JP3583045B2 - Ink jet recording device - Google Patents

Description

セレクタ４６から出力された高周波信号は、ドライバ４７により電圧増幅された後、対応する圧電素子４８に印加される。１つの圧電素子４８には、実質的に１０〜３０Ｖ程度の振幅の電圧が印加される。また、６００ｄｐｉ程度の画素密度に適したインク滴を吐出させるためには、高周波信号の周波数が５０ＭＨｚ程度に選ばれる。
【００４４】
このようにして圧電素子４８に対するハースト状の高周波信号の印加が行われている間に、２番目の高周波信号印加のための駆動データがシフトレジスタ４４に転送され、最初の高周波信号の印加期間ＤＲＩＶＥ１、つまり最初のインク液滴吐出動作が終了すると、２番目の高周波信号印加期間ＤＲＩＶＥ２が始まる。以下同様に、高周波信号の印加を繰り返し行い、必要回数だけ行った時点で１ラインの記録動作が終了する。図６では、簡単のために１ラインを４回の吐出動作で記録する例を示している。
【００４５】
（駆動データ生成部４３について）
図５に、図４中の駆動データ生成部４３の概略構成を示す。図５において、駆動データ列生成ブロック５３，６３は、駆動データ列設定部５４および６４により１つのインク液滴を吐出するために必要な複数の圧電素子を駆動するためのデータ列を設定して、駆動データ列バッファ５５，６５を介して出力するものであり、例えば４つの圧電素子を同時駆動することにより１つのインク液滴を吐出する場合には、４つの駆動データを１組のデータ列として設定する。駆動データ列は、前述した位相の異なる２種類の高周波信号ＳＩＧＮＡＬ ＺＥＲＯ、ＳＩＧＮＡＬ ＰＡＩさらにＧＮＤを選択するために２種類用意される。
【００４６】
すなわち、駆動データ列生成ブロック５３，６３は、３種類の高周波信号ＳＩＧＮＡＬ ＺＥＲＯ、ＳＩＧＮＡＬ ＰＡＩさらにＧＮＤ対応する２種類の駆動データ列ＺＥＲＯ−ＤＡＴＥを生成する。これら２つの駆動データ列生成ブロック５３，６３は同一の構成で実現できる。駆動データ列設定部５４，６４は、単純なスイッチ構成にすることもできるし、ＲＡＭやＲＯＭを用いて構成することも可能である。
【００４７】
駆動データ列バッファ５５，６５は、駆動データ列設定部５４，６４からの駆動データ列を取り込み、駆動データ列を構成するデータを１個ずつ時系列的に順次読み出すバッファである。本実施形態では、駆動データ列バッファ５５，６５はパラレル入力／シリアル出力のシフトレジスタからなり、制御部４０からのロード信号ＬＯＡＤ ＣＬＯＣＫによって駆動データ列設定部５４，６４から駆動データ列を読み込み、制御部４０からの読み出し信号ＲＥＡＤ ＣＬＯＣＫによって駆動データ列のうちの１つのデータを読み出す構成となっている。
【００４８】
セレクタ５６，６６は、それぞれ駆動データ列バッファ５５，６５から送出される駆動データを制御部４０からのタイミング選択信号ＴＩＭＩＮＧ ＳＥＬＥＣＴに従って選択してＡＮＤ回路５７，６７に送出する。ＡＮＤ回路５７，６７は、セレクタ５６，６６からの駆動データと図４中のラインメモリ４２からの画像データとの論理積を図４中のシフトレジスタ４４に駆動データＤＲＩＶＥ ＥＤＡＴＡとして送出する。ここで、画像データ１画素分に対して駆動データは複数個を対応させる必要があるので、この例では４つの読み出し信号ＲＥＡＤ ＣＬＯＣＫに対応させた４個の駆動データと１つの画像データとの論理値をそれぞれ送出した後、次の画素に対する画像データの処理に移る。このために、ラインメモリ４２から読み出した１つの画像データを４回読み出す期間だけ保持しておくためのラッチ５２が設けてある。
【００４９】
また、図５では図４中のラインメモリ４２からの画像データが量子化部５１を介してラッチ５２に入力されるように構成されているが、画像データとして２値データを扱う場合は、量子化部５１は何も機能する必要はない。しかし、本実施形態のように、例えばラインメモリ４２に入力される画像データが１画素当たり８ビットなどの多値データの場合には、この量子化部５１において適当な値で例えば４値化処理が行われる。この多値化処理に基づき、駆動データ列設定部５４，６４に駆動データ列が設定される。
【００５０】
このようにしてＡＮＤ回路５７，６７から送出されるデータは、所定の圧電素子を駆動するための駆動データであり、高周波信号ＳＩＧＮＡＬ ＺＥＲＯ、ＳＩＧＮＡＬ ＰＡＩを選択するための２値のデータである。高周波信号ＳＩＧＮＡＬ ＺＥＲＯを選択するための駆動データＺＥＲＯ−ＤＡＴＥの生成と同様に、高周波信号ＳＩＧＮＡＬ ＰＡＩを選択するための駆動データＰＡＩ−ＤＡＴＥも出力される。すなわち、図４中のシフトレジスタ４４には２ビットのデータが入力される。
【００５１】
（駆動データ生成部４３の動作）
次に、図４に示す駆動データの生成と転送に関するタイミングチャートを参照して、駆動データ生成部４３の動作をさらに詳しく説明する。
図７（ａ）に示すように、まず制御部４０からのロード信号ＬＯＡＤ ＣＬＯＣＫにより駆動データ列設定部５４，６４から駆動データ列が駆動データ列バッファ５５，６５に取り込まれる。このとき、１画素目の画像データＩＭＡＧＥ ＤＡＴＥがラインメモリ４２から読み出されてラッチ５２に一時記憶される。この１画素目の画像データに対して、４つの駆動データＤＲＩＶＥ ＤＡＴＥが読み出し信号ＲＥＡＤ ＣＬＯＣＫに同気同期して生成される。次に、１画素目の画像データから４つ先の５画素目の画像データがラインメモリ４２から読み出され、この５画素目の画像データに対しても４つの駆動データが生成されて送出される。以下、同様にラインメモリ４２からは４番地づつずれた画像データが読み出される。すなわち、圧電素子の位置で４つおきにインク液滴が吐出するように駆動データが設定される。
【００５２】
このようにして駆動データが４９６０個転送されると、先に図６のタイミングチャートで説明したように、ラッチ信号ＬＡＣＨ ＣＬＯＣＫによりラッチ４５に駆動デー夕を取り込み、圧電素子の４素子おきの位置からインク液滴を吐出させるという一連の記録動作が行われる。
【００５３】
インク液滴の吐出は４素子おきの位置なので、次回のインク液滴吐出に際しては吐出位置を１素子分ずらして吐出させる。すなわち、図７（ｂ）に示すようにシフトレジスタ４４に対する転送クロックＳＨＩＦＴ ＣＬＯＣＫの送出が開始されるが、１個目の転送クロックに対しては、制御部４０からのタイミング選択信号ＴＩＭＩＮＧ ＳＥＬＥＣＴはオフであり、図５のセレクタ５６，６６の出力は駆動データ列を選択せずに非駆動データ（ここでは接地信号ＧＮＤ）を送出する。これは、前回のインク液滴吐出時に用いられた圧電素子の位相を１つずらす役目をしており、一番端に対応する圧電素子を強制的に非駆動状態にするものである。この後、タイミング選択信号ＴＩＭＩＮＧ ＳＥＬＥＣＴがオンになり、ロード信号ＬＯＡＤ ＣＬＯＣＫ以下の信号が図７（ａ）と同様に送出される。このとき、ラインメモリ４２から読み出される画像データは２画素目、６画素目、１０画素目、１４画素目・・・のように４つおきに読み出される。
【００５４】
同様に、３回目のインク液滴吐出時には図７（ｃ）に示すように、端から２素子分だけ非駆動となるように、タイミング選択信号ＴＩＭＩＮＧ ＳＥＬＥＣＴと転送クロックＳＩＦＴ ＣＬＯＣＫの関係が設定される。図示しないが、４回目のインク液滴吐出時も同様の動作が行われ、１ライン分の全てのインク液滴の吐出が完了し、１ライン目と同様な動作で次ラインの吐出が行われる。
【００５５】
（駆動データ列の具体例）
上述のように４つの圧電素子を同時駆動する場合に必要な４つの駆動データを下記表１のようにあらわした時の駆動データ列の具体例を表２に示す。なお、表２（ａ）は、素子の並び順に選択される高周波信号の位相を示し、表２（ｂ）は、その時の駆動データ列を示している。この例では、圧電素子４８の並び順にＰＡＩ、ＺＥＲＯ、ＺＥＲＯ、ＰＡＩとなるデータ列である。ここで、ＺＥＲＯ、ＰＡＩは互いに位相が１８０°異なる高周波信号をそれぞれ選択するためのデータを意味する。このような駆動データを与えた場合のインク液滴の吐出原理は、先の図２および図３で説明した通りである。
【表２】

さらに、表３乃至５に同時駆動する圧電素子の素子数（同時駆動素子数）の異なる場合の駆動データ列の例も示す。表３は同時駆動素子数が８素子、表４は同時駆動素子数が９素子、表５は、同時駆動素子数が１０素子の場合の例である。
【表３】

【表４】

【表５】

次に、インク滴の粒径情報を含む画像情報が入力された場合の駆動方法を図８を用いて説明する。
【００５６】
まず、第１の粒径のインク滴を吐出させる時の吐出量制御素子の制御法（インク吐出量制御駆動１）を説明する。圧電素子アレイを形成する複数の圧電素子の内、ｍ番目〜ｍ＋ｎ番目のｎ＋１個の素子を圧電素子グループとし、その中のｍ番目およびｍ＋ｎ番目の素子を吐出量制御用素子としている。この圧電素子グループ内の個々の圧電素子へ、フレネル輪帯理論に基づく０相あるいはπ相の位相を表６（ａ），（ｂ）にしたがって割り当てて駆動する。すなわち、吐出量制御用素子も含め、圧電素子グループの全ての素子を同時駆動している。
【００５７】
それぞれの圧電素子から発生した超音波は、主走査方向の超音波はインク液面近傍に集束し、副走査方向の超音波の集束は図１中の音響レンズ兼音響マッチング層１０５によって行われ、液面近傍のインク１０６が第１の粒径のインク滴となって吐出する。
【表６】

次に、第２の粒径のインク滴を吐出させる時の吐出量制御素子の制御法（インク吐出量制御駆動２）を説明する。
【００５８】
（インク吐出量制御駆動１）と同じ圧電素子グループのうち、吐出量制御素子に直流電圧を印加し、ｍ＋１番目〜ｍ＋ｎ−１番目のｎ−１個の圧電素子をフレネル輪帯理論に基づく０相あるいはπ相の位相で表７（ｃ）、（ｄ）にしたがって割り当てて同時駆動する。
【００５９】
すなわち圧電素子グループの素子配列の中心位置を基準に、左右対称な位置にある少なくとも１対の素子（この例ではｍ＋ｎ番目の素子と、さらにこのｍ＋ｎ番目の圧電素子に対して、圧電素子グループの素子配列の中心位置を基準に、左右対称な位置にあるｍ番目の素子）を同時駆動させずに非駆動状態（ここでは接地状態）とする駆動手段である。これにより、発生する超音波エネルギー量が減少し、インク滴の吐出量は、「インク滴吐出量制御駆動１」と比較して減少し、小粒のインク滴（第２の粒径のインク滴）が吐出する。
【表７】

次に、第３の粒径のインク滴を吐出させる時の吐出量制御素子の制御法（インク吐出量制御駆動３）を説明する。
【００６０】
（インク吐出量制御駆動１）と同じ圧電素子グループのうち、ｍ＋１番目〜ｍ＋ｎ−１番目のｎ−１個の圧電素子をフレネル輪帯理論に基づく０相あるいはπ相の位相で駆動し、吐出量制御用素子にはフレネル輪帯に基づく位相と反対の位相で高周波電圧を印加し、表８（ｅ）、（ｆ）にしたがって割り当てて同時駆動する。
【００６１】
すなわち圧電素子グループの素子配列の中心位置を基準に、左右対称な位置にある少なくとも一対の素子（この例ではｍ＋ｎ番目の素子と、さらにこのｍ＋ｎ番目の圧電素子に対して、圧電素子グループの素子配列の中心位置を基準に、左右対称な位置にあるｍ番目の素子）を本来の位相とは逆位相の駆動信号を印加する調整用駆動素子とし、集束点での音波のエネルギー量を減少させる駆動とする制御方法である。これにより、インク滴の吐出量は、「インク滴吐出量制御駆動１」と比較して減少する。特に、本来の位相とは逆位相の駆動信号を印加して、集束点での音波のエネルギー量の一部を相殺し、吐出のためのエネルギーを減少させる駆動の場合は、「インク滴吐出量制御法２」のように、単純に発生エネルギーを減少させる場合よりも、さらに小粒のインク滴（第３の粒径のインク滴）が吐出することが可能である。
【表８】

次に、第４の粒径のインク滴を吐出させる時の吐出量制御素子の制御法（インク吐出量制御駆動４）を説明する。圧電素子アレイを形成する複数の圧電素子の内、ｍ−１番目〜ｍ＋ｎ＋１番目のｎ＋３個の素子を圧電素子グループとし、その中のｍ−１番目およびｍ＋ｎ＋１番目の素子を吐出量制御用素子としている。この圧電素子グループ内の個々の圧電素子へ、フレネル輪帯理論に基づく０相あるいはπ相の位相を表９（ａ），（ｂ）にしたがって割り当てて駆動する。すなわち、吐出量制御用素子も含め、圧電素子グループの全ての素子を同時駆動している。
【００６２】
これにより、インク滴（第４の粒径のインク滴）は、［インク滴吐出量制御駆動１］と比較して大粒となる。
【表９】

インク粒径の情報にしたがって、前記インク滴吐出量制御手段１〜４を選択し、画点サイズを変化させることで、画像の階調制御を行うことができるようになる。
【００６３】
なお、超音波ビームのエネルギー量によってインク粒径が変化するメカニズムは明らかでないが、以下のような理由であると推察される。
【００６４】
図９は、インク吐出時の様子を示す模式図である。
【００６５】
図９（ａ）に示すように超音波の収束部近傍においてインク液面にメニスカス１が形成され、さらにメニスカスの先端部から波長λの位置にくびれが生じ、この先端部が、図９（ｂ）に示すようにインク滴２となって突出するが、超音波ビームのエネルギー量が増加すると、先端部の幅（図中ｄで示す）が大きくなるためであると思われる。
【００６６】
以下、上述した表６〜９に示した「インク滴吐出量制御駆動１〜４」による具体的な実施例と結果についてのべる。
【００６７】
【実施例】
まず、以下の要領で、図１に示すようなインクジェット記録装置を作成した。
【００６８】
圧電体層１０２には、比誘電率２００のチタン酸塩系圧電セラミック板を用いた。この圧電セラミック板の両一面にＴｉ／Ａｕ積層電極をスパッタで、それぞれの厚さが０．０５μｍ、０．３μｍになるように形成した後、３ｋＶ／ｍｍの電界を印加して分極処理を行った。その後、エッチングにより個別電極１０３を形成し、１素子当たりの電極幅６０μｍ、電極間隔２６μｍ、配列ピッチ８６μｍとなるようにした。また、圧電体層１０２の副走査方向の幅は５ｍｍとした。一方、ガラス製の支持部材１００にもＴｉ／Ａｕのアレイ状個別電極を８６μｍ間隔で形成した。圧亀体層１０２上のアレイ状の個別電極１０３と支持部材１００上のアレイ状電極を位置合わせした状態でエポキシ樹脂で接着し、両電極が導通するように加圧した。
【００６９】
次に、圧電体層１０２を約５０ＭＨｚで共振を得られるように厚さ４５μｍになるように研磨した後、Ｔｉ／Ａｕ積層電極からなる共通電極１０４をスパッタ法でそれぞれ０．０５μｍ、１μｍの厚さに形成した。このとき副走査方向の電極の長さ、すなわち副走査方向の口径は２．０ｍｍとした。
【００７０】
次のステップで形成する音響レンズ兼音響マッチング層１０５には、エポキシ樹脂とアルミナ粉末の混合物を用いた。まず音速が３×１０^３ｍ／ｓ近傍になるように混合比を調整し、密度２．２０×１０^３ｋｇ／ｓ、音速２．９５×１０^３ｍ／ｓを得た。この混合物を共通電極１０４の面に塗布して硬化させ、厚さが約４５μｍになるように研磨した。その後、焦点距離が目的の値になるように深さ１／２波長（約３０μｍ）の溝を主走査方向に平行に入れて、一次元フレネルレンズを形成した。そして、超音波放射面とインク液１０６の液面との距離が音響レンズ１０５の焦点距離とほぼ一致するようにインク液保持室７を取り付け、駆動手段１１０の配線を行って、図１に示す構成のインクジェット記録ヘッドを完成した。
（第１の実施例）
まず、焦点距離２．５ｍｍ、同時駆動する圧電素子グループの素子数１６である図１のインクジェット記録ヘッドを、図８（ａ）に示した［インク滴吐出量制御駆動１］に従い、駆動周波数５０ＭＨｚ、電圧１５Ｖ、信号印加持問５０μｓｅｃとしたバースト信号で駆動した。
【００７１】
この時の印字記録実験の結果は、画点サイズ直径６０μｍとなった。
【００７２】
次に、同じインクジェット記録ヘッドを、図８（ｂ）に示した［インク滴吐出量制御駆動２］に従い、１４個の圧電素子を駆動周波数５０ＭＨｚ、電圧１５Ｖ、信号印加時間５０μｓｅｃにしたバースト信号で同時駆動した。
【００７３】
この時の印字記録実験の結果は、画点サイズが直径５０μｍになった。
【００７４】
次に、図８（ｃ）に示した［インク滴吐出量制御駆動３］に従い、１４個の圧電素子を同時駆動するとともに、この同時駆動素子に隣接する両端の素子を本来印加すべき位相とは逆位相の駆動信号を印加した。駆動条件は駆動周波数５０ＭＨｚ、電圧１５Ｖ、信号印加時間５０μｓｅｃにしたバースト信号とした。
【００７５】
この時の印字記録実験の結果は、画点サイズが直径４０μｍとなった。
【００７６】
さらに、同様なインクジェット記録ヘッドにおいて、図８（ｄ）に示した［インク滴吐出量制御駆動４］に従い、圧電素子１８個の圧電素子グループに、５０ＭＨｚ、電圧１５Ｖ信号印加時間５０μｓｅｃとしたバースト信号を印加した。
【００７７】
この時の印字記録実験の結果は、画点サイズが直径７０μｍとなった。
【００７８】
上述した４つの［インク滴吐出量制御駆動１〜４］インク粒径情報にしたがって選択しながら、カラー写真画像を印字したところ、インク滴制御法を使用しない場合に比べて階調性が向上し、高品位な印字記録ができた。
（第２の実施例）
本実施例２では、３２素子の圧電素子グループを基本素子数としてインク吐出を確認した。すなわち、圧電素子グループを下記表１０〜表１２にしたがってそれぞれ同時駆動させた。
【００７９】
また、この実施例ではインクジェット記録ヘッドの音響レンズを焦点距離が４．０ｍｍのものに変更し、液面が圧電素子アレイから４．０ｍｍの位置に来るインク液保持室を用いて行った。
【００８０】
表１０にしたがって、１番目〜３２番目の３２素子を５０ＭＨｚ、電圧２５Ｖ、信号印加時間５０μｓｅｃの条件で同時駆動させてインク滴を吐出させたところ、画点サイズ８０μｍになった。
【表１０】

表１１にしたがって、２番目〜３１番目の３０素子を同様の条件で同時駆動させてインク滴を吐出させたところ、画点サイズが７０μｍになった。
【表１１】

表１２にしたがって、３番目から３０番目の２８素子を同様の条件で同時駆動させてインク滴を吐出させたところ、画点サイズが６０μｍにとなった。
【表１２】

表１３にしたがって、４番目〜２９番目の２６素子を同様の条件で同時駆動させてインク滴を吐出させたところ、画点サイズが５０μｍになった。
【表１３】

上述した４つの駆動条件を画像情報に応じて選択しながらカラー写真画像を印字したところ、インク滴制御法を使用しない場合に比べて階調性が向上し、高品位な印字記録ができた。
【００８１】
このように本実施形態によると、複数の音波発生素子を所定ピッチで配列した音波発生素子アレイと該音波発生素子アレイ中の隣接す局所定数個の音波発生素子からなるグループを同時に駆動する駆動手段をそれぞれ有する記録ヘッドを備え、前記駆動手段は、前記音波発生素子アレイを構成する複数の音波発生素子の少なくとも一部を、インク滴の吐出量制御用素子として、議制御用素子に対する駆動条件を調整することにより該インク滴の吐出量制御手段を有することにより、記録紙上の画点サイズを変化させて、階調性の向上を図ることができ、高品位な記録を実現することが可能となる。
【００８２】
【発明の効果】
上述したように、本発明によれば、超音波を利用したインクジェット記録装置において、吐出するインク滴の粒径を簡便に制御することが可能になり、ひいては画像の階調制御を行うことが可能になる。
【図面の簡単な説明】
【図１】本発明の一実施形態に係るインクジェット記録装置のヘツドの斜視図。
【図２】本発明の一実施形態に係るインクジェット記録ヘッドにおける超音波収束方法の原理を説明する図。
【図３】本発明の一実施形態に係るインクジェット記録ヘッドにおいて超音波ビームを１点に集中させる場合の１例を模式的に示す図。
【図４】本発明の一実施形態に係るインクジェット記録ヘッドの駆動手段の要素構成を示すブロック図。
【図５】本発明の一実施形態に係るインクジェット記録ヘッドの駆動手段の駆動データ生成部の概略構成因。
【図６】本発明の一実施形態に係るインクジェット記録ヘッドの駆動手段の動作説明図。
【図７】本発明の一実施形態に係るインクジェット記録ヘッドの、駆動手段の駆動データ生成部の動作説明図。
【図８】本発明の一実施形態に係るインク滴吐出量制御方法の一例を説明するための図。
【図９】本発明のインクジェット記録装置によるインク滴吐出時の様子を示す模式図。
【符号の説明】
１・・・メニスカス
２・・・インク滴
４０・・・制御部
４１・・・高周波信号発生部
４２・・・ラインメモリ
４３・・・駆動データ生成部
４４・・・シフトレジスタ
４５・・・ラッチ
４６・・・セレクタ
４７・・・ドライバ
４８、４８ａ〜ｃ・・・圧電素子
５１・・・量子化部
５２・・・ラッチ
５３，６３・・・駆動データ列生成ブロック
５４，６４・・・駆動データ列設定部
５５，６５・・・駆動データ列バッファ
５６，６６・・・セレクタ
５７，６７・・・ＡＮＤ回路
１００・・・ガラス板
１０１・・・圧電素子アレイ
１０２・・・圧電体層
１０３，１０３ａ〜ｈ・・・個別電極（圧電体側）
１０４・・・共通電極
１０５・・・音響レンズ
１０６・・・インク液
１０７・・・インク液保持室
１０８・・・スリット板
１０９・・・スリット開口部（インク滴吐出口）
１１０・・・駆動手段
１１１・・・ボンディングワイヤ
１１２ ・・・個別電極（ガラス板側）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ink jet recording apparatus, and more particularly to an ink jet recording apparatus using ultrasonic waves and capable of controlling the particle diameter of ink droplets.
[0002]
[Prior art]
2. Description of the Related Art Inkjet printers that form recording dots by discharging an ink liquid onto a recording medium have been conventionally known. This ink-jet printer has the advantages that it has less noise than other recording methods and does not require processing such as development and fixing, and has thus attracted attention as a plain paper recording technique. To date, a number of ink jet printer methods have been proposed, but in particular, a method in which ink droplets are ejected with the pressure of steam generated by the heat of a heating element and a method in which ink droplets are ejected with a pressure pulse due to displacement of a piezoelectric body. Are typical.
[0003]
However, in these ink jet printers, since the diameter of the ink droplet is determined by the diameter of the nozzle that discharges the ink droplet, it is necessary to reduce the nozzle diameter in order to increase the resolution, and as a result, nozzle clogging is likely to occur. Problems arise.
[0004]
In order to overcome these drawbacks, there has been proposed an ultrasonic system in which ink droplets are ejected from an ink liquid surface using the pressure of an ultrasonic beam generated from a thin-film piezoelectric body.
[0005]
In the ultrasonic method, since a nozzleless configuration can be adopted, clogging of nozzles does not occur, and ink droplets having a very small diameter can be stably ejected.
[0006]
Among the ultrasonic inkjet printers, a piezoelectric element array inkjet printer has been proposed. In this method, a part of the piezoelectric elements (piezoelectric element group) arranged in an array are simultaneously driven with a phase-controlled voltage, and the phase-controlled ultrasonic waves are excited from each of the simultaneously driven piezoelectric elements, and the ink liquid level is increased. This is a method that concentrates on one point in the vicinity. According to this method, linear electronic scanning can be performed in the array direction by sequentially shifting the piezoelectric element groups that are simultaneously driven on the array.
[0007]
In this method, if the number of simultaneously driven piezoelectric element groups is kept constant, scanning can be performed only by switching the combination of piezoelectric element groups. It is only necessary to control the delay time pattern of one piezoelectric element group.
[0008]
Furthermore, as a method of setting the delay time in the linear electronic scanning method, the piezoelectric array is further divided into two groups based on the Fresnel diffraction theory, instead of setting the quadratic function of the delay time used in the normal electronic focusing method. A simpler method of setting the delay time so that the phases are different from each other by a half wavelength has also been proposed (Japanese Patent Laid-Open No. 8-132607).
[0009]
However, since the ink droplet diameter in an ultrasonic ink jet printer is conventionally controlled by the frequency of ultrasonic waves, that is, the thickness of the piezoelectric element, one pixel is required to perform gradation control using the same piezoelectric element array. It is necessary to control the number of ink droplets to be formed. Therefore, there is a problem that the printing speed is reduced.
[0010]
[Problems to be solved by the invention]
As described above, in the conventional ultrasonic inkjet printer, in order to control the image gradation by changing the size of one pixel, a plurality of ink droplets must be ejected to one pixel. Therefore, there has been a problem that the printing speed is reduced.
[0011]
The present invention has been made in view of such a problem, and it is possible to change the diameter of an ink droplet according to image gradation information, and perform image gradation control without lowering printing speed. It is an object of the present invention to provide an ink jet recording apparatus capable of performing the following.
[0012]
[Means for Solving the Problems]
The inkjet recording apparatus of the present invention emits convergent ultrasonic waves toward ink, discharges ink near the convergence point of the convergent ultrasonic waves as ink droplets, and performs recording on a recording medium. And a driving unit for simultaneously driving a piezoelectric element group consisting of a predetermined number of piezoelectric elements in the piezoelectric element array, wherein the driving unit sets a center position of the piezoelectric element group. At least one pair of piezoelectric elements located at symmetrical positions as a reference is used as an ejection amount control element, and the ejection amount control element is provided with an ejection amount control means for selecting driving / non-driving according to ink droplet diameter information. .
[0013]
The present inventors have confirmed that the particle size of the ejected ink droplet changes not only with the wavelength of the ultrasonic waves but also with the energy amount of the converged ultrasonic waves, and have reached the present invention. That is, according to the present invention, gradation control can be performed by changing the number of simultaneously driven piezoelectric elements in accordance with the particle diameter information of ink droplets.
[0014]
Further, the discharge amount control means may be a means for applying a DC voltage to the discharge amount control element when not driven.
[0015]
Since the piezoelectric elements are usually arranged at a narrow pitch, there is a possibility that undesired vibration may occur due to the influence of the voltage applied to the adjacent piezoelectric elements. By applying a DC voltage to the piezoelectric elements that are not simultaneously driven, the vibration can be suppressed.
[0016]
Further, the discharge amount control means may be a means for applying a high frequency voltage having a phase for weakening a convergent sound wave at the convergence point to the discharge amount control element when not driven.
[0017]
By generating an ultrasonic wave that weakens the convergent ultrasonic wave in the ejection amount control element when not driven, it is possible to reduce the energy amount of the convergent ultrasonic wave at the ink ejection position, thereby increasing the difference in ink droplet particle size. Can be.
[0018]
Another inkjet recording apparatus of the present invention emits convergent ultrasonic waves toward ink, ejects ink near the convergence point of the convergent ultrasonic waves as ink droplets, and performs recording on a recording medium. A piezoelectric element array in which the piezoelectric elements are arranged at a predetermined pitch; and driving means for simultaneously driving a piezoelectric element group including a predetermined number of piezoelectric elements in the piezoelectric element array, wherein the driving means responds to ink droplet diameter information. And a discharge amount control means for changing the number of the piezoelectric elements to be driven simultaneously and simultaneously.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0020]
FIG. 1 is a perspective view showing a configuration of a recording head unit of an ink jet recording apparatus according to the present invention.
[0021]
An individual electrode (glass plate side) 112 is formed on the upper surface of the glass substrate as the support member 100, and an individual electrode (piezoelectric layer side) 103 corresponding to the position of the individual electrode (glass plate side) 112 is formed on the upper surface. A piezoelectric element array 101 including a piezoelectric layer 102 on which is formed and a common electrode 104 provided on the upper surface thereof is formed. That is, a piezoelectric element array is formed in which piezoelectric elements including the individual electrodes 112 and 103, the common electrode 104, and the piezoelectric layer 102 sandwiched between both electrodes are arranged.
[0022]
An ink liquid holding chamber 107 is attached to the support member 100 on the side where the piezoelectric element array 101 is formed so as to surround the piezoelectric element array 101, and a slit plate 108 is provided on the upper surface thereof. The inside of the ink liquid holding chamber 107 is filled with the ink liquid 106.
[0023]
Then, the ultrasonic waves emitted from the piezoelectric elements are respectively converged by the acoustic lens 105 and are converged on a slit formed by the slit plate 108.
[0024]
In the present embodiment, the piezoelectric layer 102 of the piezoelectric element array 101 is not divided into an array, but is divided into a plurality of piezoelectric elements by dividing only the individual electrodes 103 into an array. In this example, on the surface of the pointing member 100 that contacts the piezoelectric element array 101, individual electrodes 112 provided on the glass plate side at the same interval as the individual electrodes 103 provided on the piezoelectric layer 102 side are arranged in an array. It is formed by pressing and wiring the array-shaped individual electrodes on the support member 100 via an adhesive. The array-shaped individual electrodes on the support member 100 are wired by bonding wires 111 to driving means 110 arranged on the same support member 100. The common electrode 104 is also wired to the driving unit 110 by a bonding wire (not shown).
[0025]
The piezoelectric element array 101 is connected to the driving unit 110, and drives a part of the piezoelectric elements of the piezoelectric element array 101 substantially simultaneously so that the ultrasonic waves converge to a predetermined position near the ink liquid level. Ejects ink droplets from the ink liquid surface.
[0026]
Hereinafter, the plurality of simultaneously driven piezoelectric elements will be referred to as a piezoelectric element group.
[0027]
In the present embodiment, as the acoustic lens 105, a one-dimensional Fresnel lens in which irregularities based on the Fresnel zone theory are formed in parallel with the main scanning direction (array direction) is used. The thickness of the concave and convex portions of the acoustic lens 105 is set so as to be close to (2N + 1) / 4 times (N is an integer of 0 or more) the wavelength in the acoustic lens. By using a material having a value close to the square root of the product of the acoustic impedance 103 and that of the ink liquid 106, for example, an epoxy resin in which alumina powder is dispersed, the acoustic lens 105 also has a function as an acoustic matching layer.
[0028]
Next, a method for driving the piezoelectric element array 101 will be described.
[0029]
As a method of driving the piezoelectric element array 101, a method of driving each of the piezoelectric elements of the group of piezoelectric elements that are simultaneously driven by giving a phase difference is used. And a method of allocating two phases (hereafter, referred to as 0 phase and π phase) which are shifted by half a wavelength to simulate focusing like a Fresnel lens. The latter is an excellent method that can greatly simplify the driving circuit. In the present embodiment, the driving method using only the 0 phase and the π phase is used.
[0030]
2A and 2B are views for explaining the principle of the ultrasonic focusing method in the ink jet recording head shown in FIG. 1, wherein FIG. 2A shows a sub-scanning direction (a direction perpendicular to the array direction), and FIG. Respectively show the state of the ultrasonic collection. As shown in FIG. 2A, the ultrasonic wave radiated from the piezoelectric layer 102 is focused in the sub-scanning direction in the ink so that the acoustic lens (Fresnel lens) focuses on the vicinity of the slit opening 109. . Further, as shown in FIG. 2B, the ultrasonic wave radiated from the piezoelectric layer 102 passes through the acoustic lens layer 105 and is focused in the ink in the main scanning direction by driving based on the Fresnel cycle theory. In this manner, a large pressure is generated by the focused ultrasonic wave near the slit opening 109, so that an ink droplet is ejected.
[0031]
(Driving method of inkjet recording apparatus)
FIGS. 3A to 3D schematically show an operation in which four adjacent piezoelectric elements of the piezoelectric element array 2 are simultaneously driven as one piezoelectric element group to concentrate an ultrasonic beam at one point. This is shown in FIG. This is an operation in the case where the image points for one line are formed by dividing the image into at least 1/4 lines or more, and the operation is performed on the individual electrode layers 103a, 103b, 103c, 103d, 103e, 103f, 103g, and 103h. The driving voltage is applied while shifting in the main scanning direction by the linear scanning operation.
[0032]
In FIG. 3A, a predetermined burst voltage is applied to the inner two individual electrode layers 103c and 103d among the grouped individual electrode layers 103b, 103c, 103d and 103e, and the outer two individual electrode layers By applying a burst voltage having a phase advanced from the phase of the burst voltage applied to the inner two individual electrode layers 103c and 103d to 103a and 103e, a central portion of the piezoelectric element group, that is, between the individual electrodes 103c and 104d is applied. Ink droplets are ejected from directly above.
[0033]
In FIG. 3B, a predetermined burst voltage is applied to the inner two individual electrode layers 103d and 103e of the next grouped individual electrode layers 103c, 103d, 103e and 103f, and the outer two A burst voltage whose phase is advanced from the phase of the burst voltage applied to the inner two individual electrode layers 103d and 103e is applied to the electrode layers 103c and 103f, and ink droplets are ejected from immediately above between the 103d and 103e. .
[0034]
In FIG. 3C, a predetermined burst voltage is applied to two inner individual electrode layers 103e and 103f of the next grouped individual electrode layers 103d, 103e, 103f, and 103g, and two outer individual To the electrode layers 103d and 103g, a burst voltage having a phase advanced from the phase of the burst voltage applied to the inner two individual electrode layers 103e and 103f is applied.
[0035]
In FIG. 3D, the individual electrode layers 103a, 103b, 103c, 103d, 103e, 103f, 103g, and 103h are represented by a group of the individual electrode layers 103a, 103b, 103c, and 103d, and the individual electrode layers 103e, 103f, and 103g. , 103h, and the two groups are simultaneously driven to eject two ink droplets at a predetermined pitch.
[0036]
In this operation example, one piezoelectric element groove is formed by four piezoelectric elements in order to record one image point. However, if the number of piezoelectric elements constituting one piezoelectric element group is increased, the piezoelectric element becomes centripetal. Since the wavefront of the focused ultrasonic beam becomes smooth and the energy density becomes high, it is possible to reduce variation in ink droplets and drive voltage applied to the piezoelectric element array 101.
[0037]
(Configuration example of driving means)
Next, a configuration example of the driving unit 110 in FIG. 1 will be described. FIG. 4 is a block diagram illustrating a main configuration of the driving unit 110. In FIG. 4, a control unit 40 controls the timing of the system, and may include a CPU. The line memory 42 is controlled by a timing signal from the control unit 40, and writes and reads image data.
[0038]
The drive data generation unit 43 generates drive data for driving the piezoelectric elements 48 of the piezoelectric element array 101 in FIG. 1 based on the image data sent from the line memory 42. Here, for the sake of simplicity, the piezoelectric elements 48 are individually shown as 48a, 48b, 48c,..., But can be considered to correspond to the individual electrodes 103 in FIGS. The details of the drive data generator 43 will be described later in detail with reference to FIG.
[0039]
The output of a scanner (not shown) or image data sent from a transmission path is input to the line memory 42, and the timing is controlled by the control unit 40 and written into the line memory 42. The image data is composed of 1-bit data per pixel in this example. The line memory 42 has a capacity of, for example, 4960 bits and can store image data for one line of A4 paper size at a resolution of 600 dpi.
[0040]
Of course, the image data may be multi-valued data such as 8 bits per pixel, and the line memory 42 at that time has a capacity corresponding to the number of bits.
[0041]
The image data temporarily stored in the line memory 42 is sequentially read out and sent to the drive data generation unit 43. The drive data generation unit 43 generates a selection signal for driving the piezoelectric element 48.
[0042]
(Operation of driving means 110)
Next, the operation of the driving unit 110 will be described with reference to the driving data transfer and the piezoelectric element driving timing chart shown in FIG.
The driving means 110 starts operating at the rise of the horizontal synchronization signal HSYNC. The drive data generated by the drive data generation unit 43 is supplied to the input of the first-stage shift register element 44a of the shift register 44, and sequentially synchronized with the clock SIFT CLOCK from the control unit 40, the next-stage shift register element 44b , 44c... When all 4960 drive data are transferred to the shift register 44, the drive data in the shift register 44 is taken into the latch 45 by the latch signal LATCH CLOCK from the control unit 40.
[0043]
Further, in the selector 46, one of two types of high-frequency signals SIGNAL ZERO, SIGNAL PAI and ground signal GND having different phases from the high-frequency signal generation unit 41 is selectively output according to the drive data output from the latch 45. Is done. The drive data generated by the drive data generation unit 43 is data for controlling on / off of driving of the piezoelectric element 48 by each of these two kinds of high-frequency signals SHIGNEL ZERO and SHIGNAL PAI. Is 1-bit data. The drive data is output as 2-bit data by turning on / off two types of high-frequency signals. Accordingly, the shift register 44 and the latch 45 corresponding to one piezoelectric element 48 are configured so as to form a set of two bits. The selection of the high-frequency signal in the selector 46 is performed based on a truth table as shown in Table 1.
[Table 1]

The high frequency signal output from the selector 46 is amplified by a driver 47 and then applied to a corresponding piezoelectric element 48. A voltage having an amplitude of substantially 10 to 30 V is applied to one piezoelectric element 48. In order to eject ink droplets suitable for a pixel density of about 600 dpi, the frequency of the high-frequency signal is selected to be about 50 MHz.
[0044]
In this manner, while the application of the hearst-like high-frequency signal to the piezoelectric element 48 is performed, the drive data for applying the second high-frequency signal is transferred to the shift register 44, and the application period DRIVE1 of the first high-frequency signal is applied. That is, when the first ink droplet discharging operation is completed, the second high-frequency signal application period DRIVE2 starts. Hereinafter, similarly, the application of the high frequency signal is repeatedly performed, and the recording operation of one line is completed when the required number of times is performed. FIG. 6 shows an example in which one line is printed by four ejection operations for simplicity.
[0045]
(About the drive data generation unit 43)
FIG. 5 shows a schematic configuration of the drive data generation unit 43 in FIG. In FIG. 5, drive data string generation blocks 53 and 63 set data strings for driving a plurality of piezoelectric elements necessary for discharging one ink droplet by drive data string setting units 54 and 64. Are output via the drive data string buffers 55 and 65. For example, when one ink droplet is ejected by simultaneously driving four piezoelectric elements, the four drive data are converted into a set of data strings. Set as Two types of drive data strings are prepared for selecting the two types of high-frequency signals SIGNAL ZERO, SIGNAL PAI, and GND having different phases described above.
[0046]
That is, the drive data string generation blocks 53 and 63 generate two kinds of drive data strings ZERO-DATE corresponding to three kinds of high-frequency signals SIGNAL ZERO, SIGNAL PAI and GND. These two drive data string generation blocks 53 and 63 can be realized by the same configuration. The drive data string setting units 54 and 64 can have a simple switch configuration, or can be configured using a RAM or a ROM.
[0047]
The drive data string buffers 55 and 65 are buffers that take in the drive data strings from the drive data string setting units 54 and 64 and sequentially read out data constituting the drive data strings one by one in time series. In the present embodiment, the drive data string buffers 55 and 65 are composed of shift registers of parallel input / serial output, and read the drive data strings from the drive data string setting sections 54 and 64 in response to the load signal LOAD CLOCK from the control section 40 and control the data. A configuration is such that one data of the drive data sequence is read by a read signal READ CLOCK from the unit 40.
[0048]
The selectors 56 and 66 select the drive data sent from the drive data string buffers 55 and 65, respectively, according to the timing selection signal TIMING SELECT from the control unit 40, and send them to the AND circuits 57 and 67. The AND circuits 57 and 67 send the logical product of the drive data from the selectors 56 and 66 and the image data from the line memory 42 in FIG. 4 to the shift register 44 in FIG. 4 as drive data DRIVE EDATA. Here, since a plurality of drive data need to correspond to one pixel of image data, in this example, the logic of four drive data and one image data corresponding to four read signals READ CLOCK is used. After transmitting the values, the processing shifts to processing of image data for the next pixel. For this purpose, a latch 52 is provided to hold one image data read from the line memory 42 for a period of four readings.
[0049]
Further, in FIG. 5, the image data from the line memory 42 in FIG. 4 is configured to be input to the latch 52 via the quantization unit 51. The conversion unit 51 does not need to function at all. However, when the image data input to the line memory 42 is multi-valued data such as 8 bits per pixel, as in the present embodiment, the quantization unit 51 uses a suitable value, for example, a quaternary processing. Is performed. Based on this multi-value processing, a drive data string is set in the drive data string setting units 54 and 64.
[0050]
The data transmitted from the AND circuits 57 and 67 in this manner is drive data for driving a predetermined piezoelectric element, and is binary data for selecting the high-frequency signals SIGNAL ZERO and SIGNAL PAI. Similarly to the generation of the drive data ZERO-DATE for selecting the high-frequency signal SIGNAL ZERO, the drive data PAI-DATE for selecting the high-frequency signal SIGNAL PAI is also output. That is, 2-bit data is input to the shift register 44 in FIG.
[0051]
(Operation of Drive Data Generation Unit 43)
Next, the operation of the drive data generation unit 43 will be described in more detail with reference to a timing chart related to generation and transfer of drive data shown in FIG.
As shown in FIG. 7A, first, drive data strings are taken into the drive data string buffers 55 and 65 from the drive data string setting sections 54 and 64 by a load signal LOAD CLOCK from the control section 40. At this time, the image data IMAGE DATE of the first pixel is read from the line memory 42 and temporarily stored in the latch 52. For the image data of the first pixel, four drive data DRIVE DATE are generated in synchronism with the read signal READ CLOCK. Next, the image data of the fifth pixel, which is four pixels ahead of the image data of the first pixel, is read from the line memory 42, and four drive data are also generated and transmitted for the image data of the fifth pixel. You. Thereafter, similarly, image data shifted by four addresses is read from the line memory 42. That is, the driving data is set so that every fourth ink droplet is ejected at the position of the piezoelectric element.
[0052]
When 4960 pieces of drive data are transferred in this way, the drive data is fetched into the latch 45 by the latch signal LACH CLOCK as described earlier with reference to the timing chart of FIG. A series of recording operations of discharging ink droplets are performed.
[0053]
Since ink droplets are ejected at every fourth element, the ejection position is shifted by one element at the time of the next ink droplet ejection. That is, transmission of the transfer clock SHIFT CLOCK to the shift register 44 is started as shown in FIG. 7B, but the timing selection signal TIMING SELECT from the control unit 40 is turned off for the first transfer clock. The outputs of the selectors 56 and 66 in FIG. 5 transmit the non-drive data (here, the ground signal GND) without selecting the drive data string. This serves to shift the phase of the piezoelectric element used at the time of the previous ink droplet ejection by one, and forcibly puts the piezoelectric element corresponding to the extreme end into the non-drive state. Thereafter, the timing selection signal TIMING SELECT is turned on, and a signal equal to or less than the load signal LOAD CLOCK is transmitted in the same manner as in FIG. At this time, the image data read from the line memory 42 is read every fourth pixel, such as the second pixel, the sixth pixel, the tenth pixel, the fourteenth pixel, and so on.
[0054]
Similarly, the relationship between the timing selection signal TIMING SELECT and the transfer clock SIFT CLOCK is set so that two elements from the end are not driven at the time of the third ink droplet ejection, as shown in FIG. 7C. . Although not shown, the same operation is performed at the time of the fourth ink droplet discharge, the discharge of all the ink droplets for one line is completed, and the next line is discharged by the same operation as the first line. .
[0055]
(Specific example of driving data sequence)
Table 2 shows a specific example of a drive data string when the four drive data required for simultaneously driving the four piezoelectric elements as described above are shown in Table 1 below. Table 2 (a) shows the phase of the high-frequency signal selected in the arrangement order of the elements, and Table 2 (b) shows the drive data sequence at that time. In this example, the data sequence is PAI, ZERO, ZERO, and PAI in the order in which the piezoelectric elements 48 are arranged. Here, ZERO and PAI mean data for selecting high-frequency signals whose phases are different from each other by 180 °. The principle of ejecting ink droplets when such drive data is given is as described with reference to FIGS.
[Table 2]

Further, Tables 3 to 5 also show examples of driving data strings when the number of simultaneously driven piezoelectric elements (the number of simultaneously driven elements) is different. Table 3 shows an example in which the number of simultaneously driven elements is eight, Table 4 shows an example in which the number of simultaneously driven elements is nine, and Table 5 shows an example in the case where the number of simultaneously driven elements is ten.
[Table 3]

[Table 4]

[Table 5]

Next, a driving method when image information including ink droplet diameter information is input will be described with reference to FIG.
[0056]
First, a method of controlling the ejection amount control element when ejecting ink droplets of the first particle diameter (ink ejection amount control drive 1) will be described. Of the plurality of piezoelectric elements forming the piezoelectric element array, the (m + 1) -th to (m + n) -th elements are a piezoelectric element group, and the m-th and (m + n) -th elements among them are ejection amount controlling elements. Each of the piezoelectric elements in this piezoelectric element group is assigned a phase of 0 or π based on the Fresnel zone theory according to Tables 6 (a) and 6 (b) and driven. That is, all the elements of the piezoelectric element group, including the ejection amount control elements, are simultaneously driven.
[0057]
As for the ultrasonic waves generated from the respective piezoelectric elements, the ultrasonic waves in the main scanning direction are focused near the ink liquid surface, and the ultrasonic waves in the sub-scanning direction are focused by the acoustic lens and acoustic matching layer 105 in FIG. The ink 106 near the liquid surface is ejected as an ink droplet having the first particle diameter.
[Table 6]

Next, a method of controlling the ejection amount control element when ejecting ink droplets of the second particle size (ink ejection amount control drive 2) will be described.
[0058]
In the same piezoelectric element group as in (ink discharge amount control drive 1), a DC voltage is applied to the discharge amount control element, and the (m + 1) th to (m + n-1) th n-1 piezoelectric elements are set to 0 based on the Fresnel zone theory. In accordance with Tables 7 (c) and 7 (d), the phase and π phase are assigned and driven simultaneously.
[0059]
That is, at least one pair of elements (in this example, the (m + n) -th element and the (m + n) -th element), which are symmetrical with respect to the center position of the element array of the piezoelectric element group, This is driving means for setting the non-driving state (here, the ground state) without simultaneously driving the m-th element symmetrically positioned with respect to the center position of the element array. As a result, the amount of generated ultrasonic energy is reduced, and the ejection amount of the ink droplet is reduced as compared with the “ink droplet ejection amount control drive 1”, and a small ink droplet (an ink droplet having a second particle size) is obtained. Is discharged.
[Table 7]

Next, a method of controlling the ejection amount control element when ejecting ink droplets of the third particle diameter (ink ejection amount control drive 3) will be described.
[0060]
In the same piezoelectric element group as in (ink ejection amount control drive 1), the (m + 1) th to (m + n-1) th n-1 piezoelectric elements are driven with a phase of 0 phase or π phase based on the Fresnel zone theory and ejected. A high-frequency voltage is applied to the quantity control element at a phase opposite to the phase based on the Fresnel zone, and the elements are allocated and driven simultaneously according to Tables 8 (e) and 8 (f).
[0061]
That is, at least a pair of elements (in this example, the (m + n) -th element and the (m + n) -th element, and the (m + n) -th element in the left-right symmetric position with respect to the center position of the element arrangement of the element group of the element group, The m-th element located symmetrically with respect to the center position of the array) is used as an adjustment drive element for applying a drive signal having a phase opposite to the original phase, and the energy amount of the sound wave at the focal point is reduced. This is a control method for driving. As a result, the ejection amount of the ink droplet is reduced as compared with “ink droplet ejection amount control drive 1”. In particular, in the case of driving in which a drive signal having a phase opposite to the original phase is applied to offset a part of the energy amount of the sound wave at the focal point and reduce the energy for ejection, the “ink droplet ejection amount” It is possible to discharge even smaller ink droplets (ink droplets having a third particle size) than in the case where the generated energy is simply reduced as in “Control method 2”.
[Table 8]

Next, a method of controlling the ejection amount control element when ejecting ink droplets of the fourth particle diameter (ink ejection amount control drive 4) will be described. Among the plurality of piezoelectric elements forming the piezoelectric element array, the (m-1) th to (m + n + 1) th n + 3 elements are set as a piezoelectric element group, and the (m-1) th and (m + n + 1) th elements are set as ejection amount control elements. I have. A phase of 0 phase or π phase based on the Fresnel zone theory is assigned to each piezoelectric element in the piezoelectric element group according to Tables 9 (a) and 9 (b) and driven. That is, all the elements of the piezoelectric element group, including the ejection amount control elements, are simultaneously driven.
[0062]
As a result, the ink droplet (the ink droplet having the fourth particle diameter) becomes larger than the ink droplet ejection amount control drive 1.
[Table 9]

The tone control of the image can be performed by selecting the ink droplet ejection amount control means 1 to 4 according to the information of the ink particle diameter and changing the image spot size.
[0063]
The mechanism by which the particle diameter of the ink changes depending on the energy amount of the ultrasonic beam is not clear, but is presumed to be as follows.
[0064]
FIG. 9 is a schematic diagram showing a state at the time of ink ejection.
[0065]
As shown in FIG. 9A, a meniscus 1 is formed on the ink liquid surface in the vicinity of the convergence portion of the ultrasonic wave, and a neck is formed at the wavelength λ from the tip of the meniscus. As shown in FIG. 2), the ink droplets 2 protrude, but it is considered that the width of the tip (shown by d in the figure) increases as the energy amount of the ultrasonic beam increases.
[0066]
Hereinafter, specific examples and results of “ink droplet ejection amount control driving 1 to 4” shown in Tables 6 to 9 will be described.
[0067]
【Example】
First, an ink jet recording apparatus as shown in FIG. 1 was prepared in the following manner.
[0068]
As the piezoelectric layer 102, a titanate-based piezoelectric ceramic plate having a relative dielectric constant of 200 was used. Ti / Au laminated electrodes are formed on both surfaces of the piezoelectric ceramic plate by sputtering so that the thicknesses thereof become 0.05 μm and 0.3 μm, respectively, and then a polarization process is performed by applying an electric field of 3 kV / mm. Was. Thereafter, the individual electrodes 103 were formed by etching, and the electrode width per element was 60 μm, the electrode interval was 26 μm, and the arrangement pitch was 86 μm. The width of the piezoelectric layer 102 in the sub-scanning direction was 5 mm. On the other hand, arrayed individual electrodes of Ti / Au were also formed on the supporting member 100 made of glass at intervals of 86 μm. The arrayed individual electrodes 103 on the impression body layer 102 and the arrayed electrodes on the support member 100 were bonded with an epoxy resin in a state where they were aligned, and pressure was applied so that both electrodes were conducted.
[0069]
Next, the piezoelectric layer 102 is polished so as to have a thickness of 45 μm so as to obtain resonance at about 50 MHz, and then the common electrodes 104 composed of Ti / Au laminated electrodes are respectively formed by sputtering to a thickness of 0.05 μm and 1 μm. Formed. At this time, the length of the electrode in the sub-scanning direction, that is, the aperture in the sub-scanning direction was 2.0 mm.
[0070]
For the acoustic lens / acoustic matching layer 105 formed in the next step, a mixture of epoxy resin and alumina powder was used. First, the sound speed is 3 × 10 ³ The mixing ratio was adjusted to be near m / s, and the density was 2.20 × 10 ³ kg / s, sound speed 2.95 × 10 ³ m / s was obtained. This mixture was applied to the surface of the common electrode 104, cured, and polished to a thickness of about 45 μm. Then, a one-dimensional Fresnel lens was formed by inserting a groove having a half wavelength (about 30 μm) in parallel with the main scanning direction so that the focal length became a target value. Then, the ink liquid holding chamber 7 is mounted so that the distance between the ultrasonic wave emitting surface and the liquid surface of the ink liquid 106 substantially coincides with the focal length of the acoustic lens 105, and wiring of the driving means 110 is performed. An ink jet recording head having the above configuration was completed.
(First embodiment)
First, the inkjet recording head of FIG. 1 having a focal length of 2.5 mm and the number of elements of a piezoelectric element group to be simultaneously driven is 16 is driven at a driving frequency of 50 MHz according to [ink droplet ejection amount control driving 1] shown in FIG. It was driven by a burst signal with a voltage of 15 V and a signal applied voltage of 50 μsec.
[0071]
The result of the print recording experiment at this time was a dot size diameter of 60 μm.
[0072]
Next, the same ink jet recording head was subjected to a burst signal in which 14 piezoelectric elements were set to a driving frequency of 50 MHz, a voltage of 15 V, and a signal application time of 50 μsec in accordance with [ink droplet ejection amount control driving 2] shown in FIG. 8B. Driven simultaneously.
[0073]
As a result of the print recording experiment at this time, the pixel size was 50 μm in diameter.
[0074]
Next, according to [ink droplet ejection amount control drive 3] shown in FIG. 8C, the fourteen piezoelectric elements are simultaneously driven, and the elements at both ends adjacent to the simultaneous drive element are set to the phase to be originally applied. Applied drive signals of opposite phases. The driving conditions were a burst signal with a driving frequency of 50 MHz, a voltage of 15 V, and a signal application time of 50 μsec.
[0075]
As a result of the print recording experiment at this time, the pixel size was 40 μm in diameter.
[0076]
Further, in the same ink jet recording head, according to [ink droplet ejection amount control drive 4] shown in FIG. 8D, a burst signal of 50 MHz, voltage 15 V signal application time 50 μsec was applied to the 18 piezoelectric element groups. Was applied.
[0077]
As a result of the printing and recording experiment at this time, the pixel size was 70 μm in diameter.
[0078]
When a color photographic image was printed while selecting according to the above-described four [ink droplet ejection amount control drives 1 to 4] ink particle size information, the gradation was improved as compared with the case where the ink droplet control method was not used. , High quality print record was obtained.
(Second embodiment)
In Example 2, ink ejection was confirmed using a piezoelectric element group of 32 elements as the basic number of elements. That is, the piezoelectric element groups were simultaneously driven according to Tables 10 to 12 below.
[0079]
Further, in this embodiment, the acoustic lens of the ink jet recording head was changed to a lens having a focal length of 4.0 mm, and an ink liquid holding chamber whose liquid level was 4.0 mm from the piezoelectric element array was used.
[0080]
According to Table 10, when the first to 32nd 32 elements were simultaneously driven under the conditions of 50 MHz, a voltage of 25 V, and a signal application time of 50 μsec to eject ink droplets, the pixel size became 80 μm.
[Table 10]

According to Table 11, the second to 31st 30 elements were simultaneously driven under the same conditions to eject ink droplets. As a result, the pixel size became 70 μm.
[Table 11]

According to Table 12, the third to thirty-eighth elements were simultaneously driven under the same conditions to eject ink droplets. As a result, the pixel size became 60 μm.
[Table 12]

According to Table 13, the fourth to 29th 26 elements were simultaneously driven under the same conditions to eject ink droplets, and the pixel size became 50 μm.
[Table 13]

When a color photographic image was printed while selecting the above four driving conditions according to the image information, the gradation was improved as compared with the case where the ink droplet control method was not used, and high-quality print recording was possible.
[0081]
As described above, according to the present embodiment, the driving unit that simultaneously drives a group consisting of a sound wave generating element array in which a plurality of sound wave generating elements are arranged at a predetermined pitch, and a local constant number of sound wave generating elements in the sound wave generating element array And a driving unit, wherein at least a part of the plurality of sound wave generating elements constituting the sound wave generating element array is used as an ink droplet ejection amount controlling element, and a driving condition for the control element is set. By having the means for controlling the ejection amount of the ink droplet by adjusting, it is possible to improve the gradation by changing the pixel size on the recording paper, thereby realizing high quality recording. Become.
[0082]
【The invention's effect】
As described above, according to the present invention, in an ink jet recording apparatus using ultrasonic waves, it is possible to easily control the particle diameter of ejected ink droplets, and it is possible to control the gradation of an image. become.
[Brief description of the drawings]
FIG. 1 is a perspective view of a head of an inkjet recording apparatus according to an embodiment of the present invention.
FIG. 2 is a view for explaining the principle of an ultrasonic convergence method in the ink jet recording head according to one embodiment of the present invention.
FIG. 3 is a diagram schematically illustrating an example of a case where an ultrasonic beam is focused on one point in the inkjet recording head according to an embodiment of the present invention.
FIG. 4 is a block diagram showing an element configuration of a driving unit of the inkjet recording head according to the embodiment of the present invention.
FIG. 5 is a schematic configuration diagram of a driving data generation unit of a driving unit of an inkjet recording head according to an embodiment of the present invention.
FIG. 6 is an explanatory diagram of an operation of a driving unit of the inkjet recording head according to the embodiment of the present invention.
FIG. 7 is an operation explanatory diagram of a drive data generation unit of a driving unit of the inkjet recording head according to one embodiment of the present invention.
FIG. 8 is a diagram for explaining an example of an ink droplet ejection amount control method according to an embodiment of the present invention.
FIG. 9 is a schematic diagram showing a state when ink droplets are ejected by the inkjet recording apparatus of the present invention.
[Explanation of symbols]
1 ... meniscus
2 ... Ink drops
40 ... Control unit
41 ... high frequency signal generator
42 ... Line memory
43 ... Drive data generation unit
44 ・ ・ ・ Shift register
45 ... Latch
46 ... Selector
47 ・ ・ ・ Driver
48, 48a to c ... piezoelectric element
51 Quantizer
52 ... Latch
53, 63... Drive data string generation block
54, 64... Drive data string setting unit
55, 65... Drive data string buffer
56, 66 ... selector
57, 67 ... AND circuit
100 ... glass plate
101: Piezoelectric element array
102: Piezoelectric layer
103, 103a-h ... individual electrode (piezoelectric body side)
104 common electrode
105 ・ ・ ・ Acoustic lens
106 ・ ・ ・ Ink liquid
107 ・ ・ ・ Ink liquid holding chamber
108 ・ ・ ・ Slit plate
109 ··· Slit opening (ink drop ejection port)
110 ・ ・ ・ Drive means
111 ... bonding wire
112 ··· Individual electrode (glass plate side)

Claims (4)

In an ink jet recording apparatus that radiates convergent ultrasonic waves toward ink and ejects ink near the convergence point of the convergent ultrasonic waves as ink droplets to perform recording on a recording medium,
A piezoelectric element array in which a plurality of piezoelectric elements are arranged at a predetermined pitch, and driving means for simultaneously driving a piezoelectric element group including a predetermined number of piezoelectric elements in the piezoelectric element array,
The driving unit sets at least a pair of piezoelectric elements symmetrically positioned with respect to a center position of the piezoelectric element group as an ejection amount control element, and drives / non-drives the ejection amount control element according to ink droplet diameter information. An ink jet recording apparatus comprising a discharge amount control means for selecting. 2. The ink jet recording apparatus according to claim 1, wherein the ejection amount control unit is a unit that applies a DC voltage to the ejection amount control element when the device is not driven. 2. The ink jet recording apparatus according to claim 1, wherein the discharge amount control means is a means for applying a high-frequency voltage having a phase for weakening the converging ultrasonic wave at the convergence point to the discharge amount control element when not driven. In an ink jet recording apparatus that radiates convergent ultrasonic waves toward ink and ejects ink near the convergence point of the convergent ultrasonic waves as ink droplets to perform recording on a recording medium,
A piezoelectric element array in which a plurality of piezoelectric elements are arranged at a predetermined pitch, and driving means for simultaneously driving a piezoelectric element group including a predetermined number of piezoelectric elements in the piezoelectric element array,
The ink jet recording apparatus according to claim 1, wherein the driving unit includes an ejection amount control unit that changes the number of the simultaneously driven piezoelectric elements according to ink droplet diameter information.

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