JP3982054B2 - Inkjet head - Google Patents

Description

【００４０】
次に、インクジェットプリンタ１の制御部について脱明する。
図６は、インクジェットプリンタ１の制御部の構成を説明するためのブロック図である。
【００４１】
インクジェットプリンタ１の制御部は、ＣＰＵ１０１、ＲＡＭ１０２、ＲＯＭ１０３、データ受信郭１０４、ヘッド吐出駆動部１０５、ヘッド移動駆動部１０６、紙送りモータ駆動部１０７、回復系モータ駆動部１０８、および各種センサ部１０９を含んでいる。
【００４２】
全体を制御するＣＰＵ１０１は、必要に応じてＲＡＭ１０２を用い、ＲＯＭ１０３に記憶されているプログラムを実行する。このプログラムには、ホストとなるコンピュータ等に接続され記録すべき画像データを受信する、データ受信部１０４から読み込まれる画像データに基づいて、ヘッド吐出駆動部１０５、ヘッド移動駆動部１０６、紙送りモータ駆動部１０７、各種センサ部１０９を制御し記録シート２上に画像を記録するための部分と、必要な際に、各種センサ部１０９からの情報を処理し、回復系モータ駆動部１０８を制御して、ヘッドユニット３のノズル面を良好な状態に回復させるための部分とが含まれる。
【００４３】
ＣＰＵ１０１の制御に基づいて、ヘッド吐出駆動部１０５は、画像データに対応するパルス電圧を印加することによりヘッドユニット３内のインクジェットヘッド３１を駆動する。具体的には、ヘッド吐出駆動部１０５から画像データに対応するパルス電圧が第２電極８３に所定のタイミングで印加される。なお、ヘッド吐出駆動部１０５には、図示しない充放電回路、反転回路、反転増幅回路が含まれる。
【００４４】
また、ＣＰＵ１０１の制御に基づいて、ヘッド移動駆動部１０６はヘッドユニット３を保持するキャリッジ４を移動させる駆動モータ７を駆動し、紙送りモータ駆動部１０７は紙送りローラを駆動する。さらに、ＣＰＵ１０１の制御に基づいて、回復系モータ駆動部１０８は、ヘッドユニット３のノズル面を良好な状態に回復させるために必要なモータ等を駆動する。
【００４５】
本発明は、上記のように構成されており、次に、インクジェットヘッドの動作について説明する。
【００４６】
図７は、インク液滴を吐出させる際の動作を説明するための図、図８は、インク液滴を吐出させる際の駆動電圧の波形とこのときの諸量の変化とを示す図である。
【００４７】
インク液滴の吐出を行う場合には、まず図７Ａ（図８のＴＡ区間）の状態から、ヘッド吐出駆動部１０５内の各回路に基づく制御により、第１電極である振動板７０と第２電極８３との間に、所定の駆動電圧を印加する（図８のＴＢ区間）。この駆動電圧を印加したことによって生じる静電気力により、図７Ｂに示すように、振動板７０を第２電極８３側に引き付ける。このインク吸引動作時には、振動板７０を比較的ゆっくり動かすようにする。そして、図示のように振動板７０は第２電極８３側に撓み変形する。
【００４８】
なお、本実施形態では、第１電極である振動板７０をアースとしているので、駆動電圧は、第２電極８３に＋の電位を印加している。この駆動電圧により振動板７０には、図７における下方に、次式により算出される力Ｆが作用する。
Ｆ＝１／２・｛εｒεｏＳ（Ｖ／ｄ）² ｝ ……（１）
ただし式中、εｒは第１電極および第２電極間の比誘電率、εｏは真空の比誘電率（＝８．８５４×１０^-12 Ｆ／ｍ）、Ｓは電極の面積、Ｖは電圧、ｄは第１電極および第２電極間の長さである。
【００４９】
これにより、インク供給室９１から連通孔８１を通って空間８２に充填されているインクは、振動板７０に形成された貫通孔７１を通りインクチャンネル６１内に流入する。このとき振動板７０が比較的ゆっくり動かされるので、貫通孔７１を通過するインクは、層流に近い流れとなる。したがって、流路抵抗が低いので、インクはほとんど逆方向に引き込まれることがなく、貫通孔７１を通ってインクチャンネル６１内にスムーズに供給される。
【００５０】
このとき、図８に示すように、振動板７０の変形体積ΔＸ1 が徐々に変化するにともなって（図８のＴＢ区間）、振動板７０の貫通孔７１を通過するインク体積ΔＸ2 がスムーズに変化し、ノズル５１の先端に形成されるインクのメニスカス３９の変化体積ΔＸ3 も比較的変化が小さいことがわかる。
【００５１】
そして、一定時間（数μｓｅｃ〜数十μｓｅｃ）駆動電圧を印加した状態で保持してから、駆動電圧を遮断停止する（図８のＴＣ区間）。この駆動電圧の遮断により、第２電極８３側に引き付けられていた振動板７０は、図７Ｃに示すように、振動板７０自身の剛性によって元の位置の方へ引き戻される。
【００５２】
このように、インク吐出動作時には、上記インク吸引動作時と比較して振動板７０を急速に動かすようにしたため、貫通孔７１を通るインクは乱流に近い流れになる。したがって流路抵抗が高くなり、貫通孔７１を通って逆方向に戻るインクはごく僅かであり、ほとんどが吐出に寄与するようになる。一方、対向基板８０には、振動板７０の貫通孔７１よりも十分大きな連通孔８１を設けてあるため、インクの流れをほとんど阻害することがない。
【００５３】
こうしてインクチャンネル６１の容積が収縮し、このとき発生する圧力により、インクチャンネル６１内に充填されたインクは、ノズル５１から液滴として飛翔し、記録シート２上に着弾して所定の画像が形成される。
【００５４】
このように本実施形態によれば、電極間ギャップにインクが充填されるような構成にしたので、電極間ギャップに何も充填しない場合と比べて、同じ電極間ギャップ距離であっても電界強度を大幅に向上することができる。すなわち、上記式（１）からわかるように、電極間物質の誘電率が大きくなるほど所定の力Ｆを得るための電圧値は低くなるので、低電圧で駆動することができる。インクの比誘電率は例えば水系インクの場合は約６０なので、同じ電界強度でよければ電極間ギャップを約８倍に広げることが可能となる。このように、電界強度の面でギャップ間が空気の時と比べて有利となるため、電極間ギャップを３μｍと従来例と比較して広く形成でき、加工が大幅に容易になる。
【００５５】
また、振動板７０にインクが通過可能な貫通孔７１を開け、この貫通孔７１の裏側からインクを供給することによって、インクはほとんど一方向に移動させられることになるので、インク吐出（飛翔）効率が高くなり、かつインクジェットヘッドの駆動周波数に対する追随性の向上を達成することができる。
【００５６】
さらに、上記インクジェットヘッドの構成において、インク吐出動作時とインク吸引動作時における振動板７０に設けた貫通孔７１の流路抵抗の違いについて実験を行った。図９は、貫通孔をストレート孔とした場合のその形状と印加圧力に対する流路抵抗とを示す図、図１０は、貫通孔をテーパ孔とした場合のその形状と印加圧力に対する流路抵抗とを示す図である。
【００５７】
この実験では、孔形状の違う２種類の振動板に対してそれぞれ、所定の圧力でインクを通過させ、その時の流速から、流路抵抗Ｒの印加圧力Ｐ依存性を求めたものである。この図９および図１０の結果から、まず、印加圧力Ｐが大きい時ほど流路抵抗Ｒが大きくなることが確認できた。このことは、振動板７０の速度が速いほど乱流が起こりやすく流路抵抗Ｒが大きくなるので、インクを通しにくくなることを裏付けるものである。したがって、インク吸引動作時には、振動板７０をゆっくり動かし、インク吐出動作時には、振動板７０を急速に動かすことで、インクの流れが吐出方向に向かうことがわかる。
【００５８】
また、図１０から、振動板７０に開ける貫通孔７１の形状は、吐出方向に対して断面積が拡大していく形状の方が、インク流れの一方向化の観点から好ましいことがわかる。これは、図示のように、インク吐出時にインクが通過する可能性のある方向２の方が、インク吸引時にインクが通過する方向１よりも流路抵抗Ｒが大きくなるからである。
【００５９】
（実施形態２）
図１１は、本発明の実施形態２に係るインクジェットヘッドの断面図である。上記実施形態１と共通した機能を有する部材には同一の符号を付し、その説明は省略する。
【００６０】
この実施形態２では、図１１に示すように、第２電極８３は、第１電極である振動板７０に対しノズル５１側に形成されている点で、上記実施形態１と相違しており、その他の点については上記実施形態１と同様である。すなわち、振動板７０と対向基板８０の位置関係が上記実施形態１と逆になっている。なお、実施形態２では、第２電極８３が形成された対向基板８０に、インクが通過可能な連通孔８１を有することが必須となる。
【００６１】
したがって、上記実施形態１では駆動電圧の遮断時（放電時）にインクを吐出するが、この実施形態２では、逆に駆動電圧の印加時に、静電吸引力によって直接インクを吐出することができる。これにより、上記実施形態１と同様の効果を得ることができるほか、印加する駆動電圧の波形によって振動板７０の過渡的な挙動を比較的容易に制御することが可能となる。
【００６２】
（実施形態３）
図１２は、本発明の実施形態３に係るインクジェットヘッドの断面図である。上記実施形態１と共通した機能を有する部材には同一の符号を付し、その説明は省略する。
【００６３】
この実施形態３では、図１２に示すように、第１電極である振動板７０と第２電極８３との間の側方から図示矢印方向にインクが供給されるようにした点で、上記実施形態１と相違しており、その他の点については上記実施形態１と同様である。このようにすれば、上記実施形態１と同様の効果を得ることができるほか、第２電極８３が形成された対向基板８０に、インクが通過可能な連通孔８１を形成する必要がなくなり、インクジェットヘッドの製造が一層容易となる。
【００６４】
（実施形態４）
図１３は、本発明の実施形態４に係るインクジェットヘッドの断面図である。上記実施形態１と共通した機能を有する部材には同一の符号を付し、その説明は省略する。
【００６５】
この実施形態４では、図１３に示すように、第１電極である振動板７０に対し第２電極８３側と反対側の対向する位置に間隙を有して第３電極８６が設けられる。この第３電極８６は、第２電極８３と同様に金属スパッタなどにより成膜される。これら第２電極側８３および第３電極８６の表面には、樹脂蒸着などで成膜することにより、所定厚さの絶縁層８３ａ，８６ａが形成される。振動板７０は、可撓性を有するシート状の導電体である導電性フィルムで構成され、その一端が第２電極８３側近傍に固定されると共に他端が第３電極８６側近傍に固定され、Ｓ字状を呈して、インクチャンネル６１内に設置されている。そして、ノズル５１は、第２電極８３と第３電極８６との間の側方に設けられている。その他の点については上記実施形態１と同様である。
【００６６】
この実施形態４にあっては、図示上下に設けた第２電極側８３または第３電極８６に駆動電圧を印加することで、導電性フィルムである振動板７０を、図示２点鎖線で示すように、静電吸着力により前後に動かす。振動板７０には、インクが通過可能な貫通孔７１が設けられているので、上記実施形態と同様の原理によりインクをノズル５１に向けて前方へ押し出すことができる。このようにすれば、上記実施形態１と同様の効果を得ることができる。
【００６７】
なお、以上説明した実施形態は、本発明を限定するために記載されたものではなく、本発明の技術的思想内において当業者により種々変更が可能である。
【００６８】
例えば上述した実施形態では、振動板７０ないし対向基板８０に対して孔７１，８３を開けるようにしたが、その代わりに、メッシュが形成された板を用いてもよい。このようにすれば、多数の孔が均一に分布しているので、インクジェットヘッドの組み立て時に、振動板７０の位置合せの必要性をなくすことができる。また、万一１つの孔が詰まったとしてもその影響が少ない利点がある。
【００６９】
また、インク吐出動作時に、高周波振動により、振動板７０を複数回振動させて、１滴のインク滴を飛翔させるようにしてもよい。インクジェットヘッドの構成において、振動板７０の固有振動周期を、インクの固有振動周期よりも十分速くなるように設計しておき（例えば振動板７０の厚みを厚くすると、変位量は減るが固有振動周期を速くすることができる。）、振動板７０の固有振動周期に合った高周波で駆動すると、―回の振動あたり所定量ずつインクが前方に送られるので、印加信号としてあたえられた振動数によってインク滴の体積を変調することも可能になる。
【００７０】
【発明の効果】
以上述べたように、請求項１に記載の発明によれば、電極間ギャップにインクが充填されるような構成にしたので、電界強度の面でギャップ間が空気の時と比べて有利となるため、電極間ギャップを従来と比較して広く形成でき、加工が大幅に容易になる。
【００７１】
また、振動板にインクが通過可能な貫通孔を開け、この貫通孔の裏側からインクを供給することにより、インクはほとんど一方向に移動させられることになるので、インク吐出効率が高くなり、かつインクジェットヘッドの駆動周波数に対する追随性が向上する。
【図面の簡単な説明】
【図１】 インクジェットプリンタの概略構成を説明するための斜視図である。
【図２】 図１に示したヘッドユニットの１色分のインクジェットヘッドを含むキャリッジ周辺の構成を説明するための斜視図である。
【図３】 本発明の実施形態１に係るインクジェットヘッドの全体斜視図である。
【図４】 同分解斜視図である。
【図５】 図３におけるＶ−Ｖ線に沿う断面図である。
【図６】 インクジェットプリンタの制御部の構成を説明するためのブロック図である。
【図７】 インク液滴を吐出させる際の動作を説明するための図である。
【図８】 インク液滴を吐出させる際の駆動電圧の波形とこのときの諸量の変化とを示す図である。
【図９】 貫通孔をストレート孔とした場合のその形状と印加圧力に対する流路抵抗とを示す図である。
【図１０】 貫通孔をテーパ孔とした場合のその形状と印加圧力に対する流路抵抗とを示す図である。
【図１１】 本発明の実施形態２に係るインクジェットヘッドの断面図である。
【図１２】 本発明の実施形態３に係るインクジェットヘッドの断面図である。
【図１３】 本発明の実施形態４に係るインクジェットヘッドの断面図である。
【符号の説明】
１…インクジェットプリンタ、
２…記録シート（記録媒体）、
３…ヘッドユニット、
３１…インクジェットヘッド、
５１…ノズル、
６１…インクチャンネル（加圧室）、
７０…振動板（第１電極）、
７１…貫通孔、
９１…インク供給室、
８１…連通孔、
８２…空間、
８３…第２電極、
８６…第３電極、
１０５…ヘッド吐出駆動部（振動板駆動手段）。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ink jet head of a type in which a diaphragm is deformed by electrostatic force to fly ink and a driving device thereof.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, one of ink jet heads used in an ink jet recording apparatus is known that uses an electrostatic actuator (see JP-A-7-214769, JP-A-7-214770, etc.).
[0003]
This ink jet head forms an image on a recording medium by ejecting ink according to the following operation principle.
[0004]
First, when a voltage is applied between a pair of electrodes provided with a gap at opposite positions, an electrostatic force is generated between the electrodes, and this electrostatic force causes the diaphragm to move in the direction opposite to the pressurizing chamber communicating with the nozzle. Attract to. As a result, the ink is drawn into the pressure chamber from the common ink chamber and is filled. Then, by removing the voltage applied between the opposing electrodes, the diaphragm returns to its original position by the restoring force due to its own rigidity, and the volume of the pressurizing chamber is contracted rapidly. Due to the pressure generated at this time, the ink filled in the pressurizing chamber is ejected and flying as droplets from the nozzles, and the ink droplets land on the recording medium to form an image.
[0005]
[Problems to be solved by the invention]
By the way, in the ink jet head using the conventional electrostatic actuator, the gap between the pair of electrodes is a gap. For this reason, in order to drive the ink jet head by deforming the diaphragm at a low voltage, the gap interval has to be considerably narrowed (for example, 0.3 μm), and therefore, highly accurate processing is required. There was a problem of being.
[0006]
In addition, a part of the ink pressed by the deformation of the diaphragm moves in the inlet direction communicating with the common ink chamber (ink supply chamber) for supplying ink separately from the nozzle direction, so that the ink ejection efficiency is low. In addition, there is a problem that the followability to the drive frequency of the inkjet head does not increase. Here, the drive frequency of the inkjet head refers to the frequency of the voltage applied between a pair of electrodes when continuous printing is performed.
[0007]
The present invention has been made in view of the above-described problems of the prior art, and its object is to facilitate processing, increase the ink ejection efficiency, and improve the followability to the drive frequency of the inkjet head. There is.
[0008]
[Means for solving the problems]
  In order to achieve the above object, an invention according to claim 1 is directed to a nozzle, a pressurizing chamber communicating with the nozzle, and a pressure for changing the pressure in the pressurizing chamber.The first electrodeA diaphragm,Said1st electrodeIs a diaphragmA second electrode formed with a gap at a position facing the first electrode, and the first electrodeDiaphragm that is an electrodeandSaidBy applying a voltage between the second electrodes,The first electrodeIn the inkjet head that causes the ink in the pressure chamber to be ejected as droplets from the nozzle by deforming the diaphragm,The first electrodeInk is filled between the diaphragm and the second electrode, andThe first electrodeA through-hole through which ink can pass is formed in the diaphragm, and the first electrodeIs a diaphragmA third electrode with a gap at a position opposite to the second electrode side with respect to the second electrode side,The first electrodeThe diaphragm has flexibility,The second electrode is viewed from a direction perpendicular to the ink ejection direction in a plane parallel to the surface facing the pressurizing chamber.An S-shaped sheet-like conductor, one end of which is fixed in the vicinity of the second electrode side and the other end thereof is fixed in the vicinity of the third electrode side, and the nozzle is connected to the second electrode and the third electrode. It is provided on the side between the electrodes.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0015]
(Embodiment 1)
FIG. 1 is a perspective view for explaining a schematic configuration of the ink jet printer 1.
[0016]
The ink jet printer 1 prints on a recording sheet 2 which is a recording medium such as paper or an OHP sheet, and includes an ink jet head scanning system and a recording sheet feeding system.
[0017]
The ink jet head scanning system includes a head unit 3 including an ink jet print head for one color or a plurality of colors (for example, three colors, four colors, seven colors, etc.), a carriage 4 that holds the head unit 3, and a carriage 4 that is a recording sheet. The scanning shaft 5 and the guide shaft 6 for reciprocating in parallel with the recording surface 2, the pulse motor 7 for reciprocating the carriage 4 along the guide shaft 6, and the rotation of the pulse motor 7 for the reciprocating motion of the carriage 4. It comprises an idle pulley 8 for changing and a timing belt 9.
[0018]
On the other hand, the recording sheet feeding system includes a platen 10 that also serves as a guide plate for guiding the recording sheet 2 along the conveyance path, a paper pressing plate 11 that presses the recording sheet 2 between the platen 10 and prevents floating, and a recording A discharge roller 12 for discharging the sheet 2, a paper discharge pressing roller 13, a maintenance device 14 for cleaning the nozzle surface of the head unit 3 that discharges ink and recovering defective ink discharge to a good state, and a recording sheet 2. It comprises a paper feed knob 15 for manual conveyance.
[0019]
The recording sheet 2 is sent to a recording unit where the head unit 3 and the platen 10 are opposed to each other by a sheet feeding device such as a manual feed or a cut sheet feeder (not shown). At this time, the rotation amount of a paper feed roller (not shown) is controlled, and the conveyance to the recording unit is controlled. The paper feed roller is driven by a paper feed motor (not shown).
[0020]
The print head of the head unit 3 uses an inkjet head 31 described in detail later, and ink droplets ejected from the inkjet head 31 land on the recording sheet 2 to form an image. .
[0021]
The carriage 4 scans the recording sheet 2 in the horizontal direction (main scanning) by the pulse motor 7, the idle pulley 8, and the timing belt 9, and the head unit 3 attached to the carriage 4 records an image for one line. Each time recording for one line is completed, the recording sheet 2 is sent in the vertical direction (sub-scanning) and recorded on the next line.
[0022]
In this way, the image is recorded on the recording sheet 2, and the recording sheet 2 that has passed through the recording unit is discharged by the discharge roller 12 disposed on the downstream side in the transport direction and the discharge pressing roller 13 that contacts the discharge roller 12 with a constant pressure. It is configured to be discharged.
[0023]
FIG. 2 is a perspective view for explaining a configuration around the carriage 4 including the ink-jet heads 31 for one color of the head unit 3 shown in FIG.
[0024]
In the vicinity of the carriage 4, an ink cartridge 403 that contains ink and has a vent hole 404, a casing 401 that houses the ink cartridge 403, a casing lid 405, and an ink cartridge 403 that is detachable and supplies ink to the inkjet head 31. The direction opposite to the direction in which the ink supply pipe 402, the hook 406 for fixing the casing lid 405 to the casing 401 when the casing lid 405 is closed, the lid stopper 407, and the ink cartridge 403 are accommodated (direction of arrow D3) A pressing spring 408 that holds the ink cartridge 403 in the casing 401 between the casing lid 405 and the ink cartridge 403 is provided.
[0025]
When the carriage 4 having such a configuration moves in the scanning direction (the direction of the arrow D1), the recording sheet 2 is main-scanned. Further, when the recording sheet 2 is fed, printing is performed in the sub-scanning direction (direction of the arrow D2).
[0026]
3 is an overall perspective view of the inkjet head according to the first embodiment of the present invention, FIG. 4 is an exploded perspective view thereof, and FIG. 5 is a cross-sectional view taken along line VV in FIG. In each figure, for easy understanding, the nozzle is shown in a state where it is positioned above.
[0027]
As illustrated, the inkjet head 31 includes a nozzle plate 50, a channel plate 60, a vibration plate 70, a counter substrate 80, and an ink supply plate 90, and has a stacked configuration of these five element members.
[0028]
The nozzle plate 50 is made of, for example, nickel or an alloy thereof, and is manufactured by an electroforming method. In the nozzle plate 50, a plurality of holes to be the nozzles 51 are formed on the surface at equal intervals.
[0029]
The channel plate 60 is made of a resin, for example, and is molded by a mold. In the channel plate 60, an ink channel 61 as a pressurizing chamber is formed at a position corresponding to the nozzle 51. The ink channel 61 is a through hole having a square cross section.
[0030]
The diaphragm 70 is made of nickel or an alloy thereof, for example, like the nozzle plate 50, and is manufactured by an electroforming method. In the vibration plate 70, a plurality of through holes 71 through which ink can pass are formed at positions corresponding to the ink channels 61. In this embodiment, the diaphragm 70 is also the first electrode itself, and is formed as a common electrode as illustrated. The vibration plate 70 may be made by punching a hole in a metal plate such as nickel or stainless steel by punching or electric discharge machining in addition to being manufactured by nickel electroforming, and a plate made of resin or ceramic. (Film) may be drilled with a drill or YAG laser.
[0031]
As the counter substrate 80, a glass plate in which a plurality of communication holes 81 through which ink can pass is formed in advance at positions corresponding to the ink channels 61 is used. By forming the communication hole 81 in the counter substrate 80, there is an advantage that the ink flow from the ink supply chamber 91 to the nozzle 51 becomes linear and the inkjet head can be made compact.
[0032]
A space 82 is formed by performing a well-known etching process at a predetermined depth on the portion of the glass plate where the gap between the electrodes is formed. Further, the second electrode 83 is formed as an individual electrode only on the bottom surface inside the space 82 by sputtering or electroless plating. For example, SiC is deposited on the second electrode 83 by vacuum deposition as an insulating film, thereby preventing current from flowing in the ink. If the ink is insulating, it is not necessary to form the above film.
[0033]
The ink supply plate 90 is made of resin, for example, like the channel plate 60, and is molded by a mold. The ink supply plate 90 is formed with an ink supply chamber 91 that opens to the counter substrate 80 side. A connection hole 92 is formed at the bottom of the ink supply chamber 91, and an ink supply pipe 93 is connected to the connection hole 92.
[0034]
The interelectrode gap dimension D1 formed by the space 82 between the diaphragm 70, which is the first electrode, and the second electrode 83 can be made considerably larger than the conventional one, and is set to be 3 μm here. did. Further, twelve through holes 71 formed in the vibration plate 70 are provided for each ink channel 61 with a diameter of 10 μm, and the communication holes 81 formed in the counter substrate 80 are 30 μm wide × 100 μm long. Five long holes were provided for each ink channel 61. The ink channel 61 formed on the channel plate 60 was formed with a width of 300 μm and an adjacent pitch of 564 μm, and the diameter of the nozzle 51 was 23 μm. However, the above dimensions and the like are examples and can be appropriately changed.
[0035]
The element members formed as described above are bonded together so as to have a sandwich structure as shown in the figure, and the diaphragm 70 as the first electrode and the contact line of the second electrode 83 formed on the counter substrate 80 are respectively connected. The inkjet head 31 is completed by connecting the wirings 72 and 84. In addition, the manufacturing method of each said element member of the inkjet head 31 can take various methods, Here, the example is demonstrated.
[0036]
The diaphragm 70 functions to vary the internal pressure of the ink channel 61 by the deformation thereof in order to eject ink from the nozzles 51. The ink supply chamber 91 stores ink for supplying ink to the ink channel 61. The ink filled in the space 82 through the communication hole 81 is guided to the ink channel 61 through the through hole 71 formed in the vibration plate 70.
[0037]
The diaphragm 70 and the second electrode 83, which are the first electrodes, are connected to the head discharge driving unit 105 as the diaphragm driving means by wires 72 and 84, respectively. In the present embodiment, the wiring 72 from the diaphragm 70 that is the first electrode is grounded, and the voltage from the head ejection driving unit 105 is applied to the second electrode 83 by the wiring 84. Yes. And it is set as the structure which deform | transforms the diaphragm 70 by applying a predetermined voltage between both electrodes. In addition, the code | symbol 85 in FIG. 3 shows the sealing member for preventing the leakage to the exterior of an ink.
[0038]
Next, the ink used in this embodiment will be described.
The composition of the ink used in the present embodiment is as shown in Table 1 below, using four color inks of black (K), yellow (Y), magenta (M), and cyan (C). As shown in the table, each color is adjusted with a dye, but a pigment may be used instead of the dye.
[0039]
[Table 1]

[0040]
Next, the control unit of the ink jet printer 1 is unlighted.
FIG. 6 is a block diagram for explaining the configuration of the control unit of the inkjet printer 1.
[0041]
The control unit of the inkjet printer 1 includes a CPU 101, a RAM 102, a ROM 103, a data reception box 104, a head ejection drive unit 105, a head movement drive unit 106, a paper feed motor drive unit 107, a recovery system motor drive unit 108, and various sensor units 109. Is included.
[0042]
The CPU 101 that controls the whole uses the RAM 102 as necessary, and executes a program stored in the ROM 103. This program is connected to a host computer or the like and receives image data to be recorded. Based on image data read from the data receiving unit 104, a head ejection driving unit 105, a head movement driving unit 106, a paper feed motor A part for controlling the driving unit 107 and various sensor units 109 to record an image on the recording sheet 2 and, if necessary, processing information from the various sensor units 109 to control the recovery system motor driving unit 108. And a portion for recovering the nozzle surface of the head unit 3 to a good state.
[0043]
Based on the control of the CPU 101, the head ejection driving unit 105 drives the inkjet head 31 in the head unit 3 by applying a pulse voltage corresponding to the image data. Specifically, a pulse voltage corresponding to the image data is applied from the head ejection driving unit 105 to the second electrode 83 at a predetermined timing. The head ejection driving unit 105 includes a charge / discharge circuit, an inverting circuit, and an inverting amplifier circuit (not shown).
[0044]
Further, based on the control of the CPU 101, the head movement drive unit 106 drives the drive motor 7 that moves the carriage 4 that holds the head unit 3, and the paper feed motor drive unit 107 drives the paper feed roller. Further, based on the control of the CPU 101, the recovery system motor drive unit 108 drives a motor and the like necessary for recovering the nozzle surface of the head unit 3 to a good state.
[0045]
The present invention is configured as described above. Next, the operation of the ink jet head will be described.
[0046]
FIG. 7 is a diagram for explaining the operation when ejecting ink droplets, and FIG. 8 is a diagram showing the waveform of the drive voltage when ejecting ink droplets and changes in various quantities at this time. .
[0047]
When ink droplets are ejected, the diaphragm 70 and the second electrode, which are the first electrodes, are first controlled from the state of FIG. 7A (TA section in FIG. 8) based on each circuit in the head ejection driving unit 105. A predetermined drive voltage is applied between the electrode 83 (TB section in FIG. 8). As shown in FIG. 7B, the diaphragm 70 is attracted to the second electrode 83 side by the electrostatic force generated by applying the drive voltage. During this ink suction operation, the vibration plate 70 is moved relatively slowly. As illustrated, the diaphragm 70 is bent and deformed toward the second electrode 83 side.
[0048]
In this embodiment, since the vibration plate 70 as the first electrode is grounded, a positive potential is applied to the second electrode 83 as the driving voltage. Due to this drive voltage, a force F calculated by the following equation acts on the diaphragm 70 in the lower part of FIG.
F = 1/2 · {εrεoS (V / d)²} …… (1)
Where εr is the relative dielectric constant between the first electrode and the second electrode, and εo is the relative dielectric constant of vacuum (= 8.854 × 10^-12F / m), S is the area of the electrode, V is the voltage, and d is the length between the first electrode and the second electrode.
[0049]
As a result, the ink filled in the space 82 from the ink supply chamber 91 through the communication hole 81 flows into the ink channel 61 through the through hole 71 formed in the vibration plate 70. At this time, since the vibration plate 70 is moved relatively slowly, the ink passing through the through hole 71 becomes a flow close to a laminar flow. Accordingly, since the flow path resistance is low, the ink is hardly drawn in the reverse direction and is smoothly supplied into the ink channel 61 through the through hole 71.
[0050]
At this time, as shown in FIG. 8, as the deformation volume ΔX1 of the vibration plate 70 gradually changes (TB section in FIG. 8), the ink volume ΔX2 passing through the through hole 71 of the vibration plate 70 changes smoothly. The change volume ΔX3 of the ink meniscus 39 formed at the tip of the nozzle 51 is also relatively small.
[0051]
Then, after the drive voltage is held for a certain time (several μsec to several tens of μsec), the drive voltage is cut off and stopped (TC interval in FIG. 8). Due to the interruption of the drive voltage, the diaphragm 70 attracted to the second electrode 83 side is pulled back to the original position by the rigidity of the diaphragm 70 itself, as shown in FIG. 7C.
[0052]
As described above, when the ink ejection operation is performed, the vibration plate 70 is moved more rapidly than in the ink suction operation, so that the ink passing through the through hole 71 has a flow similar to a turbulent flow. Accordingly, the flow resistance becomes high, and very little ink returns in the reverse direction through the through hole 71, and most of the ink contributes to ejection. On the other hand, the counter substrate 80 is provided with a communication hole 81 that is sufficiently larger than the through hole 71 of the diaphragm 70, so that the ink flow is hardly obstructed.
[0053]
Thus, the volume of the ink channel 61 contracts, and the ink filled in the ink channel 61 flies as a droplet from the nozzle 51 due to the pressure generated at this time, and lands on the recording sheet 2 to form a predetermined image. Is done.
[0054]
As described above, according to the present embodiment, since the gap between the electrodes is filled with ink, the electric field strength is the same even when the gap distance between the electrodes is the same as compared with the case where nothing is filled in the gap between the electrodes. Can be greatly improved. That is, as can be seen from the above formula (1), the voltage value for obtaining the predetermined force F decreases as the dielectric constant of the interelectrode substance increases, so that it can be driven at a low voltage. Since the relative dielectric constant of the ink is about 60 in the case of water-based ink, for example, the gap between the electrodes can be expanded by about 8 times if the same electric field strength is sufficient. As described above, the gap between the gaps is more advantageous than the case of air in terms of electric field strength, so that the gap between the electrodes can be formed as wide as 3 μm as compared with the conventional example, and the processing is greatly facilitated.
[0055]
Also, by opening a through hole 71 that allows ink to pass through the vibration plate 70 and supplying ink from the back side of the through hole 71, the ink can be moved in almost one direction. The efficiency can be improved, and improvement in the followability with respect to the driving frequency of the inkjet head can be achieved.
[0056]
Further, in the configuration of the ink jet head, an experiment was conducted on a difference in flow path resistance of the through hole 71 provided in the vibration plate 70 during the ink discharge operation and the ink suction operation. FIG. 9 is a diagram showing the shape when the through-hole is a straight hole and the flow resistance against the applied pressure, and FIG. 10 is the shape when the through-hole is a tapered hole and the flow resistance against the applied pressure. FIG.
[0057]
In this experiment, ink was passed through two types of diaphragms having different hole shapes at a predetermined pressure, and the dependence of the channel resistance R on the applied pressure P was determined from the flow velocity at that time. From the results of FIG. 9 and FIG. 10, it was confirmed that the flow path resistance R increases as the applied pressure P increases. This confirms that the higher the speed of the diaphragm 70, the more likely the turbulent flow occurs and the greater the flow path resistance R, making it difficult to pass ink. Therefore, it can be seen that the ink flow is directed in the ejection direction by slowly moving the diaphragm 70 during the ink suction operation and rapidly moving the diaphragm 70 during the ink ejection operation.
[0058]
Further, it can be seen from FIG. 10 that the shape of the through hole 71 opened in the vibration plate 70 is preferably a shape in which the cross-sectional area is enlarged with respect to the ejection direction from the viewpoint of unidirectional ink flow. This is because, as illustrated, the flow path resistance R is larger in the direction 2 in which ink may pass when ink is ejected than in the direction 1 in which ink passes when ink is sucked.
[0059]
(Embodiment 2)
FIG. 11 is a cross-sectional view of an inkjet head according to Embodiment 2 of the present invention. Members having the same functions as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.
[0060]
In the second embodiment, as shown in FIG. 11, the second electrode 83 is different from the first embodiment in that the second electrode 83 is formed on the nozzle 51 side with respect to the diaphragm 70 as the first electrode. The other points are the same as in the first embodiment. That is, the positional relationship between the diaphragm 70 and the counter substrate 80 is opposite to that of the first embodiment. In the second embodiment, it is essential that the counter substrate 80 on which the second electrode 83 is formed has a communication hole 81 through which ink can pass.
[0061]
Therefore, in Embodiment 1 described above, ink is ejected when the drive voltage is interrupted (during discharge). However, in Embodiment 2, ink can be directly ejected by electrostatic attraction when a drive voltage is applied. . As a result, the same effects as those of the first embodiment can be obtained, and the transient behavior of the diaphragm 70 can be controlled relatively easily by the waveform of the drive voltage to be applied.
[0062]
(Embodiment 3)
FIG. 12 is a cross-sectional view of an inkjet head according to Embodiment 3 of the present invention. Members having the same functions as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.
[0063]
In the third embodiment, as shown in FIG. 12, the ink is supplied in the direction indicated by the arrow from the side between the diaphragm 70 as the first electrode and the second electrode 83. It is different from the first embodiment, and the other points are the same as in the first embodiment. In this way, the same effect as in the first embodiment can be obtained, and it is not necessary to form the communication hole 81 through which the ink can pass in the counter substrate 80 on which the second electrode 83 is formed. The manufacture of the head is further facilitated.
[0064]
(Embodiment 4)
FIG. 13 is a cross-sectional view of an inkjet head according to Embodiment 4 of the present invention. Members having the same functions as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.
[0065]
In the fourth embodiment, as shown in FIG. 13, the third electrode 86 is provided with a gap at a position opposite to the second electrode 83 side with respect to the diaphragm 70 as the first electrode. The third electrode 86 is formed by metal sputtering or the like, like the second electrode 83. On the surfaces of the second electrode side 83 and the third electrode 86, insulating layers 83a and 86a having a predetermined thickness are formed by forming a film by resin deposition or the like. The diaphragm 70 is made of a conductive film that is a flexible sheet-like conductor, one end of which is fixed near the second electrode 83 side and the other end is fixed near the third electrode 86 side. S-shaped and installed in the ink channel 61. The nozzle 51 is provided on the side between the second electrode 83 and the third electrode 86. The other points are the same as in the first embodiment.
[0066]
In the fourth embodiment, by applying a driving voltage to the second electrode side 83 or the third electrode 86 provided at the top and bottom in the drawing, the diaphragm 70 that is a conductive film is indicated by a two-dot chain line in the drawing. And move back and forth by electrostatic attraction. Since the diaphragm 70 is provided with a through hole 71 through which ink can pass, the ink can be pushed forward toward the nozzle 51 by the same principle as in the above embodiment. In this way, the same effect as in the first embodiment can be obtained.
[0067]
The embodiments described above are not described for limiting the present invention, and various modifications can be made by those skilled in the art within the technical idea of the present invention.
[0068]
For example, in the embodiment described above, the holes 71 and 83 are formed in the vibration plate 70 or the counter substrate 80, but a plate on which a mesh is formed may be used instead. In this way, since a large number of holes are uniformly distributed, it is possible to eliminate the need for alignment of the vibration plate 70 when assembling the inkjet head. In addition, even if one hole is clogged, there is an advantage that the influence is small.
[0069]
Further, during the ink ejection operation, the vibration plate 70 may be vibrated a plurality of times by high-frequency vibrations so that one ink droplet is caused to fly. In the configuration of the ink jet head, the natural vibration period of the vibration plate 70 is designed to be sufficiently faster than the natural vibration period of the ink (for example, when the vibration plate 70 is thickened, the displacement amount decreases but the natural vibration period). When driving at a high frequency that matches the natural vibration period of the vibration plate 70, the ink is fed forward by a predetermined amount per vibration, so that the ink is generated according to the frequency given as the applied signal. It is also possible to modulate the drop volume.
[0070]
【The invention's effect】
As described above, according to the first aspect of the present invention, since the gap between the electrodes is filled with ink, the gap between the gaps is advantageous in comparison with air in terms of electric field strength. Therefore, the gap between the electrodes can be formed wider than in the prior art, and the processing is greatly facilitated.
[0071]
Also, by opening a through-hole through which ink can pass through the diaphragm and supplying ink from the back side of the through-hole, the ink can be moved almost in one direction, so that the ink ejection efficiency is increased, and The followability with respect to the drive frequency of the inkjet head is improved.
[Brief description of the drawings]
FIG. 1 is a perspective view for explaining a schematic configuration of an ink jet printer.
2 is a perspective view for explaining a configuration around a carriage including an inkjet head for one color of the head unit shown in FIG. 1. FIG.
FIG. 3 is an overall perspective view of the inkjet head according to the first embodiment of the invention.
FIG. 4 is an exploded perspective view of the same.
FIG. 5 is a cross-sectional view taken along line VV in FIG.
FIG. 6 is a block diagram for explaining a configuration of a control unit of the inkjet printer.
FIG. 7 is a diagram for explaining an operation when ink droplets are ejected.
FIG. 8 is a diagram illustrating a waveform of a driving voltage when ink droplets are ejected and changes in various amounts at this time.
FIG. 9 is a diagram showing the shape and flow path resistance against applied pressure when the through hole is a straight hole.
FIG. 10 is a diagram showing the shape and flow path resistance with respect to applied pressure when the through hole is a tapered hole.
FIG. 11 is a cross-sectional view of an inkjet head according to a second embodiment of the invention.
FIG. 12 is a cross-sectional view of an inkjet head according to a third embodiment of the present invention.
FIG. 13 is a cross-sectional view of an inkjet head according to a fourth embodiment of the present invention.
[Explanation of symbols]
1 ... Inkjet printer,
2. Recording sheet (recording medium),
3 ... head unit,
31. Inkjet head,
51 ... Nozzle,
61: Ink channel (pressure chamber),
70: Diaphragm (first electrode),
71 ... through hole,
91 ... Ink supply chamber,
81 ... communication hole,
82 ... space,
83 ... the second electrode,
86 ... third electrode,
105: Head ejection drive unit (vibration plate drive means).

Claims (1)

Includes a nozzle, a pressure chamber communicating with the nozzle, a diaphragm is a first electrode for changing the pressure in the pressurized chamber, a gap at a position opposing to the vibration plate is the first electrode and a second electrode formed Te, said by deforming the vibration plate is the first electrode by applying a voltage between the first electrode and a diaphragm and the second electrode, the pressure In an inkjet head that ejects ink in the chamber as droplets from the nozzle,
Ink is filled between the diaphragm that is the first electrode and the second electrode, and a through-hole through which ink can pass is formed in the diaphragm that is the first electrode ,
A third electrode is provided with a gap at a position opposite to the second electrode side with respect to the diaphragm which is the first electrode,
The diaphragm as the first electrode has flexibility, and has an S-shape when viewed from a direction perpendicular to the ink ejection direction in a plane parallel to the surface of the second electrode facing the pressurizing chamber. Sheet-like conductor to be exhibited, one end is fixed near the second electrode side and the other end is fixed near the third electrode side,
An ink jet head, wherein the nozzle is provided on a side between the second electrode and the third electrode.

Images