JP3755569B2 - Ink jet recording head driving method and circuit thereof - Google Patents

Description

【００３８】
次に、図１０（ｂ）に示すような、複雑な形状（台形状）の駆動波形信号を用いた場合の粒子速度は、駆動波形信号の節部（Ａ，Ｂ，Ｃ，Ｄの各点）で発生する圧力波を重ね合わせてゆくことによって求めることができる。すなわち、図１０（ｂ）の駆動波形信号を用いた場合に発生する、ノズル３４における粒子速度ｖ３［ｍ／ｓ］は、式（２）で与えられる。
【００３９】
【数２】

【００４０】
ここで、図１１に示す駆動波形信号を用いた場合の粒子速度の時間変化を、式（１）の振動成分のみを考慮して、式（２）を用いて求めた結果を図１２に示す。図１１に示す駆動波形信号は、圧力発生室の体積を増加させてメニスカスを後退させるために、基準電圧Ｖ１（＞０Ｖ）に設定されている圧電アクチュエータの印加電圧Ｖを、例えば、０Ｖにまで減少させる第１の電圧変化プロセス４１と、０Ｖにまで減少した印加電圧Ｖを暫時（時間ｔ２）保持する電圧保持プロセス４２と、この後、圧力発生室の体積を減少させてインク滴を吐出させると共に、次の吐出動作に備えさせるために、圧電アクチュエータの印加電圧Ｖを電圧Ｖ２の高さにまで増加させる第２の電圧変化プロセス４３とを有している。図１２において、各細線ａ〜ｄは、図１１に示す駆動波形信号の各節部Ａ，Ｂ，Ｃ，Ｄにおいてそれぞれ発生する粒子速度の時間変化を表しており、太線ｓは、各粒子速度を重ね合わせた合計の粒子速度の時間変化、すなわち、実際にメニスカスにおいて生じる粒子速度の時間変化を表している。
【００４１】
（１） 図１１に示す駆動波形信号において、時間ｔ１を圧力発生室内に発生する圧力波の固有周期Ｔｃ（＝２π／Ｅｃ）の１／２に設定すると共に、時間ｔ２を極めて短く設定した場合、図１２（ａ）に示すように、節部Ａ，Ｂ，Ｃにおいて発生する粒子速度の時間変化の位相はほぼ一致する。そのため、時間範囲（ｔ＞ｔ１＋ｔ２）では、粒子速度の非常に急激な増加が生じる。次に、このような粒子速度に非常に急激な変化が生じた際のメニスカスの形状変化について、図１２及び図１３を参照して、説明する。図１２（ａ）に示す粒子速度の時間変化がメニスカス５４に加わると、時間範囲Ｔ１において、メニスカス５４はノズル５１の開口面からノズル５１の内部に引き込まれ、凹状となる。次に、時間範囲Ｔ２において、メニスカス５４はノズル５１の外側に向かって押し出される。上記したように、メニスカス５４を凹状にした状態でメニスカス５４に「押し」を加えると、メニスカス５４の中央部に細い液柱５２が形成される。
【００４２】
この液柱５２の形成メカニズムについて詳細に検討された例はないが、発明者等は、インク滴の吐出観察実験及び流体解析によって、形成される液注５２の太さがメニスカス５４を押し出す際の液面の速度に依存することを明らかにした。すなわち、凹状のメニスカス５４に対して、ノズル５１の外側に向かって押し出すように圧力を加えると、図１３に示すように、メニスカス５４の各部は液面の法線方向（図中矢印）に移動しようとする。その結果、ノズル５１の中央部に多量のインクが集中し、この局所的なインクの体積の増加によってノズル５１の中央部に液注５２が形成される。この時、液面の移動速度が速い場合には、ノズル５１の中央部でのインクの体積が増加する速度も大きくなるため、非常に細い液注５２が速い成長速度で形成される（図１３（ａ）参照）。これに対し、液面の移動速度が遅い場合には、ノズル５１の中央部でのインクの体積が増加する速度も小さくなるため、液注５２は太くなり、成長速度も遅くなる（図１３（ｂ）参照）。
【００４３】
なお、上記したように、「メニスカス制御」方式を用いてノズル５１から吐出されるインク滴５３の滴径は、形成される液柱５２の太さとほぼ等しい。また、インク滴の飛翔速度（滴速）は、液柱５２の成長速度とほぼ等しい。したがって、微小なインク滴を高速で吐出させるためには、「押し」のプロセスの際の液面移動速度を増加させ、ノズル５１の中央部において急激なインクの体積増加を生じさせることが重要な条件となる。
【００４４】
上記した観点から考察すると、図１１に示す駆動波形信号において、時間ｔ１を固有周期Ｔｃの１／２に設定すると共に、時間ｔ２を極めて短く設定することは、微小なインク滴を吐出するために非常に有利な条件となる。すなわち、このような条件の下では、図１２（ａ）に示すように、図１１に示す駆動波形信号の節部Ａ，Ｂ，Ｃにおいて発生する粒子速度の時間変化の位相はほぼ一致するので、時間範囲（ｔ＞ｔ１＋ｔ２）では、粒子速度が急激に増加し、液面の移動速度が大きくなる。そのため、ノズル５１の中央部において急激なインクの体積増加が生じるので、細い液柱５２が形成され、その結果、非常に微小なインク滴５３を高速で吐出させることが可能となる。つまり、液柱５２の形成時にメニスカス５４の液面の移動速度を急激に増加させることが、微小なインク滴５３を吐出させる上で重要な条件となるのである。
【００４５】
（２） 一方、図１１に示す駆動波形信号において、時間ｔ１を固有周期Ｔｃの１／２に設定しなかった場合には、図１２（ｂ）に示すように、節部Ａ，Ｂ，Ｃにおいて発生する粒子速度の時間変化の位相は一致しなくなり、各粒子速度を重ね合わせた合計の粒子速度の時間変化（太線ｓ）は、非常に緩慢な変化となってしまう。すなわち、時間ｔ１が固有周期Ｔｃの１／２より短い場合には、節部Ａによって発生した粒子速度が負であるうちに節部Ｂによって正の粒子速度が発生してしまうため、両者が相殺し合い、メニスカス５４の液面の移動速度の増加が鈍化してしまう。一方、時間ｔ１が固有周期Ｔｃの１／２より長い場合には、節部Ｂによって正の粒子速度が発生する前に節部Ａによって発生した粒子速度が正となってしまうため、やはり、メニスカス５４の液面の移動速度の急激な増加を得ることができなくなる。このような条件の下では、ノズル５１の中央部において急激なインクの体積増加が発生し難くなるため、形成される液柱５２の太さは太くなり、その結果、吐出されるインク滴５３の滴径は大きく、滴速も遅くなってしまう（図１３（ｂ）参照）。したがって、高画質記録に要求される滴径２０μｍ以下の微小なインク滴を得ることは不可能になる。
【００４６】
以上説明したように、「メニスカス制御」方式を用いてノズル５１から吐出されるインク滴５３の滴径及び滴速は、図１１に示す駆動波形信号における第１の電圧変化プロセス４１の電圧変化時間ｔ１と、第１の電圧変化プロセス４１の終了時刻と第２の電圧変化プロセス４３の開始時刻との時間間隔、すなわち、電圧保持プロセス４２での電圧保持時間ｔ２とに大きく依存し、電圧変化時間ｔ１を固有周期Ｔｃの約１／２に設定すると共に、電圧保持時間ｔ２を充分短く設定することにより、非常に微小な滴径のインク滴を高速で吐出させることができる。なお、この場合、圧電アクチュエータ自体の固有振動を利用しないので、圧電アクチュエータの信頼性及び耐久性が損なわれることはなく、また、インクジェット記録ヘッドの駆動回路、特に、圧電アクチュエータの駆動回路は、従来の構成と特に変わることはないため、インクジェット記録ヘッドの駆動回路のコストやサイズが増大することはない。
【００４７】
【発明の実施の形態】
以下、図面を参照して、この発明の実施の形態について説明する。説明は、実施例を用いて具体的に行う。
Ａ．本発明の前提となる実施例
まず、本発明の前提となる実施例について説明する。図１（ａ）は、本発明の前提となる実施例であるインクジェット記録ヘッドの駆動方法を適用したインクジェット記録装置に搭載されるインクジェット記録ヘッドの構成の一例を示す断面図、同図（ｂ）は、同インクジェット記録ヘッドを分解して示す分解断面図である。この例のインクジェット記録ヘッドは、図１（ａ）に示すように、必要に応じてインク滴３７を吐出させて、記録媒体上に文字や画像を印刷するドロップ・オン・デマンド・カイザー型マルチノズル式記録ヘッドに係り、図１に示すように、細長立方体形状にそれぞれ形成され、かつ、図中紙面垂直方向に並べられた複数の圧力発生室３１と、各圧力発生室３１の図中底面を構成する振動板３５と、この振動板３５の裏面に、かつ、各圧力発生室３１に対応して並設された複数の圧電アクチュエータ３６と、図示せぬインクタンクと連結されて、各圧力発生室３１にインクを供給するための共通インク室（インクプール）３２と、この共通インク室３２と各圧力発生室３１とを一対一に連通させるための複数のインク供給孔（インク供給路）３３と、各圧力発生室３１と一対一に設けられ、各圧力発生室３１の屈曲上方に突起した先端部からインク滴３７を吐出させる複数のノズル３４とから概略構成されている。ここで、共通インク室３２、インク供給孔３３、圧力発生室３１及びノズル３４によって、インクがこの順に移動する流路部が形成され、圧電アクチュエータ３６と振動板３５とから、圧力発生室３１内のインクに圧力波を加える駆動部が構成され、流路部と駆動部との接点が、圧力発生室３１の底面（すなわち、振動板３５の図中上面）となっている。
【００４８】
圧電アクチュエータ３６は、圧電定数ｄ３３を利用した縦振動モードであって、積層型圧電セラミックスからなり、その圧力発生室３１に変位を加えるための駆動柱の形状は、長さ（Ｌ）が６９０μｍ、幅（Ｗ）が１．８μｍ、奥行き長さ（図１の紙面垂直方向の長さ）が１２０μｍである。圧電アクチュエータ３６を構成する圧電材料には、その密度ρｐが８．０×１０３［ｋｇ／ｍ３］、その弾性係数Ｅｐが６８ＧＰａであるものを用いている。そして、実測した圧電アクチュエータ３６自体の固有周期Ｔａは、１．０μｓであった。
【００４９】
この実施例のヘッド製造工程では、図１（ｂ）に示すように、精密プレス加工で円形に穿孔されることで、複数のノズル３４が列状に又は千鳥状に配列されたノズルプレート３４ａと、共通インク室３２の空間部が形成されたプールプレート３２ａと、インク供給孔３３が穿孔された供給孔プレート３３ａと、複数の圧力発生室３１の空間部が形成された圧力発生室プレート３１ａと、複数の振動板３５を構成する振動プレート３５ａとを予めエッチング等により穿孔加工して用意した後、これらのプレート３１ａ〜３５ａを厚さ約５μｍの図示せぬ熱硬化性樹脂による接着剤層を用いて接着接合して積層プレートを作成し、次に、作成された積層プレートと圧電アクチュエータ３６とを熱硬化性樹脂による接着剤層やエポキシ系接着剤層を用いて接合することで、上記構成のインクジェット記録ヘッドを製造することが行われる。なお、この例では、振動プレート３５ａには、電鋳（エレクトロフォーミング）で成形された厚さ５０〜７５μｍのニッケル板が用いられるのに対し、他のプレート３１ａ〜３４ａには、厚さ５０〜７５μｍのステンレス板が用いられる。また、この例のノズル３４は、開口径略３０μｍ、裾径略６５μｍ、長さ略７５μｍとされ、圧力発生室３１側に向かって径が徐々に増加するテーパ形状に形成されている。また、インク供給孔３３も、ノズル３４と同一形状に形成されている。
【００５０】
次に、図２及び図３を参照して、この例のインクジェット記録装置を構成して、上記構成のインクジェット記録ヘッドを駆動する駆動回路の電気的構成について説明する。この例のインクジェット記録装置は、図示せぬＣＰＵ（中央処理装置）やＲＯＭやＲＡＭ等のメモリを有している。ＣＰＵは、ＲＯＭに記憶されたプログラムを実行して、ＲＡＭに確保された各種レジスタやフラグを用いて、インターフェイスを介してパーソナル・コンピュータ等の上位装置から供給された画像データに基づいて、記録媒体上に文字や画像を記録するために、装置各部を制御する。
【００５１】
まず、図２に示す駆動回路は、図４に示す増幅駆動波形信号に対応した駆動波形信号を発生して電力増幅した後、圧電アクチュエータ３６に供給して駆動することにより、滴径が常に略同じインク滴３７を吐出させて、記録媒体上に文字や画像を記録させるもので、波形発生回路６１と、増幅回路６２と、スイッチング回路６３とから概略構成されている。波形発生回路６１は、デジタル・アナログ変換回路と積分回路とから構成され、ＣＰＵによりＲＯＭの所定の記憶エリアから読み出された駆動波形データをアナログ変換した後、積分処理して図４に示す増幅駆動波形信号に対応した駆動波形信号を生成する。増幅回路６２は、波形発生回路６１から供給された駆動波形信号を電力増幅して、図４に示す増幅駆動波形信号として出力する。スイッチング回路６３は、例えば、トランスファ・ゲートからなり、入力端が増幅回路６２の出力端に接続され、出力端が圧電アクチュエータ３６の一端に接続され、制御端に、図示せぬ駆動制御回路において画像データに基づいて生成され、供給された制御信号が入力されると、オンとなって、増幅回路６２から出力される増幅駆動波形信号（図４参照）を圧電アクチュエータ３６に印加する。圧電アクチュエータ３６は、このとき、印加される増幅駆動波形信号に応じた変位を振動板３５に与え、振動板３５の変位により、圧力発生室３１を急激に体積変化（増加・減少）させて、インクが充填された圧力発生室３１に所定の圧力波を発生させ、この圧力波によってノズル３４から滴径が２０μｍ程度の微小なインク滴３７を吐出させる。なお、この実施例のインクジェット記録ヘッドでは、インクが充填された圧力発生室３１内における圧力波の固有周期Ｔｃは、１０μｓである。吐出したインク滴３７は、記録媒体上に着弾し、記録ドットを形成する。このような記録ドットの形成を画像データに基づいて繰り返し行うことにより、記録媒体上に文字や画像が２値記録される。
【００５２】
次に、図３に示す駆動回路は、ノズル３４から吐出するインク滴の滴径を多段階（この例では、滴径４０μｍ程度の大滴、３０μｍ程度の中滴、２０μｍ程度の小滴の３段階）に切り替えて、多階調で記録媒体上に文字や画像を記録させる、いわゆる滴径変調型の駆動回路であり、滴径に応じた３種類の波形発生回路７１ａ，７１ｂ，７１ｃと、これらの波形発生回路７１ａ，７１ｂ，７１ｃと一対一に接続された増幅回路７２ａ，７２ｂ，７２ｃと、圧電アクチュエータ３６，３６，…と一対一に接続された複数個のスイッチング回路７３，７３，…とから概略構成されている。波形発生回路７１ａ〜７１ｃは、いずれも、デジタル・アナログ変換回路と積分回路とから構成され、これらの波形発生回路７１ａ〜７１ｃのうち、波形発生回路７１ａは、ＣＰＵによりＲＯＭの所定の記憶エリアから読み出された大滴吐出用の駆動波形データをアナログ変換した後、積分処理して大滴吐出用の駆動波形信号を生成する。波形発生回路７１ｂは、ＣＰＵによりＲＯＭの所定の記憶エリアから読み出された中滴吐出用の駆動波形データをアナログ変換した後、積分処理して中滴吐出用の駆動波形信号を生成する。また、波形発生回路７１ｃは、ＣＰＵによりＲＯＭの所定の記憶エリアから読み出された小滴吐出用の駆動波形データをアナログ変換した後、積分処理して図４に示す増幅駆動波形信号に対応した小滴吐出用の駆動波形信号を生成する。増幅回路７２ａは、波形発生回路７１ａから供給された大滴吐出用の駆動波形信号を電力増幅して大滴吐出用の増幅駆動波形信号として出力する。増幅回路７２ｂは、波形発生回路７１ｂから供給された中滴吐出用の駆動波形信号を電力増幅して中滴吐出用の増幅駆動波形信号として出力する。また、増幅回路７２ｃは、波形発生回路７１ｃから供給された小滴吐出用の駆動波形信号を電力増幅して小滴吐出用の増幅駆動波形信号（図４参照）として出力する。
【００５３】
また、スイッチング回路７３は、図示せぬ第１，第２，第３のトランスファ・ゲートから構成され、第１のトランスファ・ゲートの入力端が増幅回路７２ａの出力端に接続され、第２のトランスファ・ゲートの入力端が増幅回路７２ｂの出力端に接続され、第３のトランスファ・ゲートの入力端が増幅回路７２ｃの出力端に接続され、第１，第２，第３のトランスファ・ゲートの出力端が対応する共通の圧電アクチュエータ３６の一端に接続されている。そして、図示せぬ駆動制御回路において画像データに基づいて生成された階調制御信号が第１のトランスファ・ゲートの制御端に供給されると、第１のトランスファ・ゲートがオンとなって増幅回路７２ａから出力される大滴吐出用の増幅駆動波形信号を圧電アクチュエータ３６に印加する。圧電アクチュエータ３６は、このとき、印加される増幅駆動波形信号に応じた変位を振動板３５に与え、この振動板３５の変位により、圧力発生室３１を急激に体積変化（増加・減少）させて、インクが充填された圧力発生室３１に所定の圧力波を発生させ、この圧力波によってノズル３４から大滴のインク滴３７を吐出させる。図示せぬ駆動制御回路において画像データに基づいて生成された階調制御信号が第２のトランスファ・ゲートの制御端に供給されると、第２のトランスファ・ゲートがオンとなって増幅回路７２ｂから出力される中滴吐出用の増幅駆動波形信号を圧電アクチュエータ３６に印加する。圧電アクチュエータ３６は、このとき、印加される増幅駆動波形信号に応じた変位を振動板３５に与え、振動板３５の変位により、圧力発生室３１を急激に体積変化（増加・減少）させて、インクが充填された圧力発生室３１に所定の圧力波を発生させ、この圧力波によってノズル３４から中滴のインク滴３７を吐出させる。また、図示せぬ駆動制御回路において画像データに基づいて生成された階調制御信号が第３のトランスファ・ゲートの制御端に供給されると、第３のトランスファ・ゲートがオンとなって増幅回路７２ｃから出力される小滴吐出用の増幅駆動波形信号（図４参照）を圧電アクチュエータ３６に印加する。圧電アクチュエータ３６は、このとき、印加される増幅駆動波形信号に応じた変位を振動板３５に与え、振動板３５の変位により、圧力発生室３１を急激に体積変化（増加・減少）させて、インクが充填された圧力発生室３１内に所定の圧力波を発生させ、この圧力波によってノズル３４から小滴のインク滴３７を吐出させる。吐出したインク滴３７は、記録媒体上に着弾し、記録ドットを形成する。このような記録ドットの形成を画像データに基づいて繰り返し行うことにより、記録媒体上に文字や画像が多階調記録される。この実施例では、２値記録専用のインクジェット記録装置には、図２の駆動回路が組み込まれ、階調記録も行うインクジェット記録装置には、図３の駆動回路が組みまれる。
【００５４】
上記した増幅駆動波形信号は、図４に示すように、圧力発生室３１の体積を増加させてメニスカスを後退させるために、圧力発生室３１内に発生する圧力波の固有周期Ｔｃの１／２の立ち下げ時間ｔ１で、基準電圧Ｖｂに設定されている圧電アクチュエータ３６の印加電圧Ｖを、電圧（Ｖｂ−Ｖ１）にまで減少させる第１の電圧変化プロセス８１と、電圧（Ｖｂ−Ｖ１）にまで減少した印加電圧Ｖを暫時（時間ｔ２）保持する第１の電圧保持プロセス８２と、圧力発生室３１の体積を減少させてメニスカスの中央部に液柱を形成させるために、立ち上げ時間ｔ３で、圧電アクチュエータ３６の印加電圧Ｖを電圧（Ｖｂ−Ｖ１＋Ｖ２）の高さにまで増加させる第２の電圧変化プロセス８３と、電圧（Ｖｂ−Ｖ１＋Ｖ２）にまで増加した印加電圧Ｖを暫時（時間ｔ４）保持する第２の電圧保持プロセス８４と、圧力発生室３１の体積を減少させてインク滴３７を吐出させると共に、次の吐出動作に備えさせるために、圧電アクチュエータ３６の印加電圧Ｖを基準電圧Ｖｂの高さにまで増加させる第３の電圧変化プロセス８５とから構成されている。
【００５５】
次に、この例のインクジェット記録ヘッドの駆動方法について、以下に示す駆動波形信号の波形条件でインク滴３７の吐出実験を行った。すなわち、
基準電圧Ｖｂ＝２５Ｖ
第１の電圧変化プロセス８１での電圧変化量Ｖ１＝１５Ｖ
第２の電圧変化プロセス８３での電圧変化量Ｖ２＝１２Ｖ
第１の電圧変化プロセス８１での電圧変化時間ｔ１＝５μｓ
第１の電圧保持プロセス８２での電圧保持時間ｔ２＝０．３μｓ
第２の電圧変化プロセス８３での電圧変化時間ｔ３＝１．５μｓ
第２の電圧保持プロセス８４での電圧保持時間ｔ４＝６μｓ
第３の電圧変化プロセス８５での電圧変化時間ｔ５＝２０μｓ
にそれぞれ設定し、第１の電圧変化プロセス８１での電圧変化時間ｔ１を変化させて、滴径の変化を調べた。なお、電圧保持時間ｔ２は、式（３）を満足するように設定し、第１の電圧変化プロセス８１での電圧変化量Ｖ１は、メニスカス後退時の後退量が一定になるように設定し、第２の電圧変化プロセス８３での電圧変化量Ｖ２は、常に、滴速が６ｍ／ｓとなるようにそれぞれ調整した。但し、式（３）において、ｔ１が１／２Ｔｃ以上の値である場合は、ｔ２＝０とした。
【００５６】
【数３】
ｔ１＋ｔ２＝１／２Ｔｃ…（３）
【００５７】
図５は、第１の電圧変化プロセス８１での電圧変化時間ｔ１とインク滴３７の滴径との関係を示す特性図である。図５を参照すると、電圧変化時間ｔ１が圧力発生室３１内に発生する圧力波の固有周期Ｔｃの１／２である時、インク滴３７の滴径が最小となり、微小なインク滴を吐出させるのに最適な条件であることが分かる。実験では、滴径２１μｍのインク滴が滴速６．２ｍ／ｓで吐出されることが観察された。これに対し、比較のために、図４に示す増幅駆動波形信号において、電圧変化時間ｔ１を２μｓに設定すると共に、電圧保持時間ｔ２を３μｓに設定してインク滴３７の吐出実験を行った結果、電圧変化量Ｖ１及びＶ２等をどのように調整しても、吐出可能なインク滴の最小滴径は、２５μｍであった。
【００５８】
なお、図５から分かるように、電圧変化時間ｔ１は、固有周期Ｔｃの１／２に完全に一致させる必要はなく、固有周期Ｔｃの１／２にほぼ一致していれば、微小なインク滴を吐出させることができる。具体的には、電圧変化時間ｔ１は、式（４）を満足することが望ましい。
【００５９】
【数４】
１／３Ｔｃ≦ｔ１≦２／３Ｔｃ…（４）
【００６０】
また、第１の電圧保持プロセス８２での電圧保持時間ｔ２は、図４に示す節部Ｂ及び節部Ｃによって発生する粒子速度の位相を一致させるために、可能な限り短いことが望ましいが、式（５）を満足するのであれば、微小なインク滴を吐出させることができる。
【００６１】
【数５】
ｔ２≦１／５Ｔｃ…（５）
【００６４】
Ｂ．本発明に係る第１の実施例
次に、本発明に係る第１の実施例について説明する。図６は、本発明に係る第１の実施例であるインクジェット記録ヘッドの駆動方法に採用される増幅駆動波形信号の波形プロファイルの一例を示す図である。この実施例では、増幅駆動波形信号は、図６に示すように、圧力発生室３１の体積を増加させてメニスカスを後退させるために、圧力発生室３１内に発生する圧力波の固有周期Ｔｃの１／２の立ち下げ時間ｔ１で、基準電圧Ｖｂに設定されている圧電アクチュエータ３６の印加電圧Ｖを、電圧（Ｖｂ−Ｖ１）にまで減少させる第１の電圧変化プロセス８６と、電圧（Ｖｂ−Ｖ１）にまで減少した印加電圧Ｖを暫時（時間ｔ２）保持する第１の電圧保持プロセス８７と、圧力発生室３１の体積を減少させてメニスカスの中央部に液柱を形成させるために、立ち上げ時間ｔ３で、圧電アクチュエータ３６の印加電圧Ｖを電圧（Ｖｂ−Ｖ１＋Ｖ２）の高さにまで増加させる第２の電圧変化プロセス８８と、電圧（Ｖｂ−Ｖ１＋Ｖ２）にまで増加した印加電圧Ｖを暫時（時間ｔ４）保持する第２の電圧保持プロセス８９と、圧力発生室３１の体積を増加させて液柱先端部からインク滴３７を早期に分離させるために、立ち下げ時間ｔ５で、電圧（Ｖｂ−Ｖ１＋Ｖ２）に保持された印加電圧Ｖを、電圧（Ｖｂ−Ｖ１）にまで減少させる第３の電圧変化プロセス９０と、電圧（Ｖｂ−Ｖ１）にまで減少した印加電圧Ｖを暫時（時間ｔ６）保持する第３の電圧保持プロセス９１と、圧力発生室３１の体積を減少させてインク滴３７を吐出させると共に、次の吐出動作に備えさせるために、圧電アクチュエータ３６の印加電圧Ｖを基準電圧Ｖｂの高さにまで増加させる第４の電圧変化プロセス９２とから構成されている。
【００６４】
Ｂ．第２の実施例次に、この発明の第２の実施例について説明する。図６は、この発明の第２の実施例であるインクジェット記録ヘッドの駆動方法に採用される増幅駆動波形信号の波形プロファイルの一例を示す図である。この第２の実施例では、増幅駆動波形信号は、図６に示すように、圧力発生室３１の体積を増加させてメニスカスを後退させるために、圧力発生室３１内に発生する圧力波の固有周期Ｔｃの１／２の立ち下げ時間ｔ１で、基準電圧Ｖｂに設定されている圧電アクチュエータ３６の印加電圧Ｖを、電圧（Ｖｂ−Ｖ１）にまで減少させる第１の電圧変化プロセス８６と、電圧（Ｖｂ−Ｖ１）にまで減少した印加電圧Ｖを暫時（時間ｔ２）保持する第１の電圧保持プロセス８７と、圧力発生室３１の体積を減少させてメニスカスの中央部に液柱を形成させるために、立ち上げ時間ｔ３で、圧電アクチュエータ３６の印加電圧Ｖを電圧（Ｖｂ−Ｖ１＋Ｖ２）の高さにまで増加させる第２の電圧変化プロセス８８と、電圧（Ｖｂ−Ｖ１＋Ｖ２）にまで増加した印加電圧Ｖを暫時（時間ｔ４）保持する第２の電圧保持プロセス８９と、圧力発生室３１の体積を増加させて液柱先端部からインク滴３７を早期に分離させるために、立ち下げ時間ｔ５で、電圧（Ｖｂ−Ｖ１＋Ｖ２）に保持された印加電圧Ｖを、電圧（Ｖｂ−Ｖ１）にまで減少させる第３の電圧変化プロセス９０と、電圧（Ｖｂ−Ｖ１）にまで減少した印加電圧Ｖを暫時（時間ｔ６）保持する第３の電圧保持プロセス９１と、圧力発生室３１の体積を減少させてインク滴３７を吐出させると共に、次の吐出動作に備えさせるために、圧電アクチュエータ３６の印加電圧Ｖを基準電圧Ｖｂの高さにまで増加させる第４の電圧変化プロセス９２とから構成されている。
【００６５】
次に、この例のインクジェット記録ヘッドの駆動方法について、以下に示す駆動波形信号の波形条件でインク滴３７の吐出実験を行った。すなわち、 基準電圧Ｖｂ＝２５Ｖ 第１の電圧変化プロセス８６での電圧変化量Ｖ１＝１５Ｖ 第２の電圧変化プロセス８８での電圧変化量Ｖ２＝１２Ｖ 第１の電圧変化プロセス８６での電圧変化時間ｔ１＝５μｓ 第１の電圧保持プロセス８７での電圧保持時間ｔ２＝０．３μｓ 第２の電圧変化プロセス８８での電圧変化時間ｔ３＝１．５μｓ 第２の電圧保持プロセス８９での電圧保持時間ｔ４＝０．２μｓ 第３の電圧変化プロセス９０での電圧変化時間ｔ５＝１．５μｓ 第３の電圧保持プロセス９１での電圧保持時間ｔ６＝６μｓ 第４の電圧変化プロセス９２での電圧変化時間ｔ７＝２０μｓにそれぞれ設定して、インク滴３７の吐出実験を行った。この結果、滴径１６μｍのインク滴が滴速６．０ｍ／ｓで吐出されることが観察された。
【００６６】
このように、この例の構成によれば、図６に示す増幅駆動波形信号において、第２の電圧変化プロセス８８の直後に第３の電圧変化プロセス９０を設け、圧力発生室３１の体積を増加させて液柱先端部からインク滴３７を早期に分離させているので、上記した本発明の前提となる実施例の増幅駆動波形信号（図４参照）を採用した場合に比べて、さらに微小なインク滴３７を吐出させることができる。なお、第２の電圧保持プロセス８９での電圧保持時間ｔ４は、液柱先端部からインク滴３７を早期に分離させる効果を大きくさせるためには、可能な限り短いことが望ましい。具体的には、電圧保持時間ｔ４は、式（７）を満足することが望ましい。
【００６７】
【数７】
ｔ４≦１／５Ｔｃ…（７）
【００６８】
また、第３の電圧変化プロセス９０での電圧変化時間ｔ５は、液柱先端部からインク滴３７を早期に分離させる際に充分な粒子速度がメニスカスに生じさせるためには、可能な限り短いことが望ましい。具体的には、電圧変化時間ｔ５は、式（８）を満足することが望ましい。
【００６９】
【数８】
ｔ５≦１／３Ｔｃ…（８）
【００７０】
Ｃ．本発明に係る第２の実施例
次に、本発明に係る第２の実施例について説明する。図７は、本発明に係る第２の実施例であるインクジェット記録ヘッドの駆動方法に採用される増幅駆動波形信号の波形プロファイルの一例を示す図である。この実施例では、増幅駆動波形信号は、図７に示すように、圧力発生室３１の体積を増加させてメニスカスを後退させるために、圧力発生室３１内に発生する圧力波の固有周期Ｔｃの１／２の立ち下げ時間ｔ１で、基準電圧Ｖｂに設定されている圧電アクチュエータ３６の印加電圧Ｖを、電圧（Ｖｂ−Ｖ１）にまで減少させる第１の電圧変化プロセス９３と、電圧（Ｖｂ−Ｖ１）にまで減少した印加電圧Ｖを暫時（時間ｔ２）保持する第１の電圧保持プロセス９４と、圧力発生室３１の体積を減少させてメニスカスの中央部に液柱を形成させるために、立ち上げ時間ｔ３で、圧電アクチュエータ３６の印加電圧Ｖを電圧（Ｖｂ−Ｖ１＋Ｖ２）の高さにまで増加させる第２の電圧変化プロセス９５と、電圧（Ｖｂ−Ｖ１＋Ｖ２）にまで増加した印加電圧Ｖを暫時（時間ｔ４）保持する第２の電圧保持プロセス９６と、圧力発生室３１の体積を増加させて液柱先端部からインク滴３７を早期に分離させるために、立ち下げ時間ｔ５で、電圧（Ｖｂ−Ｖ１＋Ｖ２）に保持された印加電圧Ｖを、例えば、０Ｖにまで減少させる第３の電圧変化プロセス９７と、０Ｖにまで減少した印加電圧Ｖを暫時（時間ｔ６）保持する第３の電圧保持プロセス９８と、圧力発生室３１の体積を減少させてインク滴３７吐出後に残存する圧力波の残響を抑止するために、立ち下げ時間ｔ７で、圧電アクチュエータ３６の印加電圧Ｖを電圧Ｖ４の高さにまで増加させる第４の電圧変化プロセス９９と、圧力発生室３１の体積を減少させてインク滴３７を吐出させると共に、次の吐出動作に備えさせるために、基準電圧Ｖｂの高さにまで増加させる第５の電圧変化プロセス１００とから構成されている。
【００７１】
次に、この例のインクジェット記録ヘッドの駆動方法について、以下に示す駆動波形信号の波形条件でインク滴３７の吐出実験を行った。すなわち、 基準電圧Ｖｂ＝２５Ｖ 第１の電圧変化プロセス９３での電圧変化量Ｖ１＝１５Ｖ 第２の電圧変化プロセス９５での電圧変化量Ｖ２＝１２Ｖ 第３の電圧変化プロセス９７での電圧変化量Ｖ３＝１６Ｖ 第４の電圧変化プロセス９９での電圧変化量Ｖ４＝１４Ｖ 第１の電圧変化プロセス９３での電圧変化時間ｔ１＝５μｓ 第１の電圧保持プロセス９４での電圧保持時間ｔ２＝０．３μｓ 第２の電圧変化プロセス９５での電圧変化時間ｔ３＝１．５μｓ 第２の電圧保持プロセス９６での電圧保持時間ｔ４＝０．２μｓ 第３の電圧変化プロセス９７での電圧変化時間ｔ５＝１．５μｓ 第３の電圧保持プロセス９８での電圧保持時間ｔ６＝１．５μｓ 第４の電圧変化プロセス９９での電圧変化時間ｔ７＝２μｓ 第５の電圧変化プロセス１００での電圧変化時間ｔ８＝１５μｓにそれぞれ設定して、インク滴３７の吐出実験を行った。この結果、滴径１４μｍのインク滴が滴速６．３ｍ／ｓで吐出されることが観察された。
【００７２】
ここで、図７に示す増幅駆動波形信号を用いた場合の粒子速度の時間変化を、式（１）の振動成分のみを考慮して、式（２）を用いて求めた結果を図８に示す。図８において、各細線ａ〜ｄは、図７に示す増幅駆動波形信号の各節部Ａ，Ｂ，Ｃ，Ｄにおいてそれぞれ発生する粒子速度の時間変化を表しており、太線ｓは、各粒子速度を重ね合わせた合計の粒子速度の時間変化、すなわち、実際にメニスカスにおいて生じる粒子速度の時間変化を表している。この例の構成によれば、図７に示す増幅駆動波形信号において、第１の電圧変化プロセス９３での電圧変化時間ｔ１を圧力発生室内に発生する圧力波の固有周期Ｔｃの１／２に設定しているので、図８から分かるように、節部Ａ，Ｂ，Ｃにおいて発生する粒子速度の時間変化の位相はほぼ一致する。そのため、時間範囲Ｔ２では、粒子速度の非常に急激な増加が生じる。また、図７に示す増幅駆動波形信号において、第３の電圧変化プロセス９７を設け、第３の電圧変化プロセス９７での電圧変化量Ｖ３を第２の電圧変化プロセス９５での電圧変化量Ｖ２よりも高く設定しているので、図８から分かるように、時間範囲Ｔ３では、粒子速度が急激に減少する。これにより、液柱先端部からインク滴３７がより早期に分離させることができ、上記した本発明に係る第１の実施例の増幅駆動波形信号（図６参照）を採用した場合に比べて、さらに微小なインク滴３７を吐出させることができる。
【００７３】
また、この例の構成によれば、図７に示す増幅駆動波形信号において、第３の電圧変化プロセス９０の直後に立ち下げ時間ｔ７を有する第４の電圧変化プロセス９９を設け、第１〜第３の電圧変化プロセス９３，９５，９７で発生し、インク滴３７吐出後に残存する圧力波の残響を抑止しているので、前回のインク滴３７の吐出時に発生した圧力波が次回のインク滴３７の吐出時に影響を及ぼすことがない。したがって、増幅駆動波形信号の周波数がより高い場合でも、安定してインク滴３７を吐出させることができる。上記した本発明の前提となる実施例及び本発明に係る第１の実施例の増幅駆動波形信号（図４及び図６参照）を採用した場合には、増幅駆動波形信号の周波数を８ｋＨｚ以上に設定すると、インク滴３７の吐出状態が多少不安定になったのに対し、この例の増幅駆動波形信号（図７参照）を採用した場合には、増幅駆動波形信号の周波数が１２ｋＨｚまではインク滴３７が安定して吐出することが確認された。図８においても、時間範囲Ｔ４では、粒子速度の時間変化が非常に小さくなることが示されている。さらに、この例の構成によれば、インク滴３７の吐出方向等の飛翔特性も改善されることが確認された。これは、上記したように、図７に示す増幅駆動波形信号において、第４の電圧変化プロセス９９を設け、インク滴３７吐出後に残存する圧力波の残響を抑止しているので、インク滴３７を吐出した直後のメニスカスが安定し、サテライトの吐出方向等の飛翔状態が安定化及び均一化するからである。
【００７４】
なお、第３の電圧保持プロセス９８での電圧保持時間ｔ６は、効果的に残響を抑制するためには、可能な限り短いことが望ましい。具体的には、電圧保持時間ｔ６は、式（９）を満足することが望ましい。
【００７５】
【数９】
ｔ６≦１／３Ｔｃ…（９）
【００８５】
また、第４の電圧変化プロセス９９での電圧変化時間ｔ７は、残響抑制用の圧力波を効率的に発生させるためには、可能な限り短いことが望ましい。具体的には、電圧変化時間ｔ７は、式（１０）を満足することが望ましい。
【００７６】
【数１０】
ｔ７≦１／２Ｔｃ…（１０）
【００７７】
以上、この発明の実施例を図面を参照して詳述してきたが、具体的な構成はこの実施例に限られるものではなく、この発明の要旨を逸脱しない範囲の設計の変更等があってもこの発明に含まれる。例えば、上述の各実施例では、この発明によるインクジェット記録ヘッドの駆動方法をノズルから着色インクを吐出させて紙やＯＨＰフィルム等の記録媒体上に文字や画像を記録するプリンタ、プロッタ、複写機、ファクシミリ等のインクジェット記録装置に適用する例を示したが、これに限定されない。すなわち、記録媒体として高分子フィルムやガラスを用いても良いし、ノズルから吐出する液体として溶融状態のハンダを用いても良い。つまり、この発明によるインクジェット記録ヘッドの駆動方法は、例えば、ノズルから着色インクを吐出させて高分子フィルムやガラス上にディスプレイ用のカラーフィルタを作製する液滴噴射装置や、ノズルから溶融状態のハンダを吐出させて基板上に部品実装用のバンプを形成する液滴噴射装置など、液滴噴射装置一般に適用しても良い。
【００７８】
また、上述の各実施例では、ノズル３４の形状をテーパ状にする例を示したが、これに限定されない。同様に、ノズル３４の開口形状は、円形状に限らず、長方形や三角形やその他の形状でも良い。また、ノズル３４、圧力発生室３１、インク供給孔３３のそれぞれの位置関係も、この実施例で示した構造に限定されるものではなく、例えば、ノズル３４を圧力発生室３１の中央部等に配置してももちろん良い。また、上述の各実施例では、細長立方体形状に形成された圧力発生室３１を用いる例を示したが、これに限定されず、圧力発生室３１の形状はどのようなものでも良い。
【００７９】
また、上述の各実施例では、圧電アクチュエータ３６への印加電圧が常に正極性となるようにバイアス電圧（基準電圧）Ｖｂを設定する例を示したが、これに限定されず、圧電アクチュエータ３６に負極性の電圧を印加しても問題ない場合には、バイアス電圧Ｖｂとして、０Ｖなど、他の電圧を設定するように構成しても良い。また、上述の各実施例では、インクジェット記録ヘッドとして、カイザー型を用いる例を示したが、圧力発生手段によって圧力発生室内に圧力変化を生じさせることにより、ノズルからインク滴を吐出させるインクジェット記録ヘッドである限り、カイザー型に限定されない。インクジェット記録ヘッドとして、例えば、圧電アクチュエータに設けた溝を圧力発生室とするインクジェット記録ヘッドを用いても良い。
【００８０】
また、上述の各実施例では、圧力発生室内に発生する圧力波の固有周期Ｔｃが１０μｓであるインクジェット記録ヘッドについての実験結果を示したが、固有周期Ｔｃがこれと異なる場合においても、上述の各実施例で述べたと略同様の効果が得られる。ただし、固有周期Ｔｃが長すぎると、微小なインク滴の形成が困難となるため、滴径１５〜２０μｍ程度の微小なインク滴を吐出させるためには、固有周期Ｔｃは１５μｓ以下に設定することが望ましい。また、上述の各実施例では、圧電アクチュエータ３６に圧電定数ｄ３３を利用した縦振動モードの圧電アクチュエータを用いる例を示したが、これに限定されず、圧電アクチュエータ３６として、圧電定数ｄ３１を利用した縦振動モードの圧電アクチュエータなど、他の形態の圧電アクチュエータを用いても良い。
【００８１】
また、上述の各実施例では、圧力発生手段として、積層型圧電セラミックスからなる圧電アクチュエータ３６を用いる例を示したが、これに限定されず、単板型等他の構造の圧電アクチュエータ、別種の電気機械変換素子や磁歪素子、あるいは静電アクチュエータを用いても、上記した効果と略同様の効果を得ることができる。また、上述の各実施例では、図２及び図３に示す駆動回路を用いる例を示したが、これに限定されず、図４、図６又は図７に示す増幅駆動波形信号を圧電アクチュエータ３６に印加できるのであれば、他の構成の駆動回路を用いても良い。
【００８２】
【発明の効果】
以上説明したように、この発明の構成によれば、駆動波形信号において、第１の電圧変化プロセスでの電圧変化時間を、圧力発生室内に発生する圧力波の固有周期Ｔｃの１／３から２／３までの範囲の長さに設定すると共に、第２の電圧変化プロセスの開始時刻を第１の電圧変化プロセスの終了時刻の直後に設定したので、滴径２０μｍ程度の微小なインク滴を安定して吐出させることができる。また、圧電アクチュエータ自体の固有振動が励起されないので、圧電アクチュエータに流れる電流が増大したり、圧電アクチュエータの信頼性及び耐久性が損なわれることはない。これにより、安価かつ小型の構成で、滴径２０μｍ以下の微小なインク滴を吐出することができる。また、この発明の別の構成によれば、駆動波形信号において、第２の電圧変化プロセスの直後に第３の電圧変化プロセスを設け、圧力発生室の体積を増加させて液柱先端部からインク滴を早期に分離させているので、さらに微小なインク滴を吐出させることができる。また、この発明の別の構成によれば、駆動波形信号において、第３の電圧変化プロセスの直後に第４の電圧変化プロセスを設け、インク滴吐出後に残存する圧力波の残響を抑止しているので、駆動波形信号の周波数がより高い場合でも、安定してインク滴を吐出させることができると共に、インク滴の吐出方向等の飛翔特性も改善される。
【図面の簡単な説明】
【図１】（ａ）は、本発明の前提となる実施例であるインクジェット記録ヘッドの駆動方法を適用したインクジェット記録装置に搭載されるインクジェット記録ヘッドの構成の一例を示す断面図、同図（ｂ）は、同インクジェット記録ヘッドを分解して示す分解断面図である。
【図２】同インクジェット記録ヘッドを駆動する滴径非変調型駆動回路の電気的構成を示すブロック図である。
【図３】同インクジェット記録ヘッドを駆動する滴径変調型駆動回路の電気的構成を示すブロック図である。
【図４】同インクジェット記録ヘッドの駆動方法に採用される増幅駆動波形信号の波形プロファイルの一例を示す図である。
【図５】第１の電圧変化プロセスでの電圧変化時間ｔ１とインク滴の滴径との関係を示す特性図である。
【図６】本発明に係る第１の実施例であるインクジェット記録ヘッドの駆動方法に採用される増幅駆動波形信号の波形プロファイルの一例を示す図である。
【図７】本発明に係る第２の実施例であるインクジェット記録ヘッドの駆動方法に採用される増幅駆動波形信号の波形プロファイルの一例を示す図である。
【図８】図７に示す増幅駆動波形信号を用いた場合の粒子速度の時間変化の一例を示す図である。
【図９】この発明に適用されるインクジェット記録ヘッドのインク充填状態における等価回路図である。
【図１０】同インクジェット記録ヘッドの駆動方法の妥当性の理論的根拠を説明するための波形図である。
【図１１】同インクジェット記録ヘッドの駆動方法の妥当性の理論的根拠を説明するための波形図である。
【図１２】同インクジェット記録ヘッドの駆動方法の妥当性の理論的根拠を説明するための波形図である。
【図１３】同インクジェット記録ヘッドの駆動方法の妥当性の理論的根拠を説明するための波形図である。
【図１４】従来技術を説明するための図で、ドロップ・オン・デマンド型インクジェット記録ヘッドのうち、カイザー型と呼ばれるインクジェット記録ヘッドの基本構成を示す概略断面図である。
【図１５】従来におけるインクジェット記録ヘッドの駆動方法に採用される駆動波形信号の波形プロファイルの一例を示す図である。
【図１６】従来のインクジェット記録ヘッドの駆動方法におけるインク滴吐出過程を説明するためのノズル開口面近傍の断面図である。
【図１７】従来における別のインクジェット記録ヘッドの駆動方法に採用される駆動波形信号の波形プロファイルの一例を示す図である。
【図１８】従来におけるさらに別のインクジェット記録ヘッドの駆動方法に採用される駆動波形信号の波形プロファイルの一例を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ink jet recording head driving method and a circuit therefor, and more particularly, by driving an ink jet recording head having nozzles to selectively eject minute ink droplets from the nozzles to paper or OHP (overhead projector). The present invention relates to a driving method of an ink jet recording head for recording characters and images on a recording medium such as a film and a circuit thereof.
[0002]
[Prior art]
Conventionally, as one of the ink jet recording heads, a nozzle and a pressure generating chamber corresponding to the nozzle are provided, and a drive waveform signal corresponding to image data is supplied to a pressure generating means such as a piezoelectric actuator provided at a position corresponding to the pressure generating chamber. Drop-on recording of characters and images on a recording medium such as paper or OHP film by ejecting ink droplets from nozzles by applying a pressure to rapidly change the volume of the pressure generating chamber filled with ink. A drop on demand type ink jet recording head is widely known (for example, see Japanese Patent Publication No. 53-12138 and Japanese Patent Laid-Open No. 10-193857).
[0003]
FIG. 14 is a schematic cross-sectional view showing the basic configuration of an ink jet recording head called a “Kyser” type among such ink jet recording heads. As shown in the drawing, the ink jet recording head of this example includes a pressure generating chamber 1, a common ink chamber 2 connected to an ink tank (not shown) for supplying ink to the pressure generating chamber 1, and the common ink. An ink supply hole (ink supply path) 3 for communicating the chamber 2 and the pressure generation chamber 1, a nozzle 4 for ejecting ink droplets 7, and a diaphragm 5 constituting the lower plate of the pressure generation chamber 1 in FIG. And a piezoelectric actuator 6 attached to the lower surface of the diaphragm 5.
[0004]
In such a configuration, during the recording operation, the piezoelectric actuator 6 is driven according to the image data to displace the diaphragm 5, thereby rapidly changing the volume of the pressure generating chamber 1 and applying pressure to the pressure generating chamber 1. Generate waves (acoustic waves). Due to this pressure wave, a part of the ink filled in the pressure generating chamber 1 is ejected to the outside through the nozzle 4 and discharged as ink droplets 7. The ejected ink droplets 7 land on the recording medium and form recording dots. By repeatedly forming such recording dots based on the image data, characters and images are recorded on the recording medium.
[0005]
By the way, in this type of ink jet recording head, normally, one ink droplet lands on a recording medium to form one recording dot (pixel), and the size of the recording dot and the image quality are approximately inversely proportional. Are in a relationship. Therefore, in order to meet the recent increase in demand for image quality, it is necessary to form recording dots having a small diameter on the recording medium. The diameter (dot diameter) of the recording dots for obtaining a smooth image (high image quality) with little graininess is 40 μm or less from the viewpoint of human eye identification, and if it is 30 μm or less, the image Even in the highlighted portion, since the individual recording dots are difficult to visually recognize, the image quality is greatly improved.
[0006]
The relationship between the ink droplet diameter (droplet diameter) and the dot diameter depends on the ink droplet flying speed (droplet speed), ink physical properties (viscosity, surface tension), the type of recording medium, etc. This is about twice the ink droplet diameter. Therefore, in order to obtain a dot diameter of 30 μm, it is necessary to make the droplet diameter about 15 μm. In this specification, the droplet diameter means a value obtained by converting the total amount of ink (including satellites) discharged from the nozzles by discharging one ink droplet into the diameter of one spherical droplet. Here, the satellite refers to a small ink droplet that is formed secondary to the back of the ink droplet (main droplet) that is ejected from the nozzle.
[0007]
On the other hand, it has been empirically known that the minimum value of the droplet diameter obtained from a nozzle having a predetermined opening diameter is about the same as the opening diameter (nozzle diameter). Therefore, in order to obtain a droplet diameter of 15 μm, the nozzle diameter is required to be 15 μm or less. However, reducing the nozzle diameter to 15 μm or less is accompanied by many manufacturing difficulties and increases the probability of nozzle clogging, which significantly impairs the reliability and durability of the ink jet recording head. . Therefore, in practice, about 20 to 25 μm is the lower limit of the nozzle diameter for the time being. Therefore, it has been difficult to stably eject ink droplets having a droplet diameter of 15 μm or less. In addition, if the nozzle diameter is reduced by paying attention only to the miniaturization of the ink droplets, there also arises a problem that it becomes difficult to eject ink droplets having the maximum droplet diameter that meets the desired resolution.
[0008]
As means for solving the above inconvenience, conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 55-17589, an inverted trapezoidal drive waveform signal shown in FIG. There has been proposed an ink jet recording head driving method in which ink droplets smaller than the nozzle diameter are ejected by performing so-called “meniscus control” immediately before the ejection of the droplets.
[0009]
The drive waveform signal shown in FIG. 15 is a first waveform that reduces the applied voltage V of the piezoelectric actuator set to the reference voltage V1 (> 0 V) to 0 V, for example, in order to increase the volume of the pressure generating chamber. A voltage change process 8, a voltage holding process 9 for holding the applied voltage V reduced to 0V for a while (time t2), and then discharging the ink droplet by reducing the volume of the pressure generating chamber, and the next discharge In order to prepare for the operation, it comprises a second voltage change process 10 for increasing the applied voltage V of the piezoelectric actuator to the height of the voltage V2. Note that the movement of the piezoelectric actuator due to the increase or decrease in the voltage of the drive waveform signal depends on the structure of the piezoelectric actuator, the polarization direction, etc. Therefore, there is a piezoelectric actuator that moves in the opposite direction to the movement of the piezoelectric actuator described above. For a piezoelectric actuator that operates, if the voltage of the drive waveform signal is also reversed, the discharge operation is the same as described above. Therefore, in this specification, for the sake of simplicity, the voltage of the drive waveform signal is used. As a representative example, the piezoelectric actuator moves so that the volume of the pressure generating chamber decreases when the pressure increases, and the volume of the pressure generating chamber increases when the voltage of the drive waveform signal decreases.
[0010]
FIG. 16 is a diagram schematically showing the movement of the meniscus 12 on the opening surface 11a of the nozzle 11 when the drive waveform signal shown in FIG. 15 is applied to the piezoelectric actuator. First, when it is not necessary to eject ink droplets, the meniscus 12 is on the opening surface 11a of the nozzle 11 as shown in FIG. Then, when it is necessary to eject ink droplets, first, when the first voltage change process 8 of the drive waveform signal is applied to the piezoelectric actuator in order to increase the volume of the pressure generation chamber, FIG. As shown, the meniscus 12 on the opening surface 11a of the nozzle 11 is drawn into the nozzle 11, and the shape of the meniscus 12 becomes concave ("pulling" process). Thereafter, when the second voltage change process 10 of the drive waveform signal is applied to the piezoelectric actuator in order to reduce the volume of the pressure generation chamber, the liquid column 13 is formed at the center of the meniscus 12 as shown in FIG. Then, the tip of the liquid column 13 is separated, and the ink droplets 14 are ejected as shown in FIG. 16D (“push” process). The droplet diameter of the ink droplet 14 ejected at this time is substantially equal to the thickness of the liquid column 13 and smaller than the diameter of the nozzle 11.
[0011]
However, in the conventional ink jet recording head driving method using the inverted trapezoidal driving waveform signal shown in FIG. 15, the ink droplet diameter actually obtained is about 25 μm, which is a demand for higher image quality. I cannot respond enough. In view of this, the inventor disclosed in Japanese Patent Application No. 10-318443 a method for driving an ink jet recording head in which a minute ink droplet is ejected by applying a driving waveform signal having the waveform shown in FIG. 17 to a piezoelectric actuator. did. The drive waveform signal shown in FIG. 17 indicates that the applied voltage V of the piezoelectric actuator set to the reference voltage V1 (> 0V) is reduced to, for example, 0V in order to increase the volume of the pressure generation chamber and to retract the meniscus. A first voltage changing process 15 for reducing, a first voltage holding process 16 for holding the applied voltage V reduced to 0 V for a while (time t2), and a volume of the pressure generating chamber is reduced to the central part of the meniscus. In order to form the liquid column, the second voltage change process 17 for increasing the applied voltage V of the piezoelectric actuator to the height of the voltage V2, and the applied voltage V increased to the voltage V2 are held for a while (time t4). For example, the second voltage holding process 18 and the applied voltage V held at the voltage V2 in order to increase the volume of the pressure generation chamber and quickly separate the ink droplets from the liquid column front end portion are as follows. , A third voltage changing process 19 for reducing to 0 V, a third voltage holding process 20 for holding the applied voltage V reduced to 0 V for a while (time t6), and a volume of the pressure generating chamber by reducing the volume. In order to suppress the reverberation of the pressure wave remaining after the droplet discharge, the fourth voltage change process 21 is performed to increase the applied voltage V of the piezoelectric actuator to the height of the voltage V1. That is, the drive waveform signal shown in FIG. 17 is obtained by adding pressure wave control for the purpose of early separation of ink droplets and suppression of reverberation to the conventional “meniscus control” method, whereby the droplet diameter is about 20 μm. Ink droplets can be ejected stably.
[0012]
However, in the conventional inkjet recording head driving method using the driving waveform signal having the waveform shown in FIG. 17, it is difficult to eject ink droplets having a droplet diameter of 20 μm or less, and in particular, the droplet diameter is 15 μm or less. Ink droplets cannot be ejected. Therefore, the inventors have applied a driving waveform signal having the waveform shown in FIG. 18 to the piezoelectric actuator to thereby eject an ink droplet having a droplet diameter of 15 μm or less. Disclosed in US Pat. The drive waveform signal shown in FIG. 18 is larger than the natural period Ta of the natural vibration of the drive unit composed of the piezoelectric actuator and the diaphragm and increases in the pressure generation chamber in order to increase the volume of the pressure generation chamber and retract the meniscus. The applied voltage V of the piezoelectric actuator set to the reference voltage Vb (> 0 V) is decreased to, for example, a voltage (Vb−V1) at a falling time t1 smaller than the natural period Tc of the generated pressure wave. 1 voltage change process 22, a first voltage holding process 23 that holds the applied voltage V reduced to the voltage (Vb−V 1) for a while (time t 2), and the center of the meniscus by reducing the volume of the pressure generating chamber In order to form a liquid column in the part, the applied voltage V of the piezoelectric actuator is reduced to the voltage (Vb−V1 + V2) with a rise time t3 smaller than the natural period Ta. A second voltage change process 24 for increasing, a second voltage holding process 25 for holding the applied voltage V increased to the voltage (Vb−V1 + V2) for a while (time t4), and increasing the volume of the pressure generating chamber. In order to quickly separate the ink droplet from the liquid column front end, the applied voltage V held at the voltage (Vb−V1 + V2) is decreased to, for example, 0 V at the falling time t5 smaller than the natural period Ta. 3, a third voltage holding process 27 for holding the applied voltage V reduced to 0 V for a while (time t6), and a pressure wave remaining after the ink droplet discharge by reducing the volume of the pressure generating chamber. In order to suppress the reverberation, a fourth voltage change process 28 for increasing the applied voltage V of the piezoelectric actuator to the height of the reference voltage Vb is configured. That is, the drive waveform signal shown in FIG. 18 is obtained by adding the ejection mechanism using the natural vibration of the piezoelectric actuator itself to the conventional “meniscus control” method, and thereby the natural vibration of the piezoelectric actuator itself is excited. Since vibration having a high frequency can be generated in the meniscus, ink droplets having a droplet diameter of 15 μm or less can be ejected.
[0013]
[Problems to be solved by the invention]
However, in the conventional ink jet recording head driving method using the driving waveform signal having the waveform shown in FIG. 18, the deformation speed of the piezoelectric actuator increases, so that the reliability and durability of the piezoelectric actuator are significantly impaired. Become. Further, as described above, in order to excite the natural vibration of the piezoelectric actuator itself, the applied voltage V of the piezoelectric actuator is changed with a rise time t3 and a fall time t5 (for example, 1 μs) smaller than the natural period Ta. It is necessary to let In this case, since a large current instantaneously flows to the piezoelectric actuator, a semiconductor integrated circuit or the like having a high current driving capability capable of supplying a large current instantaneously to the drive circuit of the inkjet recording head, particularly the piezoelectric actuator drive circuit. It is necessary to use circuit components. Therefore, the cost of circuit components increases, and the amount of heat generated when a large current flows through the circuit also increases, so a countermeasure for heat dissipation is required. As a result, the cost and size of the drive circuit for the ink jet recording head increase.
[0014]
The present invention has been made in view of the above-described circumstances, and discharges minute ink droplets having a droplet diameter of 20 μm or less with a low-cost and compact configuration without impairing the reliability and durability of the piezoelectric actuator. It is an object of the present invention to provide a method and a circuit for driving an ink jet recording head capable of performing the above.
[0015]
[Means for Solving the Problems]
In order to solve the above problems, the invention according to claim 1 is a pressure generation chamber filled with ink, a pressure generation means for generating pressure in the pressure generation chamber, and a nozzle communicated with the pressure generation chamber. An ink jet recording head driving method for ejecting ink droplets from the nozzles by changing a volume of the pressure generating chamber by applying a driving waveform signal to the pressure generating means. The first voltage change process in which a voltage is applied in a direction to increase the volume of the pressure generating chamber, a voltage is applied in a direction to decrease the volume of the pressure generating chamber, and the waveform of the nozzle is set in the nozzle. Forming a liquid column having a diameter smaller than the opening diameter and separating the ink droplet from the tip of the liquid column to discharge a minute ink droplet; The voltage change time in the first voltage change process in the waveform of the drive waveform signal is from 1/3 to 2/2 of the natural period Tc of the pressure wave generated in the pressure generating chamber. The time interval between the end time of the first voltage change process and the start time of the second voltage change process in the waveform of the drive waveform signal is set to a length in the range up to 3. The natural period Tc The voltage change time in the second voltage change process in the waveform of the drive waveform signal is set to a length of 1/3 or less of the natural period Tc. The waveform of the drive waveform signal includes a third voltage change process in which a voltage is applied in the direction of increasing the volume of the pressure generation chamber following the second voltage change process. In the above The time interval between the end time of the second voltage changing process and the start time of the third voltage changing process is characterized in that set to 1/5 or less of the length of the natural period Tc.
[0016]
According to a second aspect of the present invention, there is provided the method for driving an ink jet recording head according to the first aspect, wherein the voltage change time in the first voltage change process in the waveform of the drive waveform signal is the natural period Tc. It is characterized in that the length is set to ½.
[0017]
According to a third aspect of the present invention, there is provided the method for driving an ink jet recording head according to the first aspect, wherein a voltage change time in the third voltage change process in the waveform of the drive waveform signal is represented by the natural period Tc. It is characterized in that the length is set to 1/3 or less.
[0018]
According to a fourth aspect of the present invention, there is provided the method for driving an ink jet recording head according to the third aspect, wherein the voltage change amount in the third voltage change process in the waveform of the drive waveform signal is the second voltage. It is characterized by being set larger than the voltage change amount in the change process.
[0019]
According to a fifth aspect of the present invention, there is provided the method for driving an ink jet recording head according to the third or fourth aspect, wherein the waveform of the drive waveform signal includes a volume of the pressure generating chamber after the third voltage changing process. It is characterized by including the 4th voltage change process which applies a voltage in the direction which decreases.
[0020]
According to a sixth aspect of the present invention, there is provided the method for driving an ink jet recording head according to the fifth aspect, wherein the voltage change time in the fourth voltage change process in the waveform of the drive waveform signal is the natural period. It is characterized in that the length is set to 1/2 or less of Tc.
[0021]
According to a seventh aspect of the present invention, there is provided the method for driving an ink jet recording head according to the fifth or sixth aspect, wherein an end time of the third voltage change process and the fourth time in the waveform of the driving waveform signal are included. The time interval from the start time of the voltage change process is set to a length of 1/3 or less of the natural period Tc.
[0022]
The invention according to claim 8 relates to the driving method of an ink jet recording head according to any one of claims 1 to 7, wherein the natural period Tc is 15 μs or less.
[0023]
According to a ninth aspect of the present invention, there is provided the ink jet recording head driving method according to any one of the first to eighth aspects, wherein the pressure generating means is an electromechanical conversion element.
[0024]
A tenth aspect of the present invention relates to the ink jet recording head driving method according to the ninth aspect, wherein the electromechanical transducer is a piezoelectric actuator.
[0025]
The invention described in claim 11 comprises a pressure generating chamber filled with ink, a pressure generating means for generating pressure in the pressure generating chamber, and a nozzle connected to the pressure generating chamber. A drive circuit for an ink jet recording head that ejects ink droplets from the nozzles by applying a drive waveform signal to the means and changing the volume of the pressure generating chamber, and increasing the volume of the pressure generating chamber Applying a voltage in a direction to reduce the volume of the pressure generating chamber, and forming a liquid column having a diameter smaller than the opening diameter of the nozzle in the nozzle. And a second voltage change process for discharging a minute ink drop by separating the ink drop from the tip of the liquid column, and the first voltage change The voltage change time in the process is set to a length in the range from 1/3 to 2/3 of the natural period Tc of the pressure wave generated in the pressure generating chamber, and the end time of the first voltage change process The time interval from the start time of the second voltage change process is set to a length of 1/5 or less of the natural period Tc, and the voltage change time in the second voltage change process is 1 of the natural period Tc. Waveform generating means for generating a drive waveform signal having a waveform set to a length of / 3 or less, the waveform generating means increasing the volume of the pressure generating chamber after the second voltage change process. Generating a drive waveform signal having a waveform including a third voltage change process for applying a voltage in the direction;
The waveform generating means has a waveform in which the time interval between the end time of the second voltage change process and the start time of the third voltage change process is set to a length of 1/5 or less of the natural period Tc. A drive waveform signal having the following is generated.
[0026]
According to a twelfth aspect of the present invention, there is provided the drive circuit for an ink jet recording head according to the eleventh aspect, wherein the waveform generating means has a voltage change time in the first voltage change process of 1 of the natural period Tc. A drive waveform signal having a waveform set to a length of / 2 is generated.
[0027]
A thirteenth aspect of the present invention relates to the drive circuit for an ink jet recording head according to the eleventh aspect, wherein the waveform generating means has a voltage change time in the third voltage change process of 1 of the natural period Tc. A drive waveform signal having a waveform set to a length of / 3 or less is generated.
[0028]
A fourteenth aspect of the present invention relates to the drive circuit for an ink jet recording head according to the eleventh or thirteenth aspect, wherein the waveform generating means has a voltage change amount in the third voltage change process equal to the second voltage. A drive waveform signal having a waveform set larger than a voltage change amount in the change process is generated.
[0029]
The invention according to claim 15 relates to the drive circuit for an ink jet recording head according to any one of 11, 13, or 14, wherein the waveform generating means is configured to apply the pressure after the third voltage change process. A drive waveform signal having a waveform including a fourth voltage change process for applying a voltage is generated in a direction of decreasing the volume of the generation chamber.
[0030]
According to a sixteenth aspect of the present invention, there is provided the drive circuit for an ink jet recording head according to the fifteenth aspect, wherein the voltage change time in the fourth voltage change process is not more than ½ of the natural period Tc. And generating a drive waveform signal having a waveform set to.
[0031]
According to a seventeenth aspect of the present invention, there is provided the driving circuit for an ink jet recording head according to the fifteenth or sixteenth aspect, wherein the waveform generating means includes an end time of the third voltage change process and the fourth voltage change process. A drive waveform signal having a waveform in which a time interval from the start time is set to a length of 1/3 or less of the natural period Tc is generated.
[0032]
The invention according to claim 18 relates to the drive circuit for an ink jet recording head according to any one of claims 11 to 17, wherein the natural period Tc is 15 μs or less.
[0033]
According to a nineteenth aspect of the present invention, there is provided the ink jet recording head drive circuit according to any one of the eleventh to eighteenth aspects, wherein the pressure generating means is an electromechanical conversion element.
[0034]
A twentieth aspect of the invention relates to the drive circuit for an ink jet recording head according to the nineteenth aspect, wherein the electromechanical transducer is a piezoelectric actuator.
[0035]
[Action]
According to the configuration of the present invention, fine ink droplets having a droplet diameter of 20 μm or less can be ejected without impairing the reliability and durability of the piezoelectric actuator and with an inexpensive and compact configuration.
[0036]
[Theoretical validity of the invention]
First, the rational basis for the validity of the present invention will be described using a lumped parameter equivalent circuit model. FIG. 9A is an equivalent circuit diagram of the ink jet recording head shown in FIG. In FIG. 9, m0 is an inertance (acoustic mass) [kg / m4] of a drive unit composed of the piezoelectric actuator 36 and the diaphragm 35, m2 is an inertance of the ink supply hole 33, m3 is an inertance of the nozzle 34, and r0 is a drive unit. Acoustic resistance [Ns / m5], r2 is the acoustic resistance of the ink supply hole 33, r3 is the acoustic resistance of the nozzle 34, c0 is the acoustic capacity of the drive unit [m5 / N], c1 is the acoustic capacity of the pressure generating chamber 31, c3 is the acoustic capacity of the nozzle 34, u1 is the volume velocity [m3 / s] in the pressure generating chamber 31, u2 is the volume velocity in the ink supply hole 33, u3 is the volume velocity in the nozzle 34, φ is the pressure applied to the ink [Pa ]. Here, if a highly rigid laminated piezoelectric actuator is used for the piezoelectric actuator 36, the inertance m0, the acoustic resistance r0, and the acoustic capacitance c0 of the drive unit can be ignored. Further, the acoustic capacity c3 of the nozzle 34 can be ignored when analyzing the pressure wave. Therefore, the equivalent circuit in FIG. 9A is approximately represented by the equivalent circuit in FIG. Further, the relational expression m2 = km3 between the ink supply holes 33 and the inertances m2 and m3 of the nozzles 34 is the relation of r2 = kr3 between the ink supply holes 33 and the acoustic resistances r2 and r3 of the nozzles 34. Assuming that the equations hold, as shown in FIG. 10A, when a circuit analysis is performed for a case where a drive waveform signal having a rising angle θ is input, the nozzle 34 within the rising time of 0 ≦ t ≦ t1. The particle velocity v3 ′ [m / s] at is given by equation (1). In Expression (1), A3 is the area of the opening of the nozzle 34, and the particle velocity v3 ′ at the nozzle 34 is a value obtained by dividing the volume velocity u3 at the nozzle 34 by the area A3 of the opening of the nozzle 34.
[0037]
[Expression 1]

[0038]
Next, as shown in FIG. 10B, the particle velocity in the case of using a drive waveform signal having a complicated shape (trapezoidal shape) is represented by each point (A, B, C, D) of the drive waveform signal. ) Can be obtained by superimposing the pressure waves generated in step 1). That is, the particle velocity v3 [m / s] at the nozzle 34, which is generated when the drive waveform signal of FIG. 10B is used, is given by Expression (2).
[0039]
[Expression 2]

[0040]
Here, FIG. 12 shows a result obtained by using the equation (2) for the time change of the particle velocity when the driving waveform signal shown in FIG. 11 is used, considering only the vibration component of the equation (1). . The drive waveform signal shown in FIG. 11 indicates that the applied voltage V of the piezoelectric actuator set to the reference voltage V1 (> 0V) is reduced to, for example, 0V in order to increase the volume of the pressure generation chamber and to retract the meniscus. A first voltage change process 41 for decreasing, a voltage holding process 42 for holding the applied voltage V reduced to 0 V for a while (time t2), and then discharging the ink droplets by reducing the volume of the pressure generating chamber. In addition, in order to prepare for the next discharge operation, a second voltage change process 43 for increasing the applied voltage V of the piezoelectric actuator to the height of the voltage V2 is provided. In FIG. 12, each thin line a to d represents a temporal change in the particle velocity generated at each node A, B, C, D of the drive waveform signal shown in FIG. 11, and a thick line s represents each particle velocity. Represents the time change of the total particle velocity obtained by superimposing the particles, that is, the time change of the particle velocity actually occurring in the meniscus.
[0041]
(1) In the drive waveform signal shown in FIG. 11, when the time t1 is set to ½ of the natural period Tc (= 2π / Ec) of the pressure wave generated in the pressure generating chamber, and the time t2 is set to be extremely short As shown in FIG. 12A, the phases of the temporal changes in the particle velocities generated at the nodes A, B, and C substantially coincide. Therefore, in the time range (t> t1 + t2), a very rapid increase in particle velocity occurs. Next, the meniscus shape change when such a very rapid change in the particle velocity occurs will be described with reference to FIGS. When the time change in the particle velocity shown in FIG. 12A is applied to the meniscus 54, the meniscus 54 is drawn into the nozzle 51 from the opening surface of the nozzle 51 in the time range T1, and becomes concave. Next, the meniscus 54 is pushed out of the nozzle 51 in the time range T2. As described above, when the meniscus 54 is “pushed” with the meniscus 54 concave, a thin liquid column 52 is formed at the center of the meniscus 54.
[0042]
Although there is no example in which the formation mechanism of the liquid column 52 has been studied in detail, the inventors have found that when the thickness of the formed liquid injection 52 pushes out the meniscus 54 by an ink droplet discharge observation experiment and fluid analysis. It was clarified that it depends on the velocity of the liquid surface. That is, when pressure is applied to the concave meniscus 54 so as to push it toward the outside of the nozzle 51, as shown in FIG. 13, each part of the meniscus 54 moves in the normal direction of the liquid surface (arrow in the figure). try to. As a result, a large amount of ink concentrates in the central portion of the nozzle 51, and the liquid injection 52 is formed in the central portion of the nozzle 51 due to this local increase in the volume of ink. At this time, when the moving speed of the liquid surface is high, the speed at which the volume of ink increases at the center of the nozzle 51 also increases, so that a very thin liquid injection 52 is formed at a high growth speed (FIG. 13). (See (a)). On the other hand, when the moving speed of the liquid surface is slow, the speed at which the volume of ink increases at the center of the nozzle 51 becomes small, so that the liquid injection 52 becomes thick and the growth speed slows (FIG. 13 ( b)).
[0043]
As described above, the droplet diameter of the ink droplet 53 ejected from the nozzle 51 using the “meniscus control” method is substantially equal to the thickness of the liquid column 52 to be formed. Further, the flying speed (dropping speed) of the ink droplet is substantially equal to the growth speed of the liquid column 52. Therefore, in order to eject minute ink droplets at high speed, it is important to increase the liquid level movement speed during the “push” process and cause a sudden increase in the ink volume at the center of the nozzle 51. It becomes a condition.
[0044]
Considering from the above viewpoint, setting the time t1 to ½ of the natural period Tc and setting the time t2 to be extremely short in the drive waveform signal shown in FIG. 11 in order to eject minute ink droplets. This is a very advantageous condition. That is, under such conditions, as shown in FIG. 12A, the phase of the time change of the particle velocity generated at the nodes A, B, and C of the drive waveform signal shown in FIG. In the time range (t> t1 + t2), the particle velocity increases rapidly and the liquid surface moving velocity increases. For this reason, a sudden increase in the volume of the ink occurs in the central portion of the nozzle 51, so that a thin liquid column 52 is formed. As a result, it is possible to eject very minute ink droplets 53 at high speed. That is, it is an important condition for ejecting the minute ink droplets 53 to rapidly increase the moving speed of the liquid surface of the meniscus 54 when the liquid column 52 is formed.
[0045]
(2) On the other hand, in the drive waveform signal shown in FIG. 11, when the time t1 is not set to ½ of the natural period Tc, as shown in FIG. 12B, the nodes A, B, C The phase of the time change of the particle velocity generated in FIG. 3 does not match, and the time change (thick line s) of the total particle velocity obtained by superimposing the particle velocities becomes a very slow change. That is, when the time t1 is shorter than ½ of the natural period Tc, a positive particle velocity is generated by the node B while the particle velocity generated by the node A is negative. The increase in the moving speed of the liquid surface of the meniscus 54 is slowed down. On the other hand, when the time t1 is longer than ½ of the natural period Tc, the particle velocity generated by the node A before the positive particle velocity is generated by the node B becomes positive. It becomes impossible to obtain a rapid increase in the moving speed of the liquid level of 54. Under such conditions, since it is difficult for the volume of the ink to suddenly increase in the central portion of the nozzle 51, the thickness of the liquid column 52 to be formed becomes thick. The droplet diameter is large and the droplet speed is slow (see FIG. 13B). Therefore, it is impossible to obtain a fine ink droplet having a droplet diameter of 20 μm or less required for high-quality recording.
[0046]
As described above, the droplet diameter and the droplet velocity of the ink droplet 53 ejected from the nozzle 51 using the “meniscus control” method are the voltage variation time of the first voltage variation process 41 in the drive waveform signal shown in FIG. The voltage change time greatly depends on t1 and the time interval between the end time of the first voltage change process 41 and the start time of the second voltage change process 43, that is, the voltage hold time t2 in the voltage hold process 42. By setting t1 to about ½ of the natural period Tc and setting the voltage holding time t2 sufficiently short, it is possible to eject ink droplets with a very small droplet diameter at high speed. In this case, since the natural vibration of the piezoelectric actuator itself is not used, the reliability and durability of the piezoelectric actuator are not impaired, and the drive circuit of the ink jet recording head, in particular, the drive circuit of the piezoelectric actuator is conventionally used. Therefore, the cost and size of the drive circuit for the ink jet recording head do not increase.
[0047]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. The description will be made specifically with reference to examples.
A. It is a premise of the present invention Example
First, It is a premise of the present invention Examples will be described. FIG. 1 (a) It is a premise of the present invention Sectional drawing which shows an example of a structure of the inkjet recording head mounted in the inkjet recording device to which the drive method of the inkjet recording head which is an Example is applied, The figure (b) is the decomposition | disassembly cross section which decomposes | disassembles and shows the inkjet recording head FIG. As shown in FIG. 1A, the ink jet recording head of this example is a drop-on-demand-Kaiser type multi-nozzle that ejects ink droplets 37 as necessary to print characters and images on a recording medium. As shown in FIG. 1, a plurality of pressure generating chambers 31 each formed in an elongated cubic shape and arranged in the direction perpendicular to the paper surface in the drawing, and the bottom surface of each pressure generating chamber 31 in the drawing, as shown in FIG. A vibration plate 35, a plurality of piezoelectric actuators 36 arranged in parallel on the back surface of the vibration plate 35 and corresponding to the pressure generation chambers 31, and an ink tank (not shown) are connected to generate each pressure. A common ink chamber (ink pool) 32 for supplying ink to the chamber 31 and a plurality of ink supply holes (ink supply passages) for communicating the common ink chamber 32 and the pressure generating chambers 31 on a one-to-one basis. 3, provided in one-to-one with each of the pressure generating chamber 31, is schematically composed of a plurality of nozzles 34 for ejecting ink droplets 37 from the distal end portion which is protruding the bent over each pressure generating chamber 31. Here, the common ink chamber 32, the ink supply hole 33, the pressure generation chamber 31, and the nozzle 34 form a flow path portion in which the ink moves in this order, and the piezoelectric actuator 36 and the diaphragm 35 form the pressure generation chamber 31. A drive unit that applies a pressure wave to the ink is configured, and a contact point between the flow path unit and the drive unit is a bottom surface of the pressure generation chamber 31 (that is, an upper surface of the diaphragm 35 in the drawing).
[0048]
The piezoelectric actuator 36 is a longitudinal vibration mode using the piezoelectric constant d33, and is made of laminated piezoelectric ceramics. The shape of the drive column for applying displacement to the pressure generating chamber 31 is 690 μm in length (L), The width (W) is 1.8 μm and the depth length (the length in the direction perpendicular to the plane of FIG. 1) is 120 μm. As the piezoelectric material constituting the piezoelectric actuator 36, a material having a density ρp of 8.0 × 103 [kg / m3] and an elastic coefficient Ep of 68 GPa is used. The measured natural period Ta of the piezoelectric actuator 36 itself was 1.0 μs.
[0049]
In the head manufacturing process of this embodiment, as shown in FIG. 1 (b), a nozzle plate 34a in which a plurality of nozzles 34 are arranged in a row or in a staggered manner by being perforated circularly by precision pressing. A pool plate 32a in which the space portion of the common ink chamber 32 is formed, a supply hole plate 33a in which the ink supply holes 33 are formed, and a pressure generation chamber plate 31a in which the space portions of the plurality of pressure generation chambers 31 are formed. After the vibration plates 35a constituting the plurality of vibration plates 35 are prepared by perforating by etching or the like in advance, the plates 31a to 35a are formed with an adhesive layer made of a thermosetting resin (not shown) having a thickness of about 5 μm. Then, the laminated plate and the piezoelectric actuator 36 are bonded to each other using a thermosetting resin adhesive layer or an epoxy adhesive layer. By had been joined, possible to manufacture the ink jet recording head of the above construction is performed. In this example, a 50 to 75 μm thick nickel plate formed by electroforming is used for the vibration plate 35a, whereas the other plates 31a to 34a have a thickness of 50 to 50 μm. A 75 μm stainless plate is used. Further, the nozzle 34 in this example has an opening diameter of about 30 μm, a skirt diameter of about 65 μm, and a length of about 75 μm, and is formed in a tapered shape whose diameter gradually increases toward the pressure generating chamber 31 side. The ink supply hole 33 is also formed in the same shape as the nozzle 34.
[0050]
Next, with reference to FIG. 2 and FIG. 3, an electrical configuration of a drive circuit that configures the inkjet recording apparatus of this example and drives the inkjet recording head having the above configuration will be described. The ink jet recording apparatus of this example has a CPU (Central Processing Unit) (not shown) and a memory such as a ROM and a RAM. The CPU executes a program stored in the ROM, and uses various registers and flags secured in the RAM, based on image data supplied from a host device such as a personal computer via an interface. In order to record characters and images on the top, each part of the apparatus is controlled.
[0051]
First, the drive circuit shown in FIG. 2 generates a drive waveform signal corresponding to the amplified drive waveform signal shown in FIG. The same ink droplet 37 is ejected to record characters and images on a recording medium, and is schematically composed of a waveform generation circuit 61, an amplification circuit 62, and a switching circuit 63. The waveform generation circuit 61 is composed of a digital / analog conversion circuit and an integration circuit. After the drive waveform data read from a predetermined storage area of the ROM is converted into an analog signal by the CPU, the integration processing is performed and the amplification shown in FIG. A drive waveform signal corresponding to the drive waveform signal is generated. The amplifier circuit 62 power-amplifies the drive waveform signal supplied from the waveform generation circuit 61 and outputs it as an amplified drive waveform signal shown in FIG. The switching circuit 63 is composed of, for example, a transfer gate, the input end is connected to the output end of the amplifier circuit 62, the output end is connected to one end of the piezoelectric actuator 36, and the control end is an image in a drive control circuit (not shown). When a control signal generated and supplied based on the data is input, the control signal is turned on, and an amplification drive waveform signal (see FIG. 4) output from the amplifier circuit 62 is applied to the piezoelectric actuator 36. At this time, the piezoelectric actuator 36 gives a displacement according to the applied amplification drive waveform signal to the diaphragm 35, and the displacement of the diaphragm 35 causes the pressure generating chamber 31 to rapidly change (increase / decrease) in volume. A predetermined pressure wave is generated in the pressure generating chamber 31 filled with ink, and a minute ink droplet 37 having a droplet diameter of about 20 μm is ejected from the nozzle 34 by this pressure wave. In the ink jet recording head of this embodiment, the natural period Tc of the pressure wave in the pressure generating chamber 31 filled with ink is 10 μs. The ejected ink droplets 37 land on the recording medium and form recording dots. By repeatedly forming such recording dots based on the image data, characters and images are binary recorded on the recording medium.
[0052]
Next, the drive circuit shown in FIG. 3 has three stages of ink droplet diameters ejected from the nozzles 34 (in this example, three droplets: a large droplet having a droplet diameter of about 40 μm, a medium droplet having a size of about 30 μm, and a small droplet having a size of about 20 μm. A so-called droplet diameter modulation type driving circuit that records characters and images on a recording medium with multiple gradations, and has three types of waveform generation circuits 71a, 71b, 71c according to the droplet diameter; Amplifying circuits 72a, 72b, 72c connected to the waveform generating circuits 71a, 71b, 71c on a one-to-one basis, and a plurality of switching circuits 73, 73,. It is roughly composed of Each of the waveform generation circuits 71a to 71c includes a digital / analog conversion circuit and an integration circuit. Among these waveform generation circuits 71a to 71c, the waveform generation circuit 71a is moved from a predetermined storage area of the ROM by the CPU. The read driving waveform data for large droplet ejection is converted into analog data, and then integrated to generate a driving waveform signal for large droplet ejection. The waveform generation circuit 71b analog-converts the drive waveform data for medium droplet discharge read from the predetermined storage area of the ROM by the CPU, and then integrates to generate a drive waveform signal for medium droplet discharge. Further, the waveform generation circuit 71c converts the drive waveform data for droplet ejection read out from a predetermined storage area of the ROM by the CPU into an analog signal, and then integrates to correspond to the amplified drive waveform signal shown in FIG. A drive waveform signal for droplet ejection is generated. The amplifier circuit 72a amplifies the power of the large droplet ejection drive waveform signal supplied from the waveform generation circuit 71a and outputs the amplified signal as an amplified drive waveform signal for large droplet ejection. The amplifying circuit 72b amplifies the power of the driving waveform signal for ejecting medium droplets supplied from the waveform generating circuit 71b and outputs the amplified driving waveform signal for ejecting medium droplets. In addition, the amplifier circuit 72c amplifies the power of the droplet ejection drive waveform signal supplied from the waveform generation circuit 71c and outputs it as an amplified drive waveform signal for droplet ejection (see FIG. 4).
[0053]
The switching circuit 73 includes first, second, and third transfer gates (not shown). The input terminal of the first transfer gate is connected to the output terminal of the amplifier circuit 72a, and the second transfer gate is connected. The input terminal of the gate is connected to the output terminal of the amplifier circuit 72b, the input terminal of the third transfer gate is connected to the output terminal of the amplifier circuit 72c, and the outputs of the first, second, and third transfer gates One end is connected to one end of a corresponding common piezoelectric actuator 36. When the gradation control signal generated based on the image data in the drive control circuit (not shown) is supplied to the control terminal of the first transfer gate, the first transfer gate is turned on and the amplifier circuit An amplification drive waveform signal for discharging large droplets output from 72 a is applied to the piezoelectric actuator 36. At this time, the piezoelectric actuator 36 gives a displacement corresponding to the applied amplification drive waveform signal to the diaphragm 35, and the displacement of the diaphragm 35 causes the pressure generating chamber 31 to rapidly change (increase / decrease) in volume. A predetermined pressure wave is generated in the pressure generating chamber 31 filled with ink, and a large ink droplet 37 is ejected from the nozzle 34 by this pressure wave. When a gradation control signal generated based on image data in a drive control circuit (not shown) is supplied to the control terminal of the second transfer gate, the second transfer gate is turned on and the amplifier circuit 72b The output amplification drive waveform signal for ejecting medium droplets is applied to the piezoelectric actuator 36. At this time, the piezoelectric actuator 36 gives a displacement according to the applied amplification drive waveform signal to the diaphragm 35, and the displacement of the diaphragm 35 causes the pressure generating chamber 31 to rapidly change (increase / decrease) in volume. A predetermined pressure wave is generated in the pressure generating chamber 31 filled with ink, and a medium-sized ink droplet 37 is ejected from the nozzle 34 by this pressure wave. When a gradation control signal generated based on image data in a drive control circuit (not shown) is supplied to the control terminal of the third transfer gate, the third transfer gate is turned on and the amplifier circuit An amplification drive waveform signal (see FIG. 4) for discharging a small droplet output from 72c is applied to the piezoelectric actuator 36. At this time, the piezoelectric actuator 36 gives a displacement according to the applied amplification drive waveform signal to the diaphragm 35, and the displacement of the diaphragm 35 causes the pressure generating chamber 31 to rapidly change (increase / decrease) in volume. A predetermined pressure wave is generated in the pressure generating chamber 31 filled with ink, and a small ink droplet 37 is ejected from the nozzle 34 by this pressure wave. The ejected ink droplets 37 land on the recording medium and form recording dots. By repeatedly forming such recording dots based on image data, characters and images are recorded on the recording medium in multiple gradations. In this embodiment, the drive circuit of FIG. 2 is incorporated in an inkjet recording apparatus dedicated to binary recording, and the drive circuit of FIG. 3 is incorporated in an inkjet recording apparatus that also performs gradation recording.
[0054]
As shown in FIG. 4, the amplification drive waveform signal described above is ½ of the natural period Tc of the pressure wave generated in the pressure generation chamber 31 in order to increase the volume of the pressure generation chamber 31 and to retract the meniscus. The first voltage change process 81 for reducing the applied voltage V of the piezoelectric actuator 36 set to the reference voltage Vb to the voltage (Vb−V1) and the voltage (Vb−V1) at the falling time t1 of A first voltage holding process 82 for holding the applied voltage V reduced to a certain time (time t2), and a rise time t3 in order to reduce the volume of the pressure generating chamber 31 and form a liquid column at the center of the meniscus. Thus, the second voltage change process 83 for increasing the applied voltage V of the piezoelectric actuator 36 to the height of the voltage (Vb−V1 + V2) and the applied voltage increased to the voltage (Vb−V1 + V2). For a period of time (time t4), and the application of the piezoelectric actuator 36 to reduce the volume of the pressure generation chamber 31 to discharge the ink droplet 37 and prepare for the next discharge operation. And a third voltage changing process 85 for increasing the voltage V to the level of the reference voltage Vb.
[0055]
Next, with respect to the driving method of the ink jet recording head of this example, an ejection experiment of the ink droplet 37 was performed under the following waveform condition of the driving waveform signal. That is,
Reference voltage Vb = 25V
Voltage change amount V1 = 15V in the first voltage change process 81
Voltage change amount V2 = 12V in the second voltage change process 83
Voltage change time t1 = 5 μs in the first voltage change process 81
Voltage holding time t2 = 0.3 μs in the first voltage holding process 82
Voltage change time t3 = 1.5 μs in the second voltage change process 83
Voltage holding time t4 = 6 μs in the second voltage holding process 84
Voltage change time t5 = 20 μs in the third voltage change process 85
And the change of the droplet diameter was examined by changing the voltage change time t1 in the first voltage change process 81. The voltage holding time t2 is set so as to satisfy the expression (3), the voltage change amount V1 in the first voltage change process 81 is set so that the retreat amount at the time of meniscus retraction is constant, The voltage change amount V2 in the second voltage change process 83 was adjusted so that the droplet speed was always 6 m / s. However, in the formula (3), when t1 is a value of 1 / 2Tc or more, t2 = 0.
[0056]
[Equation 3]
t1 + t2 = 1 / 2Tc (3)
[0057]
FIG. 5 is a characteristic diagram showing the relationship between the voltage change time t1 in the first voltage change process 81 and the droplet diameter of the ink droplet 37. As shown in FIG. Referring to FIG. 5, when the voltage change time t <b> 1 is ½ of the natural period Tc of the pressure wave generated in the pressure generation chamber 31, the droplet diameter of the ink droplet 37 is minimized and a minute ink droplet is ejected. It can be seen that this is the optimum condition. In the experiment, it was observed that an ink droplet having a droplet diameter of 21 μm was ejected at a droplet speed of 6.2 m / s. On the other hand, for comparison, in the amplification drive waveform signal shown in FIG. 4, the result of conducting the ink droplet 37 discharge experiment with the voltage change time t1 set to 2 μs and the voltage holding time t2 set to 3 μs. Regardless of how the voltage change amounts V1 and V2 are adjusted, the minimum droplet diameter of the ink droplets that can be ejected is 25 μm.
[0058]
As can be seen from FIG. 5, the voltage change time t1 does not have to be completely coincident with ½ of the natural period Tc. Can be discharged. Specifically, it is desirable that the voltage change time t1 satisfies the formula (4).
[0059]
[Expression 4]
1 / 3Tc ≦ t1 ≦ 2 / 3Tc (4)
[0060]
Further, the voltage holding time t2 in the first voltage holding process 82 is desirably as short as possible in order to match the phase of the particle velocities generated by the nodes B and C shown in FIG. If the expression (5) is satisfied, minute ink droplets can be ejected.
[0061]
[Equation 5]
t2 ≦ 1 / 5Tc (5)
[0064]
B. First according to the present invention Examples of
next, The first according to the present invention Examples will be described. FIG. The first according to the present invention It is a figure which shows an example of the waveform profile of the amplification drive waveform signal employ | adopted for the drive method of the inkjet recording head which is an Example. In this embodiment, as shown in FIG. 6, the amplified drive waveform signal has a natural period Tc of the pressure wave generated in the pressure generation chamber 31 in order to increase the volume of the pressure generation chamber 31 and retract the meniscus. A first voltage change process 86 for reducing the applied voltage V of the piezoelectric actuator 36 set to the reference voltage Vb to the voltage (Vb−V1) at the falling time t1 of ½, and the voltage (Vb− The first voltage holding process 87 for holding the applied voltage V reduced to V1) for a while (time t2), and the volume of the pressure generating chamber 31 is reduced to form a liquid column at the center of the meniscus. At the raising time t3, the applied voltage V of the piezoelectric actuator 36 is increased to the voltage (Vb−V1 + V2) and the second voltage change process 88 for increasing the voltage to the voltage (Vb−V1 + V2). A second voltage holding process 89 for holding the applied voltage V for a while (time t4), and a falling time t5 in order to increase the volume of the pressure generating chamber 31 and separate the ink droplet 37 from the liquid column tip at an early stage. The third voltage changing process 90 for reducing the applied voltage V held at the voltage (Vb−V1 + V2) to the voltage (Vb−V1), and the applied voltage V reduced to the voltage (Vb−V1). The third voltage holding process 91 to be held for a while (time t6) and the voltage applied to the piezoelectric actuator 36 in order to discharge the ink droplet 37 by reducing the volume of the pressure generating chamber 31 and to prepare for the next discharging operation. And a fourth voltage change process 92 for increasing V to the height of the reference voltage Vb.
[0064]
B. Second Embodiment Next, a second embodiment of the present invention will be described. FIG. 6 is a diagram showing an example of a waveform profile of an amplified drive waveform signal employed in the ink jet recording head drive method according to the second embodiment of the present invention. In this second embodiment, as shown in FIG. 6, the amplified drive waveform signal is generated by the characteristic of the pressure wave generated in the pressure generation chamber 31 in order to increase the volume of the pressure generation chamber 31 and to retract the meniscus. A first voltage changing process 86 for reducing the applied voltage V of the piezoelectric actuator 36 set to the reference voltage Vb to the voltage (Vb−V1) at the falling time t1 that is ½ of the period Tc; In order to form a liquid column at the center of the meniscus by reducing the volume of the pressure generation chamber 31 by the first voltage holding process 87 for holding the applied voltage V reduced to (Vb−V1) for a while (time t2). In addition, at the start-up time t3, the voltage V applied to the piezoelectric actuator 36 is increased to the level of the voltage (Vb−V1 + V2) and increased to the voltage (Vb−V1 + V2). The second voltage holding process 89 for holding the applied voltage V for a while (time t4), and the fall time in order to increase the volume of the pressure generating chamber 31 and separate the ink droplet 37 from the liquid column tip at an early stage. At t5, a third voltage change process 90 for reducing the applied voltage V held at the voltage (Vb−V1 + V2) to the voltage (Vb−V1) and the applied voltage V decreased to the voltage (Vb−V1). For a period of time (time t6), and the application of the piezoelectric actuator 36 to reduce the volume of the pressure generation chamber 31 to discharge the ink droplet 37 and prepare for the next discharge operation. And a fourth voltage change process 92 for increasing the voltage V to the level of the reference voltage Vb.
[0065]
Next, with respect to the driving method of the ink jet recording head of this example, an ejection experiment of the ink droplet 37 was performed under the following waveform condition of the driving waveform signal. That is, the reference voltage Vb = 25V The voltage change amount V1 in the first voltage change process 86 = 15V The voltage change amount V2 in the second voltage change process 88 = 12V The voltage change time t1 in the first voltage change process 86 = 5 μs Voltage holding time t2 in the first voltage holding process 87 = 0.3 μs Voltage changing time t2 in the second voltage changing process 88 = 1.5 μs Voltage holding time t4 in the second voltage holding process 89 = 0.2 μs Voltage change time t5 in the third voltage change process 90 = 1.5 μs Voltage hold time t6 in the third voltage hold process 91 = 6 μs Voltage change time t4 in the fourth voltage change process 92 = 20 μs And an ink drop 37 discharge experiment was conducted. As a result, it was observed that an ink droplet having a droplet diameter of 16 μm was ejected at a droplet speed of 6.0 m / s.
[0066]
Thus, according to the configuration of this example, the third voltage change process 90 is provided immediately after the second voltage change process 88 in the amplified drive waveform signal shown in FIG. 6 to increase the volume of the pressure generation chamber 31. Since the ink droplet 37 is separated early from the liquid column tip, It is a premise of the present invention Compared with the case where the amplification drive waveform signal (see FIG. 4) of the embodiment is employed, it is possible to eject a smaller ink droplet 37. The voltage holding time t4 in the second voltage holding process 89 is desirably as short as possible in order to increase the effect of separating the ink droplets 37 from the liquid column tip at an early stage. Specifically, it is desirable that the voltage holding time t4 satisfies the formula (7).
[0067]
[Expression 7]
t4 ≦ 1 / 5Tc (7)
[0068]
In addition, the voltage change time t5 in the third voltage change process 90 is as short as possible in order to cause a sufficient particle velocity in the meniscus when the ink droplet 37 is separated early from the liquid column tip. Is desirable. Specifically, it is desirable that the voltage change time t5 satisfies the formula (8).
[0069]
[Equation 8]
t5 ≦ 1 / 3Tc (8)
[0070]
C. The second according to the present invention Example
next, The second according to the present invention Examples will be described. FIG. The second according to the present invention It is a figure which shows an example of the waveform profile of the amplification drive waveform signal employ | adopted for the drive method of the inkjet recording head which is an Example. In this embodiment, as shown in FIG. 7, the amplified drive waveform signal has a natural period Tc of the pressure wave generated in the pressure generation chamber 31 in order to increase the volume of the pressure generation chamber 31 and to retract the meniscus. A first voltage change process 93 for reducing the applied voltage V of the piezoelectric actuator 36 set to the reference voltage Vb to the voltage (Vb−V1) at the falling time t1 of ½, and the voltage (Vb− The first voltage holding process 94 for holding the applied voltage V reduced to V1) for a while (time t2), and a standoff in order to reduce the volume of the pressure generating chamber 31 and form a liquid column at the center of the meniscus. At the raising time t3, the voltage applied to the piezoelectric actuator 36 is increased to the voltage (Vb−V1 + V2), and the second voltage change process 95 is increased to the voltage (Vb−V1 + V2). A second voltage holding process 96 for holding the applied voltage V for a while (time t4), and a falling time t5 in order to increase the volume of the pressure generating chamber 31 and quickly separate the ink droplets 37 from the liquid column tip. Thus, for example, the third voltage change process 97 for reducing the applied voltage V held at the voltage (Vb−V1 + V2) to 0V, for example, and the first voltage holding process of the applied voltage V reduced to 0V for a while (time t6). 3 to reduce the volume of the pressure generation chamber 31 and suppress the reverberation of the pressure wave remaining after the ink droplet 37 is discharged, the voltage V applied to the piezoelectric actuator 36 is set to the voltage at the fall time t7. In order to prepare for the next discharge operation, the fourth voltage change process 99 that increases to the height of V4 and the volume of the pressure generation chamber 31 are decreased to discharge the ink droplet 37. And a fifth voltage change process 100 Metropolitan increased to the height of the voltage Vb.
[0071]
Next, with respect to the driving method of the ink jet recording head of this example, an ejection experiment of the ink droplet 37 was performed under the following waveform condition of the driving waveform signal. That is, the reference voltage Vb = 25V The voltage change amount V1 in the first voltage change process 93 = 15V The voltage change amount V2 in the second voltage change process 95 = 12V The voltage change amount V3 in the third voltage change process 97 = 16V Voltage change amount V4 in the fourth voltage change process 99 = 14V Voltage change time t1 in the first voltage change process 93 = 5 μs Voltage hold time t1 in the first voltage hold process 94 = 0.3 μs Voltage change time t3 in the second voltage change process 95 = 1.5 μs Voltage hold time t4 in the second voltage hold process 96 = 0.2 μs Voltage change time t5 in the third voltage change process 97 = 1.5 μs Voltage holding time t6 in the third voltage holding process 98 = 1.5 μs Voltage changing time t7 in the fourth voltage changing process 99 = 2 μs Fifth voltage changing process 10 Respectively set to a voltage change time t8 = 15 [mu] s in, we perform the discharge experiment of the ink droplet 37. As a result, it was observed that an ink droplet having a droplet diameter of 14 μm was ejected at a droplet speed of 6.3 m / s.
[0072]
Here, FIG. 8 shows the result obtained by using the equation (2) for the time variation of the particle velocity when the amplification drive waveform signal shown in FIG. 7 is used, considering only the vibration component of the equation (1). Show. In FIG. 8, each thin line a to d represents a time change of the particle velocity generated at each node A, B, C, D of the amplification drive waveform signal shown in FIG. 7, and a thick line s represents each particle. It represents the time variation of the total particle velocity overlaid with the velocity, that is, the time variation of the particle velocity that actually occurs in the meniscus. According to the configuration of this example, in the amplified drive waveform signal shown in FIG. 7, the voltage change time t1 in the first voltage change process 93 is set to ½ of the natural period Tc of the pressure wave generated in the pressure generating chamber. Therefore, as can be seen from FIG. 8, the phase of the time change of the particle velocity generated at the nodes A, B, and C is almost the same. Therefore, in the time range T2, a very rapid increase in particle velocity occurs. Further, in the amplified drive waveform signal shown in FIG. 7, a third voltage change process 97 is provided, and the voltage change amount V3 in the third voltage change process 97 is greater than the voltage change amount V2 in the second voltage change process 95. Therefore, as can be seen from FIG. 8, in the time range T3, the particle velocity rapidly decreases. As a result, the ink droplet 37 can be separated earlier from the liquid column tip, and the above-described The first according to the present invention Compared to the case where the amplification drive waveform signal (see FIG. 6) of the embodiment is employed, it is possible to eject a smaller ink droplet 37.
[0073]
Further, according to the configuration of this example, the fourth voltage change process 99 having the fall time t7 is provided immediately after the third voltage change process 90 in the amplified drive waveform signal shown in FIG. 3, which suppresses the reverberation of the pressure wave remaining after the ink droplet 37 is discharged, so that the pressure wave generated when the previous ink droplet 37 is discharged is the next ink droplet 37. There is no effect on the discharge. Therefore, even when the frequency of the amplified drive waveform signal is higher, the ink droplet 37 can be stably ejected. Above The embodiment which is the premise of the present invention and the first embodiment according to the present invention When the amplification drive waveform signal of the embodiment (see FIGS. 4 and 6) is employed, if the frequency of the amplification drive waveform signal is set to 8 kHz or more, the ejection state of the ink droplet 37 becomes somewhat unstable. On the other hand, when the amplification drive waveform signal of this example (see FIG. 7) is employed, it has been confirmed that the ink droplets 37 are stably ejected until the frequency of the amplification drive waveform signal is 12 kHz. FIG. 8 also shows that the time variation of the particle velocity is very small in the time range T4. Further, according to the configuration of this example, it has been confirmed that the flight characteristics such as the ejection direction of the ink droplet 37 are also improved. As described above, in the amplification drive waveform signal shown in FIG. 7, the fourth voltage change process 99 is provided to suppress the reverberation of the pressure wave remaining after the ink droplet 37 is discharged. This is because the meniscus immediately after ejection is stabilized, and the flight state such as the satellite ejection direction is stabilized and made uniform.
[0074]
Note that the voltage holding time t6 in the third voltage holding process 98 is desirably as short as possible in order to effectively suppress reverberation. Specifically, it is desirable that the voltage holding time t6 satisfies the formula (9).
[0075]
[Equation 9]
t6 ≦ 1 / 3Tc (9)
[0085]
In addition, the voltage change time t7 in the fourth voltage change process 99 is desirably as short as possible in order to efficiently generate a reverberation suppressing pressure wave. Specifically, it is desirable that the voltage change time t7 satisfies the formula (10).
[0076]
[Expression 10]
t7 ≦ 1 / 2Tc (10)
[0077]
The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. Are also included in the present invention. For example, in each of the above-described embodiments, the inkjet recording head driving method according to the present invention is a printer, plotter, copier, or the like that records colored characters or images on a recording medium such as paper or an OHP film by discharging colored ink from nozzles. Although the example applied to inkjet recording apparatuses, such as a facsimile, was shown, it is not limited to this. That is, a polymer film or glass may be used as the recording medium, and molten solder may be used as the liquid discharged from the nozzle. That is, the ink jet recording head driving method according to the present invention includes, for example, a droplet ejecting apparatus for producing a color filter for display on a polymer film or glass by discharging colored ink from a nozzle, or solder in a molten state from a nozzle. In general, the present invention may be applied to a liquid droplet ejecting apparatus such as a liquid droplet ejecting apparatus that forms a bump for mounting a component on a substrate by discharging the liquid.
[0078]
Further, in each of the above-described embodiments, an example in which the shape of the nozzle 34 is tapered is shown, but the present invention is not limited to this. Similarly, the opening shape of the nozzle 34 is not limited to a circular shape, and may be a rectangle, a triangle, or other shapes. Further, the positional relationship between the nozzle 34, the pressure generation chamber 31, and the ink supply hole 33 is not limited to the structure shown in this embodiment. For example, the nozzle 34 is arranged at the center of the pressure generation chamber 31. Of course, it can be arranged. Further, in each of the above-described embodiments, the example in which the pressure generating chamber 31 formed in the shape of an elongated cube is used, but the present invention is not limited to this, and the pressure generating chamber 31 may have any shape.
[0079]
In each of the above-described embodiments, the bias voltage (reference voltage) Vb is set so that the voltage applied to the piezoelectric actuator 36 is always positive. However, the present invention is not limited to this. When there is no problem even if a negative voltage is applied, another voltage such as 0 V may be set as the bias voltage Vb. Further, in each of the above-described embodiments, an example in which a Kaiser type is used as an ink jet recording head has been described. However, an ink jet recording head that discharges ink droplets from nozzles by causing a pressure change in a pressure generating chamber by pressure generating means. As long as it is, it is not limited to the Kaiser type. As the ink jet recording head, for example, an ink jet recording head using a groove provided in a piezoelectric actuator as a pressure generating chamber may be used.
[0080]
Further, in each of the above-described embodiments, the experimental results for the ink jet recording head in which the natural period Tc of the pressure wave generated in the pressure generating chamber is 10 μs are shown. The substantially same effect as described in each embodiment can be obtained. However, if the natural period Tc is too long, it is difficult to form minute ink droplets. Therefore, in order to eject minute ink droplets having a droplet diameter of about 15 to 20 μm, the natural period Tc should be set to 15 μs or less. Is desirable. Further, in each of the above-described embodiments, an example in which a piezoelectric actuator in a longitudinal vibration mode using the piezoelectric constant d33 is used as the piezoelectric actuator 36 is shown, but the present invention is not limited to this, and the piezoelectric constant d31 is used as the piezoelectric actuator 36. Other types of piezoelectric actuators such as a longitudinal vibration mode piezoelectric actuator may be used.
[0081]
In each of the above-described embodiments, the piezoelectric actuator 36 made of laminated piezoelectric ceramics is used as the pressure generating means. However, the present invention is not limited to this, and other types of piezoelectric actuators such as a single plate type, Even if an electromechanical conversion element, a magnetostrictive element, or an electrostatic actuator is used, an effect substantially similar to the above effect can be obtained. Further, in each of the above-described embodiments, the example using the drive circuit shown in FIG. 2 and FIG. 3 is shown, but the present invention is not limited to this, and the amplified drive waveform signal shown in FIG. Any other driving circuit may be used as long as it can be applied.
[0082]
【The invention's effect】
As described above, according to the configuration of the present invention, in the drive waveform signal, the voltage change time in the first voltage change process is changed from 1/3 to 2 of the natural period Tc of the pressure wave generated in the pressure generating chamber. Since the start time of the second voltage change process is set immediately after the end time of the first voltage change process, it is possible to stabilize a minute ink droplet having a droplet diameter of about 20 μm. Can be discharged. In addition, since the natural vibration of the piezoelectric actuator itself is not excited, the current flowing through the piezoelectric actuator is not increased, and the reliability and durability of the piezoelectric actuator are not impaired. Thereby, a small ink droplet having a droplet diameter of 20 μm or less can be ejected with an inexpensive and small configuration. According to another configuration of the present invention, in the drive waveform signal, a third voltage change process is provided immediately after the second voltage change process, and the volume of the pressure generation chamber is increased to increase the ink from the liquid column tip. Since the droplets are separated at an early stage, even smaller ink droplets can be ejected. According to another configuration of the present invention, in the drive waveform signal, the fourth voltage change process is provided immediately after the third voltage change process to suppress the reverberation of the pressure wave remaining after ink droplet ejection. Therefore, even when the frequency of the drive waveform signal is higher, the ink droplets can be ejected stably, and the flight characteristics such as the ejection direction of the ink droplets can be improved.
[Brief description of the drawings]
FIG. 1 (a) It is a premise of the present invention Sectional drawing which shows an example of a structure of the inkjet recording head mounted in the inkjet recording device to which the drive method of the inkjet recording head which is an Example is applied, The figure (b) is the decomposition | disassembly cross section which decomposes | disassembles and shows the inkjet recording head FIG.
FIG. 2 is a block diagram showing an electrical configuration of a droplet diameter non-modulation type driving circuit for driving the ink jet recording head.
FIG. 3 is a block diagram showing an electrical configuration of a droplet diameter modulation type driving circuit for driving the ink jet recording head.
FIG. 4 is a diagram showing an example of a waveform profile of an amplified drive waveform signal employed in the inkjet recording head drive method.
FIG. 5 is a characteristic diagram showing a relationship between a voltage change time t1 and a droplet diameter of an ink droplet in the first voltage change process.
[Fig. 6] The first according to the present invention It is a figure which shows an example of the waveform profile of the amplification drive waveform signal employ | adopted for the drive method of the inkjet recording head which is an Example.
[Fig. 7] The second according to the present invention It is a figure which shows an example of the waveform profile of the amplification drive waveform signal employ | adopted for the drive method of the inkjet recording head which is an Example.
8 is a diagram illustrating an example of a temporal change in particle velocity when the amplification drive waveform signal shown in FIG. 7 is used.
FIG. 9 is an equivalent circuit diagram in the ink filling state of the ink jet recording head applied to the present invention.
FIG. 10 is a waveform diagram for explaining the theoretical basis of the validity of the driving method of the inkjet recording head.
FIG. 11 is a waveform diagram for explaining the theoretical basis of the validity of the driving method of the inkjet recording head.
FIG. 12 is a waveform diagram for explaining the theoretical basis of the validity of the driving method of the inkjet recording head.
FIG. 13 is a waveform diagram for explaining the theoretical basis of the validity of the driving method of the inkjet recording head.
FIG. 14 is a schematic cross-sectional view illustrating a basic configuration of an ink jet recording head called a Kaiser type among drop-on-demand ink jet recording heads, for explaining a conventional technique.
FIG. 15 is a diagram illustrating an example of a waveform profile of a drive waveform signal employed in a conventional method for driving an inkjet recording head.
FIG. 16 is a cross-sectional view in the vicinity of a nozzle opening surface for explaining an ink droplet ejection process in a conventional ink jet recording head driving method.
FIG. 17 is a diagram illustrating an example of a waveform profile of a drive waveform signal employed in another conventional method for driving an inkjet recording head.
FIG. 18 is a diagram illustrating an example of a waveform profile of a drive waveform signal employed in still another conventional method of driving an inkjet recording head.

Claims (20)

A pressure generation chamber filled with ink, pressure generation means for generating pressure in the pressure generation chamber, and a nozzle connected to the pressure generation chamber, and applying a drive waveform signal to the pressure generation means, An inkjet recording head driving method for discharging ink droplets from the nozzles by changing the volume of the pressure generating chamber,
The waveform of the drive waveform signal is
A first voltage change process for applying a voltage in a direction to increase the volume of the pressure generating chamber;
A voltage is applied in the direction of decreasing the volume of the pressure generating chamber, a liquid column having a diameter smaller than the opening diameter of the nozzle is formed in the nozzle, and ink droplets are separated from the tip of the liquid column. And at least a second voltage change process for discharging minute ink droplets,
In the waveform of the drive waveform signal, the voltage change time in the first voltage change process is set to a length in the range from 1/3 to 2/3 of the natural period Tc of the pressure wave generated in the pressure generating chamber. Set,
In the waveform of the drive waveform signal, a time interval between the end time of the first voltage change process and the start time of the second voltage change process is set to a length of 1/5 or less of the natural period Tc. ,
A voltage change time in the second voltage change process in the waveform of the drive waveform signal is set to a length of 1/3 or less of the natural period Tc;
The waveform of the drive waveform signal includes a third voltage change process for applying a voltage in a direction to increase the volume of the pressure generation chamber following the second voltage change process,
In the waveform of the drive waveform signal, a time interval between the end time of the second voltage change process and the start time of the third voltage change process is set to a length equal to or shorter than 1/5 of the natural period Tc. A method of driving an ink jet recording head.  2. The ink jet recording head according to claim 1, wherein a voltage change time in the first voltage change process in the waveform of the drive waveform signal is set to a length of ½ of the natural period Tc. Driving method.  3. The ink jet recording head according to claim 2, wherein a voltage change time in the third voltage change process in the waveform of the drive waveform signal is set to a length of 1/3 or less of the natural period Tc. Driving method.  The inkjet according to claim 3, wherein a voltage change amount in the third voltage change process in the waveform of the drive waveform signal is set to be larger than a voltage change amount in the second voltage change process. Driving method of the recording head.  The waveform of the drive waveform signal includes a fourth voltage change process in which a voltage is applied in a direction of decreasing the volume of the pressure generation chamber after the third voltage change process. 5. A method for driving an ink jet recording head according to 3 or 4.  6. The ink jet recording head according to claim 5, wherein a voltage change time in the fourth voltage change process in the waveform of the drive waveform signal is set to a length of ½ or less of the natural period Tc. Driving method.  The time interval between the end time of the third voltage change process and the start time of the fourth voltage change process in the waveform of the drive waveform signal is set to a length equal to or shorter than 1/3 of the natural period Tc. The method of driving an ink jet recording head according to claim 5 or 6.  The method of driving an ink jet recording head according to claim 1, wherein the natural period Tc is 15 μs or less.  9. The method of driving an ink jet recording head according to claim 1, wherein the pressure generating means is an electromechanical conversion element.  The method of driving an ink jet recording head according to claim 9, wherein the electromechanical transducer is a piezoelectric actuator. A pressure generation chamber filled with ink, pressure generation means for generating pressure in the pressure generation chamber, and a nozzle connected to the pressure generation chamber, and applying a drive waveform signal to the pressure generation means, A drive circuit for an ink jet recording head that ejects ink droplets from the nozzles by changing a volume of the pressure generating chamber;
A first voltage change process for applying a voltage in a direction to increase the volume of the pressure generating chamber;
A voltage is applied in the direction of decreasing the volume of the pressure generating chamber, a liquid column having a diameter smaller than the opening diameter of the nozzle is formed in the nozzle, and ink droplets are separated from the tip of the liquid column. And at least a second voltage change process for ejecting minute ink droplets,
The voltage change time in the first voltage change process is set to a length ranging from 1/3 to 2/3 of the natural period Tc of the pressure wave generated in the pressure generating chamber, and the first voltage The time interval between the end time of the change process and the start time of the second voltage change process is set to a length of 1/5 or less of the natural period Tc, and the voltage change time in the second voltage change process Waveform generating means for generating a drive waveform signal having a waveform set to a length of 1/3 or less of the natural period Tc;
The waveform generation means generates a drive waveform signal having a waveform including a third voltage change process for applying a voltage in a direction to increase the volume of the pressure generation chamber following the second voltage change process. ,
The waveform generating means has a waveform in which the time interval between the end time of the second voltage change process and the start time of the third voltage change process is set to a length of 1/5 or less of the natural period Tc. A drive circuit for an ink jet recording head, wherein a drive waveform signal is generated.  The waveform generation means generates a drive waveform signal having a waveform in which a voltage change time in the first voltage change process is set to a half length of the natural period Tc. Item 12. An ink jet recording head drive circuit according to Item 11.  The waveform generating means generates a drive waveform signal having a waveform in which a voltage change time in the third voltage change process is set to a length of 1/3 or less of the natural period Tc. 12. A drive circuit for an ink jet recording head according to claim 11.  The waveform generating means generates a drive waveform signal having a waveform in which a voltage change amount in the third voltage change process is set larger than a voltage change amount in the second voltage change process. 14. The drive circuit for an ink jet recording head according to claim 11 or 13.  The waveform generation means generates a drive waveform signal having a waveform including a fourth voltage change process for applying a voltage in a direction of decreasing the volume of the pressure generating chamber following the third voltage change process. The drive circuit for an inkjet recording head according to claim 11, wherein the drive circuit is an inkjet recording head.  The waveform generating means generates a drive waveform signal having a waveform in which a voltage change time in the fourth voltage change process is set to a length of ½ or less of the natural period Tc. 16. A drive circuit for an ink jet recording head according to claim 15.  The waveform generating means has a waveform in which the time interval between the end time of the third voltage change process and the start time of the fourth voltage change process is set to a length of 1/3 or less of the natural period Tc. 17. The drive circuit for an ink jet recording head according to claim 15, wherein a drive waveform signal having the following is generated.  The drive circuit for an ink jet recording head according to claim 11, wherein the natural period Tc is 15 μs or less.  The drive circuit for an ink jet recording head according to claim 11, wherein the pressure generating unit is an electromechanical conversion element.  20. The ink jet recording head drive circuit according to claim 19, wherein the electromechanical transducer is a piezoelectric actuator.

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