JPH05338147A - Ink jet printer - Google Patents

Abstract

PURPOSE:To simplify a structure of an ink jet head by a method wherein a suitable ink discharge pressure is obtained by making an arranged interval of a pressure chamber dense. CONSTITUTION:A piezoelectric material 3 is provided wherein many grooves 5 of which each one end is connected to an orifice 10 and of which an inside is connected to an ink feed part and many side walls 6 which are polarized in a parallel direction with a depth direction of the grooves 5, are in parallel with each other alternately arranged. An ink jet head 1 is provided wherein a pair of electrodes 8, 9 are arranged at both ends of a polarization direction of the side wall 6 and many pressure chambers 7 are formed by blocking up an opening surface of the groove 5 by bonding a freely flexible sheet 4 set to a specific thickness to a crest part of the side wall 7. Then, a voltage impression control means is provided wherein voltage of a different polarity is impressed to the electrodes 8, 9 arranged on the side walls 6 opposed to each other via the pressure chamber 7 in order to discharge ink and to the electrodes 8, 9 arranged on the other side walls 6 positioned outside the side wall 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet printer.

[0002]

2. Description of the Related Art First, FIGS. 7 to 10 show a conventional example described in JP-A-62-56150. First, a first conventional example is shown in FIG. The piezoelectric plate 50 has a plurality of side walls 51 and a protrusion 5 having a height lower than those of the side walls 51.
2 are arranged alternately, a deep groove 53 is formed between the side wall 51 and the protrusion 52, and a cover plate 54 is joined to the top of each side wall 51, whereby between the side walls 51. A cavity 55 for storing ink is formed. Further, an electrode 56 is formed on the top of the protrusion 52,
An electrode 57 paired with these electrodes 56 is formed on one surface of the piezoelectric plate 50. In this case, the piezoelectric plate 50 is polarized in the plate thickness direction. Therefore,
By applying voltages having different potential differences to the pair of electrodes 56 and 57 corresponding to a specific cavity 55 and extending the protrusion 52 to reduce the volume of the cavity 55, the internal ink pressure is increased, and the cavity 55 has a higher pressure. Ink droplets are ejected from the orifice formed at the end portion in the longitudinal direction.

Next, a second conventional example is shown in FIGS. First, as shown in FIG. 9, a plurality of cavities 55 and side walls 51 are alternately arranged in parallel in a piezoelectric plate 50, and slits 58 are formed in the side walls 51 located between adjacent cavities 55. Are formed. At both ends of each cavity 55, a supply hole 59 and an orifice 60 connected to the ink supply section are formed. Further, as shown in FIG. 10, a long hole 61 facing the slit 58 is formed in the cover plate 54. Then, as shown in FIG. 8, the electrodes 5 are formed on both upper and lower ends of the side wall 51.
6 and 57 are formed, and the cavity 55 is closed by joining the cover plate 54 to the top of the side wall 51. In this case, the piezoelectric plate 50 is polarized in the plate thickness direction. Therefore, the pair of electrodes 56, 57 formed on the sidewalls 51 located on both sides of the specific cavity 55.
By applying voltages having different potential differences to the side walls 51 in the polarization direction and extending in the direction orthogonal to the polarization direction to reduce the volume of the cavity 55, the ink pressure inside the cavity 55 is increased. Ink droplets are ejected from the orifice 60 formed at the end portion in the longitudinal direction of the.

Further, a conventional example described in Japanese Patent Laid-Open No. 60-90770 is shown in FIGS. 11 and 12. That is, as shown in FIG. 12, the substrate 62 includes a plurality of pressure chambers 6.
3, an orifice 64 is formed at one end of these pressure chambers 63, and the other end is connected to the ink supply path 65. Further, the substrate 62 is provided with an ink supply pipe 66 that connects the ink supply path 65 to an ink supply unit (not shown). Vibration plate 6 bonded to the upper surface of the substrate 62
An electrode 68 facing the upper surface of the pressure chamber 63 is formed at 7. Further, the pressure chamber 6 is provided in the piezoelectric element 69.
3 are formed by alternately arranging a plurality of columns 70 and a plurality of grooves 71, and the electrodes 6 are formed at the lower ends of the columns 70.
The electrode 72 connected to 8 is formed, and the electrode 73 is formed on the upper surface of the piezoelectric element 69. Further, a rigid member 75 having columns 74 on both sides is provided.
An electrode 76 connected to the electrode 73 is formed on the lower surface of the electrode 5. Then, as shown in FIG.
An ink jet head is formed by sequentially joining 2, the vibration plate 67, the piezoelectric element 69, and the rigid member 75.

Therefore, by grounding the electrode 76 and applying a voltage to the electrode 68 corresponding to the specific pressure chamber 63, the support column 70 corresponding to the specific pressure chamber 63 extends, so that a part of the vibration plate 67 is formed. Is deformed and its specific pressure chamber 6
The volume of 3 is reduced, the ink pressure inside is increased, and the ink is ejected from the orifice 64.

[0006]

In the structure shown in FIG. 7, a slit 58 is formed between each protrusion 52 and each side wall 51 in order to reduce crosstalk (pressure interference between adjacent cavities 55). However, in order to reduce the volume of the cavity 55, the projection 52 is polarized in the vertical direction.
When extended to, the protrusion 52 contracts in the direction orthogonal to the polarization direction. As a result, the volume reduction of the cavity 55 becomes small, and the internal ink pressure cannot be effectively increased. If the width of the protrusion 52 is widened, the reduction rate of the volume of the cavity 55 with respect to the upward extension of the protrusion 52 can be increased, and the pressure increase value of the ink can be increased.
In this case, a large number of cavities 55 within a certain width dimension.
Cannot be arranged in high density.

In FIGS. 8 to 10, the side wall 51 is contracted in the polarization direction (vertical direction) in order to reduce the volume of the cavity 55. At this time, the side wall 51 is arranged in the width direction orthogonal to the polarization direction. Is extended, the cavity 55
The volume decrease rate can be increased to increase the ink pressure increase value. However, the slit 58 and the long hole 61 formed to reduce the crosstalk are aligned with each other while the piezoelectric plate 50 is covered with the cover plate 5.
4 must be joined, and the assembly work is difficult.

In FIGS. 11 and 12, the thickness Lg of the rigid member 75 is sufficiently thicker than the thickness of the vibration plate 67, and almost all distortion of the piezoelectric element 69 is transmitted to the vibration plate 67. Specifically, the thickness of the diaphragm 67 is 10
The thickness Lg of the rigid member 75 is set to 1 mm with respect to μm. However, since the pressure chamber 63 is filled with ink, the internal pressure should instantaneously rise by several atmospheres. Assuming that the number of pressure chambers 63 is n, the volumetric modulus of ink is K, the volumetric strain of ink is ε, the width of the column 70 of the piezoelectric element 69 is Wp, and the depth dimension is b, the pressure rise value of one pressure chamber 63. Is Δp = K · ε [pa], and the reaction force received by the piezoelectric element 69 at this time is f = Δp · Wp · b [N]. In addition, the expansion of the piezoelectric element 69 is ΔL, the pressure chamber 63
Is Dc and the width of the pressure chamber 63 is Wc, the volumetric strain of the ink is ε = Wp · ΔL · b / Wc · Dc · b = Wp · ΔL / W
c · Dc.

Next, consider the case where ink droplets are simultaneously ejected from the n pressure chambers 63. In this case, as shown in FIG. 13, it is considered that the reaction force f is applied to the n portion of the rigid member 75. The range in which this reaction force f is received varies depending on n, as in l = (2n−1) · Wp [m]. A state in which the reaction force f is applied to the n points is considered to be a distributed load, and a value obtained by converting the distributed load into a force per unit length is w = nf / l [N / m]. Deflection of the central portion of the rigid member 75 by the force w, as is revealed by machining Binran a ^{δmax = wl 4/384 · E} · I. However, E is the Young's modulus of the rigid member 75,
I is the second moment of area.

Here, depending on the rigidity of the rigid member 75, n
In the case of = 1, assuming that the bending amount δ at the center of the rigid member 75 is close to zero, the pressure increase value of one pressure chamber 63 is Δp = K · ε [pa] = K · Wp · ΔL / Wc · Dc, but when n = n, the rigid member 75 has δ at the center.
Since the pressure chamber 63 is bent with a maximum bending amount, the pressure increase value of the pressure chamber 63 is Δp ′ = K · Wp · (ΔL−δmax) / Wc · Dc. Here, if the variation in the pressure increase value is 20%, it must be Δp ′ ≧ 0.8Δp, and therefore δmax ≧ ΔL × 0.2. Further, δmax changes according to the number n of the pressure chambers 63 that pressurize at once. The change is expressed by the following equation.

[0011]

[Equation 1]

That is, even if the number n of the pressure chambers 63 to be pressurized at one time is increased, in order to reduce the bending of the rigid member 75, the rigid member 75 having extremely high rigidity must be used. Further, the substrate 62, the diaphragm 67, and the piezoelectric element 6
9 and the rigid member 75 are required, the number of parts and the number of processed parts are increased. Therefore, there is a problem that the cost becomes high.

[0013]

According to the present invention, a large number of grooves, one end of which is connected to an orifice and the inside of which is connected to an ink supply unit, are polarized in a direction parallel to the depth direction of these grooves. A plurality of side walls are provided with piezoelectric bodies alternately arranged in parallel, and electrodes that form a pair are arranged at both ends of the side walls in the polarization direction. An ink jet head is provided in which a plurality of pressure chambers are formed by joining a sheet to the top of the side wall and closing the opening surface of the groove, and the pressure chambers specified for ejecting ink are faced to each other. Voltage applying control means for applying voltages having different polarities to the electrode arranged on the side wall and the electrode arranged on the other side wall located outside the side wall. ..

[0014]

According to the present invention, by controlling the voltage application operation to the electrodes by the voltage application control means, the side wall facing the pressure chamber specified for ejecting the ink and the outside of these side walls. It is possible to reverse the expansion and contraction operation with the other side wall located at, and furthermore, since the thickness of the flexible sheet that bends due to the expansion and contraction operation of the side wall is set to a predetermined thickness, the ink should be ejected. A sufficient ink ejection pressure can be obtained by increasing the pressure rise value of the specified pressure chamber. Further, when ink of two or more pressure chambers is ejected at the same time, the voltage application control means specifies two or more pressure chambers that are not adjacent to each other, so that crosstalk between adjacent pressure chambers may occur. The impact can be reduced. Thereby, the arrangement interval of the pressure chambers can be reduced. Furthermore, since the pressure chamber can be formed only by closing the groove formed in the piezoelectric body with the flexible sheet,
The structure of the inkjet head can be simplified.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. 1 and 2 show the configuration of the inkjet head 1. The substrate 2, the piezoelectric body 3, and the film 4, which is a flexible sheet made of a resin such as polyimide, are bonded to each other. On the piezoelectric body 3, a large number of grooves 5 and a large number of side walls 6 are alternately arranged in parallel.
The piezoelectric body 3 is polarized in the plate thickness direction. In other words, the side wall 6 is polarized in a direction parallel to the depth direction of the groove 5, as shown by an arrow in FIGS. Then, the upper surface opening of the groove 5 is connected to the film 4
A large number of pressure chambers 7 are formed by being closed by. An electrode 8 is formed on one surface of the side wall 6 on the film 4 side, and an electrode 9 forming a pair with the electrode 8 is formed.
Are formed on the bottom surface of the piezoelectric body 3. In FIG. 1, the tip of the pressure chamber 7 is connected to an orifice 10. In FIG. 2, a block 11 is joined to the tip of the film 4, and an orifice plate (not shown) having the orifice 10 is fixed to the block 11.

FIG. 4 is a plan view of the piezoelectric body 3, FIG. 5 is a vertical side view thereof, and FIG. 6 is a bottom view thereof. An opening 12 is formed in a part of the groove 5. Also, as shown in FIG.
A conductive film 1 continuous with the electrode 9 is formed on the bottom surface of the piezoelectric body 3.
3 is formed. FIG. 3 shows a relationship between the piezoelectric body 3 and the substrate 2 by cutting out a part thereof. In order to connect the opening 12 to an ink supply unit (not shown) such as an ink tank, the substrate 2 is connected. The ink supply path 14 is formed. The electrode 8 is connected to a voltage application control means (not shown) via a flexible substrate 15, and the conductive film 13 is grounded via a flexible substrate 16.

Here, the thickness hf of the film 4 and the pressure chamber 7
The width t of is set to a value that satisfies the condition of the following equation.
However, Ef is the Young's modulus of the film 4.

[0018]

[Equation 2]

In such a structure, in FIG.
A case where ink is ejected from a specific pressure chamber 7a among the large number of pressure chambers 7 will be described. Here, the pressure chamber for ejecting ink is 7a, the pressure chambers on both sides thereof are 7b, 7c,
Pressure chambers 7d and 7e adjacent to both outsides thereof are defined as electrodes 7a and 8b on both sides of the pressure chamber 7a, and electrodes 8a and 8b on both sides of the pressure chamber 7a.
When it is distinguished as c and 8d, when a voltage of + V is applied to the electrodes 8a and 8b and a voltage of -V is applied to the electrodes 8c and 8d, the side walls 6 on both sides of the pressure chamber 7a extend upward and the side walls on the outer side thereof. 6 shrinks. At this time, a part of the film 4 is pressed by the extending side wall 6 and is deformed upward as shown by an imaginary line, so that the volume of the pressure chamber 7a for ejecting ink is once expanded, and the ink is supplied from the ink supply path 14. Inhale ink. The volumes of the pressure chambers 7b and 7c located on the both outer sides are reduced by the downward deformation of the film 4 accompanying the reduction of the side wall 6, and the internal pressure is gradually increased. Therefore, the ink in the pressure chambers 7b and 7c is not ejected unintentionally.

Next, when the applied voltage is suddenly turned off or the polarity of the applied voltage is switched, the side wall 6 in the expanded state abruptly returns to the original length or abruptly contracts, so that the intended pressure chamber is reduced. The volume of 7 is rapidly reduced, the internal pressure is rapidly increased, and the ink inside is ejected from the orifice 10.
On the contrary, since the pressure chambers 7b and 7c on both sides increase in volume, the ink in the ink supply passage 14 is sucked. Therefore, when ejecting ink from another pressure chamber 7 at the same time when ejecting ink from the pressure chamber 7a, at least the pressure chamber 7a
The pressure chambers 7 separated from each other by two or more are specified. Thereby, the influence of crosstalk between the adjacent pressure chambers 7 can be reduced, and the arrangement density of the pressure chambers 7 can be made dense.

As described above, by controlling the voltage application operation to the electrode 8 by the voltage application control means, the side walls 6 facing the pressure chambers 7 specified for ejecting ink, and the side walls 6 thereof. The expansion and contraction operation with the other side wall 6 located outside the can be reversed. Further, the thickness of the film 4 that is bent by the expansion and contraction of the side wall 6 is set to the pressure chamber 7
By setting the thickness to a predetermined value according to the width, the pressure rise value of the pressure chamber 7 specified for ejecting ink can be increased to obtain a sufficient ink ejection pressure. Thereby, the arrangement interval of the pressure chambers can be reduced.

Next, setting the thickness of the film 4 according to the width of the pressure chamber 7 will be described. First, in FIG. 1, when the thickness a from the bottom surface of the piezoelectric body 3 to the bottom surface of the groove 5 has an extremely small value, when a voltage is applied to a specific electrode 8, the height of the piezoelectric body 3 is l. It is considered that a potential difference is generated between both ends of the side wall 6. When the part 1 of the side wall 6 of the piezoelectric body 3 extends upward, the side wall 6 receives a force F [m] from the film 4 which hinders the extension. Assuming that the film 4 is not present, the extension amount of the side wall 6 is Δl
If [m] is set, the extension amount of the side wall 6 in that case is Δl = d ₃₃ V Formula 2 However, d ₃₃ is a piezoelectric constant in the polarization direction of the piezoelectric body 3, and V is a potential difference applied to the piezoelectric body 3. Δl = 0
The force from the film 4 as Fs [N], the side wall 6
The width h and the length b of the
[M ² ] and the Young's modulus of the piezoelectric body 3 is Ep.

The Young's modulus of the film 4 is Ef [N / m
² ], the second moment of area of the film 4 is If [m
⁴ ], the width of the pressure chamber 7 is t [m], and the thickness of the film 4 is h
When f [m] is set, the force received from the film 4 when the side wall 6 extends x [m] is generally calculated by the cantilever calculation formula as follows: F = 6 · Ef · If · x / t ³ [N] Equation 4 is obtained. Further, the amount of expansion of the side wall 6 when the force of F is applied to the side wall 6 is expressed by x = Δl− (F / Fs) Δl [m] Equation 5 From Equations 4 and 5, the actual amount of elongation is: x = t ³ · Δl · Fs / (Fs · t ³ + 6 · Ef · If · Δl) Equation 6

The change in the width h of the side wall 6 of the piezoelectric body 3, that is, the amount of contraction Δh is represented by Δh = d ₃₁ (h / l) V Formula 7. However, d ₃₁ is a piezoelectric constant in a direction orthogonal to the polarization direction of the piezoelectric body 3, and V is a potential difference applied to the piezoelectric body 3.

The length b of the side wall 6 is much larger than the height 1 and the width h of the side wall 6, and if it is calculated as constant here, it is calculated when the voltage applied to the electrode 8 is zero. The volume V ₀ of the pressure chamber 7 is as follows: V ₀ = l · t · b [m ³ ] Formula 8 When a voltage is applied to the electrode 8, the volume Vx of the pressure chamber 7 is represented by Vx = (l + x) {t + Δh−νh (Δl−x) / l} b [m ³ ] Formula 9 where ν is a Poisson's ratio. If the voltage is set to zero from this state, film 4
The volume of the pressure chamber 7 does not return to V ₀ due to the bending of the pressure chamber 7. That is, assuming that the volume of the pressure chamber 7 at this time is Vy, the volume change of Vy−V _{0 is} the volume change due to the bending of the film 4.

The relationship between the volume change Vy-V ₀ and the pressure increase value Δp of the pressure chamber 7 is Δp = 60 · Ef · hf ³ (Vy−V ₀ ) / b · t ⁵ [pa] Equation 10 Become. This is the distributed load w = Δp · b on the beam fixed at both ends.
It is a calculation formula in a state where [N / m] is applied.

The pressure rise value is also expressed as Δp = K (Vx−Vy) / Vx [pa] Equation 11, and from Equation 10 and Equation 11,

[0028]

[Equation 3]

Is satisfied. Therefore, by substituting the equation 12 into the equation 11, the pressure increase value Δp of the pressure chamber 7 can be obtained. Specifically, the following data are given as parameters.

Young's modulus of piezoelectric body 3 Ep = 6.01 × 10 ¹⁰ [N / m ² ] Bulk modulus of ink K = 2.2 × 10 ⁹ [pa] In the direction orthogonal to the polarization direction of piezoelectric body 3. Piezoelectric constant d ₃₁ = −207 × 10 to ¹² [m / V] Piezoelectric constant in the polarization direction of the piezoelectric body 3 d ₃₃ = 410 × 10 to ¹² [m / V] Potential difference V = 120 [V] applied to the piezoelectric body 3. Height of side wall 6 of piezoelectric body 3 = 375 [μm] Width of side wall 6 of piezoelectric body h = 83 [μm] Length of side wall 6 of piezoelectric body 3 b = 18 [mm] Width of pressure chamber 7 t = 86 [μm] Young's modulus of film 4 Ef = 3.332 × 10 ⁹ [N / m ² ] Poisson's ratio ν = 0.36 Thickness of film 4 hf = 40 [μm] Pressure rise value Δp in chamber 7
Of 414 [Kpa] was obtained.

Next, consider the case where the material of the film 4 (Young's modulus Ef [N / m ² ] of the film 4) and the width t of the pressure chamber 7 are changed. The width t of the pressure chamber 7 is 40 μm, 86
Three types of μm and 180 μm are applied. As the Young's modulus Ef of the film 4, five kinds of 3.3 × 10 ⁷ to 3.3 × 10 ¹¹ are applied. Then, the pressure rise value Δp of the pressure chamber 7
Thickness hf of film 4 when ≧ 300 [Kpa]
Find out. The results are shown in Table 1.

[0032]

[Table 1]

When the atmospheric pressure is 100 [Kpa],
Pressure increase value Δp of the pressure chamber 7 required for ejecting ink
Is considered to be substantially satisfied if it is 300 [Kpa] or more. By setting the thickness hf of the film 4 so as to satisfy this condition, the film 4 can be deformed by a necessary amount due to the expansion and contraction of the side wall 6, whereby the volume of the pressure chamber 7 can be reduced by a necessary amount. A proper ink ejection pressure can be obtained by changing the pressure.

[0034]

As described above, according to the present invention, the electrode disposed on the side wall facing the pressure chamber specified for ejecting the ink and the other side wall located outside the side wall. Since the voltage application control means for applying voltages having different polarities is provided to the electrodes disposed on the electrodes, the voltage application control means controls the voltage application operation to the electrodes to specify the ink ejection. The expansion and contraction operation of the side wall facing the pressure chamber and the other side wall located outside these side walls can be reversed, and the thickness of the flexible sheet that bends due to the expansion and contraction operation of the side wall can be reversed. Since the thickness is set to a predetermined thickness, the pressure rise value of the pressure chamber specified to eject ink can be increased to obtain a sufficient ink ejection pressure, and ink in two or more pressure chambers can be simultaneously ejected. When discharging, voltage Since the pressure control means identifies two or more pressure chambers that are not adjacent to each other and is apart from each other, it is possible to reduce the influence of crosstalk between the adjacent pressure chambers, and thus to closely arrange the pressure chambers. Further, since the pressure chamber can be formed only by closing the groove formed in the piezoelectric body with the flexible sheet, there is an effect that the structure of the inkjet head can be simplified. ..

[Brief description of drawings]

FIG. 1 is a vertical sectional front view showing an embodiment of the present invention.

FIG. 2 is a perspective view.

FIG. 3 is a perspective view showing a relationship with a substrate by cutting out a part of a piezoelectric body.

FIG. 4 is a plan view of a piezoelectric body.

FIG. 5 is a vertical sectional side view of a piezoelectric body.

FIG. 6 is a bottom view of the piezoelectric body.

FIG. 7 is a vertical sectional front view showing a first conventional example.

FIG. 8 is a vertical sectional front view showing a second conventional example.

FIG. 9 is a plan view of a piezoelectric plate.

FIG. 10 is a plan view of a cover plate.

FIG. 11 is a vertical sectional front view showing a third conventional example.

FIG. 12 is an exploded perspective view.

FIG. 13 is an explanatory diagram showing a state in which a distributed load is applied to the rigid member.

[Explanation of Codes] 1 Inkjet head 3 Piezoelectric body 4 Flexible film 5 Groove 6 Side wall 7 Pressure chamber 8, 9 Electrode 10 Orifice

Claims (1)

[Claims] 1. A plurality of grooves, one end of which is connected to an orifice and the inside of which is connected to an ink supply unit, and a plurality of side walls which are polarized in a direction parallel to the depth direction of these grooves are alternately arranged in parallel. And a pair of electrodes are provided at both ends of the side wall in the polarization direction, and a flexible sheet having a predetermined thickness is joined to the top of the side wall. Then, an ink jet head having a large number of pressure chambers formed by closing the opening surface of the groove is provided, and the ink jet head is disposed on the side wall facing the pressure chambers specified for ejecting ink. An ink jet printer characterized in that voltage application control means for applying voltages having different polarities is provided to the electrode and the electrode arranged on the other side wall located outside the side wall.