to the other direction. Considered large.

  Therefore, the crosstalk received by the cavity from the cavity adjacent to the cavity of interest in the first arrangement direction, that is, the adjacent crosstalk F0 ′ is defined as F0 ′ = dVv / dVc. As shown in FIG. 6, dVv is an amount related to the volume change of the piezoelectric element corresponding to the cavity adjacent to the cavity of interest in the first arrangement direction. Here, the amount (change amount difference) corresponds to the difference in the volume change amount of the piezoelectric element corresponding to the adjacent cavity with respect to the volume change amount of the piezoelectric element corresponding to the cavity of interest.

The number of active layers of the piezoelectric elements provided in the actuator unit 21 is A, the occupied area of each virtual grid including the cavity is Spin [mm ² ], and the occupation of the active portion in the piezoelectric element provided in each cavity is Assuming that the area is Spzt [mm ² ], the deformation efficiency F1 of the cavity is defined by the following relational expression (B).

F1 = dVc / (Spzt ・ A ・ Spin)… (B)
The deformation efficiency F1 represents the efficiency of deformation when the cavity of interest is regarded as a single body. Of the terms included in the above-mentioned relational expression (B), Spzt · A is proportional to the capacitance, and therefore becomes smaller in proportion to the input power. The dVc representing the volume change amount is the desired small and the desired large, respectively. Therefore, the deformation efficiency F1 can be said to be a large function because the denominator includes a small-term term and the numerator includes a large-term term. Further, the deformation efficiency F1 is a function indicating how large a volume change can be generated in the cavity with a small area and a small driving voltage, as represented by the above-mentioned relational expression (B). is there.

  Here, further deformation efficiency F2 and deformation efficiency F3 are defined as shown in the following relational expressions (C) and (D). The deformation efficiency F2 is a function obtained by adding the influence of the total crosstalk of all the surrounding cavities adjacent to the cavity of interest to the deformation efficiency F1, and the deformation efficiency F3 is a specific arrangement for the cavity of interest. This is a function to which the influence of the crosstalk applied to the cavity from the cavity adjacent in the direction (in this example, the first arrangement direction) is added.

F2 = F1 / dVs = dVc / (dVs ・ Spzt ・ A ・ Spin)… (C)
F3 = F1 / dVv = dVc / (dVv ・ Spzt ・ A ・ Spin)… (D)
The number A of active layers represents the number of active layers sandwiched between the common electrode 34 and the drive electrode 35 connected to the ground among the piezoelectric elements forming the actuator 21 as shown in FIG. In addition, the number N of layers of the piezoelectric element indicates the number of layers of each piezoelectric material layer forming the laminated structure of the piezoelectric element. 8A shows the case where N = 2, A = 1, FIG. 8B shows the case where N = 4, A = 1, and FIG. 8C shows the case where N = 4, A = 2. 8 (d), N = 4, A = 3, FIG. 8 (e), N = 6, A = 3, FIG. 8 (f), N = 6, A = 3 FIG. 8 (g) is a schematic diagram showing the laminated structure of the piezoelectric element when N = 6 and A = 3, and FIG. 8 (h) is a schematic diagram showing the laminated structure of the piezoelectric element when N = 6 and A = 4.

  Here, among the internal angles in the virtual lattice including the cavity, an angle of 90 ° or less is α, the area occupied by the cavity is Scav, and an approximate function shown below for Fi (i = 0, 0 ′, 1, 2, 3) (E). At this time, it was assumed that the shape of the virtual grid projected on the ink ejection surface and the shape of the cavity had a similar relationship. In the print head 1 in this example, the driving voltage of the actuator unit 21 is 20 V, the thickness of one piezoelectric element material layer in the actuator unit 21 is 15 μm, the thickness of the cavity plate 22 is 50 μm, and the thickness of the base plate 23 is It is assumed to be 150 μm.

Fi = Ki ・ N ^ai・ A ^bi・ α ^ci・ Spin ^di・ (Scav / Spin) ^ei・ (Spzt / Scav) ^fi … (E)
Here, in the above approximation function (E), for each of the cases where i = 0, 0 ′, 1, 2, and 3, the parameters ai to fi and Ki obtained as a result of the approximation are shown in Table 1 below. Show.

Next, the interior angle α of the virtual grid is 30 °, 60 °, 90 °, the occupied area Spin of the virtual grid is 0.4, 0.6, 0.8 (unit: mm ² ), Scav / Spin is 0.4, 0.6, 0.8, and Spzt / Scav is The values of the surrounding crosstalk F0 = dVs / dVc and the above-mentioned values were respectively changed when the number of layers N and the number of active layers A of the piezoelectric element were changed as shown in FIG. And the value when i = 0 was determined by the approximate function (E). FIG. 9 shows the results obtained by stippling the relationship between the value of the surrounding crosstalk F0 and the value obtained by the approximation function (E) in each case obtained as a result. The solid line shown in FIG. 9 is a straight line connecting points when the value of the surrounding crosstalk F0 is equal to the value obtained by the approximation function (E).

  As is clear from FIG. 9, in the region (F0 ≦ 0.1) where the value of the surrounding crosstalk F0 is 0.10 or less, the approximation by the approximation function (E) shows a good result. Therefore, when it is desired to suppress the landing accuracy q to 10 μm or less, the value calculated by the approximation function (E) should be suppressed to about 9.6%. When it is desired to suppress the landing accuracy q to 5 μm or less, the value calculated by the approximation function (E) should be suppressed to about 5.0%.

  Therefore, in the print head 1, by setting the angles and dimensions of the respective parts so that the value of the approximate function (E) when i = 0 is set to 0.1 or less, the paper transport speed vp is set to vp = 846.7 mm. Even when the speed is increased to about / s, it is possible to obtain a high quality output result while minimizing the influence of crosstalk generated between adjacent cavities.

  In the print head 1, the effects described below can be obtained by setting the angles and dimensions of the respective parts so that the value of the approximation function (E), that is, the value of the crosstalk, is 0.1 or less.

  That is, for example, when printing is performed by the print head 1 with an accuracy of 600 dpi (an accuracy that is generally considered to be high quality), the interval (pitch) between pixels formed by the ejected ink droplets is about 42.3 μm. Become. Therefore, when a deviation of about ± 20 μm occurs in each pixel, the centers of gravity of adjacent pixels overlap, and when a deviation amount of about half or more of this occurs, that is, about ± 10 μm or more in each pixel When the deviation occurs, the position deviation of the dot is recognized by the sensitivity evaluation.

  Therefore, in the print head 1, it is required that the landing position of the ink droplet is ejected with an accuracy of about ± 10 μm irrespective of the resolution at the time of printing. In order to achieve such a requirement, when the head gap G is set to 1 mm and the sheet conveyance speed vp is set to 846.7 mm / s, it is necessary to suppress the crosstalk value to 0.1 or less. In other words, in the print head 1 according to the present embodiment, by setting the angles and dimensions of the respective parts so that the value of the crosstalk is 0.1 or less, the paper conveyance with a high accuracy of 600 dpi and a very high speed of 846.7 mm / s is achieved. Even when printing is performed at a high speed, it is possible to secure a good image quality that does not cause displacement of dots.

  By the way, in the print head 1, a value obtained by adding the influence of the total crosstalk of all the surrounding cavities adjacent to the cavity of interest to the deformation efficiency F1, that is, the value of the deformation efficiency F2 satisfies F2> 800. By setting the angles and dimensions of the respective parts, the actuator unit 21 can be deformed with high efficiency with respect to the electric power supplied to the piezoelectric elements without depending on the driving order of the piezoelectric elements arranged in a matrix. Will be done.

  Therefore, in the print head 1, by setting the angles and dimensions of the respective parts so that the value of the approximation function (E) when i = 2 exceeds 800, the cavity 10 can be largely displaced with little power consumption. Becomes possible. As a result, not only can the power consumption be reduced, but also, for example, by arranging more ejection nozzles in the main scanning direction and the sub-scanning direction, the printing speed can be further increased, or a larger size can be achieved. Even when printing on a recording medium (paper) is possible, not only good print quality is obtained with the landing accuracy corresponding to the generated crosstalk of 10 μm or less, but also the power consumption of the print head 1 as a whole. Can be minimized.

  Also, in the print head 1, each part is adjusted so that the value obtained by adding the influence of the crosstalk received by the cavity from the cavity adjacent to the cavity of interest in the first arrangement direction, that is, the value of the deformation efficiency F3 satisfies F3> 7000. By setting the angle and the dimension of, only the crosstalk in which the landing accuracy is as low as 10 μm or less occurs. For this reason, it is not necessary to increase the input power in accordance with the crosstalk propagating to homogenize the print quality (that is, to increase the power required to compensate for the influence of the crosstalk). Become. With this, when a particular cavity is focused on in a row of cavities adjacent in the first arrangement direction (main scanning direction), the difference in the utilization rate of the applied power is reduced at least in this row, so that attention is paid. Each actuator unit 21 in the whole cavity arranged in the first arrangement direction including the cavity is deformed with high efficiency.

  Therefore, in the print head 1, by setting the angles and dimensions of the respective parts so that the value of the approximate function (E) when i = 3 exceeds 7000, the cavity 10 can be largely displaced with little power consumption. Becomes possible.

  Next, when the value of Spzt / Scav was changed, the values F2 and F3 were calculated by setting i = 2, 3 using the approximation function (E). The results thus obtained are shown in FIGS. 10A and 10B, respectively. As is clear from FIGS. 10A and 10B, in the print head 1, the occupation area Spzt of the active portion in the piezoelectric element and the occupation of the cavity are set so as to satisfy (Spzt / Scav) <0.5. By setting the area Scav, both the relationship of F2> 800 and the relationship of F3> 7000 can be satisfied. By further consideration, the occupation area Spzt of the active portion in the piezoelectric element and the occupation area Scav of the cavity are set so as to satisfy the relationship of (Spzt / Scav) <0.55, so that the deformation efficiency F2 and the deformation efficiency F3 are set. Has been confirmed to be able to realize the print head 1 set to a more desirable value.

  Further, in this case, the occupation area Spzt of the active portion is about half of the occupation area Scav of the cavity, so that the area of the individual electrode for selectively driving the piezoelectric element of the cavity can be reduced. it can. Accordingly, it is easy to secure electrical insulation between adjacent individual electrodes, and it is possible to arrange the cavities with a higher density while reliably preventing an electrical short circuit between the individual electrodes. Can be.

  Next, the values of the deformation efficiency F2 and the deformation efficiency F3 when the number A of the active layers was changed were calculated by setting i = 2, 3 using the approximation function (E). The results are shown in FIGS. 10 (c) and 10 (d), respectively. As is clear from FIGS. 10C and 10D, by setting A = 1, both the relationship of F2> 800 and the relationship of F3> 7000 are satisfied. Therefore, it is desirable that the number of active layers provided in each cavity 10 in the print head 1 is one.

  In addition, by minimizing the number of active layers provided in the cavity 10, the total area of the electrodes provided in the actuator unit 21 can be reduced. For this reason, it is possible to reduce the amount of metal material (for example, gold, silver, platinum, etc.) that causes a high cost when manufacturing the actuator unit 21, and as a result, the cost of the actuator unit 21 can be reduced. Can be planned.

  Next, the deformation efficiency F2 and the deformation efficiency F3 when the internal angle α (unit degree) of the virtual grid is changed to 30 °, 60 °, and 90 ° are expressed as i = 2, 3 using the approximate function (E). Was calculated. The results are shown in FIGS. 11A and 11B, respectively. As is clear from FIGS. 11A and 11B, in the print head 1, by setting the internal angle α of the virtual grid within the range of 60 ° <α <90 °, F2> 800. And the relationship of F3> 7000 are both satisfied. Therefore, it is desirable to set the interior angle α of the virtual grating in the range of 60 ° <α <90 °.

  In particular, when each piezoelectric element in a plurality of cavities arranged in a matrix is driven in an order independent of the arrangement position, the change in the value of the deformation efficiency F2 with respect to the angle α is small. A highly efficient print head 1 having ejection characteristics and low crosstalk can be realized.

  Next, the deformation efficiency F2 and the deformation efficiency F3 when the value of Scav / Spin was changed were calculated by setting i = 2, 3 using the approximation function (E). The results are shown in FIGS. 11 (c) and 11 (d), respectively. As is apparent from FIGS. 11C and 11D, in the print head 1, the area occupied by the cavity Scav and the area occupied by the virtual lattice Spin satisfy the relationship of Scav / Spin <0.5. By setting to, both the relationship of F2> 800 and the relationship of F3> 7000 can be satisfied. Therefore, it is desirable that the print head 1 be set so that the area occupied by the cavity Scav and the area occupied by the virtual lattice Spin satisfy the relationship Scav / Spin <0.5.

  When assembling the print head 1, it is necessary to join the ceramic actuator unit 21 and the cavity plate 23 in which a large number of cavities 10 are formed. A predetermined load is applied. At this time, since the actuator 21 is relatively brittle, there is a possibility that cracks or cracks may occur due to physical distortion or local concentration of load. However, in the print head 1, by setting such that the relationship of Scav / Spin <0.5 is satisfied, a sufficient bonding area between the actuator unit 21 and the cavity plate 23 can be ensured. Can be prevented from occurring and the two can be securely joined to each other, and the yield at the time of assembly can be improved.

  As described above, as one embodiment to which the present invention is applied, the print head 1 based on specific drawings has been described. However, the present invention is not limited to the above-exemplified embodiment, and ink is applied to a recording medium. The present invention can be widely applied to an ink jet type print head for discharging.

FIG. 2 is a plan view illustrating an ink ejection surface of a print head exemplified as an embodiment of the present invention. FIG. 2 is an essential part enlarged schematic diagram showing an ink ejection surface of the print head and enlarging a region surrounded by a dashed line in FIG. 1. FIG. 3 is an enlarged schematic view of a main part, showing an ink ejection surface of the print head and enlarging a region surrounded by a chain line in FIG. 2. FIG. 2 is a schematic cross-sectional view illustrating a cross-sectional structure of the print head. FIG. 3A is a diagram illustrating a physical model for describing image formation by the print head, and FIG. 4A is an explanatory diagram illustrating a state in which ink droplets are ejected at different speeds on paper moving relatively to the print head; FIG. 4B is a schematic diagram illustrating landing accuracy corresponding to a difference in landing position of an ink droplet. FIG. 4A is a physical model for describing the print head, and FIG. 5A is an explanatory diagram illustrating a relationship between a virtual grid including cavities arranged in a matrix and indices related to the virtual grid; () Is a schematic diagram schematically showing a cross section of the virtual lattice. 4 is a graph showing a relationship between a discharge speed and a volume change amount of the piezoelectric element with respect to a voltage applied to the piezoelectric element in the print head. FIG. 3 is a schematic diagram showing a cross-sectional structure of an actuator unit for explaining the print head, where N is the number of piezoelectric elements and A is the number of active layers, and FIG. When 1 is set, (b) is when N = 4, A = 1, (c) is when N = 4, A = 2, (d) is when N = 4, A = 3, (E) N = 6, A = 3, (f) N = 6, A = 3, (g) N = 6, A = 3, (h) N FIG. 3 is a schematic diagram showing a laminated structure of a piezoelectric element when A = 4 and A = 4. It is a graph which shows the relationship between the value of the surrounding crosstalk obtained by analysis, and the value obtained by the approximation function. It is a graph which shows the value of F2 and F3 obtained by the approximation function when changing the value of Spzt / Scav and A, and (a) shows the value of F2 when changing the value of Spzt / Scav. A graph, (b) is a graph showing the value of F3 when the value of Spzt / Scav is changed, (c) is a graph showing the value of F2 when the value of A is changed, (d) is a graph of It is a graph which shows the value of F3 when changing a value. It is a graph which shows the value of F2 and F3 obtained by the approximation function when changing the value of (alpha) and Scav / Spin, (a) is a graph which shows the value of F2 when changing the value of (alpha), (B) is a graph showing the value of F3 when the value of α is changed, (c) is a graph showing the value of F2 when the value of Scav / Spin is changed, and (d) is a graph showing the value of Scav / Spin. It is a graph which shows the value of F3 when changing a value.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Print head 2 Ink discharge area 3 Ink pool 5 Manifold 8 Discharge nozzle 10 Cavity 21 Actuator unit 34 Common electrode 35 Drive electrode

Claims (12)

In an ink jet print head that ejects ink to a recording medium,
A plurality of cavities for holding the ink,
A plurality of piezoelectric elements respectively disposed in each of the cavities, and pressing each of the cavities,
A discharge nozzle arranged in a matrix on the discharge surface of the ink, and a discharge nozzle communicating with each of the cavities,
The number of layers of the piezoelectric element is N, the number of active layers of the piezoelectric element is A, an angle of 90 ° or less among internal angles in the virtual grid including the cavity is α [°], and the occupied area of each of the virtual grids is Spin. [mm ² ], the occupied area of each of the cavities is Scav [mm ² ], and the occupied area of the active portion in the piezoelectric element provided in each of the cavities is Spzt [mm ² ]. An ink jet print head, satisfying the relational expression (1).
K0 ・ N ^a0・ A ^b0・ α ^c0・ Spin ^d0・ (Scav / Spin) ^e0・ (Spzt / Scav) ^f0・ ≦ ・ 0.1 （１）
However, [a0 = 1.87686, b0 = 0.31786, c0 = -0.18649,
d0 = -1.09273, e0 = 3.97019, f0 = 0.93332, K0 = 0.05307]. The ink jet print head according to claim 1, wherein the following relational expression (2) is satisfied.
^{K2 · N a2 · A b2 ·} α c2 · Spin d2 · (Scav / Spin) e2 · (Spzt / Scav) f2> 800 (2)
However, [a2 = -1.87686, b2 = -1.31786, c2 = 0.18649
d2 = -0.90727, e2 = -4.97019, f2 = -1.93332, K2 = 18.84193]. The ink-jet printhead according to claim 1, wherein the angle α in the virtual grid satisfies 60 ° <α <90 °. 2. The ink jet print head according to claim 1, wherein the occupied area Spin of each of the virtual lattices and the occupied area Scav of each of the cavities satisfy the following relational expression (3). 3.
(Scav / Spin) <0.5 (3) The ink-jet printhead according to claim 1, wherein the occupied area Scav of each of the cavities and the occupied area Spzt of the active portion in the piezoelectric element satisfy the following relational expression (4).
(Spzt / Scav) <0.55 (4) The ink jet print head according to claim 1, wherein the number A of active layers of the piezoelectric element is one. In an ink jet print head that ejects ink to a recording medium,
A plurality of cavities for holding the ink,
A plurality of piezoelectric elements respectively disposed in each of the cavities, and pressing each of the cavities,
A discharge nozzle arranged in a matrix on the discharge surface of the ink, and a discharge nozzle communicating with each of the cavities,
The number of layers of the piezoelectric element is N, the number of active layers of the piezoelectric element is A, an angle of 90 ° or less among internal angles in the virtual grid including the cavity is α [°], and the occupied area of each of the virtual grids is Spin. [mm ² ], the occupied area of each of the cavities is Scav [mm ² ], and the occupied area of the active portion in the piezoelectric element provided in each of the cavities is Spzt [mm ² ]. An ink jet print head characterized by satisfying the relational expression (5).
^{K0 '· N a0' · A} b0 '· α c0' · Spin d0 '· (Scav / Spin) e0' · (Spzt / Scav) f0 '≦ 0.1 (5)
However, [a0 '= 1.55486, b0' = 0.27907, c0 '= 1.03986
d0 '=-0.97015, e0' = 4.24397, f0 '= 1.03880, K0' = 0.00013]. The ink jet print head according to claim 7, wherein the following relational expression (6) is satisfied.
^{K3 · N a3 · A b3 ·} α c3 · Spin d3 · (Scav / Spin) e3 · (Spzt / Scav) f3> 7000 (6)
However, [a3 = -1.55486, b3 = -1.27907, c3 = -1.03986
d3 = -1.02985, e3 = -5.24397, f3 = -2.03880, K3 = 7620.4]. The inkjet print head according to claim 7, wherein the angle α in the virtual grid satisfies 60 ° <α <90 °. The ink-jet printhead according to claim 7, wherein the occupied area Spin of each of the virtual gratings and the occupied area Scav of each of the cavities satisfy the following relational expression (7).
(Scav / Spin) <0.5 (7) The ink jet print head according to claim 7, wherein the occupied area Scav of each of the cavities and the occupied area Spzt of the active portion in the piezoelectric element satisfy the following relational expression (8).
(Spzt / Scav) <0.55 (8) The inkjet printhead according to claim 7, wherein the number A of active layers of the piezoelectric element is one.

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