Ink-jet head and reservoir unit included in ink-jet head

An ink-jet head comprises a passage unit and a reservoir unit. The passage unit includes a common ink chamber that extends in one direction. The reservoir unit is fixed to the passage unit, and includes an ink reservoir that stores ink and that extends in the one direction. In the reservoir unit, formed are an introduction passage extending from an ink introduction port to the ink reservoir, and a discharge passage extending from the ink reservoir to ink discharge ports. The introduction passage and the discharge passage include an inflow port and an outflow port, respectively. Both the inflow port and the outflow port face the ink reservoir. The inflow port is disposed such that at least one outflow port can exist on either side of the inflow port with respect to the one direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ink-jet head that ejects ink onto a record medium and thereby conducts a recording and to a reservoir unit included in an ink-jet head.

2. Description of Related Art

An ink-jet head is applicable to a recording apparatus such as printers and facsimile machines, etc. The ink-jet head comprises a plurality of nozzles, pressure chambers that communicate with the respective nozzles, an actuator that selectively applies ejection energy to ink contained in the pressure chambers, and the like. Ink is supplied from an ink supply source such as an ink tank, and then distributed among the respective pressure chambers. Upon driving of the actuator, the ink is ejected from the nozzles communicating with the pressure chambers. According to one of known technique, this type of ink-jet head comprises, for the purpose of stable ink supply to the pressure chambers, a reservoir that stores ink having supplied from the ink supply source and supplies the ink directly to the respective pressure chambers (see Japanese Patent No. 2992756).

In addition, the ink-jet head sometimes employs a construction in which the pressure chambers are arranged at a high density in order to meet demands for high-resolution printing and high-speed printing.

SUMMARY OF THE INVENTION

Particularly when the ink-jet head employs not only the reservoir but also the foregoing construction, a passage toward the pressure chamber becomes complicated, and therefore it becomes hard to supply ink from the reservoir directly to the respective pressure chambers.

An object of the present invention is to provide an ink-jet head capable of, even when the pressure chambers are arranged at a high density, smoothly supplying ink to respective pressure chambers using a reservoir, and to provide a reservoir unit included in an ink-jet head.

According to an aspect of the present invention, there is provided an ink-jet head comprising a passage unit and a reservoir unit. The passage unit includes a common ink-chamber extending in one direction and a plurality of individual ink passages each extending from the common ink chamber through a pressure chamber to a nozzle. The reservoir unit is fixed to the passage unit and includes an ink reservoir that stores ink. The ink reservoir extends in the one direction and has a larger capacity than that of the common ink chamber. The reservoir unit includes: an ink introduction port into which ink is introduced; an introduction passage that extends from the ink introduction port to the ink reservoir and includes an inflow port facing the ink reservoir; a plurality of ink discharge ports through which ink is discharged into the common ink chamber; and a plurality of discharge passages that extend from the ink reservoir to the ink discharge ports and include a plurality of outflow ports facing the ink reservoir. The inflow port is disposed such that at least one outflow port can exist on either side of the inflow port with respect to the one direction.

According to another aspect of the present invention, there is provided a reservoir unit fixed to a passage unit in an ink-jet head. The passage unit has a common ink chamber extending in one direction and a plurality of individual ink passages each extending from the common ink chamber through a pressure chamber to a nozzle. The reservoir unit comprises an ink reservoir for storing ink, an inflow port, and a plurality of outflow ports. The ink reservoir extends in the one direction, has a larger capacity than that of the common ink chamber, and is in fluid communication with the common ink chamber. The ink reservoir is in fluid communication with an outside of the reservoir and the common ink chamber though the inflow port and the plurality of outflow ports, respectively.

When, differently from the aforementioned configurations, the inflow port is disposed such that no outflow port can exist on one side thereof (e.g., disposed at a position corresponding to one end of the ink reservoir), distances between the inflow port and the respective outflow ports differ from one another to a larger extent. In particular, a distance between the inflow port and the outflow port nearest to the inflow port becomes largely different from a distance between the inflow port and the outflow port most remote from the inflow port. In this case, prior to ink reaching the outflow ports remote from the inflow port, ink that has passed through the outflow ports nearer to the inflow port and then through the corresponding ink discharge ports to thereby already reach the common ink chamber can disadvantageously flow back through the outflow ports remote from the inflow port into the ink reservoir again. Such an ink backflow can cause air to stay within the ink reservoir, and therefore ink cannot possibly be supplied to some of the pressure chambers.

On the other hand, since either of the aforementioned configurations can relatively reduce differences in distance between the inflow port and the respective outflow ports, the above-described backflow can be prevented. As a result, a problem of air stay within the ink reservoir and the like can be relieved, so that ink can smoothly be supplied to the respective pressure chambers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, a certain preferred embodiment of the present invention will be described with reference to the accompanying drawings.

As illustrated inFIG. 1, an ink-jet head1according to an embodiment of the present invention has a shape elongated in a main scanning direction, and comprises, from one nearest to its bottom, a head main body1a, a reservoir unit70(not shown inFIG. 1; seeFIG. 2), and a control unit80that controls driving of the head main body1a. As illustrated inFIG. 2, an upper covering51and a lower covering52are provided for the purpose of protecting against ink an upper part of the head including the control unit80and a lower part thereof including the reservoir unit70, respectively. An illustration of the upper covering51is omitted fromFIG. 1so that the control unit80may be exposed into a visible state.

Here, referring toFIGS. 1 and 2, a construction of the control unit80will be described.

The control unit includes a main substrate82, two sub substrates81disposed on both sides of the main substrate82, and driver ICs83(seeFIG. 2) each fixed to a side face of each sub substrate81confronting the main substrate82.

The main substrate82, whose plane extends in a vertical direction and in the main scanning direction, has a rectangular shape elongated in the main scanning direction and is fixed onto the reservoir unit70in a perpendicular manner. The two sub substrates81are laid in parallel with the main substrate82, and disposed on both sides of the main substrate82to be equidistantly spaced apart therefrom. The two sub substrates81are electrically connected with the main substrate82. The driver ICs83(seeFIG. 2) generate signals for driving the actuator unit21that is included in the head main body1a. A heat sink84is fixed to a face of each driver IC83confronting the main substrate82.

The sub substrate81and the driver IC83fixed to each other make a pair, and each pair is electrically connected with an FPC50acting as a power supply member. The FPC50is, at its one end, connected with the actuator unit21, too, so that the FPC50transmits to the driver IC83a signal outputted from the sub substrate81, and feeds to the actuator unit21a drive signal outputted from the driver IC83.

The upper covering51and the lower covering52will then be described.

As illustrated inFIG. 2, the upper covering51is a housing with an arched ceiling. The upper covering51covers the sub substrates81and an upper portion of the rain substrate82.

The lower covering52is a substantially rectangular-cylindrical housing that is opened out in its upper side and lower side. The lower covering52covers portions of the FPCs50which are extended out of a passage unit4included in the head main body1a. Within a space covered by the lower covering52, the FPCs50are laid in a loose manner in order to avoid stress put thereon.

At a top of the lower covering52, ends of its sidewalls are bent at approximately 90 degrees to thereby form a horizontal level. On a joint portion of this horizontal level with each sidewall, placed is a lower open end of the upper covering51.

Each sidewall of the lower covering52(only one of which is visible inFIG. 1) has, at its bottom end, two protrusions52aprotruding downward. The two protrusions52aare disposed side by side along a lengthwise direction of the sidewall. Each protrusion52acovers a portion of the FPC50disposed within a groove53of the reservoir unit70, and at the same time the protrusions52aare themselves received within the grooves53of the reservoir unit70, as illustrated inFIG. 2. A tip end of each protrusion52aconfronts the passage unit4included in the head main body1awith a certain clearance formed therebetween for absorbing manufacture errors. A silicone resin, etc., is packed into this clearance which is thereby sealed up. Except for the protrusions,52a, the bottom ends of the sidewalls of the lower covering52are disposed on the reservoir unit70.

As illustrated inFIG. 2, one end portion of the FPC50connected with the actuator unit20horizontally extends in a plane of the passage unit4. Each FPC50is, while forming a bent portion in its midway, upwardly extended out through the groove53of the reservoir unit70, so that the other end of the FPC50can be connected with the corresponding pair of sub substrate81and driver IC83of the control unit80.

Both of the lower covering52and the upper covering51have substantially the same width as that of the passage unit4.

Then, referring toFIGS. 2,3, and4, a description will be given to a construction of the reservoir unit70. For the purpose of explanatory convenience,FIG. 3is drawn on an enlarged scale in the vertical direction.

The reservoir unit70has a layered structure of four plates, i.e., an upper plate71, a filter plate72, a reservoir plate73, and an under plate74. Each of the four plates71to74has a substantially rectangular plan view shape elongated in the main scanning direction (seeFIG. 1).

Herein, a direction parallel with the elongated direction of the four plates71to74is referred to as a lengthwise direction of the four plates71to74, a direction perpendicular to the lengthwise direction in a plan is referred to a widthwise direction of the four plates71to74, and a direction perpendicular to both the lengthwise and widthwise directions is referred to as a thickness direction of the four plates71to74.

As illustrated inFIG. 4, the four plates71,72,73, and74have, at their both widthwise ends, a total of four rectangular notches53a,53b,53c, and53d, respectively. At each widthwise end of each plate, two notches are formed side by side along a lengthwise direction of the plate. The four notches are arranged in a staggered pattern. These notches53ato53dare aligned with one another in the vertical direction to thereby form a groove53(see FIG.2) that has a rectangular shape in a plan view and penetrates through the reservoir unit70in the vertical direction. Thus, two grooves53are formed on each side face of the reservoir unit70relative to its widthwise direction, that is, a total of four grooves53are formed on its side faces. The four grooves53are arranged apart from one another in a staggered pattern along the length of the reservoir unit.

At one lengthwise end of the upper plate71, a substantially circular hole71ais formed in the middle of the width by means of etching, etc. The hole71apenetrates through the upper plate71in its thickness direction, so that an ink introduction port71bcan be formed in a top face of the upper plate71.

In the filter plate72, as illustrated inFIG. 3, formed is a first depression72ahaving a depth of approximately one third of a thickness of the filter plate72. The first depression72ais, in a plan view, elongated from a portion corresponding to the hole71ato a center of the filter plate72. At the portion corresponding to the hole71a, the first depression72ais shaped in conformity with a shape of the hole71ain a plan view. At the center of the filter plate72, the first depression72ais shaped in conformity with a shape of a hole72cin a plan view (seeFIG. 4).

In the filter plate72, further, a second depression72bis formed under the first depression72a, as illustrated inFIG. 3. A depth of the second depression72bis approximately one third of the thickness of the filter plate72. The second depression72band the first depression72ahas substantially the same shape, and the second depression72bis somewhat smaller than the first depression72ain a plan view.

A step is formed at a boundary between the first depression72aand the second depression72b. On this step, disposed is a filter70fthat removes dust and dirt contained in ink. The filter70fhas substantially the same shape as that of an area of the first depression72aexcept for the portion corresponding to the hole71ain a plan view. The filter70fis slightly smaller than this area in a plan view.

In the filter plate72, still further, a substantially circular hole72cis formed under the second depression72b, so that an inflow port72dcan be formed in a bottom face of the filter plate72. The inflow port72dis disposed at a position corresponding to the center of the filter plate72and also corresponding in a plan view to a center of a later-described ink reservoir73awith respect to an extending direction of the ink reservoir73a(hereinafter referred to simply as “a center of the ink reservoir73a”). The inflow port72dconfronts the ink reservoir73a, and at the same time confronts a later-described main passage73cof the ink reservoir73a.

An ink reservoir73athat stores ink is formed in the reservoir plate73by press working, etc. The ink reservoir73apenetrates through the reservoir plate73in its thickness direction. In a plan view, as illustrated inFIG. 4, the ink reservoir73acurvedly extends in the main scanning direction while tapering toward its lengthwise ends, and the ink reservoir73ais point-symmetrical with respect to a center thereof.

The ink reservoir73ais made up of a main passage73cthat extends in the main scanning direction, and branch passages73bthat branch from the main passage73c. A width of each branch passage73bis narrower than that of the main passage73c. Among the branch passages73b, every two branch passages73bextending in the same direction make a pair. Two pairs of branch passages73brunning in different directions from each other are extended out from each widthwise end of the main passage73c. The two pairs of branch passages73bare spaced apart from each other in the extending direction of the main passage73c. The four pairs of branch passages73bare disposed in a staggered pattern.

In the ink reservoir73a, both lengthwise ends of the main passage73cand ends of the respective branch passages73bcorrespond to portions of the under plate74where holes74aare formed.

Ten holes74ain total are formed in the under plate74by etching, etc. Each of the holes74ahas substantially circular shape and penetrates through the under plate74in its thickness direction, so that ink outflow ports74ccan be formed in a top face of the under plate74and ink discharge ports74bcan be formed in a bottom face thereof. The ink outflow ports74cconfront the ink reservoir73a, and at the same time confront the respective branch passages73bof the ink reservoir73a. The ink discharge ports74bconfronts later-described receiving ports5bof the passage unit4. Ink is discharged from the ink discharge ports74btoward manifold channels5.

Five holes74aare disposed near each widthwise end of the under plate74in a staggered pattern along the lengthwise direction, and the holes74aare disposed point-symmetrically with respect to the center of the ink reservoir73a. More specifically, along one widthwise end of the under plate74, one hole74a, two holes74a, and two holes74aare spacedly disposed in this order from one side in the lengthwise direction. Along the other widthwise end of the under plate74, one hole74a, two holes74a, and two holes74aare spacedly disposed in this order from the other side in the lengthwise direction. The holes74aare so disposed as to keep away from the notches53d. In other words, each hole74ais disposed between two neighboring notches53d.

When the four plates71to74are positioned relative to one another and put in layers, an ink passage as shown inFIGS. 3 and 4is formed within the reservoir unit70.

Herein, a passage extending from the ink introduction port.71bto the ink reservoir73a, that is, a passage formed within the hole71a, the first depression72a, the second depression72b, and the hole72cis referred to as an introduction passage, and a passage extending from the ink reservoir73ato each ink discharge port74b, that is, a passage formed within the hole74cis referred to as a discharge passage. The introduction passage has, at its downstream end, the inflow port72d. Each discharge passage has, at its upstream end, the outflow port74c. Both the inflow port72dand the outflow ports74cface the ink reservoir73a. The inflow port72dis disposed such that there can exist five outflow ports74con either side of the inflow port72dwith respect to the extending direction of the ink reservoir73a(seeFIG. 4). Each discharge passage is a cylindrical passage formed within the hole74ato extend in the vertical direction. The respective outflow ports74cand the respective ink discharge ports74bcoincide with each other in a plan view.

Ink contained within an ink supply source (not illustrated) such as an ink tank is introduced, via, e.g., a tube (not illustrated) inserted into the hole71a, into the ink introduction port71b, and then supplied through the introduction passage to the ink reservoir73a. In the introduction passage, ink firstly flows into one end of the first depression72a, and spreads within the first depression72ain a horizontal direction. The ink passes through the filter70ffor removing dust and dirt therefrom, and then reaches the second depression72b. Thereafter, the ink passes through the hole72c, and flows from the inflow port72dinto the center of the ink reservoir73a, where the ink is temporarily stored. At this time, as shown by arrows inFIG. 4, the ink having flown into the center of the ink reservoir73aspreads from a center of the main passage73ctoward the ends of the respective branch passages73bas well as toward the ends of the ink reservoir73ain the extending direction thereof. Then, the ink passes, from the respective outflow ports74c, through the discharge passages formed within the respective holes74a, to be supplied into the passage unit4via the ink discharge ports74band the ink receiving ports5b(seeFIG. 5).

As illustrated inFIG. 2, a bottom of the under plate74has been processed by half etching, etc., so that only a periphery of each ink discharge port74bcan protrudes downward. Since the ink discharge ports74bare formed in the under plate74in the staggered pattern (seeFIG. 4) as mentioned above, protrusions formed on the bottom of the under plate74are also in a staggered pattern. The reservoir unit70is fixed to the top face of the passage unit4such that it can be in contact with the passage unit4only at the protrusions of the under plate74formed around the ink discharge ports74band its portions other than the protrusions can be spaced apart from the passage unit4.

As illustrated inFIG. 2, except for the grooves53, widthwise ends of the reservoir unit70are aligned with widthwise ends of the passage unit4in the vertical direction. In addition, a total width of the reservoir unit70including the lower covering52is substantially the same as the width of the passage unit4.

Then, a description will be given to a construction of the head main body1awith reference toFIGS. 2,5,6,7,8,9A, and9B. InFIG. 6, for the purpose of explanatory convenience, pressure chambers10and apertures12are illustrated with solid lines though they locate below the actuator units21and therefore should be illustrated with broken lines.

As illustrated inFIGS. 2 and 5, the head main body1aincludes the substantially rectangular parallelepiped passage unit4, and four actuator units21fixed to the top face of the passage unit4. The plan view shape of the passage unit4has substantially the same shape and the same size as those of a plane of the reservoir unit70except for the grooves53. The actuator units21serve to selectively apply ejection energy to ink contained in the pressure chambers that are formed in the passage unit4. The actuator units21are fixed on such areas of the top face of the passage unit4as to spacedly confront the reservoir unit70. The actuator units21are out of contact with the reservoir unit70and spaced apart therefrom.

As illustrated inFIG. 5, the four actuator units21each having a trapezoidal shape in a plan view are arranged on the top face of the passage unit4in a staggered pattern. The actuator units21are disposed such that parallel opposed sides of each actuator unit21may extend along a lengthwise direction, that is, an elongated direction of the passage unit4and oblique sides of every neighboring actuator units21may overlap each other in a widthwise direction, that is, a direction perpendicular to the elongated direction of the passage unit4. The four actuator units21have such a relative positional relationship that they may locate equidistantly on opposite sides of a widthwise center of the passage unit4.

As illustrated inFIGS. 5 and 6, an under face of the passage unit4provides for ink ejection regions where a large number of nozzles8are formed in a matrix. A total of ten substantially circular ink receiving ports5bare formed in areas of the top face of the passage unit4having no actuator unit21bonded thereon (i.e., areas of the top face of the passage unit4fixed to the reservoir unit70). The ink receiving ports5bare opposed to the respective ink discharge ports74b(seeFIGS. 3 and 4) of the reservoir unit70.

The passage unit4also includes manifold channels5that communicate with the ink receiving ports5b, and sub-manifold channels5athat branch from the corresponding manifold channels5(seeFIGS. 5 and 6). Similarly with the above-described ink reservoir73a, both the manifold channels5and the sub-manifold channels5aextend in the main scanning direction. Each manifold channel5has a smaller capacity than that of the ink reservoir73a.

Within the passage unit4, formed are individual ink passages32as shown inFIG. 7, each of which corresponds to each nozzle8and extends from the manifold channel5to the corresponding nozzle8via the sub-manifold channel5aand the pressure chamber10. That is, ink is introduced from the ink discharge ports74bof the reservoir unit70into the ink receiving ports5bof the passage unit4, and then branches from the manifold channels5into the respective sub-manifold channels5a, to reach the tapered nozzles8via the apertures12and the pressure chambers10. The aperture12functions as a throttle.

As illustrated inFIG. 6, the pressure chambers10each having a substantially rhombic shape in a plan view are, similarly to the nozzles8, arranged in a matrix within the respective ink ejection regions.

Nine metal plates are positioned relative to one another and put in layers so as to form the aforementioned individual ink passages32, to thereby constitute the passage unit4(seeFIGS. 7 and 8). More specifically, the passage unit4is made up of, from a top side, a cavity plate22, a base plate23, an aperture plate24, a supply plate25, manifold plates26,27, and28, a cover plate29, and a nozzle plate30.

The cavity plate22is made of metal, in which formed are a large number of substantially rhombic openings corresponding to the respective pressure chambers10. The base plate23is made of metal, in which formed are communication holes for connecting the respective pressure chambers10of the cavity plate22with the corresponding apertures12, and communication holes for connecting the respective pressure chambers10with the corresponding nozzles8. The aperture plate24is made of metal, in which formed are not only the apertures12but also communication holes for connecting the respective pressure chambers10with the corresponding ink nozzles8. Each aperture12is formed of two holes and a half-etched region connecting the two holes. The supply plate25is made of metal, in which formed are communication holes for connecting the respective apertures12with the corresponding sub-manifold channels5a, and communication holes for connecting the respective pressure chambers10with the corresponding ink nozzles8. The manifold plates26,27, and28are made of metal, in which formed are not only holes that cooperate with each other to constitute the respective sub-manifold channels5awhen these plates are put in layers, but also communication holes for connecting the respective pressure chambers10with the corresponding ink nozzles8. The cover plate29is made of metal, in which formed are communication holes for connecting the respective pressure chambers10of the cavity plate22with the corresponding nozzles8. The nozzle plate30is made of metal, in which formed are the nozzles8that correspond to the respective pressure chambers10of the cavity plate22.

As illustrated inFIG. 9A, the actuator unit21is bonded onto the cavity plate22that constitutes the uppermost layer of the passage unit4. The actuator unit21has a layered structure of four piezoelectric sheets41,42,43, and44all made of a lead zirconate titanate (PZT)-base ceramic material having ferroelectricity. The four piezoelectric sheets41to44have the same thickness of approximately 15 μm in the vertical direction, and so disposed as to span the many pressure chambers10formed within an ink ejection region.

On the uppermost piezoelectric sheet41, an individual electrode35is provided at a position corresponding to each pressure chamber10. A common electrode34having a thickness of approximately 2 μm in the vertical direction is interposed between the uppermost piezoelectric sheet41and the piezoelectric sheet42located thereunder. The common electrode34is provided throughout entire surfaces of these piezoelectric sheets. Both the individual electrodes35and the common electrode34are made of, e.g., an Ag—Pd-base metallic material. No electrode is disposed between the piezoelectric sheets42and43, and between the piezoelectric sheets43and44.

As illustrated inFIG. 9B, the individual electrode35with a thickness of approximately 1 μm in the vertical direction has, in a plan view, a substantially rhombic shape similar to the shape of the pressure chamber10(seeFIG. 6). One acute portion of the substantially rhombic individual electrode35is elongated out. This elongation has, on its end, a circular land36having a diameter of approximately 160 μm. The land36is electrically connected with the individual electrode35. The land36is made of, e.g., gold including glass frits, and bonded onto a surface of the elongation of the individual electrode35, as illustrated inFIG. 9A. The land36is electrically bonded to a contact formed in the FPC50.

The common electrode34is grounded in a non-illustrated region. Thus, the common electrode34is kept at the ground potential equally in a region corresponding to any pressure chamber10. On the other hand, the individual electrodes35are connected to the driver IC83(seeFIG. 2) via the corresponding lands36and the FPC50that includes different lead wires adapted for the respective individual electrodes35in order that the individual electrodes35corresponding to the respective pressure chambers10can be controlled in their potentials independently of one another.

Since the piezoelectric sheets41to44span the many pressure chambers10as described above, the individual electrodes35can be arranged on the piezoelectric sheet41at a high density using, e.g., a screen printing technique. Therefore, the pressure chambers10, which are positioned in correspondence with the individual electrodes35, can also be arranged in a high density to thereby achieve a high-resolution image printing.

Here will be described how to drive the actuator unit21.

Within the actuator unit21, the piezoelectric sheet41has been polarized in its thickness direction. In this state, when the individual electrode35is set at a different potential from that of the common electrode34to thereby apply an electric field to the piezoelectric sheet41in the polarization direction, a portion of the piezoelectric sheet41having the electric field applied thereto words as an active portion that distorts through a piezoelectric effect. The active portion is, due to transverse piezoelectric effect, going to extend or contract in its thickness direction and contract or extend in its plane direction. On the other hand, the other three piezoelectric sheets42to44are inactive layers having no region sandwiched between the individual electrode35and the common electrode34, and therefore cannot deform by themselves.

That is, the actuator unit21has a so-called unimorph structure in which an upper piezoelectric sheet41remote from the pressure chambers10constitutes a layer including active portions and the lower three piezoelectric sheets42to44near the pressure chambers10constitute inactive layers.

As illustrated inFIG. 9A, a bottom of the piezoelectric sheets41to44is fixed onto a top face of the cavity plate22in which the pressure chambers10are defined. Accordingly, when a difference in distortion in the polarization direction is caused between the portion of the piezoelectric sheet41having the electric field applied thereto and the other piezoelectric sheets42to44located thereunder, the piezoelectric sheets41to44are as a whole deformed into a convex shape toward the corresponding pressure chamber10, which is called “unimorph deformation”. In association with this deformation, the volume of the pressure chamber34decreases and thus pressure of ink rises, so that the ink is ejected from the corresponding nozzle8.

Then, when the individual electrode35is returned to the same potential as that of the common electrode34, the piezoelectric sheets41to44restore their original flat shape, and thus the pressure chamber10also restores its original volume. Ink is accordingly introduced from the manifold channel5into the pressure chamber10, which therefore stores the ink again.

According to the ink-jet head1of this embodiment, as described above, the inflow port72dis so formed in the reservoir unit70as to correspond to the center of the ink reservoir73a, and at the same time the inflow port72dis disposed such that there can exist the same number (five in this embodiment) of outflow ports74con either side of the inflow port72din the extending direction of the ink reservoir73a. This configuration can relatively reduce differences in distance between the inflow port72dand the respective outflow ports74c. Accordingly, ink that has passed through the outflow ports74cnearer to the inflow port72dand the corresponding ink discharge ports74bto thereby reach the manifold channel5can be prevented from flowing back through the outflow ports74cremote from the inflow port72dinto the ink reservoir73aagain prior to ink reaching the outflow ports74cremote from the inflow port72d. This can relieve a problem of air stay within the ink reservoir73aand the like, so that ink can smoothly be supplied to the respective pressure chambers10.

Moreover, in a plan view, the ink reservoir73atapers toward its lengthwise ends, and the outflow ports74care disposed at positions corresponding to the both lengthwise ends of the ink reservoir73a. Due to this configuration, ink can flow at a higher speed when it travels toward the outflow ports74cdisposed at the both lengthwise ends of the ink reservoir73a, i.e., toward the outflow ports74crelatively remote from the inflow port72d. Therefore, ink can soon reach the outflow ports74cthat are relatively remote from the inflow port72d. This can enhance the foregoing effects, i.e., the effects of prevention of air stay within the ink reservoir73aand smooth ink supply to the respective pressure chambers10.

Further, the ink reservoir73ahas a planar shape of point-symmetrical with respect to its center, and the outflow ports74care also arranged point-symmetrically with respect to the center of the ink reservoir73a. Consequently, ink that has flown through the inflow port72dinto the ink reservoir73acan be dispersed efficiently and travels toward the respective outflow ports74c. This can furthermore enhance the effects of prevention of air stay within the ink reservoir73aand smooth ink supply to the respective pressure chambers10.

As illustrated inFIGS. 3 and 4, the ink introduction port71bis further from the center of the ink reservoir73athan the inflow port72dis. This can realize an effective use of a space above the reservoir unit70, on which for example the main substrate82and the sub substrates71can be disposed.

When, as in this embodiment, the filter70fis disposed in the introduction passage, and more specifically disposed on the step formed at the boundary between the first depression72aand the second depression72b, an area of the filter70fcan become larger as compared with a filter that is to be disposed on each of the outflow ports74c. As a result, a passage resistance decreases, and therefore ink can smoothly be supplied to the respective pressure chambers10.

The ink reservoir73acomprises the main passage73c, and the branch passages73bbranching from the main passage73cand each having a narrower width than that of the main passage73c. The inflow port72dis disposed in confrontation with the main passage73c, and the outflow ports74care disposed in confrontation with the respective branch passages73b. Since the ink reservoir73ais thus formed in conformity with flow of ink toward the respective outflow ports74c, the passage resistance within the ink reservoir73acan be decreased and therefore ink can smoothly be supplied to the respective pressure chambers10.

Alternatively, the inflow port72dand the outflow ports74ccan be disposed in confrontation with the branch passages73dand the main passage73c, respectively. In this case, within the ink reservoir73a, ink flows from the branch passages73bto the main passage73c.

It is not always required that the ink reservoir73acomprises the above-described main passage73cand branch passages73b. For example, a branch passage that branches from a main passage may have substantially the same width as that of the main passage, or alternatively larger width as that of the main passage.

The planar shape of the ink reservoir73ais not limited to the one tapering toward its lengthwise ends in a plan view, but it can variously be changed. The planar shape of the ink reservoir73amay taper toward only one lengthwise end thereof or may not have the tapered shape.

The planar shape of the ink reservoir73aand the arrangement of the outflow ports74cmay not necessarily be point-symmetrical with respect to the center of the ink reservoir73a, but they may be line-symmetrical. Alternatively, they may neither be point-symmetrical nor line-symmetrical.

The outflow ports74ccan be disposed not at both lengthwise ends of the ink reservoir73a, but other various positions such as one lengthwise end alone of the ink reservoir73aand portions other than the ends of the ink reservoir73a, etc.

It is not limitative that the inflow port72dis nearer to the center of the ink reservoir73athan the ink introduction port71bis. For example, the inflow port72dmay be disposed at a position slightly out of the center of the ink reservoir73awith the ink introduction port71bbeing disposed at the center of the ink reservoir73a.

The inflow port72dmay not be disposed corresponding to the center of the ink reservoir73a, and moreover may not be disposed such that there can exist the same number of outflow ports74con either side of the inflow port72d. For example, the inflow port72dcan be disposed such that numerical difference of the existing outflow ports74cis one on either side of the inflow port72d.

The inflow port72dmay be disposed at other various positions as long as at least one outflow port74cexists on either side of the inflow port72din the extending direction of the ink reservoir73a.

Although the filter70fis disposed within the introduction passage in the above-described embodiment, the filter may be disposed at any other positions within the reservoir unit70, or the filter can be omitted.

An application of the present invention is not limited to ink-jet printers. The present invention is applicable also to, for example, ink-jet type facsimile or copying machines.