JP2004306395A - Driving circuit of ink jet head and ink jet printer comprising it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the ink ejection pressure by improving response of a driving voltage at a low cost while sustaining low power consumption. <P>SOLUTION: The driving circuit of an ink jet head comprising a capacitive load, i.e. a piezoelectric element 31, as an ink ejection means is provided with three storage capacitors C1-C3 performing charge/discharge, and switching elements SW1-SW4 for switching connection of a plurality of storage capacitors C1-C3 and the piezoelectric element 31. An inductor L is inserted into a charge/discharge passage formed between the storage capacitor C2 and the piezoelectric element 31 among charge/discharge passages formed sequentially between the storage capacitors C1-C3 and the piezoelectric element 31 when connection is switched sequentially by the switching elements SW1-SW4. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００８８】
具体的には、図４において、一端が安定した電源Ｖｉｎに接続されたＲＬＣ直列回路のスイッチング素子ＳＷをＯＮした時点を時間軸の原点とし、負荷側（圧電体素子を示すコンデンサＣ側）の電圧ＶｏｕｔがＶｉｎの９９％に達する時間を測定した。その結果が、上述のように、表１、図６、図７である。なお、図５は、インダクタンスなしの場合とインダクタンスありの場合で、Ｌ＝６３１ｎＨ（最良の結果が得られた）場合の電圧波形を代表的に示したものである。
【００８９】
上記の実験結果から、Ｌ＝６３１ｎＨにおいて立ち上がり速度が最も速く（４５．８ｎｓｅｃ）なることが分かった。この結果から、上記条件下においては、ベストモードに対するマージンを考慮して、最速の立ち上がり速度である４５．８ｎｓｅｃの５０％増の約６８ｎｓｅｃまでを許容範囲とした場合には、表１、図７より、（Ｒ^２−４Ｌ／Ｃ）≧−２９０００とすることで、常に立ち上がり速度を高い状態で維持することができることになる。
【００９０】
一方、（Ｒ^２−４Ｌ／Ｃ）の上限値については、振動的な過渡応答が得られる０を基準とすることで、所望の電圧値に収束させることができる。
【００９１】
よって、Ｒ＝５０Ω、Ｃ＝４００ｐＦの条件下においては、下記の関係式（１）を満たすようにインダクタンス成分Ｌを設定することで、常に応答速度の速い状態を維持できる。
【００９２】
−２９０００≦（Ｒ２−４Ｌ／Ｃ）≦０・・・・・（１）
また、Ｒ、Ｃについての条件を問わない、Ｒ、Ｌ、Ｃについての一般的な関係についても、以下に示すような関係式（２）または（３）を満たすようにインダクタンス成分Ｌを設定することで、常に応答速度を向上させたインクジェットヘッドの駆動回路（容量性負荷駆動回路）３０を得ることができる。
【００９３】
０．０３≦ｅｘｐ（−αＴｆ）≦０．６２・・・・・（２）
０．６３≦Φ≦１．３・・・・・（３）
なお、上記の関係式（２）、（３）についての詳細は、後述する。
【００９４】
Ｒ、Ｌ、Ｃの過渡現象については、図４に示すＲＬＣ回路において、ｔ＝０でスイッチング素子ＳＷをＯＮしたときには、以下のような式で示すことができる。
【００９５】
Ｌ（ｄＩ（ｔ）／ｄｔ）＋ＲＩ（ｔ）＋（１／Ｃ）∫Ｉ（ｔ）ｄｔ＝ｅ（ｔ）・・・・・（４）
ここで、キャパシタンスＣの初期電圧Ｖ_０、インダクタＬの初期電流ｉ_０、電源電圧Ｅとすると、キャパシタンスＣの端子電圧Ｅｃ（ｔ）は、
Ｅｃ（ｔ）＝Ｅ１（ｔ）＋Ｅ２（ｔ）＋Ｖ０・・・・・（５）
Ｅ１（ｔ）＝（Ｉ_０／Ｃ）（１／ｂ）ｅｘｐ（−αｔ）ｓｉｎ（βｔ）・・・・・（６）
Ｅ２（ｔ）＝（Ｅ−Ｖ_０）｛１−（ω／β）ｅｘｐ（−αｔ）ｓｉｎ（βｔ＋Φ）｝・・・・・（７）
（ただし、α＝Ｒ／（２Ｌ）、β＝ω^２−α^２、Ｔｆ＝（π−Φ）／β、ω^２＝１／（ＬＣ）、Φ＝ｔａｎ−１（β／α）とする。）
となる。
【００９６】
一方、キャパシタンスＣに流れる電流をＩ（ｔ）とすると、
Ｉ（ｔ）＝Ｉ_１（ｔ）＋Ｉ_２（ｔ）・・・・・（８）
Ｉ_１（ｔ）＝Ｉ_０ｅｘｐ（−αｔ）ｃｏｓ（βｔ）・・・・・（９）
Ｉ_２（ｔ）＝〔｛Ｅ−（Ｉ_０・Ｒ／２）｝／Ｌ〕（１／ｂ）ｅｘｐ（−αｔ）ｓｉｎ（βｔ）・・・・・（１０）
（ただし、α＝Ｒ／（２Ｌ）、β＝ω^２−α^２、ω^２＝１／（ＬＣ）、Φ＝ｔａｎ^−１（β／α）とする。）
以上のような式（４）〜（１０）から、正規化したＥ１、Ｅ２、および、ｅｘｐ（−αｔ）（凡例ではｅｘｐと略記）、ｓｉｎ（βｔ＋Φ）（凡例ではｓｉｎΦと略記）、ｓｉｎ（βｔ）（凡例ではｓｉｎと略記）は、図８に示すようなグラフとなる。
【００９７】
図８および上記の関係式（４）〜（１０）から明らかなように、初期電圧、初期電流がゼロの時、目標電圧に到達してスイッチング素子を切り替えるタイミング（正規化Ｅ１＝１となるタイミング）のとき、ｓｉｎ（βｔ＋Φ）＝０であり、よって、βｔ＋Φ＝πとなる。立上り時間（切替え時間）Ｔｆ＝（π−Φ）／βが小さくなるように諸条件を設定すればよい。
【００９８】
ここで、表１で示した実験結果（Ｒ＝５０Ω、Ｃ＝４００ｐＦの条件）を基準として、駆動電圧の立ち上がり時間Ｔｆを評価するために△Ｔｆ／△Ｌを求め図示したのが図９であり、◇がＴｆ（第１Ｙ軸）、△が△Ｔｆ／△Ｌ（第２Ｙ軸）を示している。
【００９９】
また、抵抗Ｒを１０倍、１／１０倍、コンデンサの蓄積容量Ｃを１０倍、１／１０倍にした場合の、インダクタＬとＴ_Ｅ（ｎｓ）の関係を示す実線（第１Ｙ軸）およびｅｘｐ（−αＴ）との関係を示す破線（第２Ｙ軸）は、図１０（ａ）〜図１０（ｄ）に示すようになる。
【０１００】
図９に示すグラフから、基準実験設定においては、△Ｔｆ／△Ｌの曲線よりＬ＞３１６（ｎＨ）に設定すればよいことがわかる。また、Ｔｆの曲線より６３１（ｎＨ）＜Ｌ＜１２５９（ｎＨ）に設定すれば切替時間をほぼ最短にできることが示されている。
【０１０１】
ところが、図１０（ａ）〜図１０（ｄ）に示すように、抵抗Ｒ、コンデンサの蓄積容量Ｃが１０倍、１／１０倍に変化すると最適のインダクタンスは１０倍、１／１０倍に変化するが、各条件を示すグラフはほぼ同じ傾向を示すことが分かる。
【０１０２】
図９、図１０（ａ）〜図１０（ｄ）に示すグラフをまとめたものを表２に示す。
【０１０３】
【表２】

【０１０４】
この表２から、応答速度が最短となるＬの値、そのときの共振周波数ω、その周期Ｔω等は、桁が変化するものの、Φ（ｒａｄ）、ｅｘｐ（−αＴｆ）は変化せず、一定となっていることがわかる。
【０１０５】
このことから、Φあるいはｅｘｐ（−αＴｆ）をある条件下に収まるように設定することで、常にベストモードに近い応答速度が得られることがわかる。
【０１０６】
そこで、ベストモードとなるＬ＝６３１ｎＨにおけるその他の条件を振って、ベストモードの５０％増を上限とするΦおよびｅｘｐ（−αＴｆ）についての条件式を求めると、表３より、以下の関係式（２）および（３）を導くことができる。
【０１０７】
【表３】

【０１０８】
０．０３≦ｅｘｐ（−αＴｆ）≦０．６２・・・・・（２）
０．６３≦Φ≦１．３・・・・・（３）
上記の関係式（２）、（３）を満たすことで、Ｒ、Ｃについての条件を問わない、Ｒ、Ｌ、Ｃについての一般的な関係において、常に応答速度を向上させたインクジェットヘッドの駆動回路（容量性負荷駆動回路）３０を得ることができる。
【０１０９】
なお、上記インクジェットプリンタ１０では、インクジェットヘッドの駆動回路３０として、図１に示す回路の他に、図１１に示す駆動回路４０、図１２に示す駆動回路５０であっても同様の効果を得ることができる。
【０１１０】
すなわち、図１では、エネルギ回収用のコンデンサがラダー抵抗（Ｒ１〜Ｒ３）によって分割された、隣り合う電位間に接続されているのに対して、図１２では、ラダー抵抗（Ｒ１〜Ｒ３）によって分割された電位とＧＮＤに接続されている点で構成上の違いはあるが、機能・効果は同じである。
【０１１１】
従って、上記のようなインクジェットヘッドの駆動回路３１をインクジェットプリンタ１０に搭載することで、非常に安価で、インクの吐出圧力の高いインクジェットプリンタを実現できる。すなわち、表示品位の高いインクジェットプリンタを安価に提供することが可能となる。
【０１１２】
また、上記のインダクタンス素子としては、本実施の形態では、固定コイルとしてのインダクタを用いたが、これに限定されるものではなく、例えばフェライトなどの電磁材料や、配線の寄生インダクタを利用するため意図的に配線長を長くしたもの等を使用することが可能である。
【０１１３】
なお、図１、図１１、図１２に示す各駆動回路は、段数が３段（ｎ＝３）であるが、これに限定されるものではなく、２段以上（ｎ≧２）であれば、本発明の効果を奏することができる。
【０１１４】
そして、本実施の形態の各駆動回路では、何れも、初段の充放電経路にインダクタンス素子が挿入されない例を示しているが、全ての段の充放電経路にインダクタンス素子を挿入してもよい。この場合、駆動電圧のオーバーシュート、アンダーシュート等の問題が生じる虞があるが、消費電力低減のために、複数段の充放電経路を備え場合に、全くインダクタンス素子を挿入しない場合に比べて、駆動電圧の応答速度は速くなる。
【０１１５】
本発明は上述した各実施形態に限定されるものではなく、請求項に示した範囲で種々の変更が可能であり、異なる実施形態にそれぞれ開示された技術的手段を適宜組み合わせて得られる実施形態についても本発明の技術的範囲に含まれる。
【０１１６】
【発明の効果】
本発明のインクジェットヘッドの駆動回路は、以上のように、インク吐出手段として容量性負荷を備えたインクジェットヘッドの駆動回路において、電荷の充放電を行なうキャパシタを含む複数の電源端子と、上記複数の電源端子と上記容量性負荷との接続を順次切り替える切替手段とを有し、上記切替手段によって接続が順次切り替えられて上記電源端子と上記容量性負荷との間で形成される充放電経路に、インダクタンスを有する回路素子が挿入されている構成である。
【０１１７】
それゆえ、切替手段によって接続が順次切り替えられて電源端子と容量性負荷との間で順次形成される充放電経路に、インダクタンスを有する回路素子（以下、インダクタンス素子と称する）を挿入することで、駆動電圧の立ち上がりに存在するなまりが解消され、駆動電圧の上昇時間（充電時間）を短縮できる。
【０１１８】
また、複数段を順次スイッチングして最終的な駆動電圧（振幅）に充放電する際において、インダクタンスを共通化した場合は、前段（前の充放電経路）の最後の充放電電流が次の段（次の充放電経路）の初期電流として引き継がれるので、スイッチングのために休止することなく、充放電を継続できる。したがって、駆動電圧トータルの充放電過渡の時間を最小化し、充放電速度を向上させることが出来る。
【０１１９】
これらにより、キャパシタを有する電源端子と容量性負荷との間における電荷のやり取りに要する時間を短縮することができるため、全ての段の充放電経路にインダクタンス素子が挿入されていない場合と比べて、駆動電圧の立ち上がりおよび立ち下がりをより急峻にすることができる。
【０１２０】
よって、駆動電圧の応答性が向上するので、容量性負荷におけるインクの吐出圧力も高めることができる。しかも、スイッチング素子のオン抵抗を小さくすることなく、駆動電圧の応答性を向上させることが可能となるので、低消費電力を維持しつつ、コストを抑えてインクの吐出圧力を大きくすることができるという効果を奏する。
【０１２１】
上記のインダクタンス素子としては、例えば、固定コイルとしてのインダクタや、フェライトなどの電磁材料や、配線の寄生インダクタを利用するため意図的に配線長を長くしたもの等を使用することが可能である。
【０１２２】
また、上記インダクタンス素子は、上記切替手段と上記容量性負荷との間に挿入されていてもよい。
【０１２３】
この場合、複数の充放電経路を切り替える切替手段と容量性負荷との間にインダクタンス素子が挿入されていることで、該インダクタンス素子を充放電経路毎に挿入する必要がなく、必要な充放電経路を、切替手段を介して一つのインダクタンス素子に接続するようにすれば、部材の共通化を図ることが可能となる。これにより、駆動回路の回路構成を簡素化することができるという効果を奏する。
【０１２４】
また、上記電源端子の抵抗成分をＲ（Ω）、上記インダクタンス素子のインダクタンス成分をＬ（ｎＨ）、上記キャパシタのキャパシタンス成分をＣ（Ｆ）とし、Ｒ＝５０Ω、Ｃ＝４００ｐＦの条件下において、下記の関係式（１）を満たすようにインダクタンス成分Ｌを設定してもよい。
【０１２５】
−２９０００≦（Ｒ^２−４・Ｌ／Ｃ）≦０・・・・・（１）
これにより、上記抵抗成分（Ｒ成分）、インダクタンス成分（Ｌ成分）、キャシタンス成分（Ｃ成分）によって構成されるＲＬＣ回路の一般的な条件として、例えば、アナログスイッチ等の切替手段のＲ成分として採用したＯＮ抵抗値Ｒ＝５０Ω、キャパシタンス成分Ｃ＝４００ｐＦの条件下においては、上記の関係式（１）を満たすようにインダクタンス成分のＬ（ｎＨ）を設定することにより、適度なダンピングを有する振動的な過渡応答を経て所望の電圧に収束させることができるとともに、最も速い立ち上がり速度と比較して１．５倍未満の立ち上がり時間を得ることができる。
【０１２６】
すなわち、実験結果より、Ｌ＝６３１ｎＨで（Ｒ^２−４・Ｌ／Ｃ）＝−３８１０の場合に、最も速い立ち上がり速度Ｔｆ＝４６ｎｓが得られ、（Ｒ^２−４・Ｌ／Ｃ）≧−２９，０００ｎＨ（Ｌ≦３．１５μＨ）の条件下であれば、Ｔｆ＝４６ｎｓの１．５倍である６９ｎｓ未満に立ち上がり時間を抑えることができ、高速応答が可能になる。
【０１２７】
これにより、高速な過渡応答が得られ、容量性負荷を所望の電圧値に収束させることができるという効果を奏する。
【０１２８】
また、最上段の充放電経路、および最下段の充放電経路に上記インダクタンスを有する回路素子を挿入しないようにしてもよい。
【０１２９】
インダクタンスを有する回路素子（インダクタンス素子）を挿入した場合、駆動電圧が過渡的にオーバーシュート、アンダーシュートとなり、該駆動電圧が不安定となって駆動回路の電源電圧範囲を超えてしまうことで該駆動回路のラッチアップや破損が発生する。
【０１３０】
従って、最上段の充放電経路、および最下段の充放電経路に上記インダクタンスを有する回路素子を挿入しないようにすることで、駆動電圧が過渡的にオーバーシュートやアンダーシュートとなることを防止し、該駆動回路のラッチアップや破損を防止することができる。
【０１３１】
さらに、上記切替手段は、任意の充放電経路とこの充放電経路の次に形成される充放電経路とが同時に存在する期間を有するように、電源端子と容量性負荷との間の接続を切り替えるようにしてもよい。
【０１３２】
この場合、連続して形成される２つの充放電経路が同時に存在する期間を有するようになるので、容量性負荷を充電する際に、充放電経路が全く形成されないことにより発生するサージパルスを未然に防止し、駆動回路のラッチアップや破損の発生を防止できる。
【０１３３】
また、前段の充放電経路に流れている電流が、次段の充放電経路の初期電流とすることができるので、駆動電圧の立ち上がり時間を短縮することができるという効果を奏する。
【０１３４】
また、上記インダクタンス素子の電源端子側配線と電源および接地電極との間に、通常逆バイアスとなるダイオードを挿入してもよい。
【０１３５】
この場合、インダクタンス素子の電源端子側配線と電源および接地電極との間に挿入されたダイオードによって、ある電源端子と容量性負荷との接続が解除された状態となった場合に、該インダクタンス素子に流れつづけようとする電流によって発生するサージパルスを吸収することができる。これによって、サージパルスの発生による駆動回路のラッチアップや破損を防止できるという効果を奏する。
【０１３６】
また、上記電源端子の抵抗成分をＲ（Ω）、上記インダクタンス素子のインダクタンス成分をＬ（ｎＨ）、上記キャパシタのキャパシタンス成分をＣ（Ｆ）としたとき、下記の関係式（２）または（３）を満たすようにインダクタンス成分Ｌを設定してもよい。
【０１３７】
０．０３≦ｅｘｐ（−α・Ｔｆ）≦０．６２・・・・・（２）
０．６３≦Φ≦１．３０ ・・・・・（３）
（ただし、α＝Ｒ／２・Ｌ，ω^２＝１／Ｌ・Ｃ，β＝ω^２−α^２，Φ＝ｔａｎ^−１（β／α），Ｔｆ＝（π−Φ）／βとする。）
これにより、ベストモードである、ｅｘｐ（−ａ・Ｔｆ）≒０．１６、Ｔｆ≒４６ｎｓ、Φ≒０．８９（５１ｄｅｇ）の１．５倍以内の範囲時間に抑えることができるとともに、残留振動を半減させて、圧電体を所望の電圧値に収束させることができるという効果を奏する。
【図面の簡単な説明】
【図１】本発明の一実施の形態にかかるインクジェットヘッドの駆動回路を示す回路図である。
【図２】インクジェットプリンタの概略斜視構成図である。
【図３】図１に示す駆動回路の駆動波形図と各スイッチング素子のＯＮ／ＯＦＦ状態との関係を示す図である。
【図４】図１に示す駆動回路のうち、Ｒ成分、Ｌ成分、Ｃ成分を直列に接続したＲＣＬ直列回路を示す回路図である。
【図５】インクジェットヘッドの駆動回路において、インダクタの有無による充電特性を示すグラフである。
【図６】図４に示すＲＣＬ直列回路において、Ｌ成分を変化させた場合の電圧到達率所要時間を測定した結果を示すグラフである。
【図７】図４に示すＲＣＬ直列回路において、Ｌ成分を変化させた場合の電圧到達率所要時間を測定した結果を示す他の例のグラフである。
【図８】図４に示すＲＣＬ直列回路において、各条件において、インダクタを流れる電流値と、キャパシタに印加される電圧との関係を示すグラフである。
【図９】図４に示すＲＣＬ直列回路において、駆動電圧の立ち上がり時間を評価するためのグラフである。
【図１０】（ａ）〜（ｄ）は、図９に示す駆動電圧の立ち上がり時間の評価の比較例を示すグラフである。
【図１１】本発明のインクジェットヘッドの駆動回路の他の例を示す回路図である。
【図１２】本発明のインクジェットヘッドの駆動回路のさらに他の例を示す回路図である。
【符号の説明】
１ 給紙部
２ 搬送部
３ 印刷部
４ 排出部
１０ インクジェットプリンタ
１１ 給紙トレイ
１２ ピックアップローラ
１３ 印字ヘッド
１６ プラテン
１８ａ・１８ｂ 排出ローラ
２０ キャリッジ
２１ ガイドシャフト
２２ インクカートリッジ
２３ インク供給経路
２５ 排出トレイ
３０ 駆動回路
３１ 圧電体素子（容量性負荷）
３２ａ・３２ｂ サージキラーダイオード（ダイオード）
４０ 駆動回路
５０ 駆動回路
Ｃ１〜Ｃ３ 電源側コンデンサ（キャパシタ、キャパシタンス成分）
Ｅ 電源電圧（電源端子）
Ｌ インダクタ（インダクタンスを有する回路素子、インダクタンス成分）
Ｒ１１〜Ｒ１４ 抵抗（抵抗成分）
ＳＷ１〜ＳＷ４ スイッチング素子（切替手段）
Ｔｆ 立上り時間
Ｔω 周期
Ｖ_１ 電圧（駆動電圧）
Ｖ_２ 電圧（駆動電圧）
ＶＨ 電源[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an inkjet head having a capacitive load such as a piezoelectric element or a capacitance element as a means for discharging ink, and more particularly to a drive circuit of an inkjet head for driving an inkjet head and an inkjet printer including the drive circuit. It is about.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a means for discharging ink, an inkjet printer having an inkjet head having a capacitive load such as a piezoelectric element (piezoelectric element) or a capacitance element has been proposed.
[0003]
For example, in an ink jet printer having an ink jet head having a piezoelectric material as a capacitive load, the piezoelectric material is deformed by repeating supply / discharge of electric charge to the piezoelectric material, and ink is ejected by an ejection pressure generated thereby. And print it.
[0004]
In recent years, various techniques have been proposed for reducing the power consumption of an inkjet head having the above-described capacitive load.
[0005]
For example, Patent Literature 1 discloses a technique in which electric charge discharged from a piezoelectric element as a capacitive load is stored in a capacitor, and the stored electric charge is used when charging the piezoelectric element, thereby reducing power consumption. Is disclosed.
[0006]
Further, in Patent Document 2, electric charge discharged from a capacitance element as a capacitive load is stored in an inductance element, and the stored electric charge is used at the time of charging the capacitance element, thereby reducing power consumption. The technology is disclosed.
[0007]
[Patent Document 1]
JP-A-11-170529 (published on June 29, 1999)
[0008]
[Patent Document 2]
Japanese Patent Application Laid-Open No. 2000-218782 (released on August 8, 2000)
[0009]
[Problems to be solved by the invention]
In the above patent documents, when charging and discharging a capacitive load such as a piezoelectric element or a capacitance element, at least one charging switching element having one end connected to a power supply and one end having a GND. Requires one switching element for discharge connected to the switch.
[0010]
Therefore, the transient phenomenon in charging / discharging is determined by an RC equivalent circuit composed of a resistance component (R) represented by the ON resistance of the switching element and the capacitance (C) of the capacitive load. That is, the time required for charging or discharging the charge to the capacitive load (the rise or fall time of the drive voltage applied to the capacitive load) is about five times the time constant of the RC equivalent circuit. Specifically, when the resistance component (R) is 50 [Ω] and the capacitance (C) is 400 [pF], 5 × RC = 100 [nsec] is the time required for charging or discharging. That is, the rise time or fall time of the drive voltage applied to the capacitive load is 100 [nsec].
[0011]
Here, as a method of reducing power consumption, a plurality of charge storage elements (capacitors, inductance elements) for storing electric charges are provided, and a switch or the like provided for each step is sequentially turned on / off. There has been proposed a method of transferring charges between a charge storage element in a stage and a capacitive load.
[0012]
For example, in the case of an n-stage charge storage element, the power consumption is 1 / n compared to a single-stage charge storage element. That is, at the time of charging, 1-1 / n of the total charge amount required for charging the capacitive load is supplied from the charge collection element (charge storage element), and only the remaining 1 / n is supplied from the power supply. This is because, at the time of discharging, 1-1 / n of the total charge amount in the charged capacitive load is collected by the charge storage element, and the remaining 1 / n is discarded to the ground.
[0013]
Therefore, in the case of Patent Documents 1 and 2, in order to further reduce power consumption, it is considered that the above-described charge storage elements (capacitors, inductance elements) are provided in a plurality of stages.
[0014]
However, when the configurations disclosed in Patent Documents 1 and 2 are simply configured in a plurality of stages (n stages), the transient phenomenon in charge and discharge of electric charges in each stage is the same as in the case of the above-described one-stage RC equivalent circuit. . Therefore, the time required for charging or discharging per stage is about five times the time constant of the RC equivalent circuit. In the case of n stages, 5RC × n is the time required for charging or discharging. Specifically, when three stages of charge storage elements are provided, and the resistance (R) at each stage is 50 [Ω] and the capacitance (C) is 400 [pF], 5RC × n = 5 × 50 × 400 × 3 = 300 [nsec] is the rise time or fall time of the drive voltage to the capacitive load. In this case, the rise or fall time of the drive voltage applied to the capacitive load is tripled as compared with the case of one stage.
[0015]
Therefore, when the configurations of Patent Documents 1 and 2 are simply arranged in a plurality of stages (n stages), the rise or fall time of the drive voltage is n times longer than in the case of one stage. In this case, a problem arises in that it is not possible to obtain a sufficient ink ejection pressure, and it is not possible to perform appropriate printing.
[0016]
Therefore, as a method of improving the rise or fall speed of the drive voltage when a plurality of charge storage elements are provided as described above, for example, it is conceivable to reduce the on-resistance of the switching element, which is a main resistance component. However, there is a problem that the cost increases. In other words, if the on-resistance is to be reduced to ３, the area of the semiconductor element constituting the switching element must be tripled, which leads to an increase in the cost of the area of the semiconductor element.
[0017]
Therefore, if the on-resistance of the switching element is reduced, the cost will increase, and as a result, the price of the ink jet printer will increase.
[0018]
The present invention has been made in view of the above-described problems, and has as its object to reduce the cost and improve the responsiveness of the drive voltage while maintaining low power consumption, so that the ink ejection pressure can be sufficiently increased. It is another object of the present invention to provide an ink-jet head drive circuit which can be obtained at the same time and an ink-jet printer having the same.
[0019]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the inventors of the present invention have conducted intensive studies and have found that a plurality of power supply terminals having a capacitor for accumulating electric charges and a plurality of stages of charge / discharge paths are used by sequentially switching connections between the terminals and a capacitive load. By inserting a circuit element having an inductance (hereinafter referred to as an inductance element) into the plurality of stages of charge / discharge paths, the driving voltage of the capacitive load quickly rises and falls, and the capacitive load Was found to improve responsiveness.
[0020]
That is, a drive circuit for an inkjet head according to the present invention includes, in a drive circuit for an inkjet head having a capacitive load as an ink discharge unit, a plurality of capacitors for charging and discharging electric charges with the capacitive load; One end of the capacitor is used as a power supply terminal, and further comprising switching means for sequentially switching the connection between the plurality of power supply terminals and the capacitive load, wherein the connection is sequentially switched by the switching means and the power supply terminal and the capacitive load are switched. A circuit element having an inductance is inserted into a charge / discharge path formed between the circuit elements.
[0021]
In general, a charging transient when there is no inductance (RC series circuit) is determined by the capacitance of a capacitive load: C and the resistance component of a switching element: R, and is expressed by the following equation.
[0022]
Vc = E {1-exp (-t / CR)}
i = E / R · exp (−t / CR) = (E−Vc) / R
Here, Vc is the voltage of the capacitive load, i is the current flowing into the capacitive load, E is the power supply voltage, and t is the charging time. As can be seen from this equation, at the beginning (t = 0) when the switching element is turned on, the charging current is large (i = E / R), and the rate of rise of the voltage of the capacitive load (dVc / dt) is also large. However, both decrease with time (as charging progresses), and as shown by the thin line in FIG. 5, the voltage of the capacitive load hardly reaches the power supply voltage near the power supply voltage. As a result, it takes about five times the time constant (CR) to reach almost equal to the power supply voltage (99% of the power supply voltage).
[0023]
When charging and discharging a capacitive load by providing a plurality of stages of charge / discharge as described above and sequentially switching by the switching means, there is a similar transient phenomenon in each stage, and the speed of increasing the total drive voltage becomes slower as the number of stages increases. I do. This phenomenon is the same in the case of discharging a capacitive load. That is, the lowering speed of the total drive voltage becomes slower as the number of stages increases.
[0024]
Therefore, as in the above configuration, a circuit element having an inductance (hereinafter, referred to as an inductance element) is provided in a charge / discharge path formed between a power supply terminal and a capacitive load by sequentially switching connections by the switching means. The insertion can increase the rise and fall speeds of the drive voltage.
[0025]
This can be realized by utilizing the characteristics of the inductance element. The inductance element acts to maintain the state of the current in the path in which the inductance element is inserted. For this reason, in a steady state in which no current flows through the path, charging and discharging are started while current flows, and when current flows through the path, the current is maintained to maintain the current. Acts as if promoting. In other words, in each stage (each charge / discharge path), there is no slowdown phenomenon of the charge / discharge speed near each power supply voltage in the case of a CR series circuit having no inductance, and it is possible to quickly reach each power supply voltage.
[0026]
Further, when a plurality of stages are sequentially switched to charge / discharge to a final drive voltage (amplitude), if the inductance is shared, the last charge / discharge current of the previous stage (previous charge / discharge path) becomes the next stage. Since the current is taken over as the initial current of the (next charge / discharge path), the charge / discharge can be continued without pausing for switching. Therefore, the charge / discharge transition time of the total drive voltage can be minimized, and the charge / discharge speed can be improved.
[0027]
Because of these, it is possible to reduce the time required for the exchange of electric charge between the power supply terminal having the capacitor and the capacitive load, so that compared to the case where the inductance element is not inserted in the charge and discharge paths of all stages, The rise and fall of the drive voltage can be made steeper.
[0028]
Therefore, the responsiveness of the drive voltage is improved, so that the ink ejection pressure under the capacitive load can be increased. Moreover, since the response of the driving voltage can be improved without reducing the on-resistance of the switching element, it is possible to increase the ink ejection pressure while suppressing cost while maintaining low power consumption. It becomes.
[0029]
As the above-mentioned inductance element, for example, it is possible to use an inductor as a fixed coil, an electromagnetic material such as ferrite, or a wire whose length is intentionally increased in order to use a parasitic inductor of the wire.
[0030]
Further, the inductance element may be inserted between the switching means and the capacitive load.
[0031]
In this case, since the inductance element is inserted between the switching means for switching the plurality of charge / discharge paths and the capacitive load, it is not necessary to insert the inductance element for each charge / discharge path, and the necessary charge / discharge path is not required. Is connected to one inductance element via the switching means, it is possible to use a common member. This makes it possible to simplify the circuit configuration of the drive circuit.
[0032]
Further, when a resistance component of the power terminal is R (Ω), an inductance component of the inductance element is L (nH), and a capacitance component of the capacitor is C (F), R = 50Ω and C = 400 pF, The inductance component L may be set so as to satisfy the following relational expression (1).
[0033]
−29000 ≦ (R ² −4 · L / C) ≦ 0 (1)
Thereby, as a general condition of the RLC circuit composed of the resistance component (R component), the inductance component (L component), and the capacitance component (C component), for example, it is adopted as an R component of a switching unit such as an analog switch. Under the condition that the ON resistance value R = 50Ω and the capacitance component C = 400 pF, by setting L (nH) of the inductance component so as to satisfy the above relational expression (1), the vibration having the appropriate damping is obtained. It is possible to converge on a desired voltage through a transient response and obtain a rise time less than 1.5 times as fast as the fastest rise speed.
[0034]
That is, from the experimental results, (R = 631 nH) ² −4 · L / C) = − 3810, the fastest rising speed Tf = 46 ns is obtained, and (R ² Under the condition of −4 · L / C) ≧ −29,000 nH (L ≦ 3.15 μH), the rise time can be suppressed to less than 69 ns, which is 1.5 times Tf = 46 ns, and high-speed response can be achieved. Will be possible.
[0035]
As a result, a high-speed transient response can be obtained, and the capacitive load can converge to a desired voltage value.
[0036]
Further, the circuit element having the inductance may not be inserted into the uppermost charge / discharge path and the lowermost charge / discharge path.
[0037]
When a circuit element having the above inductance is inserted in the uppermost charge / discharge path and the lowest charge / discharge path, the drive voltage transiently overshoots or undershoots, and exceeds the power supply voltage range of the drive circuit. This may cause damage to the drive circuit due to latch-up or the like.
[0038]
Therefore, by not inserting the circuit element having the above-described inductance into the uppermost charge / discharge path and the lowermost charge / discharge path, it is possible to prevent latch-up and breakage of the drive circuit.
[0039]
Further, the switching means switches the connection between the power supply terminal and the capacitive load such that an arbitrary charge / discharge path and a charge / discharge path formed next to the charge / discharge path have a period in which the charge / discharge path exists simultaneously. You may do so.
[0040]
In this case, since there is a period in which two charge / discharge paths that are formed continuously exist at the same time, a surge pulse generated when no charge / discharge path is formed when charging a capacitive load is generated. And the occurrence of latch-up and breakage of the drive circuit can be prevented.
[0041]
Further, since the current flowing in the preceding charge / discharge path can be used as the initial current of the next charge / discharge path, the rise time of the drive voltage can be shortened.
[0042]
Further, a diode which normally has a reverse bias may be inserted between the power supply terminal side wiring of the inductance element and the power supply and the ground electrode.
[0043]
In this case, when a connection between a certain power supply terminal and a capacitive load is released by a diode (surge killer diode) inserted between the power supply terminal side wiring of the inductance element and the power supply and the ground electrode, It is possible to absorb a surge pulse generated by a current that continues to flow through the inductance element. Thus, latch-up and breakage of the drive circuit due to generation of a surge pulse can be prevented.
[0044]
When the resistance component of the power terminal is R (Ω), the inductance component of the inductance element is L (nH), and the capacitance component of the capacitor is C (F), the following relational expression (2) or (3) ) May be set as the inductance component L.
[0045]
0.03 ≦ exp (−α · Tf) ≦ 0.62 (2)
0.63 ≦ Φ ≦ 1.30 (3)
(However, α = R / 2 · L, ω ² = 1 / LC, β = ω ² −α ² , Φ = tan ^-1 (Β / α), Tf = (π−Φ) / β. )
As a result, exp (-a · Tf) ≒ 0.16, Tf ≒ 46 ns, and ≒ 0.89 (51 deg), which are the best modes, can be suppressed to 1.5 times or less, and the residual vibration can be suppressed. Can be reduced by half to converge the piezoelectric body to a desired voltage value.
[0046]
By mounting the above-described driving circuit of the ink jet head in the ink jet printer, an ink jet printer which is very inexpensive and has a high ink ejection pressure can be realized. That is, it is possible to provide an ink jet printer with high display quality at low cost.
[0047]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below. In this embodiment, a schematic configuration of an ink jet printer will be described, and then, a driving circuit of an ink jet head provided in the ink jet printer will be described in detail.
[0048]
FIG. 2 is a schematic perspective view of the ink jet printer according to the present embodiment.
[0049]
As shown in FIG. 2, the ink jet printer 10 includes a paper feeding unit (paper feeding device) 1, a separation unit (not shown), a transporting unit 2, a printing unit 3, and a discharging unit 4.
[0050]
The paper supply unit 1 supplies the recording paper S when printing is performed, and includes a paper supply tray 11 and a pickup roller 12. When printing is not performed, the function of storing the recording paper S is performed.
[0051]
The separation unit is for supplying the recording paper S supplied from the paper supply unit 1 to the printing unit 3 one by one, and includes a paper supply roller and a separation device. In this separation device, the friction between the pad portion (the contact portion with the recording paper S) and the recording paper S is set to be larger than the friction between the recording papers S. Further, in the paper feed roller, the friction between the paper feed roller and the recording paper S is set to be larger than the friction between the pad and the recording paper S and the friction between the recording papers S. Therefore, even if two recording papers S are sent to the separation section, the recording papers S can be separated by the paper feed roller and only the upper recording paper S can be sent to the transport section.
[0052]
The transport unit 2 transports the recording paper S supplied one by one from the separation unit to the printing unit 3, and includes a guide plate (not shown) and a pair of rollers (the transport press roller 14 and the transport roller). 15). When the recording sheet S is fed between the print head (ink-jet head) 13 and the platen 16, the roller pair rotates the recording sheet S so that the ink from the print head 13 is sprayed to an appropriate position on the recording sheet S. It is a member for adjusting the conveyance.
[0053]
The printing unit 3 is for printing on the recording paper S supplied from the roller pair of the transport unit 2, and includes a print head 13, a carriage 20 on which the print head 13 is mounted, and a guide for the carriage 20. The printing apparatus includes a guide shaft (carriage holding shaft) 21 which is a member, an ink cartridge 22 for supplying ink to the print head 13, and a platen 16 serving as a table for the recording paper S during printing. The ink cartridge 22 and a sub-ink tank (not shown) provided in the carriage 20 are connected to each other by an ink supply path (tube) 23. The sub ink tank is an ink tank provided for stably supplying the ink of the main ink cartridge 22 to the print head 13.
[0054]
The discharge unit 4 is for discharging the recording paper S on which printing has been performed to the outside of the inkjet printer 10, and includes a discharge roller (discharge rollers 18a and 18b) and a discharge tray 25.
[0055]
In the above configuration, the inkjet printer 10 performs printing by the following operation.
[0056]
First, a print request based on image information is transmitted to the inkjet printer 10 from a computer or the like (not shown). Upon receiving the print request, the inkjet printer 10 carries out the recording paper S on the paper supply tray 11 from the paper supply unit 1 by the pickup roller 12.
[0057]
Next, the transported recording paper S passes through the separation unit by the paper feed roller and is sent to the transport unit 2. In the transport unit 2, the recording paper S is transported between the print head 13 and the platen 16 by a pair of rollers (transport pressing roller 14 and transport roller 15).
[0058]
Then, in the printing unit 3, ink is sprayed onto the recording paper S on the platen 16 by the nozzles of the print head 13 in accordance with the image information. At this time, the recording paper S is temporarily stopped on the platen 16. While spraying ink, the carriage 20 is guided by the guide shaft 21 and is scanned by one line in the main scanning direction. When this is completed, the recording paper S is moved on the platen 16 by a certain width in the sub-scanning direction. In the printing unit 3, printing is performed on the entire surface of the recording sheet S by continuously performing the above-described processing according to the image information.
[0059]
The recording paper S on which printing has been performed is discharged to a discharge tray 25 by discharge rollers 18a and 18b of a discharge unit 4 through an ink drying unit (not shown). Thereafter, the recording paper S is provided to the user as a printed matter.
[0060]
With the above-described configuration and operation, the inkjet printer 10 can perform printing corresponding to image data on recording paper. The print head 13 used in the ink jet printer 10 includes a plurality of piezoelectric elements (capacitive loads) as ink discharging means for discharging ink, and controls a driving voltage applied to the piezoelectric elements. By doing so, the inkjet head can control the ink ejection amount.
[0061]
FIG. 1 is a diagram showing a driving circuit of the ink jet head, that is, a driving circuit of the print head 13.
[0062]
As shown in FIG. 1, the drive circuit 30 of the inkjet head applies a voltage to the piezoelectric element 31 as a capacitive load to deform the piezoelectric element 31 and reduce the amount of ink ejected from the print head 13. Control. To this end, the driving circuit 30 includes one capacitive load C ₀ Is a capacitive load drive circuit provided with a piezoelectric element (piezo) 31 as a switching element, a plurality of switching elements SW1 to SW4 as switching means, resistors R11 to R14, and the like.
[0063]
That is, the drive circuit 30 sequentially connects a plurality of power supply terminals (including a power supply VH and the resistors R11 to R14) including a capacitor for charging and discharging electric charges, and a connection between the plurality of power supply terminals and the piezoelectric element 31. A switching element (switching elements SW1 to SW4) for switching, the connection being sequentially switched by the switching means, and a circuit element having an inductance in a charge / discharge path formed between the power supply terminal and the capacitive load. (Inductor L) is inserted.
[0064]
Specifically, the drive circuit 30 is a four-stage multi-tap type as shown in FIG. 1, and includes switching elements SW1 to SW4, resistors R11 to R14, power supply side capacitors C1 to C3, and a voltage divider. It includes resistors R1 to R3, surge killer diodes (diodes) 32a and 32b, and an inductor L.
[0065]
Switching elements SW1 to SW4 and resistors R11 to R14 are provided at each stage of the four-stage multi-tap, and between each stage, power supply side capacitors C1 to C3 as capacitors and a resistor R1 as a voltage divider are provided. To R3, and are connected to the power supply VH and the ground electrode on the side of the resistors R1 to R3.
[0066]
FIG. 1 shows a typical basic circuit of a driving circuit for an ink jet head according to the present invention. The resistances R11 to R14 are the ON resistances of the switching elements SW1 to SW4, respectively, and are not individually provided. Usually, since these switching elements are composed of semiconductor elements, the resistance at the time of ON is larger than that of a switch having mechanical contacts, and cannot be ignored in considering the operation of the drive circuit. In this figure, for convenience of description, a semiconductor switch is represented by a switch having mechanical contacts and a resistor. The capacitances (capacitances) of the power supply side capacitors C1 to C3 are sufficiently larger than the capacitances (capacitances) of the piezoelectric elements 31, and the driving voltage V1 is obtained even when electric charges are exchanged with the piezoelectric elements 31. , V2 have almost no voltage fluctuation.
[0067]
Here, the driving of the piezoelectric element 31 by the driving circuit 30 will be described.
[0068]
First, electric charges are accumulated in the power supply side capacitors C1 to C3 according to the resistors R1 to R3 as the voltage divider.
[0069]
When the switching element SW1 is ON, the piezoelectric element 31 is at the GND level and is in a completely discharged state. Next, by sequentially switching the ON state of the switching element to SW2 and SW3, electric charges are supplied from the power supply side capacitors C1, C2, and C3 to the piezoelectric element 31 and are boosted to the voltage V1 and V2 levels. Then, when the switching element SW4 is turned on, the same voltage VH as the power supply voltage is applied to the piezoelectric element 31. After that, by switching the ON state of the switching element to SW3, SW2, and SW1, the electric charge accumulated in the piezoelectric element 31 moves (recovers) to the power supply-side capacitors C3, C2, and C1 while the piezoelectric element 31 The voltage applied to the element 31 can be reduced to the ground level.
[0070]
As described above, the inkjet printer 10 according to the present embodiment includes the driving circuit 30 for the multi-tap capacitive load including the plurality of power supply side capacitors C1 to C3 for each piezoelectric element 31. In addition, the piezoelectric element 31 is driven while supplying the electric charge to the piezoelectric element 31 and collecting the electric charge to the power supply side capacitors C1 to C3. As a result, the electric charge once accumulated in the piezoelectric element 31 can be efficiently used, so that the drive power consumption of the piezoelectric element 31 can be reduced.
[0071]
Here, in the drive circuit 30 of the ink jet head (print head 13) included in the ink jet printer 10 of the present embodiment, an inductor L (having an inductance) is provided between the switching elements SW2 and SW3 and the piezoelectric element 31. Circuit element) is inserted.
[0072]
Accordingly, when the electric charge accumulated in the piezoelectric element 31 is collected by the power supply side capacitors C1 and C2, the inductor L collects the electric charge, so that the responsiveness of the piezoelectric element 31 can be improved. Conversely, the inductor L collects the charges stored in the power supply side capacitors C1 to C3, and the charges can be efficiently stored in the piezoelectric element 31. Therefore, in the inkjet printer 10 including the driving circuit 30 of the multi-tap type inkjet head, the rising speed (slew rate) and the falling speed of the driving voltage applied to the piezoelectric element 31 with a simple configuration, that is, the response speed Can be improved, and the piezoelectric element 31 can be driven at a sufficient response speed.
[0073]
Accordingly, a sufficient ink ejection pressure by the piezoelectric element 31 can be obtained, so that printing can be appropriately performed.
[0074]
FIG. 3 is a waveform diagram of a drive voltage applied to the piezoelectric element 31 in the drive circuit 30 and a diagram showing ON / OFF states of the switching elements SW1 to SW4 at that time. In this figure, the bold solid line in the waveform diagram of the drive voltage shows the voltage waveform of the drive voltage applied to the piezoelectric element 31 when the drive circuit 30 shown in FIG. 1 is operated. Similarly, a thin broken line indicates a case where there is no inductor L in FIG. Note that the state of the switching element SW when there is no inductor L is omitted. However, when there is no inductor L (when a thin broken voltage waveform is obtained in the drive waveform diagram), it is necessary to lengthen the ON time of the switching elements SW2 and SW3.
[0075]
From the drive waveform diagram shown in FIG. 3, the drive circuit 30 in which the inductor L is provided has the rising / falling speed of the drive voltage improved compared to the case where the inductor L is not provided. You can see that.
[0076]
The reason will be described in the case where the drive voltage is boosted from the GND level to the voltage V1.
[0077]
When the inductor L is not inserted, the rate of rise of the voltage decreases as the voltage rises from the GND level to the voltage V1 due to the charging characteristics of the CR series circuit composed of the resistor R12 and the piezoelectric element 31. (The thin broken line in FIG. 3). On the other hand, if there is an appropriate value of inductance (equivalent to the equivalent circuit (RLC circuit) shown in FIG. 4), the inductor L acts to maintain the current at each time. Although the current hardly flows, the voltage rises slowly, but when the current starts flowing, the voltage rises faster and can reach the voltage V1 quickly (the thick solid line in FIG. 3). Table 1 to be described later and FIGS. 5 to 7 show the results of examining the state of boosting per stage by changing the value of the inductor L.
[0078]
The same applies to the case where the drive voltage is stepped up from the voltage V1 to V2, the step down from the voltage VH to the voltage V2, and the step down from the voltage V2 to V1. However, when the voltage is increased from V2 to VH and when the voltage is decreased from V1 to GND, the voltage does not pass through the inductor L, so that the behavior is naturally the same as a thin broken line.
[0079]
In the drive circuit 30 of the present embodiment, as shown in FIG. 1, the inductor L is not inserted in the uppermost switching element SW4 and the lowermost switching element SW1. As a result, it is possible to prevent occurrence of latch-up or breakage of the drive circuit due to transient overshoot or undershoot of the drive voltage.
[0080]
Further, in the inkjet printer 10 of the present embodiment, when the driving circuit 30 drives the piezoelectric element 31, for example, when switching from the switching element SW <b> 1 to SW <b> 2, there is a period during which both SWs are in the ON state. Each switching element SW is switched.
[0081]
Thus, by suppressing a surge pulse generated when both SWs are turned off, it is possible to prevent latch-up and breakage of the drive circuit 30 from occurring. In addition, since the charging current of the previous stage SW becomes the initial current of the next stage SW, the rise time can be shortened.
[0082]
Further, between the terminal on the power supply voltage side of the inductor L, the ground electrode, and the power supply, surge killer diodes 32a and 32b which are normally reverse biased are inserted.
[0083]
Thus, even when adjacent switching switches are both turned off and a surge pulse is generated when the switching elements SW are switched in accordance with each other, the surge killer diodes 32a and 32b absorb the surge pulse, thereby latching the drive circuit 30. Up and breakage can be prevented.
[0084]
In the inkjet head drive circuit 30 provided in the inkjet printer 10 having the above configuration, the components R, L, and C are set so as to satisfy the following relationship.
[0085]
Here, in an RLC model circuit as shown in FIG. 4, an experiment was performed in which R was set to R = 50Ω and C = 400 pF, and L was changed to measure the time required to reach a desired voltage value of 5V.
[0086]
That is, the result of examining the charging characteristic of this one-stage circuit via the inductor L in FIG. 1 by changing the value of the inductor L with the RLC series circuit shown in FIG. 6 and 7.
[0087]
[Table 1]

[0088]
Specifically, in FIG. 4, the time point when the switching element SW of the RLC series circuit whose one end is connected to the stable power supply Vin is turned on is set as the origin of the time axis, and the load side (the capacitor C side indicating the piezoelectric element) is set. The time when the voltage Vout reached 99% of Vin was measured. The results are Table 1, FIG. 6, and FIG. 7, as described above. FIG. 5 exemplarily shows voltage waveforms when L = 631 nH (the best result is obtained) in a case without inductance and in a case with inductance.
[0089]
From the above experimental results, it was found that the rising speed was the fastest (45.8 nsec) when L = 631 nH. From these results, under the above conditions, taking into account the margin for the best mode, if the allowable range is up to about 68 nsec, which is a 50% increase from 45.8 nsec which is the fastest rising speed, Table 1 and FIG. From (R ² −4L / C) ≧ −29000, the rising speed can always be maintained in a high state.
[0090]
On the other hand, (R ² With respect to the upper limit value of −4 L / C), it is possible to converge to a desired voltage value by using 0 as a reference at which an oscillating transient response is obtained.
[0091]
Therefore, under the condition of R = 50Ω and C = 400 pF, by setting the inductance component L so as to satisfy the following relational expression (1), it is possible to always maintain a high response speed.
[0092]
−29000 ≦ (R2-4L / C) ≦ 0 (1)
Further, the inductance component L is set so as to satisfy the following relational expression (2) or (3) for the general relations of R, L, and C regardless of the conditions for R and C. As a result, it is possible to obtain a drive circuit (capacitive load drive circuit) 30 for an ink-jet head in which the response speed is constantly improved.
[0093]
0.03 ≦ exp (−αTf) ≦ 0.62 (2)
0.63 ≦ Φ ≦ 1.3 (3)
The details of the above relational expressions (2) and (3) will be described later.
[0094]
The transient phenomena of R, L, and C can be expressed by the following equation when the switching element SW is turned on at t = 0 in the RLC circuit shown in FIG.
[0095]
L (dI (t) / dt) + RI (t) + (1 / C) ∫I (t) dt = e (t) (4)
Here, the initial voltage V of the capacitance C ₀ , The initial current i of the inductor L ₀ , The power supply voltage E, the terminal voltage Ec (t) of the capacitance C is
Ec (t) = E1 (t) + E2 (t) + V0 (5)
E1 (t) = (I ₀ / C) (1 / b) exp (-αt) sin (βt) (6)
E2 (t) = (E−V ₀ ) {1− (ω / β) exp (−αt) sin (βt + Φ)} (7)
(However, α = R / (2L), β = ω ² −α ² , Tf = (π−Φ) / β, ω ² = 1 / (LC) and Φ = tan-1 (β / α). )
It becomes.
[0096]
On the other hand, if the current flowing through the capacitance C is I (t),
I (t) = I ₁ (T) + I ₂ (T) ... (8)
I ₁ (T) = I ₀ exp (−αt) cos (βt) (9)
I ₂ (T) = [｛E- (I ₀ ・ R / 2)｝ / L] (1 / b) exp (−αt) sin (βt) (10)
(However, α = R / (2L), β = ω ² −α ² , Ω ² = 1 / (LC), Φ = tan ^-1 (Β / α). )
From the above equations (4) to (10), normalized E1, E2, exp (−αt) (abbreviated as exp in the legend), sin (βt + Φ) (abbreviated as sinΦ in the legend), sin ( βt) (abbreviated as sin in the legend) is a graph as shown in FIG.
[0097]
As is clear from FIG. 8 and the above-described relational expressions (4) to (10), when the initial voltage and the initial current are zero, the timing at which the switching element is reached upon reaching the target voltage (timing at which the normalized E1 = 1) ), Sin (βt + Φ) = 0, and therefore βt + Φ = π. Various conditions may be set so that the rise time (switching time) Tf = (π−Φ) / β is reduced.
[0098]
Here, △ Tf / △ L was obtained and shown in FIG. 9 to evaluate the rise time Tf of the drive voltage based on the experimental results (R = 50Ω, C = 400 pF) shown in Table 1 as a reference. ◇ indicates Tf (first Y axis) and △ indicates △ Tf / △ L (second Y axis).
[0099]
In addition, when the resistance R is 10 times and 1/10 times, and the storage capacitance C of the capacitor is 10 times and 1/10 times, the inductors L and T _E A solid line (first Y axis) indicating the relationship (ns) and a broken line (second Y axis) indicating the relationship with exp (−αT) are as shown in FIGS. 10 (a) to 10 (d).
[0100]
From the graph shown in FIG. 9, it can be seen that in the reference experiment setting, L> 316 (nH) may be set from the curve of ΔTf / ΔL. Further, it is shown from the curve of Tf that the switching time can be almost minimized by setting 631 (nH) <L <1259 (nH).
[0101]
However, as shown in FIGS. 10 (a) to 10 (d), when the resistance R and the storage capacitance C of the capacitor change to 10 times and 1/10 times, the optimum inductance changes to 10 times and 1/10 times. However, it can be seen that the graphs showing the conditions show almost the same tendency.
[0102]
Table 2 summarizes the graphs shown in FIGS. 9, 10 (a) to 10 (d).
[0103]
[Table 2]

[0104]
From Table 2, the value of L at which the response speed becomes the shortest, the resonance frequency ω at that time, the period Tω, and the like change in digits, but Φ (rad) and exp (−αTf) do not change, and are constant. It turns out that it becomes.
[0105]
From this, it can be understood that setting Φ or exp (−αTf) so as to fall under a certain condition always provides a response speed close to the best mode.
[0106]
Then, by changing the other conditions at L = 631 nH, which is the best mode, and obtaining a conditional expression for Φ and exp (−αTf) with an upper limit of 50% increase of the best mode, the following relational expression is obtained from Table 3. (2) and (3) can be derived.
[0107]
[Table 3]

[0108]
0.03 ≦ exp (−αTf) ≦ 0.62 (2)
0.63 ≦ Φ ≦ 1.3 (3)
By satisfying the above-mentioned relational expressions (2) and (3), driving of an ink-jet head with a constantly improved response speed in the general relationship of R, L and C regardless of the conditions of R and C A circuit (capacitive load drive circuit) 30 can be obtained.
[0109]
In the above-described ink jet printer 10, the same effects can be obtained by using the drive circuit 40 shown in FIG. 11 and the drive circuit 50 shown in FIG. 12 in addition to the circuit shown in FIG. Can be.
[0110]
That is, in FIG. 1, the energy recovery capacitor is connected between adjacent potentials divided by the ladder resistors (R1 to R3), whereas in FIG. 12, the energy recovery capacitor is connected by the ladder resistors (R1 to R3). Although there is a difference in configuration between the divided potential and connection to GND, the functions and effects are the same.
[0111]
Therefore, by mounting the above-described drive circuit 31 of the inkjet head on the inkjet printer 10, an inkjet printer that is very inexpensive and has a high ink ejection pressure can be realized. That is, it is possible to provide an ink jet printer with high display quality at low cost.
[0112]
In the present embodiment, an inductor as a fixed coil is used as the above-described inductance element. However, the present invention is not limited to this. For example, an electromagnetic material such as ferrite or a parasitic inductor of a wiring is used. It is possible to use a wire whose length is intentionally increased.
[0113]
Each of the drive circuits shown in FIGS. 1, 11, and 12 has three stages (n = 3), but is not limited to this. If two or more stages (n ≧ 2), Thus, the effects of the present invention can be obtained.
[0114]
In each of the drive circuits of the present embodiment, an example is shown in which no inductance element is inserted in the first stage charge / discharge path, but an inductance element may be inserted in all stages of the charge / discharge path. In this case, problems such as overshoot and undershoot of the drive voltage may occur.However, in order to reduce power consumption, when a plurality of stages of charge / discharge paths are provided, compared with a case where no inductance element is inserted at all, The response speed of the driving voltage increases.
[0115]
The present invention is not limited to the embodiments described above, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.
[0116]
【The invention's effect】
As described above, the drive circuit of the inkjet head according to the present invention includes, in the drive circuit of the inkjet head having a capacitive load as an ink discharge unit, a plurality of power supply terminals including a capacitor for charging and discharging electric charges, A switching means for sequentially switching the connection between the power supply terminal and the capacitive load, and a charge / discharge path formed between the power supply terminal and the capacitive load, the connection being sequentially switched by the switching means, In this configuration, a circuit element having an inductance is inserted.
[0117]
Therefore, by inserting a circuit element having an inductance (hereinafter, referred to as an inductance element) into a charge / discharge path sequentially formed between the power supply terminal and the capacitive load by sequentially switching the connection by the switching means, Bluntness existing at the rise of the drive voltage is eliminated, and the rise time (charge time) of the drive voltage can be reduced.
[0118]
Further, when a plurality of stages are sequentially switched to charge / discharge to a final drive voltage (amplitude), if the inductance is shared, the last charge / discharge current of the previous stage (previous charge / discharge path) becomes the next stage. Since the current is taken over as the initial current of the (next charge / discharge path), the charge / discharge can be continued without pausing for switching. Therefore, the charge / discharge transition time of the total drive voltage can be minimized, and the charge / discharge speed can be improved.
[0119]
Because of these, it is possible to reduce the time required for the exchange of electric charge between the power supply terminal having the capacitor and the capacitive load, so that compared to the case where the inductance element is not inserted in the charge and discharge paths of all stages, The rise and fall of the drive voltage can be made steeper.
[0120]
Therefore, the responsiveness of the drive voltage is improved, so that the ink ejection pressure under the capacitive load can be increased. In addition, since it is possible to improve the response of the driving voltage without reducing the on-resistance of the switching element, it is possible to increase the ink ejection pressure while suppressing cost while maintaining low power consumption. This has the effect.
[0121]
As the above-mentioned inductance element, for example, it is possible to use an inductor as a fixed coil, an electromagnetic material such as ferrite, or a wire whose length is intentionally increased in order to use a parasitic inductor of the wire.
[0122]
Further, the inductance element may be inserted between the switching means and the capacitive load.
[0123]
In this case, since the inductance element is inserted between the switching means for switching the plurality of charge / discharge paths and the capacitive load, it is not necessary to insert the inductance element for each charge / discharge path, and the necessary charge / discharge path is not required. Is connected to one inductance element via the switching means, it is possible to use a common member. As a result, there is an effect that the circuit configuration of the drive circuit can be simplified.
[0124]
Further, when the resistance component of the power terminal is R (Ω), the inductance component of the inductance element is L (nH), and the capacitance component of the capacitor is C (F), R = 50Ω and C = 400 pF, The inductance component L may be set so as to satisfy the following relational expression (1).
[0125]
−29000 ≦ (R ² −4 · L / C) ≦ 0 (1)
Thereby, as a general condition of the RLC circuit composed of the resistance component (R component), the inductance component (L component), and the capacitance component (C component), for example, it is adopted as an R component of a switching unit such as an analog switch. Under the condition of the ON resistance value R = 50Ω and the capacitance component C = 400 pF, by setting L (nH) of the inductance component so as to satisfy the above relational expression (1), the vibration having appropriate damping is obtained. The voltage can be converged to a desired voltage through a transient response, and a rise time less than 1.5 times as fast as the fastest rise speed can be obtained.
[0126]
That is, from the experimental results, (R = 631 nH) ² −4 · L / C) = − 3810, the fastest rising speed Tf = 46 ns is obtained, and (R ² Under the condition of −4 · L / C) ≧ −29,000 nH (L ≦ 3.15 μH), the rise time can be suppressed to less than 69 ns, which is 1.5 times Tf = 46 ns, and high-speed response can be achieved. Will be possible.
[0127]
As a result, a high-speed transient response can be obtained, and the capacitive load can be converged to a desired voltage value.
[0128]
Further, the circuit element having the above-described inductance may not be inserted in the uppermost charge / discharge path and the lowermost charge / discharge path.
[0129]
When a circuit element having inductance (inductance element) is inserted, the driving voltage transiently overshoots and undershoots, and the driving voltage becomes unstable and exceeds the power supply voltage range of the driving circuit. Latch-up or breakage of the circuit occurs.
[0130]
Therefore, by preventing the circuit element having the above-described inductance from being inserted into the uppermost charge / discharge path and the lowermost charge / discharge path, the drive voltage is prevented from being transiently overshoot or undershoot, Latch-up and breakage of the drive circuit can be prevented.
[0131]
Further, the switching means switches the connection between the power supply terminal and the capacitive load such that an arbitrary charge / discharge path and a charge / discharge path formed next to the charge / discharge path have a period in which the charge / discharge path exists simultaneously. You may do so.
[0132]
In this case, since there is a period in which two charge / discharge paths that are formed continuously exist at the same time, a surge pulse generated when no charge / discharge path is formed when charging a capacitive load is generated. And the occurrence of latch-up and breakage of the drive circuit can be prevented.
[0133]
Further, since the current flowing in the charge / discharge path in the preceding stage can be used as the initial current in the charge / discharge path in the next stage, the rise time of the drive voltage can be shortened.
[0134]
Further, a diode which normally has a reverse bias may be inserted between the power supply terminal side wiring of the inductance element and the power supply and the ground electrode.
[0135]
In this case, when a connection between a certain power supply terminal and a capacitive load is released by a diode inserted between the power supply terminal side wiring of the inductance element and the power supply and the ground electrode, the inductance element is connected to the power supply terminal. It is possible to absorb a surge pulse generated by a current that is about to flow. As a result, there is an effect that the latch-up or breakage of the drive circuit due to the generation of the surge pulse can be prevented.
[0136]
When the resistance component of the power terminal is R (Ω), the inductance component of the inductance element is L (nH), and the capacitance component of the capacitor is C (F), the following relational expression (2) or (3) ) May be set as the inductance component L.
[0137]
0.03 ≦ exp (−α · Tf) ≦ 0.62 (2)
0.63 ≦ Φ ≦ 1.30 (3)
(However, α = R / 2 · L, ω ² = 1 / LC, β = ω ² −α ² , Φ = tan ^-1 (Β / α), Tf = (π−Φ) / β. )
As a result, exp (-a · Tf) ≒ 0.16, Tf ≒ 46 ns, and ≒ 0.89 (51 deg), which are the best modes, can be suppressed to 1.5 times or less, and the residual vibration can be suppressed. Is reduced by half, and the piezoelectric body can be converged to a desired voltage value.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a driving circuit of an inkjet head according to an embodiment of the present invention.
FIG. 2 is a schematic perspective configuration diagram of an ink jet printer.
FIG. 3 is a diagram showing a relationship between a drive waveform diagram of the drive circuit shown in FIG. 1 and ON / OFF states of each switching element.
FIG. 4 is a circuit diagram showing an RCL series circuit in which an R component, an L component, and a C component are connected in series in the drive circuit shown in FIG. 1;
FIG. 5 is a graph showing charging characteristics depending on the presence or absence of an inductor in a driving circuit of an inkjet head.
6 is a graph showing a result of measuring a required time of a voltage arrival rate when an L component is changed in the RCL series circuit shown in FIG. 4;
FIG. 7 is a graph of another example showing a result of measuring a required time of voltage arrival rate when an L component is changed in the RCL series circuit shown in FIG. 4;
8 is a graph showing a relationship between a current value flowing through an inductor and a voltage applied to a capacitor under each condition in the RCL series circuit shown in FIG. 4;
9 is a graph for evaluating a rise time of a drive voltage in the RCL series circuit shown in FIG. 4;
FIGS. 10A to 10D are graphs showing comparative examples of evaluation of the rise time of the drive voltage shown in FIG.
FIG. 11 is a circuit diagram showing another example of the driving circuit of the inkjet head of the present invention.
FIG. 12 is a circuit diagram showing still another example of the driving circuit of the inkjet head of the present invention.
[Explanation of symbols]
1 Paper feed unit
2 Transport section
3 printing section
4 discharge section
10 Inkjet printer
11 Paper tray
12 Pickup roller
13 Print head
16 Platen
18a / 18b discharge roller
20 carriage
21 Guide shaft
22 Ink cartridge
23 Ink supply path
25 discharge tray
30 Drive circuit
31 Piezoelectric element (capacitive load)
32a / 32b Surge killer diode (diode)
40 drive circuit
50 drive circuit
C1-C3 Power supply side capacitor (capacitor, capacitance component)
E Power supply voltage (power supply terminal)
L Inductor (circuit element having inductance, inductance component)
R11 to R14 Resistance (resistance component)
SW1 to SW4 switching element (switching means)
Tf rise time
Tω period
V ₁ Voltage (drive voltage)
V ₂ Voltage (drive voltage)
VH power supply

Claims (8)

In a driving circuit of an ink jet head having a capacitive load as an ink discharging means,
A plurality of capacitors for charging and discharging electric charge with a capacitive load;
One end of the plurality of capacitors is a power terminal,
Switching means for sequentially switching the connection between the plurality of power terminals and the capacitive load,
A drive circuit for an inkjet head, wherein a circuit element having an inductance is inserted in a charge / discharge path formed between the power supply terminal and the capacitive load by sequentially switching connections by the switching means. . 2. The driving circuit according to claim 1, wherein the circuit element having the inductance is inserted between the switching unit and the capacitive load. The resistance component of the power terminal is R (Ω), the inductance component of the circuit element having the inductance is L (nH), the capacitance component of the capacitor is C (F), and R = 50Ω and C = 400 pF. 2. The driving circuit according to claim 1, wherein the inductance component L is set so as to satisfy the following relational expression (1).
−29000 ≦ (R ² −4 · L / C) ≦ 0 (1) 2. The ink jet head drive circuit according to claim 1, wherein the circuit element having the inductance is not inserted in a charge / discharge path of an uppermost power supply and a lowermost power supply among the plurality of power supply terminals. . The switching unit switches the connection between the power supply terminal and the capacitive load so that an arbitrary charge / discharge path and a charge / discharge path formed next to the charge / discharge path have a period in which the charge / discharge path exists simultaneously. The driving circuit for an ink-jet head according to claim 1. 2. The driving circuit according to claim 1, wherein a diode serving as a reverse bias is inserted between the power supply terminal side wiring of the circuit element having the inductance and the power supply and the ground electrode. When the resistance component of the power supply terminal is R (Ω), the inductance component of the circuit element having the inductance is L (nH), and the capacitance component of the capacitor is C (F), the following relational expression (2) or ( 2. The driving circuit according to claim 1, wherein the inductance component L is set so as to satisfy (3).
0.03 ≦ exp (−α · Tf) ≦ 0.62 (2)
0.63 ≦ Φ ≦ 1.30 (3)
(However, α = R / 2 · L, ω ² = 1 / LC, β = ω ² −α ² , Φ = tan ⁻¹ (β / α), Tf = (π−Φ) / β .) An ink-jet printer comprising the ink-jet head drive circuit according to claim 1.

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