Ink-jet head device with multi-stacked PZT actuator

Abstract: An ink-jet head device using a stack of piezoelectric bodies, including a nozzle plate (11) on which at least one nozzle (12) is formed, a manifold portion (51) having a restrictor plate (41) on which at least one restrictor (40) is formed, a plurality of piezoelectric bodies (22) stacked in multiple layers and interposed between the nozzle plate and the manifold portion to form a chamber (20) for containing ink, each of the piezoelectric bodies having a cavity at the center; common electrodes (23) and driving electrodes (24) alternately interposed one by one between adjacent piezoelectric bodies, and a medium (25) interposed at least between the restrictor plate and a piezoelectric body adjacent to the restrictor plate, and between the nozzle plate and a piezoelectric body adjacent to the nozzle plate, the medium deformed corresponding to deformation of the piezoelectric bodies. In this device, the cavities of the piezoelectric bodies stacked in multiple layers are applied as the chamber for containing ink. Accordingly, the device can solve the problems of an existing bending- or pushing-type ink-jet head device using a vibrating plate, and reduce the area of the ink head device. Also, a pressure to ink increases, and the volume of the chamber can be greatly changed even at low voltage.

Description: The present invention relates to an ink-jet head device using a piezoelectric (PZT) actuator. Existing types of ink-jet printing methods used by drop on-demand systems include an electro-thermal transduction method and an electro-mechanical transduction method using a piezoelectric body. In an electro-thermal transduction method, a heat source generates bubbles in ink, and the force of the bubbles discharges the ink. Thus, the performance of discharge depends on the ingredients of ink. In an electro-mechanical transduction method using a piezoelectric body, discharge can be achieved using a volume change caused by the deformation of a piezoelectric body. Thus, this method has little restrictions on the kind of ink compared to the electro-thermal transduction method, and an ink-jet head device adopting this method is durable. An ink-jet head device using a piezoelectric body is roughly made up of a chamber in which ink supplied from an ink supplier is contained, a piezoelectric actuator for changing the volume of the chamber to drive ink to be launched, a nozzle having ink discharge holes, and driving electrodes. The ink-jet head devices using a piezoelectric body are roughly classified into a device using a bending method, a device using a pushing method, and a device using a shear deformation method. European Patent No. 0864425A1 discloses a bending-type ink-jet head device. This bending-type ink-jet head device has a structure in which a piezoelectric body deformed by voltage is formed on a vibrating plate. In this bending-type ink-jet head device, the vibrating plate is also bent when the piezoelectric body is bent, because of the structural characteristics of the vibrating plate and the piezoelectric body. This causes a volume change of an ink chamber which adjoins to the vibrating plate, and a change in the inside pressure of the ink chamber. The volume change of a chamber is required to discharge ink, and the pressure of the chamber is needed in relation to the discharge performance of ink drop. This bending-type ink-jet head device having such a structure has a trade-off between the volume change of the chamber and the pressure thereof, resulting in a limit in designing. A pushing-type ink-jet head device is disclosed in U.S. Patent No. 5,424,769, in which the volume of a chamber is changed by pushing a vibrating plate using the deformation of a piezoelectric body. In this structure, when the vibrating plate is reduced in size to obtain a high resolution, it must be greatly deformed in order to obtain a change in the volume of the chamber. This large deformation poses excessive stress to the vibrating plate, so that the vibrating plate is easily failed. In a device disclosed in U.S. Patent No. 4,395,719, a piezoelectric body is designed in a tube structure, and the interior space of the tube-typed piezoelectric body is directly used as a chamber, so that no problems are generated by a vibrating plate. However, this device must use a flexible rubber piezoelectric body. In this case, a chamber is easily deformed, but its performance is degraded for lack of a force to discharge ink. JP-A-04045945 discloses an ink-jet head device using a piezoelectric actuator with a nozzle member formed integrally with a facing partition member and a string partitioning member. Clearances in a string of a piezoelectric device are filled with a resin group material with a Young's modulus far less than that of the piezoelectric device and cured to form a partition as the string partitioning member. A side face of a cavity facing the piezoelectric device forms a partition member as the facing partition member and sticks fast to a substrate. A nozzle formation section forming a nozzle facing the cavity is formed with a pre-determined thickness and magnitude on end faces of the cavity, partition, piezoelectric device, and a housing opposite to the substrate, respectively. A first objective of the present invention is to provide an ink-jet head device using a piezoelectric actuator, which has an increased ink discharge capability. A second objective of the present invention is to provide an ink-jet head device using a piezoelectric actuator, which has a high ink discharge capability even at a low voltage. To achieve the above objectives, according to an aspect of the present invention, there is provided an ink-jet head device using a stacked piezoelectric actuator, including: a nozzle plate on which at least one nozzle is formed; a manifold portion having a restrictor plate on which at least one restrictor is formed; a plurality of piezoelectric bodies stacked in multiple layers and interposed between the nozzle plate and the manifold portion to form a chamber for containing ink, each of the piezoelectric bodies having a cavity at the center; common electrodes and driving electrodes alternately interposed one by one between adjacent piezoelectric bodies; and a medium interposed at least between the restrictor plate and a piezoelectric body adjacent to the restrictor plate, and between the nozzle plate and a piezoelectric body adjacent to the nozzle plate, the medium deformed corresponding to deformation of the piezoelectric bodies. The above objectives and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: FIG. 1 is a perspective view schematically illustrating an ink-jet head device using a multi-stacked piezoelectric actuator, according to a first embodiment of the present invention; FIG. 2 is an exploded perspective view schematically illustrating the ink-jet head device using a multi-stacked piezoelectric actuator of FIG. 1; FIG. 3 is an exploded perspective view illustrating the driving portion of the ink-jet head device using a multi-stacked piezoelectric actuator of FIG. 1; FIG. 4 is a perspective view illustrating the driving portion of the ink-jet head device using a multi-stacked piezoelectric actuator of FIG. 1; FIG. 5 is a plan view of a modification of the piezoelectric body applied to the ink-jet head device using a multi-stacked piezoelectric actuator of FIG. 1; FIG. 6 is a plan view of another modification of the piezoelectric body applied to the ink-jet head device using a multi-stacked piezoelectric actuator of FIG. 1; FIG. 7 is a cross-sectional view of a modification of a piezoelectric body in the driving portion of an ink-jet head device using a multi-stacked piezoelectric actuator; FIG. 8 is a cross-sectional view of a modification of a piezoelectric body without a medium in the driving portion of an ink-jet head device using a multi-stacked piezoelectric actuator; FIG. 9 is a plan view of a modification of a medium not optimized upon deformation of a piezoelectric body in the ink-jet head device using a multi-stacked piezoelectric actuator of FIG. 10; and FIG. 10 is a plan view of a modification of a medium optimized upon deformation of a piezoelectric body in the ink-jet head device using a multi-stacked piezoelectric actuator of FIG. 10. Referring to FIGS. 1 and 2, an ink-jet head device using a stacked piezoelectric driver according to the present invention is roughly made up of a manifold portion 51, a driving portion 21 and a nozzle portion 10. A restrictor plate 41 is formed between the manifold portion 51 and the driving portion 21. Here, the restrictor plate 41 has at least one restrictor 40 having a through hole structure, the upper portion of which is wide and lower portion is narrow. The nozzle portion 10 having a nozzle plate 11 on which a nozzle 12 is formed is positioned under the driving portion 21. The manifold portion 51 includes the restrictor plate 41, manifold sidewalls 52 installed on the restrictor plate 41, and a manifold cover 53 installed on the manifold sidewalls 52. Accordingly, the manifold portion 51 provides a manifold 50 as an ink supply passage through which ink is introduced from an external ink supply source and supplied to a chamber 20 within the driving portion 21 via the restrictor plate 41 and the restrictor 40. The restrictor 40 on the restrictor plate 41 is narrowed in the direction ink is supplied, so that it acts as a passage where ink within the manifold 50 moves to the chamber 20, and that ink from the chamber 20 in the driving portion 21 is prevented from flowing backward to the manifold 50 while ink is discharged. As shown in FIG. 3, the driving portion 21 positioned between the manifold portion 51 and the nozzle portion 10 includes a plurality of axially stacked ring-shaped piezoelectric bodies 22 which have a central cavity therein, common electrodes 23 and driving electrodes 24 alternately interposed between the ring-shaped piezoelectric bodies 22, and mediums 25 interposed between the restrictor plate 41 in the manifold portion 51 and the top piezoelectric body 22 among the piezoelectric bodies 22 and between the nozzle plate 11 in the nozzle portion 10 and the lowest piezoelectric body 22. A common lead line 23a and a driving lead line 24a electrically connected to the common electrodes 23 and the driving electrodes 24, respectively, are installed on both sides of a stack of the piezoelectric bodies 22, and electrically connected to pads 54 and 55 installed on the cover 53, respectively. In the piezoelectric body stack, the mediums 25 are formed of an elastic and deformable material, so they are elastically deformed and restored by the driving of the piezoelectric bodies 22. Accordingly, the chamber 20 in the driving portion 21 is formed by the central cavities of the mediums 25 and the piezoelectric bodies 22 between the mediums 25, and the upper and bottom portions of the chamber 20 are closed by the restrictor plate 41 and the nozzle plate 11, respectively. Supply of ink into the chamber 20 is achieved through the restrictor 40 of the restrictor plate 41, and discharge of the ink is achieved through the nozzle 12 of the nozzle plate 11. Here, the medium 25 can be installed on the side of one of the restrictor plate 41 and the nozzle plate 11, but it is preferable that the medium 25 is installed on the sides of both of the restrictor plate 41 and the nozzle plate 11. Preferably, the elasticity of the mediums 25 is smaller than that of the piezoelectric bodies 22. In this structure, the piezoelectric bodies 22 and the mediums 25, which form the driving portion 21, can be formed in any shapes if they are hollowed, for example, in a rectangular frame shape, instead of the above-described ring-shaped ones. The internal cavities of the piezoelectric bodies 22 and the mediums 25 can have a circular shape, a rectangular shape, or a polygonal shape such as a pentagonal shape. The driving portion 21 must have a thickness enough to have hardness that can sufficiently generate the pressure at which ink is discharged. The stack of the piezoelectric bodies 22 and the mediums 25 is protected by fixing bodies 31. Preferably, the fixing bodies 31 have higher stiffness than that of the piezoelectric bodies 22. The fixing bodies 31 are designed so that they can surround the exterior surface of the stack, and the interior surface of the fixing bodies 31 is spaced a predetermined distance apart from the exterior surface of the stack, thus providing an isolated space 30 for coping with the deformation of the stack. The nozzle plate 11 and the restrictor plate 41 can have at least nozzle 10 and at least one restrictor 40, respectively. In the operation of the ink-jet head device according to the first embodiment of the present invention having such a structure; as shown in FIG. 4, the ink-jet head device uses the piezoelectric deformation of the piezoelectric bodies 22 caused when voltage from a power source 27 is applied to each of the piezoelectric bodies 22 via the common electrode 23 and the driving electrode 24. The deformation of the driving portion 21 causes a change in the volume of the chamber 20 within the driving portion 21, and applies a pressure to ink contained in the chamber 20, thereby discharging ink drops through the nozzle 12 of the nozzle portion 10. As shown in FIG. 3, in the driving portion 21, at least one piezoelectric body 22 is stacked in the first vertically-upward direction, and the common electrode 23 and the driving electrode 24 are alternately installed one by one on each of the stacked piezoelectric bodies. The poling direction 26 of each of the piezoelectric bodies 22 alternates the forward and backward directions of the first direction. Deformation of the piezoelectric bodies 22 caused by applied voltage is shown in FIGS. 5 and 6. FIG. 5 refers to the case when a piezoelectric body 22 is ring-shaped, and FIG. 6 refers to the case when a piezoelectric body 22 is shaped of a rectangular frame having a circular interior cavity. In FIGS. 5 and 6, reference numeral 22a denotes the piezoelectric body 22 which is not deformed, and reference numeral 22b denotes the piezoelectric body 22 which is deformed. Here, when the piezoelectric body 22 is ring-shaped as shown in FIG. 5, its deformation is a function of only the diameter of the chamber 20. Thus, the displacement depends on a change in the diameter of the chamber 20. In contrast with the above-described deformation, FIG. 7, which is a cross-sectional view of FIGS. 5 or 6 taken along line B-B, shows deformation of the piezoelectric body 22 where the displacement in the first direction and the displacement in a second direction perpendicular to the first direction have opposite aspects. That is, when the piezoelectric body 22 extends in one of the first and second direction, it contracts in the other direction. In the present invention, the volume of the chamber 20 is changed using a displacement in the second direction, and the mediums 25 and the fixing bodies 31 are used to prevent a displacement in the first direction from affecting the change in the volume of the chamber 20. FIG. 8 shows deformation of a stack of piezoelectric bodies 22, which are connected directly to the restrictor plate 41 and the nozzle plate 11 without the mediums 25 and the fixing bodies 31, when voltage is applied. In this structure, since the upper and bottom ends of the stack of the piezoelectric bodies 22 are directly connected to the restrictor plate 41 and the nozzle plate 11, the connected portions of the piezoelectric body stack to the restrictor plate 41 and the nozzle plate 11 are not deformed in the second direction, that is, in the radial direction. However, the stack of the piezoelectric bodies 22 is deformed in the first direction, thus moving the nozzle plate 11 in the first direction as shown in reference numeral 11b. The deformation 11b acts in opposite to a change in the volume of the chamber 20 due to a deformation 22b in the second direction which occurs in the middle place between the restrictor plate 41 and the nozzle plate 11. That is, a valid volume change is obtained by the difference between the deformation values 11 b and 22b, thus degrading the performance of driving. FIGS. 9 and 10 show deformation of a piezoelectric body stack provided with the mediums 25 and the fixing bodies 31, when the piezoelectric body 22 operates in consideration of the internal pressure of ink. Reference numeral 22a denotes a non-deformed piezoelectric body, and reference numeral 22b denotes a deformed piezoelectric body. FIG. 9 shows deformation of the piezoelectric body 22 when the cross-section of the mediums 25 is not optimally deformed, and FIG. 10 shows preferable deformation of the piezoelectric body 22 when the cross-section of the mediums 25 is optimally deformed. The preferable deformation of the mediums 25 depends on the elasticity coefficient of the mediums 25 and the thickness thereof in the stacking direction. When the mediums 25 have a similar material property value to rubber, the deformation of the piezoelectric body 22 efficiently acts on a change in the volume of the chamber 20. In the embodiments of the present invention shown, a chamber is given by the circular or rectangular cavities of the piezoelectric bodies, and the cavities of piezoelectric bodies stacked in multiple layers inserting electrodes between them as described above are applied as the chamber for containing ink. Accordingly, the invention can solve the problems of a bending or pushing inkjet head device using a vibrating plate, and reduce the area of the ink head device. The deformation of piezoelectric bodies to increase the volume of the chamber depends on only the size of the chamber, which is the interior space of the stacked piezoelectric bodies. The pressure given to ink during driving of the ink head device depends on only the radial thickness of each of the piezoelectric bodies. Therefore, the displacement of the piezoelectric bodies and the pressure given to the ink can increase independently. Also, stacking of piezoelectric bodies enables the volume of the chamber to be greatly changed even at low voltage. Also, the multi-layered piezoelectric body structure is polarized in the polarization direction, and a great force and a great deformation can be generated even at a low driving voltage by the use of a displacement due to a piezoelectric constant in this direction, leading to a reduction in the area of the ink-jet head device.

Claims: An ink-jet head device using a piezoelectric actuator, comprising: a nozzle plate (11) on which at least one nozzle (12) is formed; a manifold portion (51) having a restrictor plate (41) on which at least one restrictor (40) is formed; a plurality of piezoelectric bodies (22) stacked in multiple layers and interposed between the nozzle plate and the manifold portion to form a chamber (20) for containing ink, each of the piezoelectric bodies having a cavity at the center; common electrodes (23) and driving electrodes (24) alternately interposed one by one between adjacent piezoelectric bodies; and a medium (25) interposed at least between the restrictor plate and a piezoelectric body adjacent to the restrictor plate, and between the nozzle plate and a piezoelectric body adjacent to the nozzle plate, the medium deformed corresponding to deformation of the piezoelectric bodies. The ink-jet head device of claim 1, wherein a fixing body is further installed between the restrictor plate and the nozzle plate, and surrounds the piezoelectric body stack a predetermined distance apart from the stack and provides an isolation space. The ink-jet head device of claim 2, wherein the fixing body has a higher coefficient of elasticity than the piezoelectric bodies. The ink-jet head device of any one of claims 1 to 3, wherein the diameter of the nozzle gradually decreases in the direction where ink is discharged. The ink-jet head device of any one of claims 1 to 4, wherein the manifold portion comprises: sidewalls installed on both sides of the restrictor plate; and a manifold cover for covering a space over the restrictor plate defined by the sidewalls. The ink-jet head device of any one of claims 1 to 5, wherein the poling direction of a piezoelectric body is opposite to that of an adjacent piezoelectric body. The ink-jet head device of any one of claims 1 to 6, wherein the coefficient of elasticity of the medium is smaller than that of each of the piezoelectric bodies.

Inventors: JEONG HEE MOON, LEE SUK HAN, OH YONG-SOO, JEONG, HEE MOON, LEE, SUK HAN, OH, YONG-SOO, Jeong, Hee Moon,, Lee, Suk Han, Samsung Advanced Inst. Technology, Oh, Yong-soo, Samsung Advanced Inst. Technology
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 2000
Main classification: B41J2
IPC codes: B41J2