Head for ink-jet printer

Abstract: A head (10) for an ink-jet printer includes a plurality of ink chambers (18a+b) arranged in parallel on a plane, a plurality of nozzles (19a+b) communicated with each of the chambers (18a+b), and a piezoelectric element (13). The piezoelectric element (13) has a laminated structure in which at least one piezoelectric layer and at least two electrode layers sandwiching the piezoelectric layer are laminated, and is attached to the chambers (18a+b) so as to overlie the chambers (18a+b) with the layers being in parallel to the plane of arrangement of the chambers (18a+b). The piezoelectric element (13) includes a plurality of pressure portions (17a+b) and a plurality of slits (16a-d). The slits (16a-d) face the chambers (18a+b) and deepen in a direction perpendicular to the plane of arrangement of the chamber (18a+b) so as to divide the pressure portions (17a+b) from other portion of the piezoelectric element (13) such that each of the pressure portions (17a+b) attaches to each of the chambers (18a+b) at an area defined by the slits (16a-d) and that each of the pressure portions (17a+b) includes the laminated structure. Each of the pressure portion (17a+b) presses each of the chambers (18a+b) at the attaching area by an expansion due to a piezoelectric effect when an electric voltage is applied across the electrode layers in each of the pressure portions (17a+b).

Description: The present invention relates to a head for an ink-jet printer. Ink-jet printers are known as one kind of terminal equipment for computers. Figure 1 is a schematic head for an ink-jet printer. As shown in Figure 1, the illustrated head has a glass container 1 provided with two recesses, a first piezoelectric element 5a, and a second piezoelectric element 5b. A first stainless plate 2a is disposed to cover one recess of the glass container 1, and this recess and the first stainless plate 2a form a first ink chamber 3a. The other recess is covered by a second stainless plate 2b, and this recess and the second stainless plate 2b form a second ink chamber 3b. The first ink chamber 3a is formed to communicate with a first nozzle 4a, while the second ink chamber 3b is formed to communicate with a second nozzle 4b. The first piezoelectric element 5a is fixed to the first stainless plate 2a, while the second piezoelectric element 5b is fixed to the second stainless plate 2b. As described above, the head in Figure 1 includes two nozzle units disposed in parallel, each of which consists of the chamber, the piezoelectric element, the stainless plate and the nozzle. The operation of the conventional head will be explained below with reference to Figure 2, which is a schematic front elevational view showing the head of Figure 1. In its operation, a voltage is applied across the first piezoelectric element 5a to cause it to contract in the direction indicated by arrow A. The first stainless plate 2a is fixed to the first piezoelectric element 5a and is, in turn, deflected in the direction indicated by arrow B. As the first stainless plate 2a is deflected in the direction of arrow B, pressure is applied to the ink in the first ink chamber 3a and a jet of ink droplets is expelled from the first nozzle 4a. Each of the first nozzle 4a and the second nozzle 4b is made to independently perform the above-described operation, thereby enabling information to be recorded. A head for an ink-jet printer is constructed such that a plurality of nozzle units, each of which is similar to the nozzle unit shown in Figure 1, are arranged in parallel. In such a construction, since each ink chamber is provided with a piezoelectric element in the above-described manner, the production of the head requires time-consuming processes to individually equip the piezoelectric element to each ink chamber and so on. It is therefore an object of the present invention to alleviate the foregoing problems and to provide a head for an ink-jet printer which can be produced at high productivity. From EP-A-0 095 911, there is known a pressure pulse droplet ejector in which a single piezoelectric transducer is shared by more than one ejector. According to the present invention, there is provided a liquid-jet printer head having a plurality of coplanar chambers and a plurality of liquid ejection nozzles communicating with said chambers, said liquid-jet printer head comprising: an integral laminated piezoelectric element including a piezoelectric layer sandwiched between electrode layers and being arranged to overlie said plurality of coplanar liquid chambers, wherein a part of said piezoelectric element lying closest to said chambers is divided into electrically isolated pressure portions by slits extending substantially perpendicularly into said part from a surface of said part adjacent said chambers, said slits separating said pressure portions from other portions of said piezoelectric element, each of said electrically isolated pressure portions overlying a respective one of said chambers, and each of said electrically isolated pressure portions including a respective separate portion of the sandwich of said piezoelectric layer and electrode layers. An advantage of this invention is that it is not necessary to mount a plurality of piezoelectric elements with respect to individual ink chambers one by one as in the conventional manner. Thus, the productivity of the head can be improved. In the head of the present invention, each of the pressure portions include the laminated structure of the piezoelectric layer and the electrode layers and presses the chamber by an expansion due to the piezoelectric effect when an electric voltage is applied across the electrode layers in each of the pressure portions. Then, the liquid in the pressed chamber is pressurized, thus producing a jet of liquid droplets from the nozzle corresponding to the pressure portion. All of the pressure portions, thus operating individually, are included in the single piezoelectric element and separated from other portions of the piezoelectric element by the slits. The above and other objects, features and advantages of the present invention will be apparent from the following description of a preferred embodiment of the invention with reference to the accompanying drawings. Figure 1 is a schematic front elevational view showing a conventional head for an ink-jet printer in one state; Figure 2 is a schematic front elevational view showing the head of Figure 1 in another state; Figure 3 is a schematic perspective view showing one embodiment of the present invention; Figure 4 is a schematic front elevational view showing the embodiment of Figure 3; and Figures 5a to 5c are process diagrams which serve to illustrate the sequence of a method of producing a piezoelectric element for use in the embodiment of Figure 3. DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the accompanying drawing. Fig. 3 is a schematic perspective view showing one embodiment of a head for an ink-jet printer according to the present invention. Fig. 4 is a schematic front elevational view showing the embodiment of Fig. 3. Referring to Fig. 3 and 4, a head 10 has a container 11 provided with two recesses and a piezoelectric element 13 which serves a piezoelectric vertical effect. The container 11 is made of, for example, glass. The piezoelectric element 13 is shaped in a rectangular parallelopiped block and has a laminated structure in which a plurality of layers of piezoelectric material and a plurality of layers of electrodes 15a, 15b are laminated as shown in Fig. 4. The layers of piezoelectric material of the piezoelectric element 13 are, for example, made of lead titanate zirconate. The layers of electrodes 15a, 15b are, for example, made of nickel. The piezoelectric element 13 has slits 16a, 16b, 16c and 16d which extend in the direction perpendicular to the surface of the sheet of Fig. 4. An area defined by the slits 16a and 16b forms a first pressure portion 17a, and a set of first electrodes 15a is disposed in the first pressure portion 17a. An area defined by the slits 16c and 16d forms a second pressure portion 17b, and a set of second electrodes 15b is disposed in the second pressure portion 17b. An elastic plate 12 is mounted above the two recesses of the container 11. The plate 12 is made of, for example, glass, stainless or the like. One recess of the container 11 and the plate 12 form a first ink chamber 18a, while the other recess of the container 11 and the plate 12 form a second ink chamber 18b. The first ink chamber 18a communicates with a first nozzle 19a, while the second ink chamber 18b communicates with a second nozzle 19b. A method of producing the piezoelectric element 13 will now be explained with reference to Figs. 5a to 5c. As shown in Fig. 5a, nine green sheets 20 made of, for example, lead titanate zirconate are stacked. Electrodes 14 are printed beforehand on opposite surfaces of each of the upper four green sheets 20 so as to form the layers of electrodes. As shown in Fig. 5b, the nine stacked green sheets 20 are sintered to form the piezoelectric element 13. As shown in Fig. 5c, the slits 16a to 16d are formed in the piezoelectric element 13 in the direction perpendicular to the surface of the sheet of the drawing. Thus, the electrodes 14 are separated into the set of first electrodes 15a and the set of second electrodes 15b. The piezoelectric element 13 is produced through the above-described process. The operation of the head 10 including the piezoelectric element 13 will now be explained with reference to Fig. 4. When a voltage is applied across the first electrodes 15a, since the piezoelectric element 13 exhibits a piezoelectric vertical effect, the first pressure portion 17a expands in the direction indicated by an arrow C, that is, in the direction perpendicular to the surfaces of the electrodes 15a. Thus, the plate 12 is deflected in the direction of the arrow C to apply pressure to the ink in the first ink chamber 18a. When the first ink chamber 18a is pressed, a jet of ink droplets is expelled from the first nozzle 19a. The second pressure portion 17b is operated in the same manner as the first pressure portion 17a by use of the electrodes 15b. Since the piezoelectric element 13 used in the above-described embodiment has a laminated structure, the amount of displacement of the piezoelectric element 13 can be increased in proportion to the number of lamination. Accordingly, in the first and second pressure portions 17a and 17b, even if the lengths of the areas denoted by corresponding double-headed arrows D in Fig. 4 are reduced to a reasonable extent, it is still possible to apply sufficient pressure to the first and second ink chambers 18a and 18b. Accordingly, since the pitch E of the first nozzle 19a and the second nozzle 19b can be made sufficiently small by reducing the length D of the ink chambers 18a and 18b, the packaging density of nozzles can be increased. In the embodiment, the electrodes 14 are printed on the opposite surfaces of some of the green sheets 20 and, by forming the slits 16a to 16d, the electrodes 14 are separated into the first electrodes 15a and the second electrodes 15b. Accordingly, the method of the embodiment enables productivity to be improved with respect to a conventional method of printing electrodes corresponding to individual ink chambers onto piezoelectric elements. Although a plurality of green sheets 20 are stacked to form the piezoelectric element 13, a single green sheet may be employed with the layers of electrodes. In the above described embodiment, the piezoelectric element 13 includes green sheets 20 and electrodes 14. However there may be included a layer of substrate, for example, made of resin on the side opposite to the plate 12 so as to maintain the shape of the piezoelectric element 13 after forming the slits 16. Although the above-described embodiment utilizes the piezoelectric element 13 which serves a piezoelectric vertical effect, a piezoelectric element having a piezoelectric lateral effect may be employed. The operation of a piezoelectric element having a piezoelectric lateral effect is as follows. Referring to Fig. 4, when a voltage is applied across the first pressure portion 17a, the first pressure portion 17a expands in the direction substantially parallel to the electrodes 15a, i.e., in such a direction that the slits 16a and 16b are closed. If the first pressure portion 17a completely closes the slits 16a and 16b and tends to expand to a further extent, it can no longer expand and is deflected in the direction indicated by the arrow C in Fig. 4. Thus, as the first ink chamber 18a is pressed, a jet of ink droplets is expelled from the first nozzle 19a. As is apparent from the foregoing, in the presently preferred embodiment, the piezoelectric element 13 is disposed to overlie the first ink chamber 18a and the second ink chamber 18b, and the slits 16a to 16d are formed in the portion of the piezoelectric element 13 which faces ink chambers. The piezoelectric element 13 has the first pressure portion 17a and the second pressure portion 17b the areas of which are defined by corresponding ones of the slits 16a to 16d. Accordingly, since it is not necessary to mount piezoelectric element with respect to individual ink chambers one by one, the productivity of heads for ink-jet printers can be improved. In the above-mentioned embodiment, two nozzle units, each of which consists of each ink chamber, each pressure portion, each nozzle and so on, are provided in one head. However, more than two nozzle units can be provided on demand in one head in the same manner as the above-described embodiment.

Claims: A liquid-jet printer head (10) having a plurality of coplanar chambers (18) and a plurality of liquid ejection nozzles (19) communicating with said chambers (18), said liquid-jet printer head (10) comprising: an integral laminated piezoelectric element (13) including a piezoelectric layer sandwiched between electrode layers (15) and being arranged to overlie said plurality of coplanar liquid chambers (18), wherein a part of said piezoelectric element (13) lying closest to said chambers (18) is divided into electrically isolated pressure portions (17) by slits (16) extending substantially perpendicularly into said part from a surface of said part adjacent said chambers (18), said slits (16) separating said pressure portions (17) from other portions of said piezoelectric element (13), each of said electrically isolated pressure portions (17) overlying a respective one of said chambers (18), and each of said electrically isolated pressure portions (17) including a respective separate portion of the sandwich of said piezoelectric layer and electrode layers (15). A head (10) according to claim 1, wherein said chambers (18) are arranged in parallel. A head (10) according to any preceding claim, wherein said layers are parallel to the plane of said coplanar liquid chambers (18). A head (10) according to any preceding claim, wherein said pressure portions (17) exert pressure in respective said chambers (18) by piezoelectric expansion when a potential difference is applied across electrodes (15) in respective portions (17). A head (10) according to any preceding claim, wherein said piezoelectric layer comprises lead titanate zirconate. A head (10) according to any preceding claim, wherein said piezoelectric layer comprises a green sheet containing lead titanate zirconate. A head (10) according to any preceding claim, wherein said chambers (18) comprise an elastic plate (12) to which said pressure portion (17) is attached and a recess which is formed in a container (11) and covered by said elastic plate (12). A head (10) according to any preceding claim, wherein said plurality of chambers (18) comprises a single elastic plate (12) to which said pressure portions (17) are attached and a plurality of recesses which are formed in a single container (11) and covered by said elastic plate (12). A head (10) according to any preceding claim, wherein said pressure portions (17) exert pressure in respective said chambers (18) by a piezoelectric expansion substantially parallel to said coplanar liquid chambers (18). A head (10) according to any of claims 1 to 8 , wherein said pressure portions (17) exert pressure in respective said chambers (18) by piezoelectric expansion substantially perpendicular to said coplanar liquid chambers (18). A head (10) according to any preceding claim, wherein said electrode layers (15) comprise nickel. A head (10) according to any preceding claim, wherein said head (10) is an ink-jet printer head.

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