Head for ink-jet printer

Abstract: A head (20) for an ink-jet printer includes an elastic plate (26), a wall member (22) defining an ink chamber (27a, 27b) together with the elastic plate, a nozzle (28a, 28b) provided in the wall member and communicated with the chamber, and a piezoelectric element (24a, 24b). The piezoelectric element is shaped in a plate, has a side face (29a, 29b), which defines a thickness of the piezoelectric element, and is disposed such that the side face faces the elastic plate (26). The piezoelectric element presses the elastic plate at the side face by an expansion due to a piezoelectric effect in a direction (B) toward the side face. The head further includes electrodes (25a, 25b) attached to the piezoelectric element (24a, 24b) for applying an electric voltage across the piezoelectric element so as to cause the piezoelectric effect.

Description: This invention relates to a head for an ink-jet printer. Ink-jet printers are known as one kind of terminal equipment for computers. Heads for on-demand type ink-jet printers which utilize piezoelectric elements as actuators are classified into two major types, namely into bimorph-type heads and piston-type heads. Fig. 1 is a schematic cross-sectional view showing a bimorph-type head. The illustrated bimorph-type head has an ink chamber defined by stainless sheets 2 which are combined in layers, and a piezoelectric element 3. The piezoelectric element 3 has two electrode sheets 8a and 8b for application of voltage, and they are disposed to extend across the opposite flat faces of the piezoelectric element 3. An ink chamber 4 and a nozzle 5 communicate with each other through an ink supply chamber 6, and the ink supply chamber 6 also communicates with an ink supply channel 7. In general form a plurality of heads each having the above-described arrangement are disposed in opposition to the surface of a recording sheet and a plurality of the nozzles 5 are therefore arranged in opposition to the same surface. The operation of the bimorph-type head will be explained below. When a voltage is applied across the electrodes 8a and 8b of the piezoelectric element 3, the piezoelectric element 3 contracts in the transverse direction indicated by arrows 9 shown parallel to the respective electrodes 8a and 8b to deform one of the stainless sheets 2 which is attached directly to the piezoelectric element 3, thereby expelling a jet of ink droplets from the nozzle 5. Each of the heads is made to independently perform the above-described operation, thereby enabling information to be recorded. The piston-type head will be explained below. Fig. 2 is a schematic cross-sectional view showing a particular piston-type head. The illustrated piston-type head has an ink chamber 11, a piston 12 and a piezoelectric element 13. The piezoelectric element 13 has two electrode sheets 17a and 17b for application of voltage, and they are disposed to extend across the opposite flat faces of the piezoelectric element 13. The ink chamber 11 includes a cylinder 14 in which ink is accommodated. The cylinder 14 is hermetically sealed by sealing member 18, and communicates with a nozzle 15. The cylinder 14 also communicates with an ink supply channel 16. The piston 12 and the piezoelectric element 13 are inserted into the cylinder 14 for movement in the axial direction. The piston 12 and the piezoelectric element 13 are fixed in alignment with each other. A plurality of heads each having the above-described arrangement are disposed in opposition to the surface of a recording sheet. The operation of the piston-type head will be explained below. When a voltage which is beforehand applied across the electrodes 17a and 17b is removed, the piezoelectric element 13 expands in the lateral direction indicated by arrows 19 shown parallel to the electrodes 17a and 17b. The piston 12 is axially moved by the expansion of the piezoelectric element 13 to apply pressure to the ink in the cylinder 14, thereby expelling a jet of ink droplets from the nozzle 15. Each of the heads is made to independently perform the above-described operation, thereby enabling information to be recorded. In order to improve printing speed, it is desirable that the pitch of nozzles be made as narrow as possible so that a multiplicity of nozzles can be mounted. However, to reduce the nozzle pitch of the bimorph-type head shown in Fig. 1, if the dimension of the piezoelectric element 3 is reduced in the direction perpendicular to the surface of the sheet of Fig. 1, the amount of displacement of the piezoelectric element 3 is also reduced. If this amount of displacement is excessively reduced, it will be impossible to reliably expel a jet of ink droplets. In order to increase the amount of displacement of the piezoelectric element 3 whose dimension is reduced in the above-described manner, it may be applied a high voltage across the piezoelectric element 3. However, this method is accompanied by an increase in the cost of parts of the driving circuit. In order to reduce the nozzle pitch of the piston-type head shown in Fig. 2, if the dimension of the piezoelectric element 13 is reduced in the direction perpendicular to the surface of the sheet of Fig. 2, the piezoelectric element 13 will be buckled due to the reduced rigidity thereof. As a result, it will be impossible to reliably expel a jet of ink droplets. For the above-described reasons, a minimum of about 1 mm is required as the nozzle pitch of either type of head. Furthermore heads for ink jet printers are known from documents GB-A-2 047 628, JP-A-60090770 and US-A-4 115 789. In accordance with the invention there is provided a head for ink an jet printer comprising: an elastic plate (26,38); a base block (21;31) attached to one side of the elastic plate and including a base portion disposed parallel to said elastic plate (26;38); a plurality of ink chambers (27a,27b;36a,36b) on the other side of said elastic plate each defined by a region of said elastic plate and wall means (22;32) and each having a nozzle (28a,28b;37a,37b) in communication with the respective ink chamber, a plurality of plate-shaped piezoelectric elements (24a,24b;33a,33b), each having an elongate edge face (29a,29b;34a,34b) which defines the thickness of the piezoelectric element and which presses on a respective portion of the region of the elastic plate defining a respective one of the ink chambers, the portion being narrower than the region of the elastic plate defining the respective ink chamber and being disposed at a position corresponding to a respective ink chamber so as to be operable to expand toward said elastic plate due to piezoelectric effect to cause ink to be ejected from a respective one of said ink chambers; electrode means (25a,25b;34a,34b) attached to each of said piezoelectric elements for applying an electric voltage across each of said piezoelectric elements so as to cause said piezoelectric effect, characterized in that said base block further includes a plurality of plate-shaped girder portions (21a,21b,21c;31a,31b,31c) extending perpendicularly from said base portion to said one side of said elastic plate at positions corresponding to boundaries of said ink chambers defined by the wall means, each piezoelectric element being disposed between adjacent said girder portions, and in that said piezoelectric elements, said girder portions and said base portion are integrally formed. In accordance with the present invention, there is provided a head for an ink jet printer including an elastic plate, a wall member defining an ink chamber together with the elastic plate, a nozzle provided in the wall member and communicated with the chamber, and a piezoelectric element. The piezoelectric element is shaped in a plate, has a side face (elongate edge face), which defines a thickness of the piezoelectric element, and is disposed such that the side face faces the elastic plate. The piezoelectric element presses the elastic plate at the side face by an expansion due to a piezoelectric effect in a direction toward the side face. The head further includes electrodes attached to the piezoelectric element for applying an electric voltage across the piezoelectric element so as to cause the piezoelectric effect. In the head according to the present invention, the piezoelectric element presses the elastic plate at the side face when an electric voltage is applied to the piezoelectric element by use of the electrode. Then, the pressed elastic plate is deflected and applies a pressure to the ink in the ink chamber, thus producing a jet of ink droplets from the nozzle. The piezoelectric element shaped in a plate can be reduced in its thickness without reducing the amount of displacement, i.e. expansion of the piezoelectric element due to the piezoelectric effect in a direction toward the side face. Accordingly, the mounting density of the nozzle in the head can be increased by reducing the thickness of the piezoelectric element. It is an advantage of the present invention that a head for an ink jet printer which can enhance the mounting density of nozzles is provided. The above and other features and advantages of embodiments of the present invention will be apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings. Fig. 1 is a schematic cross sectional view showing the structure of a bimorph type head for an ink jet printer; Fig. 2 is a schematic cross sectional view showing the structure of a piston type head for an ink jet printer; Fig. 3 is a schematic cross sectional view showing one embodiment of the present invention; Fig. 4 is a schematic perspective view showing the embodiment of Fig. 3 in exploded form; and Fig. 5 is a schematic front elevational view showing another embodiment of the present invention. Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Fig. 3 is a schematic cross-sectional view showing one embodiment of a head for an ink-jet printer according to the present invention. Fig. 4 is a schematic perspective view showing the embodiment of Fig. 3 in exploded form. Referring to Fig. 3 and 4, a head 20 for an ink-jet printer has a base block 21, an ink chamber wall 22 and a cover plate 23. The base block 21 is made of, for example, lead titanate zirconate. Piezoelectric elements 24a and 24b are formed on the base block 21. Each of the piezoelectric elements 24a, 24b is disposed between adjacent girder portions 21a, 21b, 21c of the base block 21 and is shaped in a plate i.e. plate-shaped. In Fig. 4, the piezoelectric element 24a is provided with a pair of electrodes 25a which are disposed on both planes (sides) of the piezoelectric element 24a. The piezoelectric element 24b is provided with a pair of electrodes 25b which are disposed on both planes (sides) of the piezoelectric element 24b. Each of the piezoelectric elements 24a and 25b serves a piezoelectric lateral effect; that is to say, depending on a voltage applied across the electrodes 25a, the piezoelectric element 24a selectively expands and contracts in the direction indicated by an arrow B in Fig. 4 which is perpendicular to the electric field impressed by the electrodes 25a. In the same manner, the piezoelectric element 24b expands and contracts by use of the electrodes 25b. The piezoelectric element 24a and 24b each have a depth of 8 mm, a thickness of 0.1 mm and a height of 0.5 mm. The base block 21 and the piezoelectric elements 24a and 24b are integrally formed by recessing a single plate of lead titanate zirconate. The ink chamber wall 22 is mounted on an elastic oscillation plate 26. The oscillation plate 26 is made of, for example, stainless steel, glass or the like, while the ink chamber wall 22 is made of, for example, glass, resin or the like. The ink chamber wall 22 defined ink chambers 27a and 27b, and nozzles 28a and 28b are formed to communicate with the ink chambers 27a and 27b, respectively. The oscillation plate 26 is fixed to upper side faces (elongate edge faces) 29a and 29b of the respective piezoelectric elements 24a and 24b. Each of the side faces 29a and 29b defines the thickness of each of the piezoelectric elements 24a and 24b shaped in a plate. The cover plate 23 is provided with an ink supply opening 23a, and is made of, for example, glass. In the illustrated embodiment, the pitch of the nozzles 28a and 28b, which is indicated by a double-headed arrow A in Fig. 4, is selected to be 0.5 mm. The operation of the head 20 will now be explained with reference to Fig. 4. When a voltage which is beforehand applied across the electrodes 25a is removed, the piezoelectric element 24a expands due to its piezoelectric lateral effect in the direction indicated by the arrow B. Thus, the side face 29a presses the oscillation plate 26 to expel a jet of ink droplets from the nozzle 28a. Since the piezoelectric element 24a has a configuration which extends in the depth-wise direction, it is possible to easily cause enough change in the volume of the ink chamber 27a. The thickness of the piezoelectric element 24a, i.e., the width of the side face 29a can be reduced without reducing the amount of displacement of the piezoelectric element 24a in the direction indicated by the arrow B. The piezoelectric element 24b is operated, in the same manner as the piezoelectric element 24a, by use of the pair of electrodes 25b. Another embodiment of a head for an ink-jet printer according to the present invention will be explained below. Fig. 5 is a schematic front elevational view showing a head 30 for an ink-jet printer according to the embodiment which will be described below. In Fig. 5, the head 30 is provided with a base block 31 and a cover block 32. The base block 31 is made of, for example, lead titanate zirconate. Piezoelectric elements 33a and 33b are formed on the base block 31 between adjacent girder portions 31a 31b, 31c. Each of the piezoelectric elements 33a, 33b is shaped in a plate. The piezoelectric element 33a is sandwiched between a pair of grounding electrodes 34a made of nickel. The grounding electrodes 34a are grounded. A signal electrode 35a made of nickel is interposed in the piezoelectric element 33a. Similarly, the piezoelectric element 33b is sandwiched between a pair of grounding electrodes 34b, and a signal electrode 35b made of nickel is interposed in the piezoelectric element 33b. Each of the piezoelectric elements 33a and 33b serves a piezoelectric vertical effect; that is to say, depending on a voltage applied to the electrode 35a, the piezoelectric element 33a selectively expands and contracts in the direction indicated by an arrow C which is parallel to the electric field provided by the electrode 35a and 34a. In the same manner, the piezoelectric element 33b expands and contracts by use of the electrode 35b and 34b. A method of producing the base block 31 will now be explained below. A first green sheet of 200 µm thickness containing lead titanate zirconate is prepared, and nickel for forming a grounding electrode is deposited on the first green sheet by sputtering. A second green sheet containing lead titanate zirconate is placed on this deposited nickel layer. Then, nickel for forming a signal electrode is deposited on the second green sheet by sputtering. A third green sheet containing lead titanate zirconate is placed on this deposited nickel layer. Further, nickel for forming a grounding electrode is deposited on the third green sheet by sputtering. The product thus obtained is sintered and formed into the piezoelectric element 33a or 33b by dicing technique. The cover block 32 is made of photosensitive glass. The cover block 32 is provided with ink chambers 36a and 36b formed by etching technique. The ink chambers 36a and 36b are formed to communicate with corresponding nozzles 37a and 37b. The ink chambers 36a and 36b are hermetically closed by an oscillation plate 38 made of glass. The base block 31 and the oscillation plate 38 are attached by an epoxy adhesive, while the cover block 32 and the oscillation plate 38 are attached by an ultraviolet-curing resin adhesive. Next, the operation of the head 30 will be explained below. When a voltage is applied to the signal electrode 35a, the piezoelectric element 33a expands in the direction indicated by the arrow C. Thus, the upper side face (not shown) of the piezoelectric element 33a, which defines the thickness of the piezoelectric element 33a and to which the upper ground electrode 34a is attached, apply pressure to the oscillation plate 38 via the upper ground electrode 34a, thereby expelling a jet of ink droplets from the nozzle 37a. As is apparent from the foregoing according to either of the disclosed embodiments, the side face of a piezoelectric element which defines the thickness thereof is used to apply pressure to an oscillation plate. The side face which defines the thickness of the piezoelectric element can be made thin without reducing the amount of displacement of the piezoelectric element which is created by piezoelectric lateral and/or vertical effects. Accordingly, in the head of either of the above embodiments, the nozzle can be mounted at high density and the use of such a head therefore enables high-speed printers to be realized. In each of the above-described embodiments, there are two sets of nozzles and corresponding piezoelectric elements provided in one head. However, more than two sets of nozzles and piezoelectric elements can be provided in one head in the same manner as the above-described embodiments. Many widely different embodiments of the present invention may be constructed without departing from the scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in this specification, except as defined in the appended claims.

Claims: A head for ink an jet printer comprising: an elastic plate (26,38); a base block (21;31) attached to one side of the elastic plate and including a base portion disposed parallel to said elastic plate (26;38); a plurality of ink chambers (27a,27b;36a,36b) on the other side of said elastic plate each defined by a region of said elastic plate and wall means (22;32) and each having a nozzle (28a,28b;37a,37b) in communication with the respective ink chamber, a plurality of plate-shaped piezoelectric elements (24a,24b;33a,33b), each having an elongate edge face (29a,29b;34a,34b) which defines the thickness of the piezoelectric element and which presses on a respective portion of the region of the elastic plate defining a respective one of the ink chambers, the portion being narrower than the region of the elastic plate defining the respective ink chamber and being disposed at a position corresponding to a respective ink chamber so as to be operable to expand toward said elastic plate due to piezoelectric effect to cause ink to be ejected from a respective one of said ink chambers; electrode means (25a,25b;34a,34b) attached to each of said piezoelectric elements for applying an electric voltage across each of said piezoelectric elements so as to cause said piezoelectric effect, characterized in that said base block further includes a plurality of plate-shaped girder portions (21a,21b,21c;31a,31b,31c) extending perpendicularly from said base portion to said one side of said elastic plate at positions corresponding to boundaries of said ink chambers defined by the wall means, each piezoelectric element being disposed between adjacent said girder portions, and in that said piezoelectric elements, said girder portions and said base portion are integrally formed. A head according to claim 1 further comprising driving means connected to said electrode means for driving said piezoelectric element by supplying an electric pulse to said electrode means. A head according to claim 1, wherein each of said piezoelectric elements comprises lead titanate zirconate. A head according to any preceding claim wherein each of said electrode means comprises a pair of electrodes disposed one on each side of each of said piezoelectric elements, said piezoelectric elements pressing said elastic plate by an expansion due to a piezoelectric lateral effect. A head according to any one of claims 1 to 3 wherein each said electrode means comprises a signal electrode (35a) interposed in each of said piezoelectric elements parallel to said elongate edge face, and a pair of ground electrodes (34b), one of which is disposed on said edge face and the other of which is disposed on a face opposite to said edge face of said piezoelectric element, said piezoelectric elements pressing said elastic plate by an expansion due to a piezoelectric vertical effect. A head according to claim 5, wherein each of said piezoelectric elements comprises layered green sheets containing lead titanate zirconate, said signal electrode comprising a nickel layer interposed between said green sheets. A head according to any preceding claim, wherein said elastic plate is made of material selected from the group consisting of stainless steel and glass. A head according to any preceding claim, wherein the piezoelectric elements are plate-shaped.

Inventors: KUBOTA HIROSHI, KUBOTA, HIROSHI
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1990
Main classification: B41J2
IPC codes: B41J2