Inkjet head with filter for ink supply openings

There is provided an inkjet head with a plurality of nozzle rows, each of which has a plurality of nozzles arranged along a first direction. A plurality of fluid channels connects a plurality of common ink chambers to the plurality nozzles via the plurality of pressure chambers, and a plurality of ink supply openings corresponds to the plurality of common ink chambers. Each of the plurality of ink supply openings communicates with a corresponding one of the plurality of common ink chambers. The inkjet head also includes a filter that covers the plurality of ink supply openings. The filter includes filtering portions that eliminate dust in ink flowing therethrough. Each filtering portion respectively corresponds to one of the plurality of ink supply openings, and is configured such that each filtering portion's dimension in the first direction is longer than its dimension in the second direction when viewed in plan view.

INCORPORATION BY REFERENCE

This application claims priority of Japanese Patent Application No. 2004-046637, filed on Feb. 23, 2004, the entire subject matter of the application is incorporated herein by reference thereto.

BACKGROUND OF THE INVENTION

The present invention relates to a piezoelectric type inkjet head used for an inkjet printing device.

Inkjet printers employing a piezoelectric type inkjet head for ejecting ink onto a substrate are widely used. Japanese Patent Provisional Publication No. 2002-36545 discloses one of such inkjet printers. An inkjet head disclosed in the publication has a cavity unit including a plurality of plates laminated with each other by use of an adhesive, a piezoelectric actuator adhered to a rear surface of the cavity unit, and a flexible flat cable adhered to a rear surface of the piezoelectric actuator which is electrically connected to an external device.

More specifically, the cavity unit includes a nozzle plate, a manifold plate and a base plate each of which has a rectangular shape when viewed as a plan view. The nozzle plate situated on a front side of the cavity unit is provided with a plurality of nozzles which are arranged in two rows along a longer side direction of the nozzle plate. The base plate situated on a rear side of the cavity unit is provided with a plurality of pressure chambers which are aligned in two rows along an arranging direction of the plurality of nozzles. The manifold plate situated between the nozzle plate and the base plate is provided with two common ink chambers elongated along an arranging direction of the pressure chambers.

At one end portion of the base plate, two ink supply openings are opened to be aligned in parallel with a shorter side of the base plate so that the ink supply openings communicate with the corresponding common ink chambers.

In the above mentioned configuration of the inkjet head, the number of nozzle rows, the number of pressure chamber rows, the number of common ink chambers, and the number of ink supply openings are equal to each other.

It is also disclosed in the publication that the two ink supply openings are covered with a filter.

SUMMARY OF THE INVENTION

Recently, for enhancing printing speed and printing resolution, it is required to increase the number of nozzle rows of the cavity unit. If the number of nozzle rows is increased in the configuration of the cavity unit of the above mentioned publication, it is required to increase the number of common ink chambers and the number of ink supply openings in accordance with the number of nozzle rows.

For example, if a cavity unit used for color printing based on four color components of black, yellow, magenta and cyan is designed based on the configuration of the cavity unit disclosed in the above mentioned publication, four ink supply openings will be formed on one end portion of the base plate to be aligned along the shorter side of the base plate. If the cavity unit for color printing is designed in such a manner, two filters are required to cover four ink supply openings because the filter disclosed in the publication is configured to cover only two ink supply openings. In this case, two filters will be adhered to the base plate to be aligned in parallel with the shorter side of the base plate.

In this case, in view of a size of each filtering portion of the filter, the two filters are required to be adhered to the base plate so that peripheral portions thereof do not overlap with each other. Such a configuration further requires to increase the width between inner two ink supply openings. Consequently, the length of the shorter side of the base plate increases, and thereby the size of the base plate (i.e. the inkjet head) is increased.

Also, in this case, manufacturing processes are increased by the increase of the number of filters.

The present invention is advantageous in that it provides an inkjet head configured to be compact in size even if the number nozzle rows is increased.

According to an aspect of the invention, there is provided an inkjet head which is provided with a plurality of nozzle rows each of which has a plurality of nozzles arranged along a first direction, a plurality of pressure chambers connected to the plurality of nozzles, a plurality of common ink chambers respectively corresponding to the plurality of nozzle rows, a plurality of fluid channels connecting the plurality of common ink chambers to the plurality nozzles via the plurality of pressure chambers, and a plurality of ink supply openings corresponding to the plurality of common ink chambers. The plurality of ink supply openings is arranged along a second direction different from the first direction so that each of the plurality of ink supply openings communicates with corresponding one of the plurality of common ink chambers. The inkjet head is further provided with a filter located to cover the plurality of ink supply openings.

In this structure, the filter includes filtering portions that have functions of eliminating dust in ink flowing therethrough. The filtering portions respectively correspond to the plurality of ink supply openings. Each of the filtering portions is configured such that a size of an outline thereof in the first direction is longer than a size of the outline in the second direction when viewed as a plan view.

With this configuration, since the filter covers the plurality of ink supply openings, it is not necessary to increase the number of filters in accordance with the number of ink supply openings. Also, it becomes possible to reduce the width of each filtering portion in the second direction, and thereby it becomes possible to reduce the length of the filter in the second direction while securing an adequate size of each filtering portion in a plan view.

Further, the filter can be as compact as possible while attaining the adequate filtering function. Accordingly, the inkjet head can be configured to be compact in size.

In a particular case, the inkjet head may have a rectangular shape. In this case, the first direction is parallel with a longer side direction of the rectangular shape of the inkjet head, and the second direction is parallel with a shorter side direction of the rectangular shape of the inkjet head.

In a particular case, each of the filtering portions may have an elliptical shape.

Optionally, at least one ink supply opening of the plurality of ink supply openings may communicate with two or more of the plurality of common ink chambers, and one of the filtering portions corresponding to the at least one ink supply opening may have an outline shape larger than outline shapes of all of the other filtering portions.

Still optionally, each of the filtering portions may be elongated along a direction in which each of the common ink chambers is elongated. In this case, each of the plurality of ink supply openings has a shape substantially the same as that of corresponding one of the filtering portions. Each of the filtering portions communicates with an end portion of corresponding one of the plurality of common ink chambers via corresponding one of the plurality of ink supply openings.

Still optionally, each of the filtering portions may substantially overlap with the corresponding one of the plurality of ink supply openings and the end portion of the corresponding one of the plurality of common ink chambers when viewed as a plan view so that no step portion is formed in a fluid channel formed of the each of the filtering portions, the corresponding one of the plurality of ink supply openings and the end portion of the corresponding one of the plurality of common ink chambers.

In a particular case, the filter may be formed to be a thin sheet-type member.

In a particular case, the inkjet head may have a laminated structure of a plurality of layers, and the filter may have a gluing part surrounding the filtering portions, the filter being adhered to an end portion of a layer being is provided with the plurality of ink supply openings through the gluing part.

In a particular case, the plurality of common ink chambers may include five common ink chambers, the plurality of ink supply openings may include four ink supply openings, and the filtering portions may include four filtering portions.

DETAILED DESCRIPTION OF THE EMBODIMENTS

As shown inFIG. 1, the inkjet head HD includes a cavity unit1made from metal plates and a plate type piezoelectric actuator2. InFIG. 1the cavity unit1is illustrated as an exploded view. The piezoelectric actuator2is adhered to a top surface of the cavity unit1, and a flexible flat cable3(seeFIG. 3) is adhered to a top surface of the piezoelectric actuator2for electrical connection to an external device (e.g. an external controller). On the lowest layer (plate) of the cavity unit1, a plurality of nozzles4are opened. By this structure, ink is ejected downwardly from the nozzles4.

The configuration of the cavity unit1will be explained in detail with reference toFIGS. 1 to 3. The cavity unit1includes a nozzle plate11, a first spacer plate12, a damper plate13, two manifold plates14aand14b,a second spacer plate15, a third spacer plate16, and a base plate17which are laminated with each other by adhesions. That is, the cavity unit1has eight plates in total.

In this embodiment, each of the plates12,13,14a,14b,15,16and17is made of 42% nickel alloy steel sheet having a thickness of 50 through 160 μm. The plurality of nozzles4from which ink is ejected are formed in the nozzle plate11so as to be aligned in predetermined minute intervals which correspond to printing resolution. More specifically, five nozzle rows are formed in the nozzle plate11. In each nozzle row, the nozzles4are aligned in a staggered arrangement in a longer side direction (X-direction) of the nozzle plate11.

In the base plate17, a plurality of pressure chambers36are formed in five rows along the X-direction. In each pressure chamber row, the pressure chambers36are aligned in a staggered arrangement. As shown inFIG. 2, in the base plate17, each pressure chamber36is configured to be a slender opening elongated along a shorter side direction (Y-direction) of the base plate17. One end portion36aof the pressure chamber36communicates with the nozzle4, and the other end portion36bof the pressure chamber36communicates with a common ink chamber7. In this embodiment, a longitudinal direction (a direction of a line connecting the end portions36aand36b) of the pressure chamber36equals to the Y-direction.

As shown inFIG. 2, the end portion36aof the pressure chamber36communicates with the nozzle4via through holes37which are respectively formed in the second and third spacer plates15and16, the manifold plates14aand14b,the damper plate13and the first spacer plate12. The through holes37, each of which has a minute diameter, are also aligned in a staggered arrangement on each of the plates12,13,14a,14b,15and16in accordance with the arrangement of the nozzles4.

In the third spacer plate16adhered to the bottom surface of the base plate17, through holes38are formed at positions corresponding to the end portions36bof the pressure chambers36so that the end portions36bcommunicate with the through holes38, respectively.

In the second spacer plate15adhered to the bottom surface of the third spacer plate16, channels40are formed for the ink supply from the common ink chambers7to the respective pressure chambers36. The channel40has an inlet hole40ato which ink enters from the common ink chamber7, an outlet hole40bfrom which ink exits toward the pressure chamber36(the through hole38), and a narrow space portion40cformed to connect the inlet hole40aand the outlet hole40b.The narrow space portion40cis formed to have a cross-sectional area smaller than that of the outlet hole40bso that the narrow space portion40chas the maximum fluid channel drag in the channel40.

The narrow space portion40cis formed by conducting half-etching on the top surface (adjoining to the third spacer plate16) of the second spacer plate15so that the narrow space portion40chas predetermined fluid channel drag. The inlet hole40aand outlet hole40bare aligned with end portions of the narrow space portion40c,respectively. The inlet hole40ais formed as a through hole penetrating the second spacer plate15. The outlet hole40bis formed on the top surface of the second spacer plate15as a recessed portion.

In this embodiment, five common ink chambers7are formed to penetrate the manifold plates14aand14bso that each of the common ink chambers7is elongated along the arranging direction (X-direction) of the nozzle row. By laminating the manifold plates14aand14b,adhering the second spacer plate15to the top surface of the manifold plate14b,and then adhering the damper plate13to the bottom surface of the manifold plate14a,the five common ink chambers7are hermetically sealed. Each common ink chamber7is elongated along the arranging direction of the pressure chamber row when viewed along the laminating direction of the cavity unit1(seeFIGS. 5 and 6).

As shown inFIGS. 2 and 3, damper rooms45are formed on the bottom surface of the damper plate13as recessed portions so that the damper rooms are isolated from the common ink chambers7. Outline shapes and positions of the damper rooms45coincide with those of the common ink chambers7when viewed along the laminating direction of the cavity unit1.

Since the damper plate13is made of metal having elasticity, thin plate portions of the damper plate13formed at portions corresponding to the damper rooms45freely moves toward a common ink chamber side and toward a damper room side. That is, the thin plate portions can vibrates in the vertical direction onFIG. 3. By this structure, even if the pressure variation caused in the pressure chamber36is transmitted to the common ink chamber7, the pressure variation is damped by elastic deformation (i.e. a damper effect) of the thin plate portion of the damper plate13. Therefore, a crosstalk that a pressure variation caused in one pressure chamber36is transmitted to another pressure chamber36is prevented.

On the top surface of the third spacer plate16, grooves50are formed to be elongated in the arranging direction (X-direction) of the pressure chamber row between adjacent pressure chamber rows. The groove50communicates with the outside of the cavity unit1via an opening so as to function as a fluid channel for an inspection. By detecting the outflow of air from the groove50at the opening or detecting the reduction of the pressure of ink on an ink supply opening side, leakage of ink at portions between the adjacent pressure chamber rows and leakage of ink from each pressure chamber36can be inspected.

As described above, by laminating the eight plates11through17with each other, the common ink chambers7are formed. Also, fluid channels each of which is elongated from the inlet hole40ato the corresponding nozzle4via the through hole38, the pressure chamber36and the through hole37are formed.

As shown inFIG. 1, at the one side portion of each of the base plate17and the second and third spacer plates15and16, four ink supply openings are formed to penetrate each of the base plate17and the second and third spacer plates15and16. The four ink supply openings are aligned along the shorter side direction (Y-direction) of each plate. In the following, the four ink supply openings are assigned numerical references of47a,47b,47cand47d,respectively. Positions of the four ink supply openings47a,47b,47cand47don the base plate17substantially coincide with positions of the four ink supply openings47a,47b,47cand47dof the other plates16and15.

Since five common ink chambers7are formed, the ink supply opening47ais designed to communicate with two common ink chambers7aand7a.In this structure, black ink is supplied through the ink supply opening47, considering the fact that the amount of black ink consumed per a unit time is the largest of all of color components of ink if the printing speed for monochrome printing is set to be higher than that of the color printing.

Yellow ink, magenta ink, and cyan ink are supplied to the ink supply openings47b,47cand47d,respectively. The ink supply openings47b,47cand47dcommunicate with the common ink chambers7b,7cand7d,respectively (seeFIG. 4).

As shown inFIG. 4, each of the ink supply openings47b,47cand47dis formed to substantially overlap with one end portion of the corresponding common ink chamber7when viewed along the laminated direction. Also, the ink supply opening47ais formed to substantially overlap with one end portions of the common ink chambers7aand7awhen viewed along the laminated direction.

As shown inFIG. 6, outline shapes (and sizes) of the ink supply openings47b,47cand47dare substantially equal to the one end portions (i.e. upstream end portions) of the common ink chambers7b,7cand7d,respectively. Upstream end portions of the common ink chambers7aand7aare configured so that when viewed along the laminated direction, the total of sizes of the upstream end portions of the common ink chambers7aand7ais substantially equal to the ink supply opening47afor black ink.

It should be noted that various types of processing such as etching, electrical discharge machining, plasma processing or laser processing can be used for making holes and recessed portions in the plates12through17including the ink supply openings47, common ink chambers7, through holes37and38, channels40, the damper room45and the grooves50.

Next, a filter20according to the embodiment of the invention will be described in detail with reference toFIGS. 4 to 6. To the top surface of the base plate17, the filter20is adhered, by use of an adhesive, at a portion in which a group of ink supply openings47a,47b,47cand47dis formed to cover the ink supply openings47a,47b,47cand47d.The filter20is made of resin such as a polyimide and is configured to be a thin sheet-type member having a rectangular shape when viewed as a plan view. It is noted that only one filter20is used in this embodiment.

The filter20is provided with four filtering portions20a,20b,20cand20d,at positions corresponding to positions of the ink supply openings47a,47b,47cand47d,respectively. Each of the filtering portions20a,20b,20cand20deliminates dust (and debris, etc.) from ink passing therethrough. The filtering portions20a,20b,20cand20dhave substantially the same outline shapes (and sizes) as those of the ink supply openings47a,47b,47cand47d,respectively, when viewed as a plan view. The filter20is located so that the filtering portions20a,20b,20cand20dsubstantially overlap with the ink supply openings47a,47b,47cand47d,respectively.

Each of the filtering portions20a,20b,20cand20dhas an elliptical shape (having two straight line portions) elongated along the X-direction when viewed as a plan view. A portion of the filter20except for the filtering portions20a,20b,20cand20dis adhered to the top surface of the base plate17.

In this embodiment, considering occurrence of a positional error in adhering work of the filter20, the filter20is configured such that the ink supply openings20a,20b,20cand20dare slightly larger than the ink supply openings47a,47b,47cand47d,respectively, when viewed as a plan view. The filtering portion20afor black ink has an outline shape larger than outline shapes of all of the other filtering portions20b,20cand20dwhen viewed as a plan view.

Various types of processes such as plasma processing and laser processing can be used to form the filtering portions20a,20b,20cand20din the filter20. For example, each filtering portion may be formed by forming a number of minute holes penetrating a base material of the filter20in a direction of thickness of the base material. If the filter20is made of metal, the filtering portion may be formed by electroforming.

In the above mentioned structure, ink is supplied from an ink reservoir (not shown) to the corresponding common ink chamber7after dust is removed from the ink when passing through the filter20. Then, as shown inFIG. 2, the ink in the common ink chamber7is supplied to the end portion36bof the pressure chamber36via the channel40of the second spacer plate15and the through hole38of the third spacer plate16. Then, the ink in the pressure chamber36is supplied to the corresponding nozzle4via the through holes37by the actuation of the piezoelectric actuator2.

It is noted that the filter20has a size large enough to cover all of the ink supply openings47a,47b,47cand47d,and has filtering portions respectively corresponding to the ink supply openings47a,47b,47cand47d.Therefore, it is not necessary to increase the number of filters in accordance with the number of ink supply openings (47a,47b,47cand47d).

In addition, by only adhering the filter20to the top surface of the base plate17at the portion of the ink supply openings47a,47b,47cand47d,the filtering function of removing duct (and debris, etc.) from the ink can be attained. Therefore, the deterioration of performance of the inkjet head HD due to foreign material (dust, debris, etc.) can be prevented.

As described above, the portion of the filter20surrounding the filtering portions20a,20b,20cand20dis used as a gluing part. Such a configuration enables the gluing part and the filtering portions20a,20b,20cand20dto be integrally formed on a single sheet-type member (i.e. the filter20). Therefore, it becomes possible to secure an adequate size on the filter20for the gluing part even if the length of the filter20in a longitudinal direction (Y-direction) of the filter20is within the shorter side width of the base plate17.

As described above, the filtering portion (20a,20b,20cand20d) is formed to have an elliptical shape elongated along the longer side direction of the base plate17when viewed as a plan view. By this structure, it becomes possible to reduce the width of each filtering portion in the shorter side direction (Y-direction) of the base plate17without increasing fluid channel drag. Further, it becomes possible to reduce the length of the filter20in the Y-direction while securing an adequate size of each filtering portion (20a,20b,20cand20d).

As described above the filtering portions20a,20b,20cand20d,the ink supply openings47a,47b,47cand47d,and the upstream end portions of the common ink chambers7have substantially the same sizes and shapes, respectively, when viewed along the laminating direction, and they substantially overlap with each other when viewed along the laminating direction. Therefore, a step portion causing retention in the ink flow is not formed in an inside wall of a fluid channel from the filtering portion to the common ink chamber7. Consequently, stability of ejecting motion of the inkjet head HD is enhanced.

According to the embodiment of the invention, the filter20can be formed as compact as possible while attaining the adequate filtering function and securing an adequate size of the gluing part. Such a configuration avoids the necessity for increasing the size of the base plate17in the shorter side direction, and also avoids the necessity for increasing intervals of the ink supply openings47. Accordingly, the inkjet head HD can be configured to be compact in size. Since only one filter20is used in the cavity unit1, the amount of manufacturing processes is not increased for the filter20.

As described above, the number of common ink chambers is five on the one hand, the number of ink supply openings (i.e. the number of nozzle rows and the number of pressure chamber rows) is four on the other hand. The ink supply opening47ais formed to communicate with the two common ink chambers7aand7a.With this structure, it becomes possible to reduce the intervals of the ink supply openings47in the Y-direction in comparison with a case in which the number of ink supply openings is equal to the number of common ink chambers. Therefore, it becomes possible to decrease the length in the Y-direction of each of the base plate17, second spacer plate15and third spacer plate16while securing adequate sizes of the ink supply openings47a,47b,47cand47din a plan view.

In this embodiment, the two common ink chambers7aand7aare used in combination but are not united as a single chamber. Therefore, the rigidity of the cavity unit1is enhanced.

The area of the filtering portion20ain a plan view is larger than that of the other filtering portions20b,20cand20d.By such a structure, it is prevented that the supply of ink to the common ink chambers7aand7adecreases due to the structure of the filtering portion20a.Also, in regard to the structure of the ink supply openings47, it is not necessary to increase the length in the shorter side direction of each of the base plate17, the space plates15and16. By this structure, the inkjet head1can be configured to be compact in size while keeping the adequate filtering function.

The piezoelectric sheet2has a laminated structure of a plurality of piezoelectric sheets and a top sheet, each of which has a thickness of about 30 μm. A piezoelectric sheet situated at the undermost layer of the piezoelectric actuator2is provided with a plurality of slit-like electrodes on the top surface thereof, at positions corresponding to the positions of the pressure chambers36of the cavity unit1. The slit-like electrodes in each electrode row are aligned along the X-direction. Each slit-like electrode is formed to be elongated in the Y-direction so that end portions of outward slit-like electrodes reach the peripheral portion of the undermost piezoelectric sheet.

If the layers of the piezoelectric actuator2are counted from the undermost layer, even-numbered layers is provided with common electrodes on their top surfaces, respectively. Each common electrode is used for the plurality of pressure chambers36. The uppermost layer of the piezoelectric actuator2is provided with a plurality of electrodes9respectively corresponding to the slit-like electrodes of the undermost layer. The plurality of electrodes9include electrodes electrically connected to the slit-like electrodes of the undermost layer, respectively, and an electrode connected to the common electrode.

The piezoelectric actuator2may be configured to have a configuration different from the above mentioned configuration as indicated in, for example, U.S. Pat. No. 5,402,159, the disclosure of which is incorporated herein by reference.

The piezoelectric actuator2may be assembled as follows. Firstly, an adhesive sheet made from synthetic resin adhesive having a non-penetrative property for ink is attached to the entire region of the bottom surface (a surface facing the pressure chambers36) of the electric actuator2. Then, the piezoelectric actuator2is attached to the cavity unit1so that each of the slit-like electrodes of the undermost layer faces the corresponding one of the pressure chambers36.

The flexible flat cable3is attached to the top surface of the piezoelectric actuator2by heating and pressurization so that electrical wiring patterns of the flexible flat cable3are electrically connected to the electrodes9of the top surface of the piezoelectric actuator2.

In the above mentioned structure, if a voltage is applied between the common electrode and one of the slit-like electrodes, an active part between the common electrode and the one slit-like electrode is deformed by piezoelectric vertical effect in a laminated direction of the layers of the piezoelectric actuator2.

The deformation decreases the volume of the corresponding pressure chamber36. Therefore, if the piezoelectric sheet sandwiched between the common electrode and the one slit-like electrode has a polarizing direction equal to a direction of the electric field applied thereto, ink in the pressure chamber36is ejected from the nozzle4as a drop of ink.

Although the present invention has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible.

For example, the base material of the filter20may be a thin plate-like member made of metal. In this case, various types of processing such as electroforming processing, plasma processing or laser processing can be used for making filtering portions in the base material.

In the above mentioned embodiment, the filtering portion is formed to have an elliptical form; however, various types of shapes including an oval shape, a rectangular shape and a polygonal shape may used to form the filtering portion in the base material of the filter.

Various types of ink such as gloss ink may be used by the inkjet head HD. In the above mentioned embodiment, the ink supply opening47is formed such that one or two common ink chambers communicate with the ink supply opening. However, the ink supply opening may be configured such that three or more common ink chambers communicate with the ink supply opening.

Various types of shapes including a circular shape, an ellipse, an elliptical shape, a rectangular shape and a polygonal shape may used to form the ink supply opening.

If the cavity unit1is designed so that of the shorter side of the cavity unit1has a length shorter than that of the above mentioned embodiment, the ink supply opening may be designed to have a width in the sorter side direction of the cavity unit1narrower than that of the above mentioned embodiment. The number of ink supply openings may be different from that of the above mentioned embodiment.

In view of the stability of a ink ejection property, it is preferable that the filtering portion, the ink supply opening and the upstream end portion of the common ink chamber have substantially the same shape and size as mentioned above so that they overlap with each other when viewed as a plan view. By this structure, a smooth ink flow can be secured without causing retention of air bubbles in the ink flow.