Ink jet head

Abstract: An ink jet head is disclosed for use with a drop-on demand type printer, and includes an insulating base (1), a plurality of elongated barriers (5ab-5ef) projecting upwardly from the base so as to form a plurality of slots (2a-2f) between the barriers, a plurality of nozzle holes (3a-3f) communicating with the slots, and electrodes (4a2-4f1) formed on the side walls of the elongated barriers. Voltage can be applied to the various barriers through the electrodes in order to cause deflection of the barriers and a corresponding reduction in the cross-sectional area of selected slots, so as to force ink contained in the slots to be jetted through the nozzle holes. In order to provide a uniform ink jet intensity from the outermost slots relative to the inner slots, dummy slots (12a,12b) can be formed outwardly of the outermost active slots by providing dummy barriers (15aa,15fb) outwardly of the outermost active barriers. In addition, the nozzle holes are formed in a nozzle plate. The nozzle plate can either be mounted against the ends of the slots, or atop the base. When mounted atop the base, possible breakage of the ends of the barriers is less of a problem. Further, the plurality of barriers can either be mounted to the base by an adhesive, or can be formed integrally with the base. Also, the ink jet head can be formed with two bases (31,41), one atop the other, with the barriers of the bases being polarized in opposite directions.

Description: The present invention relates to an ink jet printer head for a drop-on demand (DOD) type printer. Among non-impact type printers, ink jet printers have recently become quite popular, due, in large part, to the fact that they operate on a relatively simple principle and are suitable for use in colour printing. Of the non-impact type printers, continuous ink jet type printers were first developed, with DOD type printers being more recently developed. Such DOD type printers do not continuously jet ink, but rather jet ink only when it is necessary to form a dot. Currently, these DOD type printers are more popular than the continuous ink jet type printers. A typical DOD type printer is a Kyser-type printer such as that disclosed in Japanese patent publication No. 12138/1978. However, such Kyser DOD type printers are burdened by the fact that they are quite difficult to miniaturize. Another typical DOD type printer is a thermal jet type such as that disclosed in Japanese patent publication No. 59914/1986. However, such thermal jet type printers are burdened by the fact that the ink used therein must be heated to a relatively high temperature, thus resulting in burning and sticking of the ink. Accordingly, as disclosed in Japanese patent laid-open No. 252750/1988 (and EP-A-0278590), a shear mode type DOD printer has been developed in order to overcome the above-noted problems confronting these typical DOD type printers. The construction and principles of operation of this shear mode type printer will now be described with reference to Figures 7-10 and 11. As best shown in Figures 9(a) and 9(b), a plurality of elongated barriers 95ab, 95bc, and 95cd are bonded onto a base 105 by an adhesion layer 108 in such a manner as to form narrow slots 92a, 92b, and 92c which define ink chambers and flow paths. The ink for these narrow slots 92a, 92b and 92c is to be supplied from a common ink reservoir 187 defined at first ends of the slots 92a, 92b and 92c so as to be in communication, as best seen in Figures 10 and 11, with the narrow slots. Second ends of the slots 92 are substantially closed by a nozzle plate 100 bonded to the ends of the barriers 95. The nozzle plate 100 has a plurality of small nozzle holes 93a-93f formed therein in communication with each of the slots 92a-92f, respectively. A lid 106 is bonded to upper surfaces of the barriers 95 by a flexible elastic material 109 in such a manner that the barriers 95 are flexible in lateral directions relative to the lid 106 (see Fig. 9(b)). The base 105 is to have electrical insulation characteristics by being formed, for example, of glass or ceramics. The lid 106 is also formed of glass or ceramics in order to provide it with electrical insulation characteristics. The barriers 95, however, are formed of piezoelectric material such as titanic acid zirconic lead (PZT). Again referring to Figures 7, 9(a) and 9(b), electrodes 94a2-94f1 are mounted along the entirety of each of the side walls of the plurality of barriers 95ab-95ef. Each of the barriers 95ab-95ef is polarized in a like direction as shown by arrows 107 (or in a direction opposite thereto). Accordingly, when a sufficiently large electric potential is induced across the electrodes 94a2 and 94b1, the barrier 95ab is forced to deflect in the manner shown in Figure 9(b). As shown, because the elastic material 109 is more flexible than the adhesion layer 108, the deflection of the barrier 95ab mainly occurs at the upper portion thereof nearest the lid 106. In a like manner, when a sufficiently large electric potential is provided to the electrodes 94b1 and 94b2 (the electrodes 94b1 and 94b2 are normally of the same electric potential), the barrier 95bc is caused to deflect in the manner shown in Figure 9(b). Such deflection of the barriers 95ab and 95bc causes a reduction in the cross-sectional area of the slot 92b (and thus in the volume thereof), such that ink contained in the slot 92b is forced outwardly through the nozzle hole 93b. Thus, by selectively causing deflections of the various barriers in the above-noted manner, ink drops can be forced out (or jetted) from the selected nozzle holes 93a-93f. With this type of arrangement, the slots 92a-92f may be formed narrowly so as to allow for miniaturization, and it is also unnecessary to utilize high temperatures as in the kizer type printer discussed above. Accordingly, the ink jet head disclosed in the Japanese patent application laid-open No. 252750/1988, the problems noted above in connection with DOD type printer heads of Japanese publication 12138/1978 and 59914/1986, have been obviated. However, this ink jet head disclosed in Japanese patent application laid-open No. 252750/1988 is still beset with various shortcomings. More specifically, the reduction in cross section of each of the four slots 92b-92e is effected by deflection of the two barriers between which the particular slot is defined. However, this is not the case with respect to the two outermost slots 92a and 92f, the cross-sectional area of the slot 92a, for example, being effected by only the deflection of the barrier 95ab, and not by deflection of a second barrier. Therefore, if, when the cross-sectional area of the slot 92a is to be reduced in order to force an ink drop from the nozzle hole 93a, the barrier 95ab is caused to deflect toward the slot 92a by the same amount as each of the barriers 95ab and 95bc would be deflected toward the slot 92b in order to force an ink drop through the nozzle hole 93b, the force which will act upon the ink contained in the slot 92a will be less than that for the slot 92b. This can, in extreme cases, cause no ink to be discharged and, in other cases, can cause the dot created by the ink drop to be of a smaller or irregular size relative to dots produced from the nozzle holes 93b-93e. This results in poor printing quality due to the occurrence of missing ink dots and irregular ink dot sizes. The reduction in the force acting on the ink in the slot 92a (or 92f) relative to that which acts on ink in the slots 92b-92e, can be somewhat obviated by applying different voltages to the outermost barriers 95ab and 95ef than is applied to the other barriers 95bc-95de. This variance in the voltage is applied as illustrated in Figure 8, in which the vertical axis represents voltage and the horizontal axis represents time. The wave forms 81-86 in Figure 8 represent different voltages applied to the barriers 95ab, 95bc and 95cd, respectively, at different times, and the lines 87, 88 and 89 represent zero voltage levels for the barriers 95ab, 95bc and 95cd, respectively. As clearly illustrated in Figure 8, the voltage applied to each barrier is opposite in polarity to that applied to its neighbouring barrier, in order to cause the barriers to deflect toward or away from one another. The wave forms 81-86 also illustrate that application of voltage to the barriers is substantially instantaneous, whereas the removal of voltage from the barriers is relatively gradual. This is necessary so that the barriers are moved rapidly for the purpose of jetting ink, but moved more gradually in terminating the jetting of the ink. The wave forms 81-86 are thus shaped non-symmetrically in order to illustrate this manner of applying and removing the voltage from the barriers. As further illustrated in Figure 8, the magnitude of the voltage applied to the barrier 95ab to cause jetting of ink from the nozzle hole 93a is approximately double the magnitude of the voltage applied to each of the barriers 95ab and 95bc when it is desired to cause ink to be jetted from the nozzle hole 93b. This will increase the deflection of the barrier 95ab during jetting of ink from the nozzle hole 93a relative to the deflection of the two barriers 95ab and 95bc during jetting of ink from the nozzle hole 93b (in this regard, compare wave form 82 applied during jetting of ink from the nozzle hole 93a to the wave forms 81 and 83 illustrating the voltage applied during jetting of ink from the nozzle hole 93b). While this application of a higher magnitude of voltage to the outermost barriers during jetting of ink from the outermost nozzle holes, the above-noted reduction in the ink jetting force from the nozzle holes 93a and 93f is at least partially obviated. However, this solution to the one problem results in additional problems as follows: (1) Because the application of the higher voltage (as illustrated by wave form 82) causes a reletively greater deflection of the barrier 95ab, when ink is being jetted from the nozzle hole 93a, the cross-sectional area of the neighboring slot 92b is markedly increased, thus causing a substantial reduction in the pressure in the slot 92b. This reduction in pressure results in the formation of air bubbles in the ink contained in the slot 92b, thereby resulting in irregular jetting of ink from the nozzle hole 93b; (2) Because the deflection of the barrier 95ab in forcing ink to be jetted from the nozzle 93a is relatively large, the return of the barrier 95ab to its normal rest position causes a relatively large volume reduction in the slot 92b, thereby often resulting in ink being improperly jetted from the nozzle hole 93b; and (3) The non-symmetrical shape of the voltage wave forms 81 and 82, along with the large magnitude of the voltage of wave form 82, often results in the polarization of the barrier 95ab in the direction of the electrode 94b1 and away from the electrode 94a2. This polarization results in the reduction of deflecting force for the barrier 95ab. In addition to the problems created by the fact that the outermost slots 92a and 92f are defined by only one barrier each, the shearing mode type ink jet printer head disclosed in Japanese patent application laid-open No. 252750/1988 is also beset with a problem which will now be described with particular reference to Figure 11. As shown in Figure 11, the slots 92a-92f are substantially closed at ends thereof by the nozzle plate 100 having the nozzle holes 93 formed therein. During the manufacturing of the ink jet head, the placement and subsequent bonding of the nozzle plate 100 to the ends of the barriers 95 often results in the breakage of the end portions of the barriers 95, especially in view of the fact that the barriers 95 are formed of a piezoelectric material which is relatively brittle, and the fact that the barriers 95 are normally formed with a width of less than 100 µm. Such breakage of the barriers 95 results in ink flowing between adjoining slots 92, such that deflection of a barrier for the purpose of jetting ink from one nozzle hole 93 may cause a rise in pressure in adjoining slots. In addition, such possible ink flow between the adjoining slots can result in the loss of pressure in a slot. In DE-A-3725159 and its corresponding United States Patent No. 4695854, there is disclosed an impulse ink jet print head of the type including a plurality of operating plates held together in a contiguous superposed relationship. A plurality of piezoceramic transducers are mounted on a diaphragm such that each transducer overlies one of a plurality of ink chambers. The transducers are electrically energized and thereby caused to displace ink in the chambers resulting in the ejection of ink droplets through a plurality of nozzles, one nozzle being in fluid communication with each of the chambers. There is also disclosed the provision of passive ink chambers at the ends of an array of active ink chambers in order to equalize the ejection properties of the active ink chambers. No transducers are associated with the passive ink chambers. Accordingly, the object of the present invention is to overcome the above-noted problems of the conventional print head created by the provision of slots from which ink is to be jetted which are bounded by only one deflectable barrier. According to the present invention this object is achieved by providing a shearing mode ink jet head comprising: a base having an upper surface; a plurality of elongate barriers projecting upwardly from the upper surface of the base; a plurality of elongate active slots formed along the upper surface of the base between adjacent ones of the elongate barriers; a common ink reservoir in communication with each of the active slots; means, comprising electrodes mounted on opposing side walls of each of the elongate barriers which forms a side wall of one of the active slots, for selectively applying voltage to the barriers; and means, comprising nozzle holes communicating respectively with the active slots, for controllably dispensing ink contained in the active slots, the arrangement being such that in use voltage can be selectively applied to particular ones of the barriers causing lateral displacement of those particular barriers so as to compress ink contained in the active slots formed between those particular barriers and cause it to be controllably dispensed through the nozzle of those active slots, characterised in that the ink jet head further includes a dummy slot situated on each side of the plurality of active slots so that they are outside the outermost active slots, which dummy slots are each devoid of a nozzle hole so that ink is prevented from being dispensed from the dummy slots, and in that an electrode to which voltage can be applied is adjacent each of the dummy slots each electrode being mounted on at least the side walls of the elongate barriers forming a side wall of the dummy slots those barriers being situated between the outermost active slots and their adjacent dummy slots. It should be noted that the various improvements of the present invention and of the inventions disclosed in Divisional Applications Nos. 94112768.0 (0628413) and 94112769.8 (0627315) for overcoming the shortcomings of the conventional ink jet heads can be utilized together in a single apparatus. Additional objects and advantages of the present invention will become apparent from the following detailed description of the invention when read with reference to the accompanying drawing figures, in which: Figure 1 is a sectional view of a shearing mode type ink jet head according to a first embodiment of the present invention; Figure 2 is a graph illustrating transient wave forms of voltage applied to the shearing mode type ink jet head of Figure 1; Figure 3 is a sectional view of a shearing mode type ink jet head according to a second embodiment of the present invention; Figure 4 is a sectional view of a shearing mode type ink jet head according to a third embodiment of the present invention; Figure 5 is a sectional view of a shearing mode type ink jet head according to a fourth embodiment of the present invention; Figure 6 is a sectional view of a shearing mode type ink jet head according to a fifth embodiment of the present invention; Figure 7 is a sectional view of conventional shearing mode type ink jet head; Figure 8 is a graph illustrating transient wave forms of voltage which can be applied to the conventional shearing mode type ink jet head of Figure 7; Figure 9(a) is a partial sectional view of the conventional shearing mode type ink jet head of Figure 7; Figure 9(b) is a view similar to Figure 9(a), but with the ink jet head in an activated state; Figure 10 is a perspective view of a portion of the conventional shearing mode type ink jet head of Figure 7; Figure 11 is a perspective view of the conventional print head shown in Figure 7. A cross section of a first embodiment of the present invention is shown in Figure 1. The construction of this first embodiment is essentially the same as the construction of the prior art ink jet head shown in Figure 7, with the exception that the ink jet head of this first embodiment shown in Figure 1 includes dummy barriers 15aa and 15fb disposed outwardly of the barriers 5ab-5ef, and except that dummy slots 12a and 12b are formed outwardly of the dummy barriers 15aa and 15fb, respectively. More specifically, the ink jet head shown in Figure 1 includes a base 1 formed of an insulating material such as glass or ceramics, and preferably alumina, and a plurality of active barriers 5ab, 5bc, 5cd, 5de and 5ef bonded to the insulating base 1 by an adhesive layer 8. The barriers 5ab-ef are formed in parallel with one another and are spaced apart at equal intervals so as to form elongated narrow slots 2a-2f therebetween which define ink chambers and ink flow paths. The active slots 2a-2f are connected at first ends thereof to a common ink reservoir (not shown in Figure 1, but similar to the common ink reservoir 187 shown in prior art Figure 11), and are substantially closed at respective second ends thereof, except that nozzle holes 3a-3f are provided. In addition, a lid 6, formed of glass or ceramics, is mounted atop the base 1, and is bonded to the upper surfaces of the active barriers 5ab-5ef by a flexible elastic material 9. Active electrodes 4a2-4f1 are mounted on side walls of the active barriers 5ab-5ef, respectively, as in the prior art ink jet head shown in Figure 7. In addition, the dummy barriers 15aa and 15fb are included and project upwardly from an upper surface of the base 1. Those dummy barriers 15aa and 15fb are disposed outwardly of the outwardmost active barriers 5ab and 5ef, respectively, and are spaced apart from the outwardmost active barriers 5ab and 5ef, respectively, by intervals equal to those at which the active barriers are spaced. Outwardly of these dummy barriers 15aa and 15fb are formed dummy slots 12a and 12b, respectively. Dummy electrodes 4a1, 14a2, 4f2 and 14b1 are mounted on the side walls of the dummy barriers 15aa and 15fb, respectively. The dummy electrodes 4a1, 14a2, 4f2 and 14b1 are active in the sense that voltage can be applied thereto. As with the active slots 2a-2f, the ends of the dummy slots are connected to a common ink reservoir. However, ends of the dummy slots 12a, 12b opposite the ends connected to the ink reservoir do not have nozzle holes formed therein. Although no nozzle holes are formed in the ends of the dummy slots 12a, 12b other small holes can be formed and freely positioned, in order to allow venting of the dummy slots to facilitate filling thereof with ink from the ink reservoir, so long as the small holes are sufficiently small to prevent ink from being jetted therefrom. Furthermore, although the nozzle holes 3a-3f must be located in a limited manner as disclosed in Japanese patent application laid-open No.252750/1988, no such restriction is placed on the location of the dummy slots 12a, 12b. The active barriers 5ab-5ef and the two dummy barriers 15aa and 15fb are preferably formed of PZT and are polarized in like directions as shown by arrow 7 (or in opposite directions thereto). In addition, the adhesive layer 8 between the alumina insulating base 1 and the PZT barriers is preferably formed of epoxy resin. Each of the slots 2a-2f is preferably approximately 100 µm wide and 150 µm deep, and the electrodes 4a2-4f1, as well as the dummy electrodes 14a2, 4a1 and 14b1, are preferably formed of laminated film formed by metalizing chromium and gold and are preferably approximately 0.8 µm in thickness. The lid 6 is preferably formed of alumina plate, and is bonded to the barriers by the elastic material 9, which is preferably formed of silicone resin. The nozzle holes 3a-3f are preferably circular and have diameters of approximately 35 µm and are preferably formed by etching in the nozzle plate which is preferably formed of stainless steel. Figure 2 is a graph similar to Figure 8, except showing wave forms of the voltage to be applied to the dummy barrier 15aa, and the active barriers 5ab and 5bc of the first embodiment shown in Figure 1. The straight lines 29, 27 and 28 represent zero voltage levels for the dummy barrier 15aa, and the active barriers 5ab, 5bc. Note the marked difference between the wave forms for the active barrier 5ab as shown in Figure 2, and the wave forms for the barrier 95ab shown in Figure 8. That is, with the inclusion of the dummy barriers, dummy slots and dummy electrodes in the embodiment of Figure 1, it is unnecessary to apply a larger magnitude of voltage (as at 82) to the outermost active barrier 5ab (see wave form 22) as compared to the magnitude of voltage applied to the remaining barriers, to obtain the same amount of reduction in cross section in the outermost active slot 2a as is obtained for the remainder of the inner active slots. That is, when the voltage is applied to the dummy barrier 15aa in accordance with the wave form 20, the reduction in cross section of the slot 2a is equal to that for the slots 2b-2e upon applying equal voltage magnitudes to the remainder of the barriers. Because the dummy slot 12a is not utilized for the purpose of compressing ink and jetting it from a nozzle, it is unnecessary to cause deflection of the dummy barrier 15aa toward the slot 12a, and thus it is unnecessary to apply a voltage to the dummy barrier 15aa which is of an opposite polarity to that depicted by the wave forms 20. Although the operating principles of this embodiment shown in Figure 1 have been described with respect to only the left side of Figure 1 (i.e. with respect to dummy slot 12a and dummy barrier 15aa), it is apparent that the same principles are to be applied to the right side of Figure 1 (i.e. to dummy slot 12b and dummy barrier 15fb). Because the jetting pressure applied to the ink contained in the active slots 3a-3f can be made equal by applying equal voltages to the various barriers as described above, the equality of printing provided by the embodiment shown in Figure 1 is superior to that provided by the conventional ink jet head shown in Figures 7, 9 and 10. Figure 3 showns a sectional view of a second embodiment according to the present invention, which represents an alternative construction to that shown in Figure 1. In the embodiment of Figure 3, rather than providing a plurality of active barriers and dummy barriers which are bonded to the base with an adhesive layer, a base 31 is formed of a piezoelectric material and is integrally formed with the active barriers 5ab-5ef and the dummy barriers 15aa and 15fb. Furthermore, the second embodiment shown in Figure 3 differs from the first embodiment shown in Figure 1 in that the electrodes 4a-4f and 14a, 14b are each mounted as a continuous electrode along the two side walls and bottom surface of each of the slots 2a-2f and 12a, 12b respectively. More specifically, instead of having individual electrodes mounted on each opposing side wall of each active slot 2a, 2f, as well as the one side wall of the dummy slots 12a, 12b formed by the dummy barriers, the embodiment of Figure 3 utilizes active electrodes 4a-4f which completely line the side walls and bottom surface of each of the slots 2a-2f, respectively, as well as electrodes 14a-14b which continuously line the side walls and bottom surface of each of the dummy slots 12a, 12b. This modification is possible because, in most cases, the two electrodes (e.g. 4a1 and 4a2) on opposing sides of a slot (e.g. 2a) in Figure 1 have the same electric potential. The fact that the barriers 5ab-5ef and 15aa, 15fb of the embodiment shown in Figure 3 are formed integrally with the piezoelectric base 31 provides an added stiffness to the barriers over and above that the provided by the adhesive layer 8 in the embodiment of Figure 1. Such increased stiffness has become almost essential for a print head in order to obtain a high resolution of 300 dots per inch which has become the standard. That is, with the integrally formed barriers and base of the Figure 3 embodiment, the stress and inevitable deformation of the adhesive layer 8 is eliminated. In this second embodiment, the width of each of the barriers is preferably approximately 40 µm, and the pitch of the barriers (i.e. space between barriers) is preferably about 80 µm. Although in the Figure 3 embodiment it is unnecessary to provide the elastic bonding material 9 as provided in the Figure 1 embodiment because of the fact that the upper ends of the barriers can slide relative to the lid 6, such elastic material 9 can be provided in the second embodiment. If it is provided, however, it is preferably limited to 10 µm in thickness. It should be noted that, although the Figure 3 embodiment has been shown as utilizing both the integral barrier/base combination and the undivided electrodes, the integral barrier/base combination can be utilized with electrodes such as those present in the embodiment of Figure 1. The utilization of this integral barrier/base combination allows for the elimination of the adhesive layer 8 utilized in the embodiment of Figure 1. This is advantageous for the following reasons. Bonding of the piezoelectric materials with the adhesive layer 8 must be performed below the Curie temperature (normally below 150°C) so as to maintain polarization of the barriers. Thus, it is necessary to use a high polymeric material such as an epoxy resin. However, the use of such epoxy resin results in a relatively thick adhesive layer. The use of such relatively thick layers of high polymeric adhesive is disadvantageous in that (1) such thick adhesive layers are more subject to deformation (see Figure 9(b)), thereby working to prevent the reduction in cross sectional area of the slots when it is desired to cause jetting of the ink through the nozzle holes; and (2) such high polymeric adhesive layers do not provide sufficiently high stiffness for actions of the ink jet head which are repeated at high speed. The desired stiffness of the barriers is affected by the hardness of the adhesive layer 8, but is not affected by the elastic material 9. Accordingly, the use of such relatively thick high polymeric adhesive layers may result in the lowering of the ink jet force and the frequency of the operation, which will likely adversely affect the stability and speed of printing of the printer. A further alternative to the embodiment of Figure 1 is shown in Figure 4 in connection with a third embodiment of the present invention. This third embodiment is identical to that of Figure 3, except that, rather than utilizing an integrated barrier/base combination 31 and a lid 6, this third embodiment utilizes a lower integrated barrier/base combination 31 and upper integrated barrier/base combination 41. The upper base 41 is formed so as to include slots which align with those of the lower base 31. As shown in Fig. 4, the nozzle holes 3a-3f can be located in vertical positions of the ink slots 2a-2f corresponding to either the upper base 41 or the lower base 31. The barriers 25ab-25ef and 25aa, 25fb formed integrally with the base 41 are polarized in a direction opposite to the direction in which the barriers 5ab-5ef and 15aa, 15fb of the lower base 31 are polarized, as shown by arrows 7 and 27 in Figure 4. The bases 31 and 41 are bonded together such that the barriers and slots of the upper and lower bases align with each other. By using two such piezoelectric material bases 31, 41, the driving force for jetting the ink from the nozzle holes 3a-3f can be increased relative to that which can be provided by the embodiment of Figure 3. Another alternative to the first embodiment shown in Figure 1 is a fourth embodiment according to the present invention, which is shown in Figure 5. This fourth embodiment is substantially identical to the embodiment shown in Figure 3, except that in this fourth embodiment, an additional pair of dummy slots 12c, 12d is provided outwardly of the dummy slots 12a, 12b. When only the one pair of dummy slots 12a, 12b are utilized as in the second embodiment (Figure 3), because the outermost wall of each of the dummy slots 12a, 12b is formed by the base 1 which is stiffer than the barriers, when ink is filled into the dummy slots 12a, 12b, the dummy barriers 15aa and 15fb are faced with a more rigid force when flexing outwardly than when flexing inwardly, such that some non-uniformity of ink jetting may occur. Utilization of the additional dummy slots 12c, 12d in the fourth embodiment will obviate this problem. Because the additional dummy slots 12c, 12d are used only as mechanical buffers, it is unnecessary to mount electrodes on the walls of the dummy slots 12c, 12d, and it is also unnecessary to polarize the additional dummy barriers 15ca and 15bd formed outwardly of the first dummy barriers 15aa and 15fb. However, if, for manufacturing purpose it is more efficient to provide electrodes on the walls of the additional dummy slots 12c, 12d and/or to polarized the dummy barriers 15ca, 15bd, such will not reduce the performance of the ink jet head of this fourth embodiment. As described in connection with the dummy slots 12a, 12b of the first embodiment, small holes which are not utilized as nozzles holes may be formed in the nozzle plate at the end of the additional dummy slots 12c, 12d. In addition, it should be apparent that three or more pairs of dummy slots can be formed outwardly of the active slots. A still further alternative to the first embodiment shown in Figure 1 is a fifth embodiment which is shown in Figure 6. This fifth embodiment is substantially identical to the second embodiment shown in Figure 3, except that in this fifth embodiment, the dummy slots 42a, 42b formed outwardly of dummy barriers 45aa and 45fb are formed with larger cross-sectional areas than are the active slots 2a-2f. This formation at the dummy slots 42a, 42b with larger cross-sectional areas provides the same advantage as does the provision of two pairs of dummy slots as described above in connection with the fourth embodiment shown in Figure 5. As shown in Figure 6, dummy electrodes 44a, 44b are provided continuously along the walls and bottom surface of the dummy slots 42a, 42b. It is important to note that, although the various features of the embodiments have, in general, been described as being distinct to each of the individual embodiments, it will be apparent that the first through the fifth alternative embodiments of the present invention can be utilized in connected with the first through the fifth embodiments of the inventions disclosed in the divisional applications, in order to obtain the advantages of each, as will be apparent to those of ordinary skill in the art. While the invention has been described with reference to the foregoing embodiments, it will be understood by those skilled in the art that various changes and modifications may be made thereto which fall within the scope of the appended claims.

Claims: A shearing mode ink jet head comprising: a base having an upper surface; a plurality of elongate barriers projecting upwardly from the upper surface of the base; a plurality of elongate active slots formed along the upper surface of the base between adjacent ones of the elongate barriers; a common ink reservoir in communication with each of the active slots; means, comprising electrodes mounted on opposing side walls of each of the elongate barriers which forms a side wall of one of the active slots, for selectively applying voltage to the barriers; and means, comprising nozzle holes communicating respectively with the active slots, for controllably dispensing ink contained in the active slots, the arrangement being such that in use voltage can be selectively applied to particular ones of the barriers causing lateral displacement of those particular barriers so as to compress ink contained in the active slots formed between those particular barriers and cause it to be controllably dispensed through the nozzle of those active slots, characterised in that the ink jet head further includes a dummy slot situated on each side of the plurality of active slots so that they are outside the outermost active slots, which dummy slots are each devoid of a nozzle hole so that ink is prevented from being dispensed from the dummy slots, and in that an electrode to which voltage can be applied is in each of the dummy slots each electrode being mounted on at least the side walls of the elongate barriers forming a side wall of the dummy slots those barriers being situated between the outermost active slots and their adjacent dummy slots. A shearing mode ink jet head according to claim 1, wherein the common ink reservoir is in communication with a first end of each of the active slots; and the nozzle holes are respectively in communication with a second end of each of the active slots. A shearing mode ink jet head according to claim 1 or 2, wherein the barriers are formed of a piezoelectric material. A shearing mode ink jet according to claim 1, 2 or 3, wherein a plurality of dummy slots are formed outside of each of the outermost active slots. A shearing mode ink jet head according to any preceding claim, wherein each of the dummy slots has a cross-sectional area greater than a cross-sectional area of each of the active slots. A shearing mode ink jet head according to any preceding claim, wherein the nozzle holes are formed in a nozzle plate mounted at one end of the base so as to substantially close an end of each of the active slots. A shearing mode ink jet head according to any preceding claim, wherein each of the barriers is formed separate from the base and is adhered to the base. A shearing mode ink jet head according to any one of claims 1 to 6, wherein each of the barriers is formed integrally with the base. A shearing mode ink jet head according to any preceding claim, which further comprises a lid mounted to the base above the barriers, wherein the lid is bonded to an upper surface of each of the barriers by an elastic bonding material.

Inventors: HIRAISHI HISATO, HOSHINO MIKINOBU, KIGAWA KEISUKE, MAENO FUMIO, YANAGAWA YOSHIHIKO, HIRAISHI, HISATO, HOSHINO, MIKINOBU, KIGAWA, KEISUKE, MAENO, FUMIO, YANAGAWA, YOSHIHIKO
Applicants: CITIZEN WATCH CO LTD, CITIZEN WATCH CO., LTD.
Application year: 1991
Main classification: B41J2
IPC codes: B41J2