JP3642617B2 - Image recording device - Google Patents

Description

【００３３】
ｗ：分離された電界シャッター間の幅
ｄ：気体状インクの吐出方向に沿った電界シャッター部の長さ
Ｔ：インクの加熱温度
ｑ：気体状インクの帯電量
Ｎ：気体状インクの粒子数
Ｃ：気体定数
制御する。
【００３４】
以下に作用について説明する。
【００３５】
まず、上記のように、分離された電界シャッター間の幅ｗと、気体状インクの吐出方向に沿った電界シャッター部の長さｄとの関係を、ｄ／ｗ≧１に設定すると、後述の実施形態１のところの説明から明らかなように、電界シャッターへの印加電圧Ｖの値を可及的に小さくできる。
【００３６】
そして、電界シャッターへの印加電圧Ｖの値を可及的に小さくすると、まず、第１に、電界シャッターを構成する複数の制御電極間の絶縁性を確保できる。第２に、電源規模を小さくできるので、その分、周囲へのノイズの発散を低減できる。
【００３７】
また、上記のように、電界シャッター部の印加電圧を、√Ｖ＞（ｗ／ｄ）・√［２Ｃ／（ｑ・Ｎ）］・√Ｔとなるように制御すると、加熱状態にある気体状インクが印字ヘッド内から不測に漏れ出すのを確実に防止することができるので、印字効率をより一層向上できる。
【００３８】
更には、インクカートリッジにインクの昇華温度を示す情報を記し、この情報をインク判別装置により読み取り、この読み取り結果に従い、電界シャッター部への印加電圧を制御する場合は、インクの種類等に拘らず、常時、加熱状態にある気体状インクが印字ヘッド内から不測に漏れ出すのを確実に防止することができる。即ち、使用するインクが異なり、インクの熱特性が異なる場合においても、柔軟に対処する事が可能になる。
【００３９】
【発明の実施の形態】
以下に本発明の実施の形態を図面に従い具体的に説明する。
【００４０】
（実施形態１）
図１は本発明画像記録装置の実施形態１を示す。この画像記録装置の基本構成は以下の通りである。印字ヘッド１は、正面断面視前後に長い長方形状をなし、その内部下方に粉体のインク３が収容されている。インク収容部の下方であって、
印字ヘッド１の底部に相当する部分には、インク３を加熱するための電気ヒータ13と放熱板13’とで構成される加熱装置２が配設されている。一方、インク収容部の上方には、加熱装置２により加熱され、気化した気体状のインク３”を帯電する帯電電極４が配設されている。この帯電電極４は50〜80μｍの細いワイヤ電極で構成されている。
【００４１】
加えて、印字ヘッド１の上壁１ａの左右方向中央部には、インク３”の吐出孔14が開口されている。図２に示すように、この吐出孔14はスリット溝で構成されている。そして、この吐出孔14の長辺の両側に電界シャッター８が設けられている。スリット14の長さＬは、印字ヘッド１がラインヘッドの場合、印字幅に対応した長に設定されており、例えばＡ４サイズで200ｍｍ、Ａ５サイズで140ｍｍ程度に設定されている。また、スリット14の幅Ｗは記録密度が150ｄｐｉとして、200μｍに設定されている。
【００４２】
印字ヘッド１の上方は、記録媒体12の搬送域になっており、この記録媒体12の背面側に背面電極11が水平に配設されている。背面電極11は帯電されたインク３”を記録媒体12上に誘導する。背面電極１１はほぼ電界シャッター８と同程度の大きさであり、また、プラスに帯電したインク３”を吸引するため、マイナスの電位、例えば−１ｋＶの電圧が印加される。
【００４３】
前記電界シャッター８は、共通電極８ａと、記録密度に対応した169μｍ間隔で櫛歯状に設けられた制御電極８ｂとで構成されている。共通電極８ａは接地されている。また、制御電極８ｂには、記録すべき画像データの電気信号に対応したコントロール部９からの出力信号により、通常50Ｖ〜１ｋＶ（Ｈｉｇｈレベル；“Ｈ”）又は０Ｖ（Ｌｏｗレベル；“Ｌ”）の電圧が印加される。つまり、制御電極８ｂの電圧が、例えば500Ｖ（“Ｈ”）の場合には、電界シャッター８はONとなり、制御電極８ｂから共通電極８ｂに向けて電界が発生するため、プラスに帯電したインク３”は電界シャッター８を通り抜けることができない。一方、制御電極８ｂの電圧が０Ｖ（“Ｌ”）の場合には、制御電極８ｂと共通電極８ａとの間には電界が発生しないので、インク３”は背面電極11による電界に引き付けられて電界シャッター８を通り抜けることができる。この場合、電界シャッター８はOFFとして機能している。このように、制御電極８ｂの電圧のON/OFFによりインク３”の吐出を断続的に制御できる。また、各々の画素に対応した制御電極８ｂの電位を制御することにより、気体状のインク３”の通過を画素単位で制御できる。
【００４４】
なお、インクの色材としては、有色のインクを用いる。例えば、イエローでは、アントライソチアゾール系、キノフタロン系、ピラゾロナゾ系、ピリドンアゾ系、スチリル系等を用い、マゼンダでは、アントラキノン系、ジシアノイミダゾール系、チアジアゾールアゾ系、トリシアノビニル系等を用い、シアンでは、アゾ系、アントラキノン系、ナフトキノン系、インドアニリン系等を用いることができる。また、本実施形態１では、粉体のインク３を使用しているが、液体のインクを使用することも可能である。各インク３を使用する場合は、それぞれ上記した効果を奏する。
【００４５】
以上の画像妃記録装置においては、共通電極８ａの電位をアースしているので、制御電極８ｂの電位が“Ｌ”の時は、インク３”が吐出する（論理的にアクティブな状態）。逆に、制御電極８ｂの電位が“Ｈ”の時は、インク３”が遮断されて（論理的に非アクティブな状態）、制御電極８ｂの電位とインク３”の吐出との関係は負論理の関係になるが、共通電極８ａの電位を、例えば500Ｖとして、制御電極８ａの電位を500Ｖ（“Ｈ”）又は０Ｖ（“Ｌ”）に変化させれば正論理の動作が行える。この点は、以下の実施形態においても同様である。
【００４６】
また、上記実施形態では、気体状のインク３”を正帯電としたが、帯電電極４にマイナスの電圧を印加することにより、負帯電としてもよい。但し、負帯電の場合は、オゾン等の有害物質の発生が正帯電より多いため、発生防止の対策が必要になる。
【００４７】
ところで、本発明の画像記録装置では、印字を行うには、前以て印字ヘッド１内を気体状のインク３”で満たしておく必要があるが、加熱されたインク３が気化することにより印字ヘッド１内の圧力は上昇する。そして、ヘッド内圧がヘッド外気圧以上となると背面電極11による電界がない場合においても、インク３”が吐出孔14から漏れ出てしまうので、上記の発明が解決しようとする課題のところで述べたように、電気信号に応じた断続的なインクの吐出を可能にするには、インク３”の確実な遮断を実現する必要がある。
【００４８】
そして、そのためには、ヘッド内圧力Ｐと、インク３”の粒子を印字ヘッド１内に閉じ込めておくために制御電極８ｂに印加しなければならない電圧Ｖとの関係を求める必要がある。以下にその導出手順について説明する。
【００４９】
まず、内圧上昇に伴うインク３”の吐出方向と電界シャッター８による電界Ｅの方向とは互いに直角なので、図３に示すように、それぞれを鉛直方向（座標ｚ）及び水平方向（座標ｘ）とする。インクの実際の吐出方向はこれら二つのベクトル和として与えられ、鉛直方向（座標ｚ）の等速度運動と水平方向（座標ｘ）の等加速度とに分解できる。
【００５０】
吐出孔14及びその近傍におけるｚ方向のインク粒子の速度成分は、インク粒子相互の衝突は考慮に入れないとすると、＋ｚ方向のみとなり、ｖ⁽ⁱ⁾ _z＞０である。ただし、ｉ＝１・・・，Ｎであり、Ｎは印字ヘッド１内のインク粒子の個数である。なお、吐出孔14の近傍以外においては、ｖ⁽ⁱ⁾ _x及びｖ⁽ⁱ⁾ _yは同様に、正負両方の値をとる。但し、添え字ｙは紙面に直行する方向（座標ｙ）を示し、ｖ⁽ⁱ⁾ _yはｙ方向におけるインク粒子の速度成分を示している。
【００５１】
従って、吐出孔14の近傍におけるインク粒子の速度は、下記（４）式で表される。
【００５２】
ｖ⁽ⁱ⁾＝（ｖ⁽ⁱ⁾ _x，ｖ⁽ⁱ⁾ _y，｜ｖ⁽ⁱ⁾ _z｜）…（４）
一方、吐出孔14におけるヘッド内圧力Ｐは、吐出孔14におけるインク粒子のｚ方向速度成分ｖ⁽ⁱ⁾ _zにより引き起こされるので、気体分子運動論より、ヘッド内圧力Ｐは、下記（５）式で表される。
【００５３】
Ｐ∝Σｍ⁽ⁱ⁾・ｖ⁽ⁱ⁾ _z ²…（５）
ここで、各インク粒子の質量が同じであるとすると、上記（５）式は下記（６）式に書き直せる。
【００５４】
【数３】

【００５５】
ここで、
【００５６】
【数４】

【００５７】
はｚ方向の速度二乗平均値である。従って、上記（６）より、ヘッド内圧力Ｐは、ｚ方向の速度二乗平均値に比例することがわかる。
【００５８】
ところで、気体伏のインク３”を理想気体と仮定すれば、その状態方程式は下記（７）式で表される。
【００５９】
Ｐ・Ｕ＝Ｃ・Ｔ…（７）
ここで、Ｕはインク３”が収容されているインクヘッドの容積、Ｃは気体定数、Ｔはインク加熱温度である。
【００６０】
Ｕ＝一定なので、Ｐ∝Ｔの関係が成立する。
【００６１】
従って、上記（６）式は、インク温度Ｔを用いて、下記（８）式で表される。
【００６２】
【数５】

【００６３】
鉛直方向、水平方向それぞれの方向について運動方程式を立てると、以下の様になる。
【００６４】
〔鉛直方向〕
図４において、帯電インク粒子ｉの質量、電荷、拡散速度をそれぞれｍ⁽ⁱ⁾，ｑ⁽ⁱ⁾，ｖ⁽ⁱ⁾ _z（Ｔ）とする。但し、ｉ＝１・・・，Ｎ、また、ｖ⁽ⁱ⁾ _z（Ｔ）は温度Ｔの関数であり、温度が高いほど大きくなる。
【００６５】
簡単のため、ｍ⁽ⁱ⁾＝ｍ、ｑ⁽ⁱ⁾＝ｑとする。重力の影響は無視し、初期条件：ｔ＝０でｚ＝０及びｖ⁽ⁱ⁾ _z＝ｖ₀ ⁽ⁱ⁾、さらに、速度ｖ⁽ⁱ⁾ _z＝ｃｏｎｓｔの等速度連動であるとすれば、インク粒子が電界シャッタ８ーを通過するのに要する時間ｔ₁は、ｄ＝ｖ⁽ⁱ⁾ _z・ｔ⁽ⁱ⁾ ₁の関係が成立するので、下記（９）式で表される。
【００６６】
ｔ⁽ⁱ⁾ ₁＝ｄ／ｖ⁽ⁱ⁾ _z…（９）
但し、ｄはインク３”の吐出方向に沿った電界シャッター部の長さである。
【００６７】
実際のインク粒子は速度分布を有するので、上記時間ｔ₁も分布をもったものとなる。
【００６８】
〔水平方向〕
図５において、ｘ＝０で静かに帯電インク粒子を放した場合を考える。
【００６９】

とすると、加速度αは、Ｆ＝ｑ・Ｅ＝ｍ・αの関係が成立するので、下記（10）で表される。但し、Ｆは帯電インク粒子に作用する力である。また、Ｅは電界の大きさ示す。
【００７０】
α＝（ｑ・Ｅ）／ｍ…（10）
また、Ｅ＝Ｖ／ｗの関係が成立するので、上記（10）式は下記（11）式に書き直せる。
【００７１】
α＝（ｑ・Ｖ）／（ｍ・ｗ）…（11）
但し、Ｖは電界シャッター８の印加電圧である。
【００７２】
従って、ｘ＝ｗに到達するのに要する時間をｔ₂とすると、分離された電界シャッター間の幅ｗは、下記（12）式で表される。
【００７３】
ｗ＝（１／２）・α・ｔ₂ ²…（12）
ここでは、電界の影響によるもののみを考慮に入れるため（12）式において、インク粒子のｘ方向速度成分ｖ_xは無視した。
【００７４】
この（12）式に上記（11）式を代入して整理すると、ｔ₂は下記（13）式で表される。
【００７５】
ｔ₂＝√［（２ｍ・ｗ²）／（ｑ・Ｖ）］…（13）
以上より、帯電インク粒子が電界シャッター８の効果により確実に遮断されるためには、圧力上昇によって気体状インク３”が長さｄの吐出孔14を通過する時間ｔ₁よりも電界の作用によって電極間隔ｗの電界シャッター８間を移動する時間ｔ₂が短い、即ち、ｔ₁＞ｔ₂である必要があるので、下記（14）式の関係が成立する必要がある。
【００７６】
ｄ／ｖ⁽ⁱ⁾ _z＞√［（２ｍ・ｗ²）／（ｑ・Ｖ）］…（14）
上記（14）式を変形すると、下記（15）式のようになる。
【００７７】
√Ｖ＞ｖ⁽ⁱ⁾ _z・√［（２ｍ・ｗ²）／（ｑ・ｄ²）］…（15）
この不等式を満足する領域を図示すると、図６のようになる。実線は√Ｖ＝Ｄ・ｖ⁽ⁱ⁾ _zを表している。
【００７８】
但し、
【００７９】
【数６】

【００８０】
とおいた。
【００８１】
図６より、Ｄ＝一定の時、ｖ⁽ⁱ⁾ _zの増加と共に、Ｖは２次関数的に大きくなることがわかる。また、ｖ⁽ⁱ⁾ _z＝一定であれば、Ｄが小さいほどＶは小さいことがわかる。つまり、ｍ及びｑを一定とすれば、Ｄは（ｗ／ｄ）の関数となるが、ｗ／ｄは、印字ヘッド１の設計段階で決定される定数であるので、できるだけ小さくなるように設計する。これは、ヘッド吐出部、即ちシャッター部における吐出孔14の長さｌ及びその幅ｗの幾何学的サイズが異ならない限り、印字ヘッド１のその他の部分の形状が変わっても不変である。
【００８２】
一方、ｖ⁽ⁱ⁾ _zは、印字ヘッド１の構造（容積等）に加えインク加熱温度（このインク加熱温度はインク昇華温度に依存する）、印字ヘッド１内の温度等の動作条件及び環境によって最終的に決まるものであるので、これらが変われば変わり得るが、仮に、ｖ⁽ⁱ⁾ _zが同じであるとすれば、ｗ／ｄを小さくすることにより、電界シャッター８への印加電圧Ｖを小さくすることができる。
【００８３】
例えば、記録密度が150ｄｐｉの場合、電界シャッター８の幅（吐出孔14の幅）ｗは、ｗ＝200μｍであるので、電界シャッター部長さｄ＝100μｍを有する印字ヘッド１における電界シャッター８への印加電圧をＶ₁₀₀とすれば、ｄ＝200μｍ及びｄ＝400μｍの印字ヘッド１への印加電圧Ｖ₂₀₀、Ｖ₄₀₀は、それぞれＶ₂₀₀＝Ｖ₁₀₀／４、Ｖ₄₀₀＝Ｖ₁₀₀／１６で与えられる。即ち、電界シャッター８への印加電圧をそれぞれ１／４、１／１６に低減することができる。
【００８４】
ところで、上記のように、ｖ⁽ⁱ⁾ _z（Ｔ）は速度分布をもっており、更に温度の関数でもある。従って、全てのインク粒子、特に速度の小さい粒子に対し上記（14）式が成り立つ様にすることは実用的でないので、例えば、ｖ⁽ⁱ⁾ _zの二乗平均値の平方根
【００８５】
【数７】

【００８６】
又はｖ⁽ⁱ⁾ _zの平均値
【００８７】
【数８】

【００８８】
或いはｖ⁽ⁱ⁾ _zの最大分布値ｖ_m以上のｖ⁽ⁱ⁾ _zに対しては少なくとも（14）式が成り立つようにＶの値を決めるようにする。ここで、これら三者の間には、下記（16）式の関係が成立するので、
【００８９】
【数９】

【００９０】
二乗平均値の平方根を用いて、
【００９１】
【数１０】

【００９２】
とする。
【００９３】
ここで、上記（17）式を電界シャッター８への印加電圧Ｖについて書き直すと、下記（18）式の関係が成立する。
【００９４】
√Ｖ＞（ｗ／ｄ）・√（２ｍ／ｑ）・√（ｖ_z ²）…（18）
上記（５）式より、ｖ_z ²は圧力Ｐに比例するので、電界シャッター８への印加電圧電圧Ｖとヘッド内圧力Ｐは、線形の関係にあることがわかる。
【００９５】
（18）式より、Ｖを小さくするには、
（ｉ）ｗ／ｄ
（ii）ｍ
（iii）１／ｑ
（iv）√（ｖ_z ²）あるいはヘッド内圧力Ｐ
を小さくすればよいことがわかる。
【００９６】
それぞれに対し、以下の実施策が考えられる。
【００９７】
（ｉ）シャッターサイズ ｄ／Ｗ≧１とする
（ii）気体状のインク粒子質量を小さくする
（iii）帯電量を多くする
（iv）ヘッド内圧力の上昇を抑える（インク加熱温度を低くする、即ち低昇華温度のインクを使用する）
このような実施策のうち、本発明は（ｉ）の実施策を採用しており、具体的には請求項１に記載された画像記録装置において採用している。
【００９８】
ここで、電界シャッター８への印加電圧を小さくできることの利点は、まず第１に、制御電極８ｂ間の絶縁性を確保できる。第２に、電源規模を小さくでき、その分、周囲へのノイズの発散を低減できるので、画像記録装置の信頼性を向上できる。
【００９９】
次に、図７及び図８に従い、本実施形態１の画像記録装置の制御系の構成及び印字動作について説明する。ＣＰＵ20は、この画像記録装置の制御中枢となるものであり、図７に示すように、加熱装置２の加熱制御、帯電電極４と背面電極11とで構成される吐出装置への通電制御及びコントロール部９と電界シャッター８で構成される吐出制御装置を制御し、これらの制御内容により、印字ヘッド１の印字動作を制御する。以下にその詳細を説明する。
【０１００】
ＣＰＵ20から印字ヘッド１に対して、図８（ａ）に示す波形のヘッド制御信号が与えられると、同図（ｂ）に示すように、加熱装置２はヘッド制御信号の立ち上がり（Ａ点）をトリガとして、Ａ点より所定時間経過後のＢ点において、電気ヒータ13を駆動する。また、この時、帯電電極４に＋２〜５ｋＶの電圧が印加される（同図（ｃ）参照）。
【０１０１】
加熱装置２が駆動されると、固体又は液体状のインク３が加熱され、インク３の昇華温度Ｔ_g以上になるとインク３は気化されて気体状のインク３”になる。そして、インク３”は時間の経過と共に増加していき、Ｃ点において閾値に達する（同図（ｄ）参照）。ここで、閾値とは、吐出に十分な気体状インク量のことを意味し、閾値以上になると印字可能状態になる。この状態は高圧となったインク３”で印字ヘッド１内が満たされていることを意味する。
【０１０２】
なお、加熱装置２は、インク昇華温度Ｔ_g以上のある温度Ｔとなるように一定制御される。このため、Ｔ＝Ｔ_g＋△Ｔの関係が成立する。例えば、Ｔ_g＝140℃であれば、Ｔ＝155℃とする。
【０１０３】
また、加熱装置２の駆動開示時点は、上記Ｂ点と同じでなくともよく、例えばＣ点以前のＢ′（同図（ｆ）参照）において、電界シャッター８の全ての制御電極８ｂに50〜１ｋＶ程度の電圧を印加し、電界シャッター８をON状態にすればよい。即ち、この状態では、インク３”の吐出が阻止されるからである。
【０１０４】
同図（ｅ）に示すように、印字可能状態となった時間Ｄ点において、ＣＰＵ20からコントロール部９に印字開始／終了信号が出力される。なお、この実施形態１においては、インク３”が閾値を越えたか否かの判断は直接的には測定してしないので、電気ヒータ13を加熱してからの時間又は印字ヘッド１の温度を測定してＣＰＵ20が推測する。そして、このようにして得られた間接データを、予め目標値として入力されている時間又は温度データと比較することにより、ＣＰＵ20が印字開始／終了信号を発生する。
コントロール部９は、印字開始／終了信号の立ち上がりをトリガとして、図示しない画像メモリから画像データの送出を要求し、データの転送完了と共に電界シャッター８に対して、同図（ｆ）に示すＤ′点で画像データに応じたON/OFF信号を出力する。電界シャッター８は、500Ｖの電圧を供給する図示しない電源装置に接続されており、画像データに応じて電界シャッター８に500ＶがON/OFFされる。
【０１０５】
また、電界シャッター８がON/OFFを開始するＤ′点において、背面電極11に−１ｋＶの電圧が印加される（同図（ｇ）参照）。印字中は印字開始／終了信号は“Ｈ”レベルに維持されている。
【０１０６】
印字動作が終了すると、同図（ｅ）に示すＥ点において、印字開始／終了信号は“Ｌ”レベルに立ち下がり、この立ち下がりをトリガとして、加熱装置２、帯電電極４及び背面電極11は全てOFF状態になる。加熱装置２が電気ヒータ13への通電を停止しても、インク３”はすぐには冷却されず、印字ヘッド１内に残存するので、印字終了後、閾値Ｆ点以降のＥ′点まで電界シャッター８を強制的にONしておき、インク３”が外部に漏れ出すのを阻止する（同図（ｆ）参照）。そして、Ｅ′点以降、次の印字動作が開始される迄は電界シャッター８はOFFされる。
【０１０７】
（実施形態２）
次に、本発明画像記録装置の実施形態２について説明する。この実施形態２では、電界シャッターへの印加電圧Ｖ（以下電界シャッター電圧Ｖと称する）とインク加熱温度Ｔとの関係に着目し、両者の関係式に基づき電界シャッター電圧Ｖを制御することにより、インク３”の漏れ出しを防止するようにしたものである。
【０１０８】
まず、電界シャッター電圧Ｖとインク加熱温度Ｔとの関係を求める。
【０１０９】
上記（18）式において、左辺＝右辺の場合について考えると、下記（19）式が成立する。
【０１１０】

但し、
【０１１１】
【数１１】

【０１１２】
とおいた。
【０１１３】
（19）式の両辺を２乗すると、
Ｖ_EQUAL＝（Ｗ／ｄ）²・ｂ²・Ｔ…（20）
となる。
【０１１４】
ここで、電界シャッター電圧Ｖは、Ｖ＞Ｖ_EQUALであるので、下記（21）式で表すことができる。
【０１１５】

ここで、ΔＶは、正の定数であり、環境温度、帯電量ｑ等のばらつきを考慮して決定する。また、
【０１１６】
【数１２】

【０１１７】
とおいた。
【０１１８】
上式より、電界シャッター電圧Ｖとインク加熱温度Ｔとの間には、線形の関係があることがわかる。
【０１１９】
ここで、インク加熱温度Ｔは、インクの昇華温度Ｔ_gを基に、下記（22）式で表される。
【０１２０】
Ｔ＝Ｔ_g＋ΔＴ…（22）
例えば、Ｔ_g＝140℃の時、ΔＴ＝15℃として、Ｔ＝155℃とする。従って、加熱装置２は、Ｔ_g＝140℃＝一定となるように電気ヒータ13に加える電力を制御する。
【０１２１】
この時、制御装置の安定度及び外乱の影響、周囲温度、印字濃度の違いによる気体状インク３”の消費量の変化等によって、インク加熱温度Ｔが変動する場合があるが、その温度変動が小さいと分かっていれば、その分を△Ｖに含ませておき、Ｖ＝一定となるように制御する。また、帯電量の変動により、ｑ、従って定数ａが変動することがあるが、この場合も、その値が小さければ△Ｖに含ませておき、Ｖ＝一定としてよい。
【０１２２】
しかし、インク加熱温度Ｔの変動が大きい場合には、（21）式に基づきＶを調整するような制御を行う。
【０１２３】
以下に図９及び図10を参照しながら、その制御の仕方について説明する。図９はこの実施形態２に係る画像記録装置の制御系の構成を示しており、この制御系は、インク判別装置21を備えている他は、上記の実施形態１の画像記録装置の制御系と同一構成になっている。
【０１２４】
ここで、インク判別装置21は、インク３を収容するインクカートリッジに表示されたインク情報を読み取り、インク判別信号をＣＰＵ20に与える。そうすると、ＣＰＵ20がインク判別信号からインク昇華温度Ｔ_gを割り出して後述の制御を行う。なお、実施形態１と対応する部分には同一の符号を付して説明は省略する。
【０１２５】
上記（21）式において、△Ｖは既知量（本実施形態２では、例えば４５Ｖに設定）であるので、図10から明らかなように、あるインク加熱温度Ｔ１において電界シャッター電圧ＶがＶ１であることが分かっていれば、定数ａを求めることができるので、インク加熱温度ＴがＴ２の時の電界シャッター電圧Ｖ２は、（21）式に従い求められる。例えば、Ｔ１＝155℃、Ｖ１＝200Ｖ、△Ｖ＝45Ｖの時、これらの値を（21）式に代入すれば、ａ＝１（Ｖ／℃）となるので、Ｔ２＝140℃の時は、Ｖ２＝185Ｖとなるように電界シャッター電圧Ｖを制御する。このような状況は、上記の場合の他に、例えば、インクの改良が行われて、その昇華温度が低くなった場合、あるいは、異なるメーカーのインクを使用する場合、あるいは、カラー印字において各色間におけるインク昇華温度が異なる場合などに発生する。よって、異なる熱物性値をもつ複数のインクに対して、その昇華温度Ｔ_gが分かっている場合に、（21）式に従い電界シャッター電圧を制御すれば、各インクに対して適切な電界シャッター電圧を印加することができる。この場合、加熱装置２はインク昇華温度Ｔ_gに応じてインク加熱温度Ｔを変化するよう制御されることは言うまでもない。つまり、△Ｔ＝15℃＝一定としておいて、関係式Ｔ＝Ｔ_g＋△Ｔ、即ち上記（22）式によってインク加熱温度Ｔを与える。
【０１２６】
ここで、インク３は一般にカートリッジと呼ばれる容器に収められており、カートリッジにインクの種類を表す情報を持たせておけば、インクの識別は可能である。即ち、インクカートリッジへの情報の記入の方法により、情報を識別する方法は異なるが、物理的な凹凸に対する情報に対してはレバー等の機械的な機構を用いることができ、また、バーコードのような印刷情報であれば、フォトインタラプタ等の光学的素子を利用することができる。具体的には、物理的な凹凸情報を用いる場合には、例えば、２つの凹凸が選択的に形成されるようにしておき、それぞれの位置に対して、レバーが当接するようにしておく。各レバーは、２値のスイッチとして働き、凹凸がない時、レバー・スイッチがOFF、また、凸部あるいは凹部があれば、ONとすれば、２²＝４つの情報を持たせることができるので、それぞれの情報をＴ_g＝140℃、145℃、150℃、155℃に対応させれば、４種類のインクに対する情報を持たせることができる。さらに、３つの凹凸が選択的に形成できるようにしておけば、２³＝８つのインク情報を持たせられる。
【０１２７】
同様にして、２本のバーコードが選択的に形成されるようにしておき、各位置に反射型のフォトインタラプタを配置する。バーコードがない時、フォトインタラプタ出力がOFF、バーコードがある時、ONとすれば、２²＝４種類のインクに対応することができる。
【０１２８】
上記のようなインク情報が記入されたインクカートリッジが印字ヘッド１に装着されると、インク判別装置21はインク情報を読み取り、インク判別信号をＣＰＵ20に出力する。ＣＰＵ20は、インク判別信号に基づきインクカートリッジに収納されたインク３のインク昇華温度Ｔ_gを割り出し、上記（22）式のＴ＝Ｔ_g＋△Ｔによって、インク加熱温度Ｔを決定する。また、上記（21）式のＶ＝ａ・Ｔ＋△Ｖによって、電界シャッター８の制御電極８ｂに印加する電圧Ｖを決定する。△Ｔとして、例えば、15℃とする。
【０１２９】
本実施形態２においては、インク加熱温度Ｔを、△Ｔ＝一定として（22）式により求めたが、予めインク昇華温度Ｔ_gに対するインク加熱温度Ｔをルックアップテーブル（ＬＵＴ）として作成しておき、このＬＵＴを参照してインク加熱温度Ｔを決定するようにしてもよい。また、電界シャッター８の制御電極８ｂに印加する電圧Ｖの決定に際しても、インク昇華温度Ｔ_gに対する電界シャッター電圧ＶのＬＵＴを作成しておいて、これを参照して決定してもよい。
【０１３０】
上記手順でインク加熱温度Ｔ及び電界シャッター電圧Ｖを決定した後、ＣＰＵ20は印字ヘッド１の各装置に対して、印字開始信号を出力する。この開始信号は、電圧印加／解除のタイミングを与えるものである。図９において、この印字開始信号は点線で示されている。
【０１３１】
ＣＰＵ20は、加熱装置２に決定したインク加熱温度Ｔでインク３を加熱させるべく加熱制御信号を入力する。これにより、加熱装置２が上式の温度となるよう電気ヒータ13を駆動する。また、ＣＰＵ20は、帯電電極４に帯電開始信号を入力する。これにより、帯電電極４に２〜５ｋＶの電圧が印加され、インク３”が帯電される。そして、気体状のインク量が閾値を越える前の時点で、コントロール部９に電界シャッター電圧制御信号を入力する。これにより、電界シャッター８の全ての制御電極８ｂに電圧が印加され、つまり電界シャッター８がONし、インクの漏れを防止する。そして、印字可能状態となった時点で、ＣＰＵ20は背面電極11に電圧印加開始信号を出力して、背面電極11に−１ｋＶの電圧を印加する。そして、これと同時に、画像データに応じて電界シャッター８がON/OFFされ、これで印字動作が開始される。
【０１３２】
印字動作が終了すると、ＣＰＵ20は上記各装置に対して、制御信号を出力する。即ち、加熱装置２、帯電電極４及び背面電極11に対しては、解除信号を出力して一斉に電圧印加を終了し、気体状のインク３”の生成及び吐出を抑止する。また、電界シャッター８に対しては、印字終了後直ちに全ての制御電極８ｂに電圧を印加してインク３”の漏れを防止する。気体状の帯電インク量が、閾値を下回った任意の時点でようやく電界シャッター電圧Ｖは解除される。
【０１３３】
以上のように、インクを収容するインクカートリッジにインク情報を記録或いは形成しておくことにより、複数の物性値を有する各インク３に対して、最適なインク加熱温度Ｔ及び電界シャッター電圧Ｖを供給することができる。
【０１３４】
以下にその理由について説明する。
【０１３５】
説明の都合上、二種類のインク、すなわち、インク昇華温度がＴ_g1及びＴ_g2（Ｔ_g1＞Ｔ_g2）であるインクに対して、最適な加熱温度をそれぞれＴ₁＝Ｔ_g1＋ΔＴ，Ｔ₂＝Ｔ_g2＋ΔＴ（したがって、Ｔ₁＞Ｔ₂），また、最適な電界シャッター電圧ＶをそれぞれＶ₁，Ｖ₂（Ｖ₁＞Ｖ₂）とする。ただし、電界シャッター電圧Ｖは、前出（２１）式で与えられるものとする。
【０１３６】
昇華温度Ｔ_g1を有するインク３に対して最適化されている画像記録装置において、より低い昇華温度Ｔ₂を有するインクを用いた時、同じ加熱温度Ｔ₁でインクを加熱するので、インクが過剰に加熱されることになり、電力が無駄になるどころか、最悪の場合インクが分解してしまう。
【０１３７】
また、昇華温度Ｔ_g2を有するインクに対して最適化されている画像記録装置において、より高い昇華温度Ｔ_g1を有するインクを用いた時、インク判別装置２１を備えていない場合には、最適加熱温度Ｔ₁よりも低い温度Ｔ₂でインクを加熱するので、インクが十分に昇華しない。
【０１３８】
そこで、インクの昇華温度に応じて、加熱装置２を適宜制御し、インク加熱温度を変化する必要が生じてくる。しかし、加熱装置２のみを制御するだけでは、以下に示す理由で別の問題が発生する。
【０１３９】
つまり、昇華温度Ｔ_g1を有するインク３に対して最適化されている画像記録装置において、より低い昇華温度Ｔ_g2を有するインクを用いた時に、以上の不具合を解消するために、加熱温度をＴ₁からＴ₂に変更した場合、本来Ｖ₂の電圧でよいところ、Ｖ₁＞Ｖ₂なる余分の電圧を印加してしまっている。これは、装置の低消費電力化を考えた場合、デメリットとなる。
【０１４０】
また、昇華温度Ｔ_g2を有するインクに対して最適化されている画像記録装置において、より高い昇華温度Ｔ_g1を有するインクを用いた時に、以上の不具合を解消するために、加熱温度をＴ₂からＴ₁に変更した場合、ヘッド内の圧力が上昇するので、電界シャッター８に従来と同じ電圧Ｖ₂（＜Ｖ₁）を印加していたのでは電界シャッター８が完全に動作しないためインク漏れが生じるという恐れがある。
【０１４１】
しかしながら、本発明における画像記録装置においては、インクの種類に応じて、インク加熱温度及び電界シャッター電圧の両方を最適となるよう制御しているので、インクの過剰加熱あるいは加熱不足、また、消費電力の増加やインク漏れといった心配がない。
【０１４２】
つまり、インク昇華温度に応じて、インク加熱温度Ｔが、Ｔ＝Ｔ_g＋ΔＴとなるように加熱装置を制御するとともに、電界シャッター部のＯＮ時の印加電圧Ｖが、Ｖ＝ａ・Ｔ＋ΔＶとなるように制御を行っているので、常に最適な駆動条件で各装置を駆動することができる。
【０１４３】
（その他の実施形態）
本発明画像記録装置が適用される実施形態は、上記実施形態１及び実施形態２のものに限定されるわけではなく、以下に示すように各種の変更が可能である。
即ち、図11に示されるような、帯電したインク３’を気化して気体状インク３”を生成するタイプの画像記録装置にも同様に適用することができる。また、電界シャッター８の構造についても、図12に示されるような、複数の吐出孔14を備えたタイプのものについても同様に適用できる。更には、摩擦帯電方式を採用する画像記録装置にも同様に適用できる。
【０１４４】
【発明の効果】
以上の本発明画像記録装置によれば、気体状のインクを断続的に吐出させて印字を行うものであるので、必要、かつ十分な吐出量で印字を行うことができるので、ランニングコストを低減できる利点がある。また、加熱装置、帯電電極及び電界シャッターが一体となった印字ヘッドにより構成されているため、電界シャッターで阻止されたインクが電界シャッターへ付着して目詰まりを発生する度合いを低減でき、付着したインクの回収装置やクリーニング装置が不要になるので、装置構成の小型化に大いに寄与できる利点がある。
【０１４５】
更には、上記の効果の他に、
特に、請求項１記載の画像記録装置によれば、電界シャッターへの印加電圧Ｖの値を可及的に小さくできるので、電界シャッターを構成する複数の制御電極間の絶縁性を確保できる、電源規模を小さくできるので、その分、周辺機器へのノイズの影響を低減でき、信頼性の向上が図れる、といった効果を奏することができる。
【０１４６】
また、特に請求項２記載の画像記録装置によれば、加熱状態にある気体状インクが印字ヘッド内から不測に漏れ出すのを確実に防止することができるので、印字効率をより一層向上できる。
【０１４７】
また、特に請求項３〜５記載の画像記録装置によれば、インクの種類等に拘らず、常時、加熱状態にある気体状インクが印字ヘッド内から不測に漏れ出すのを確実に防止することができるので、使用するインクが異なり、インクの熱特性が異なる場合においても、柔軟に対処する事が可能になる。このため、特にカラー印字を行う画像記録装置に適用する場合に有効なものになる。
【図面の簡単な説明】
【図１】実施形態１に係る本発明画像記録装置の一部を切欠いて示す概略正面図。
【図２】 実施形態１に係る本発明画像記録装置の電界シャッター部の詳細を示す斜視図。
【図３】電界シャッター部における帯電インク粒子に作用する力を示す説明図。
【図４】電界シャッター部における帯電インク粒子に作用するインク吐出方向の力を示す説明図。
【図５】 電界シャッター部における帯電インク粒子に作用する電界方向の力を示す説明図。
【図６】電界シャッター電圧とインク粒子の鉛直方向の速度成分との関係を示すグラフ。
【図７】実施形態１に係る本発明画像記録装置の制御系を示すブロック図。
【図８】実施形態１に係る本発明画像記録装置の印字動作を示すタイミングチャート。
【図９】実施形態２に係る本発明画像記録装置の制御系を示すブロック図。
【図１０】電界シャッター電圧とインク加熱温度との関係を示すグラフ。
【図１１】本発明が適用される画像記録装置の他の実施形態を示す一部切欠き概略正面図。
【図１２】電界シャッターの他の実施形態を示す斜視図。
【図１３】 画像記録装置の一従来例を示す断面図。
【符号の説明】
１ 印字ヘッド
２ 加熱装置
３ 粉体のインク
３” 気体状のインク
４ 帯電電極
８ 電界シャッター
８ａ 共通電極
８ｂ 制御電極
９ コントロール部
11 背面電極
12 記録媒体
14 吐出孔
20 ＣＰＵ
21 インク判別装置
ｄ インクの吐出方向に沿った電界シャッター部の長さ
Ｖ 電界シャッター電圧
ｗ 吐出孔により分離されている電界シャッター間の幅[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image recording apparatus such as a copying machine, a facsimile machine, or a printer. More specifically, gaseous ink is intermittently ejected from ejection holes to selectively adhere or penetrate on a recording medium (recording paper). The present invention relates to an image recording apparatus that forms an image.
[0002]
[Prior art]
As a conventional example of an ejection type image recording apparatus that performs printing by ejecting ink, there are image recording apparatuses such as an ink jet system and an electrostatic recording system. In the ink jet system, printing is performed by pressurizing liquid ink stored in an ink tank using a piezoelectric element or the like by an electrical signal corresponding to image data and ejecting the ink from a nozzle. In the electrostatic recording method, powder or liquid (mist-like) ink is charged and discharged from the nozzle by an electrostatic suction force, and a shutter provided at the tip of the nozzle is received by an electrical signal corresponding to image data. Printing is performed by opening and closing.
[0003]
As another method, there is a technique of ejecting gas-like ink and depositing it on a recording medium. In this method, since gaseous ink is ejected, the nozzles are less clogged and the pixels are recorded in a molecular state. Therefore, it is possible to perform printing with high resolution, excellent gradation, and less bleeding. There are advantages.
[0004]
As a conventional example of this system, there is an image recording apparatus disclosed in Japanese Patent Publication No. 56-2020. FIG. 13 shows this image recording apparatus. The printing operation in this image recording apparatus is performed as follows. The ink 103 stored in the print head 100 is heated and vaporized by a heating device 102 including an electric heater 113 and its power source 114, and the vaporized gaseous ink 103 'is ejected. When the gaseous ink 103 ′ is ejected and passes through the charging electrode 104 at the same time, it is charged by a power source 105 inserted between the charging electrode 104 and the print head 100. The charged gaseous ink 103 ′ is focused by the electric field lenses 106 and 107, and then, when passing through the electric field shutter 115, the discharge amount is controlled by the signal source 110, flies toward the back electrode 111, and the recording medium Form an image on top.
[0005]
[Problems to be solved by the invention]
However, in the ink jet method, since air enters the ink tank, pressurization cannot be performed sufficiently and printing cannot be performed, or liquid ink is used, so clogging of ink at the nozzles or on the recording medium. There has been a problem that the image quality is deteriorated due to ink bleeding. In addition, in the electrostatic recording method, when the ink is powder, the ink particles are hardened due to blocking and clogging occurs. When the ink is liquid, clogging and bleeding are the same as those of the ink jet method. There was a point.
[0006]
Further, in the above-described method for ejecting gas-like ink, gaseous ink is always ejected, so that the ink not used for recording is wasted and the running cost is increased. was there. Furthermore, since a device for collecting unused gaseous ink and a device for cleaning the periphery of the electric field shutter 115 are required, there is a problem in downsizing and maintainability of the device. Further, the movement of the gaseous ink 103 ′ from the print head 100 to the charging electrode 104 is caused by the volume expansion due to the evaporation of the ink 103, the pressure in the print head 100 is increased, and the gaseous ink 3 ′ is ejected. Because of this, there is a problem that the responsiveness is poor. Furthermore, since the ejection amount differs depending on the amount of the ink 103 in the print head 100, there is a problem in that this effect causes deterioration in print quality such as density unevenness.
[0007]
Therefore, in order to solve the above problems, the applicant of the present application intermittently ejects gaseous ink in accordance with an electrical signal corresponding to the image data to be recorded, and adheres or permeates the image on the recording medium. Japanese Patent Application No. 7-49778 and Japanese Patent Application No. 7-234323 have been proposed previously.
[0008]
The configuration of these image recording apparatuses will be described below with reference to FIG. As shown in FIG. 1, powder ink 3 is stored inside the print head 1. The print head 1 includes a heating device 2 including an electric heater 13 for heating the ink 3 and a heat radiating plate 13 ', a charging electrode 4 for charging the heated and vaporized gaseous ink 3 ", and a gaseous ink 3". Are discharged from the print head 1 and a plurality of discharge holes 14 (see FIG. 12) and an electric field shutter 8 disposed on both sides of the discharge holes 14 are provided.
[0009]
At the time of printing, the ink 3 is heated and vaporized by the heating device 2. In this state, a voltage of +2 to 5 kV is applied to the charging electrode 4. As a result, corona discharge occurs in the direction of the grounded heating device 2, so that the gaseous ink 3 ″ is charged with positive ions. Subsequently, it is disposed on the back side of the printing surface of the recording medium 12. A voltage of −0.5 to 2 kV is applied to the back electrode 11 to induce gaseous ink 3 ″ on the recording medium 12.
[0010]
Here, the electric field shutter 8 is configured such that a voltage of 50 V to 1 kV is applied to the electrodes according to an output signal of the control unit 9 corresponding to an electric signal of image data to be recorded. It is possible to control the passage of 3 ″ or to block the passage. In other words, the ink 3 ″ is intermittently ejected by this control content.
The gaseous ink 3 ″ that has passed through the electric field shutter 8 is guided to the back electrode 11 and adheres onto the recording medium 12, whereby printing is performed. Here, the ink 3 before heating is not limited to powder. In the case of using liquid ink, there is an advantage that it has excellent transportability and requires less energy for vaporization.
[0011]
Next, the configuration of an image recording apparatus according to another embodiment proposed by the applicant of the present application in the above application will be described with reference to FIG. Liquid ink 3 ′ is stored inside the print head 1. The print head of the image recording apparatus of the present embodiment is composed of a heating device 2 similar to the above, two charge injection electrodes, a charging electrode 4 for charging ink 3 ', and an ejection hole 14 consisting of a slit hole (see FIG. 2). ) And an electric field shutter 8 disposed on both sides of the long side of the discharge hole 14.
[0012]
The printing operation is performed as follows. First, the potential difference between both ends of the charging electrode 4 is set to 2 to 5 kV, a charge is injected into the ink 3 ′, and the positive ions are charged. Subsequently, the charged ink 3 ′ is vaporized by the heating device 2. As a result, the charged ink becomes gaseous ink 3 ″. Subsequently, a voltage of −1 kV is applied to the back electrode 11 disposed on the back side of the printing surface of the recording medium 12 to record the ink 3 ″. Guide on medium 12.
[0013]
Here, the electric field shutter 8 is usually applied with a voltage of 50 V to 1 kV, and controls the passage and blocking of the ink 3 ″. That is, the electric field shutter 9 corresponds to the electric signal of the image data to be recorded. The potential of the comb-like electrode corresponding to each pixel is controlled by the output signal of the control unit 9, and the passage of the ink 3 "is controlled by this control. That is, the ink 3 ″ is intermittently ejected according to this control content.
[0014]
The ink 3 ″ that has passed through the electric field shutter 8 is guided to the back electrode 11 and adheres to the recording medium 12, and printing is performed with this. In this embodiment, powder ink can also be used. However, when liquid ink is used, there is an advantage in that charging unevenness is less than that of powder, and efficient charging is possible, whereas in the case of powder ink, leakage from the print head 1 is possible. In this embodiment, the ink is charged by injecting a charge into the ink 3 ′, but it is also possible to charge the ink by other methods, for example, frictional charging.
[0015]
As described above, in the image recording apparatus previously proposed by the applicant of the present application, the ejection of the gaseous ink 3 ″ is controlled in the print head 1 in accordance with the image data to be recorded. Is not discharged, the printing efficiency is excellent.
[0016]
In addition, since the heating device 2, the charging electrode 4, and the electric field shutter (electric field shutter part) 8 are integrated, the ink 3 "blocked by the electric field shutter part adheres to the electric field shutter part. The degree of clogging can be reduced, and a collecting device and a cleaning device for the adhering ink 3 ″ are not required.
[0017]
In particular, since the former embodiment is configured to charge the ink after vaporization, the ink can be charged even if it is an insulating substance, so that there is an advantage that the types of ink to be applied can be expanded. Further, since it is hardly affected by the environment, there is an advantage that stable charging is possible.
[0018]
On the other hand, in the latter embodiment, since solid or liquid ink is charged and then heated to be a gas, no harmful substances such as ozone are generated. For this reason, since it is not necessary to take measures against ozone, there is an advantage that it can contribute to the downsizing of the apparatus configuration.
[0019]
Further, in the case where the ejection holes 14 for the ink 3 ″ are formed by slit grooves, the ability to prevent clogging of the ink 3 ″ can be improved and the structure can be simplified as compared with the case where a large number of ejection holes 14 are provided. There is.
[0020]
As described above, the image recording apparatus previously proposed by the applicant of the present application has the above-described various advantages. However, there is still room for improvement in the following points.
[0021]
(1) In order to perform printing in this image recording apparatus, it is necessary to fill the inside of the print head 1 with gaseous ink 3 ″ in advance, but the inside of the print head 1 is caused by evaporation of the heated ink. If the internal pressure of the head becomes equal to or higher than the external pressure of the head, even if there is no electric field due to the back electrode 11, the ink 3 ″ may leak out of the ejection holes 14 due to the pressure difference. For this reason, in order to enable intermittent ink discharge in accordance with the electrical signal, it is necessary to realize reliable ink blocking.
[0022]
As an example of the countermeasure, a method of increasing the ON-state voltage V applied to the control electrode 8b of the electric field shutter 8 (0V when OFF) can be considered. By the way, since the control electrode 8b is formed at an interval according to the resolution, for example, at an interval of about 200 μm at 150 dpi, if V = 1 kV, it becomes 5 kV / mm, which greatly exceeds the dielectric breakdown voltage. Therefore, the upper limit of the voltage V applied to the control electrode 8b of the electric field shutter 8 needs to be suppressed below the breakdown voltage.
[0023]
(2) In order to perform color printing, it is necessary to use a plurality of types of ink obtained by adding yellow, magenta, cyan, or black to this, but the sublimation temperatures of these inks are different. For this reason, in order to cope with a plurality of inks having different sublimation temperatures, it is necessary to adjust the ink heating temperature according to the sublimation temperature of the ink to be used. Then, since the pressure in the head changes with the change in the head internal temperature, that is, the change in the heating temperature, the ON voltage value applied to the control electrode 8b of the electric field shutter 8 also depends on the ink heating temperature, that is, the type of ink. It is necessary to adjust accordingly.
[0024]
By the way, in the image recording apparatus previously proposed by the applicant of the present application, since the improvement described in the above (1) and (2) has not been considered appropriately, such a problem has not been solved. is the current situation.
[0025]
The present invention has been made in view of such circumstances, and certainly prevents the leakage of ink caused by heating as well as the effects of the image recording apparatus previously proposed by the applicant of the present application. Another object of the present invention is to provide an image recording apparatus that can flexibly cope with the case where the ink to be used is different and the thermal characteristics of the ink are different.
[0026]
Another object of the present invention is an image that can reduce the voltage of the electric field shutter as much as possible, can be handled by a small-scale power supply device, and consequently can suppress the influence of noise on peripheral devices as much as possible. It is to provide a recording apparatus.
[0027]
[Means for Solving the Problems]
In order to achieve the above object, the image recording apparatus of the present invention is an image recording apparatus that controls the discharge of charged ink particles by the action of an electric field, and the main electrode direction for charging the ink particles and the direction of the main electric field are The relationship between the width w of the control electrode that is perpendicular to the discharge direction of the charged ink particles and separated by the discharge holes and the length d along the discharge direction of the charged ink particles is d / w ≧ 1. An electric field shutter portion configured as described above, a print head that contains the charged ink particles and has a space in which the pressure is increased by the charged ink particles, and is opposed to the print head, and the charged ink particles are separated from the print head. And a back electrode for forming an electric field in a discharge direction.
[0028]
  The image recording apparatus according to the present invention includes a heating device that heats and vaporizes solid or liquid ink, an ejection device that ejects the vaporized gaseous ink from ejection holes formed in the print head, and an image to be recorded. The gaseous ink is ejected intermittently according to the electrical signal corresponding to the data.The discharge deviceA discharge control device that controls the charging electrode unit that charges the gaseous ink; and a back surface that is disposed on the back surface of the recording medium and guides the charged gaseous ink onto the recording medium. The discharge control device includes an electric field shutter unit that electrically controls the discharge of the gaseous ink, and the electric field shutter unit has a main electric field direction of the discharge of the gaseous ink. In the image recording apparatus perpendicular to the direction, the applied voltage of the electric field shutter unit satisfies the relationship of the following formula (1):
  √V> (w / d) · √ [2C / (q · N)] · √T (1)
  W: width between separated electric field shutters
        d: Length of electric field shutter portion along discharge direction of gaseous ink
        T: ink heating temperature
        q: Charge amount of gaseous ink
        N: Number of particles of gaseous ink
        C: Gas constant
  Is set.
[0029]
  The image recording apparatus according to the present invention includes a heating device that heats and vaporizes solid or liquid ink, an ejection device that ejects the vaporized gaseous ink from ejection holes formed in the print head, and an image to be recorded. The gaseous ink is ejected intermittently according to the electrical signal corresponding to the data.The discharge deviceA discharge control device that controls the charging electrode unit that charges the gaseous ink; and a back surface that is disposed on the back surface of the recording medium and guides the charged gaseous ink onto the recording medium. The discharge control device includes an electric field shutter unit that electrically controls the discharge of the gaseous ink, and the electric field shutter unit has a main electric field direction of the discharge of the gaseous ink. An image recording apparatus perpendicular to a direction, in which the solid or liquid ink is stored in an ink cartridge, the ink cartridge is detachably attached to the apparatus main body, and the ink sublimation is performed on the ink cartridge. Information indicating the temperature is written.
[0030]
Preferably, an ink discriminating device for reading information on the ink sublimation temperature written on the ink cartridge is provided.
[0031]
Preferably, the sublimation temperature of the set ink is determined based on a signal from the ink determination device, and the ink sublimation temperature T is determined._gSo that the ink heating temperature T satisfies the following equation (2):
T = T_g+ ΔT ... (2)
While driving and controlling the heating device, the applied voltage V when the electric field shutter unit is ON satisfies the relationship of the following equation (3):
V = a · T + ΔV (3)
However,
[0032]
[Expression 2]

[0033]
w: Width between separated electric field shutters
d: Length of electric field shutter portion along discharge direction of gaseous ink
T: Ink heating temperature
q: Charge amount of gaseous ink
N: Number of particles of gaseous ink
C: Gas constant
Control.
[0034]
The operation will be described below.
[0035]
First, as described above, when the relationship between the width w between the separated electric field shutters and the length d of the electric field shutter part along the ejection direction of the gaseous ink is set to d / w ≧ 1, the following will be described. As is clear from the description of the first embodiment, the value of the voltage V applied to the electric field shutter can be made as small as possible.
[0036]
When the value of the voltage V applied to the electric field shutter is made as small as possible, first, it is possible to secure insulation between a plurality of control electrodes constituting the electric field shutter. Second, since the power supply scale can be reduced, noise divergence to the surroundings can be reduced accordingly.
[0037]
Further, as described above, when the voltage applied to the electric field shutter portion is controlled to satisfy √V> (w / d) · √ [2C / (q · N)] · √T, the gaseous state in the heated state Since the ink can be surely prevented from leaking out of the print head, the printing efficiency can be further improved.
[0038]
Furthermore, when information indicating the sublimation temperature of ink is written on the ink cartridge, this information is read by the ink discriminating device, and the voltage applied to the electric field shutter unit is controlled according to the read result, regardless of the type of ink or the like. Thus, it is possible to reliably prevent the gaseous ink that is constantly heated from leaking out of the print head. That is, even when the ink to be used is different and the thermal characteristics of the ink are different, it is possible to cope flexibly.
[0039]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be specifically described below with reference to the drawings.
[0040]
(Embodiment 1)
FIG. 1 shows Embodiment 1 of the image recording apparatus of the present invention. The basic configuration of this image recording apparatus is as follows. The print head 1 has a long rectangular shape before and after a front sectional view, and contains powdered ink 3 below the inside thereof. Below the ink container,
A heating device 2 constituted by an electric heater 13 for heating the ink 3 and a heat radiating plate 13 ′ is disposed at a portion corresponding to the bottom of the print head 1. On the other hand, a charging electrode 4 for charging the gaseous ink 3 ″ heated and vaporized by the heating device 2 is disposed above the ink containing portion. The charging electrode 4 is a thin wire electrode of 50 to 80 μm. It consists of
[0041]
In addition, an ejection hole 14 for the ink 3 ″ is opened at the center in the left-right direction of the upper wall 1a of the print head 1. As shown in FIG. 2, the ejection hole 14 is formed by a slit groove. An electric field shutter 8 is provided on both sides of the long side of the discharge hole 14. When the print head 1 is a line head, the length L of the slit 14 is set to a length corresponding to the print width. For example, the A4 size is set to about 200 mm, and the A5 size is set to about 140 mm, and the width W of the slit 14 is set to 200 μm with a recording density of 150 dpi.
[0042]
Above the print head 1 is a conveyance area for the recording medium 12, and a back electrode 11 is horizontally disposed on the back side of the recording medium 12. The back electrode 11 guides the charged ink 3 ″ onto the recording medium 12. The back electrode 11 is approximately the same size as the electric field shutter 8, and also sucks the positively charged ink 3 ″. A negative potential, for example a voltage of −1 kV, is applied.
[0043]
The electric field shutter 8 includes a common electrode 8a and control electrodes 8b provided in a comb-teeth shape at an interval of 169 μm corresponding to the recording density. The common electrode 8a is grounded. Further, the control electrode 8b is usually 50 V to 1 kV (High level; “H”) or 0 V (Low level; “L”) depending on the output signal from the control unit 9 corresponding to the electrical signal of the image data to be recorded. Is applied. That is, when the voltage of the control electrode 8b is, for example, 500 V (“H”), the electric field shutter 8 is turned on, and an electric field is generated from the control electrode 8b toward the common electrode 8b. "Cannot pass through the electric field shutter 8. On the other hand, when the voltage of the control electrode 8b is 0 V (" L "), no electric field is generated between the control electrode 8b and the common electrode 8a. "Is attracted to the electric field by the back electrode 11 and can pass through the electric field shutter 8. In this case, the electric field shutter 8 functions as OFF. In this manner, the ejection of the ink 3 ″ can be intermittently controlled by turning on / off the voltage of the control electrode 8b. Further, the gaseous ink 3 can be controlled by controlling the potential of the control electrode 8b corresponding to each pixel. "" Can be controlled in pixel units.
[0044]
Colored ink is used as the ink coloring material. For example, for yellow, anthrisothiazole, quinophthalone, pyrazolonazo, pyridoneazo, styryl, etc. are used.For magenta, anthraquinone, dicyanoimidazole, thiadiazoleazo, tricyanovinyl, etc. are used. Azo, anthraquinone, naphthoquinone, indoaniline, and the like can be used. In the first embodiment, powder ink 3 is used, but liquid ink can also be used. When each ink 3 is used, the above-described effects are obtained.
[0045]
In the above image recording apparatus, since the potential of the common electrode 8a is grounded, the ink 3 is ejected (logically active state) when the potential of the control electrode 8b is "L". In addition, when the potential of the control electrode 8b is "H", the ink 3 "is cut off (logically inactive), and the relationship between the potential of the control electrode 8b and the ejection of the ink 3" is negative logic. Although related, if the potential of the common electrode 8a is 500 V, for example, and the potential of the control electrode 8a is changed to 500 V (“H”) or 0 V (“L”), a positive logic operation can be performed. The same applies to the following embodiments.
[0046]
In the above-described embodiment, the gaseous ink 3 ″ is positively charged, but may be negatively charged by applying a negative voltage to the charging electrode 4. However, in the case of negative charging, ozone or the like may be used. Since harmful substances are generated more than positively charged, it is necessary to take measures to prevent them.
[0047]
By the way, in the image recording apparatus of the present invention, in order to perform printing, it is necessary to fill the inside of the print head 1 with gaseous ink 3 ″ in advance, but printing is performed by heating the heated ink 3 to vaporize. The pressure in the head 1 rises, and if the head internal pressure becomes equal to or higher than the head external pressure, the ink 3 ″ leaks out from the ejection holes 14 even when there is no electric field due to the back electrode 11, so that the above invention is solved. As described above in connection with the problem to be solved, in order to enable intermittent ink discharge in accordance with an electric signal, it is necessary to realize reliable blocking of the ink 3 ″.
[0048]
For this purpose, it is necessary to obtain a relationship between the pressure P in the head and the voltage V that must be applied to the control electrode 8b in order to confine the particles of the ink 3 ″ in the print head 1. The derivation procedure will be described.
[0049]
First, since the ejection direction of the ink 3 ″ accompanying the increase in internal pressure and the direction of the electric field E by the electric field shutter 8 are perpendicular to each other, as shown in FIG. The actual ejection direction of ink is given as the sum of these two vectors, and can be broken down into a constant velocity motion in the vertical direction (coordinate z) and a constant acceleration in the horizontal direction (coordinate x).
[0050]
The velocity component of the ink particles in the z direction in the ejection hole 14 and the vicinity thereof is only in the + z direction unless the collision between the ink particles is taken into consideration.⁽ⁱ⁾ _z> 0. However, i = 1..., N, where N is the number of ink particles in the print head 1. In addition, except for the vicinity of the discharge hole 14, v⁽ⁱ⁾ _xAnd v⁽ⁱ⁾ _ySimilarly, it takes both positive and negative values. Where the subscript y indicates the direction (coordinate y) perpendicular to the paper surface, and v⁽ⁱ⁾ _yIndicates the velocity component of the ink particles in the y direction.
[0051]
Accordingly, the speed of the ink particles in the vicinity of the ejection hole 14 is expressed by the following equation (4).
[0052]
v⁽ⁱ⁾= (V⁽ⁱ⁾ _x, V⁽ⁱ⁾ _y, | V⁽ⁱ⁾ _z|) ... (4)
On the other hand, the pressure P in the head at the ejection hole 14 is the velocity component v in the z direction of the ink particles at the ejection hole 14.⁽ⁱ⁾ _zTherefore, the pressure P in the head is expressed by the following equation (5) from the kinetic theory of gas molecules.
[0053]
P∝Σm⁽ⁱ⁾・ V⁽ⁱ⁾ _z ²... (5)
Here, if the mass of each ink particle is the same, the above equation (5) can be rewritten as the following equation (6).
[0054]
[Equation 3]

[0055]
here,
[0056]
[Expression 4]

[0057]
Is the mean square value of the velocity in the z direction. Therefore, from the above (6), it can be seen that the in-head pressure P is proportional to the speed mean square value in the z direction.
[0058]
By the way, assuming that the gas ink 3 ″ is an ideal gas, its equation of state is expressed by the following equation (7).
[0059]
P ・ U = C ・ T (7)
Here, U is the volume of the ink head containing the ink 3 ″, C is the gas constant, and T is the ink heating temperature.
[0060]
Since U = constant, the relationship P∝T is established.
[0061]
Therefore, the above equation (6) is expressed by the following equation (8) using the ink temperature T.
[0062]
[Equation 5]

[0063]
The equations of motion for each of the vertical and horizontal directions are as follows.
[0064]
[Vertical direction]
In FIG. 4, the mass, charge, and diffusion rate of the charged ink particle i are represented by m.⁽ⁱ⁾, Q⁽ⁱ⁾, V⁽ⁱ⁾ _z(T). Where i = 1..., N, and v⁽ⁱ⁾ _z(T) is a function of the temperature T, and increases as the temperature increases.
[0065]
M for simplicity⁽ⁱ⁾= M, q⁽ⁱ⁾= Q. Ignoring the influence of gravity, initial conditions: t = 0, z = 0 and v⁽ⁱ⁾ _z= V₀ ⁽ⁱ⁾Furthermore, the speed v⁽ⁱ⁾ _z= Constant speed interlocking, the time t required for the ink particles to pass through the electric field shutter 8₁D = v⁽ⁱ⁾ _z・ T⁽ⁱ⁾ ₁Since this relationship is established, it is expressed by the following equation (9).
[0066]
t⁽ⁱ⁾ ₁= D / v⁽ⁱ⁾ _z... (9)
Here, d is the length of the electric field shutter portion along the ejection direction of the ink 3 ″.
[0067]
Since the actual ink particles have a velocity distribution, the time t₁Also has a distribution.
[0068]
〔horizontal direction〕
In FIG. 5, consider a case where the charged ink particles are gently released at x = 0.
[0069]

Then, the acceleration α is expressed by the following (10) because the relationship of F = q · E = m · α is established. Here, F is a force acting on the charged ink particles. E indicates the magnitude of the electric field.
[0070]
α = (q · E) / m (10)
Further, since the relationship E = V / w is established, the above equation (10) can be rewritten as the following equation (11).
[0071]
α = (q · V) / (m · w) (11)
Where V is the voltage applied to the electric field shutter 8.
[0072]
Therefore, the time required to reach x = w is t₂Then, the width w between the separated electric field shutters is expressed by the following equation (12).
[0073]
w = (1/2) · α · t₂ ²(12)
Here, in order to take into account only the effect of the electric field, the velocity component v in the x direction of the ink particles in equation (12)_xIgnored.
[0074]
Substituting the above equation (11) into this equation (12) and rearranging, t₂Is represented by the following equation (13).
[0075]
t₂= √ [(2m ・ w²) / (Q · V)] ... (13)
From the above, in order for the charged ink particles to be surely cut off by the effect of the electric field shutter 8, the time t during which the gaseous ink 3 ″ passes through the discharge hole 14 having the length d due to the pressure increase.₁The time t between the electric field shutters 8 with the electrode interval w by the action of the electric field than₂Is short, ie t₁> T₂Therefore, the relationship of the following formula (14) needs to be established.
[0076]
d / v⁽ⁱ⁾ _z> √ [(2m ・ w²) / (Q · V)] ... (14)
When the above equation (14) is modified, the following equation (15) is obtained.
[0077]
√V> v⁽ⁱ⁾ _z・ √ [(2m ・ w²) / (Q · d²]] ... (15)
A region satisfying this inequality is illustrated in FIG. The solid line is √V = D ・ v⁽ⁱ⁾ _zRepresents.
[0078]
However,
[0079]
[Formula 6]

[0080]
It was.
[0081]
From FIG. 6, when D = constant, v⁽ⁱ⁾ _zIt can be seen that V increases as a quadratic function with increasing. And v⁽ⁱ⁾ _z= If constant, it can be seen that V is smaller as D is smaller. That is, if m and q are constant, D becomes a function of (w / d), but w / d is a constant determined at the design stage of the print head 1 and is designed to be as small as possible. To do. This does not change even if the shape of the other part of the print head 1 changes unless the geometrical size of the length l and the width w of the ejection hole 14 in the head ejection part, that is, the shutter part is different.
[0082]
On the other hand, v⁽ⁱ⁾ _zIs finally determined by the operating conditions and environment such as the ink heating temperature (the ink heating temperature depends on the ink sublimation temperature), the temperature in the print head 1 in addition to the structure (volume, etc.) of the print head 1. So, if these change, it can change.⁽ⁱ⁾ _zAre the same, the applied voltage V to the electric field shutter 8 can be reduced by reducing w / d.
[0083]
For example, when the recording density is 150 dpi, the width w of the electric field shutter 8 (width of the ejection hole 14) is w = 200 μm, so that the application to the electric field shutter 8 in the print head 1 having the electric field shutter portion length d = 100 μm. The voltage is V₁₀₀Then, the applied voltage V to the print head 1 with d = 200 μm and d = 400 μm₂₀₀, V₄₀₀Are respectively V₂₀₀= V₁₀₀/ 4, V₄₀₀= V₁₀₀/ 16. That is, the voltage applied to the electric field shutter 8 can be reduced to 1/4 and 1/16, respectively.
[0084]
By the way, as mentioned above, v⁽ⁱ⁾ _z(T) has a velocity distribution and is also a function of temperature. Therefore, it is not practical to make the above equation (14) hold for all ink particles, particularly particles with a low velocity.⁽ⁱ⁾ _zSquare root of the root mean square
[0085]
[Expression 7]

[0086]
Or v⁽ⁱ⁾ _zAverage value
[0087]
[Equation 8]

[0088]
Or v⁽ⁱ⁾ _zMaximum distribution value v_mAbove v⁽ⁱ⁾ _zFor V, the value of V is determined so that at least the expression (14) holds. Here, since the relationship of the following equation (16) is established among these three parties,
[0089]
[Equation 9]

[0090]
Using the square root of the root mean square,
[0091]
[Expression 10]

[0092]
And
[0093]
Here, when the above equation (17) is rewritten with respect to the voltage V applied to the electric field shutter 8, the relationship of the following equation (18) is established.
[0094]
√V> (w / d) · √ (2 m / q) · √ (v_z ²)… (18)
From equation (5) above, v_z ²Is proportional to the pressure P, it can be seen that the voltage V applied to the electric field shutter 8 and the pressure P in the head have a linear relationship.
[0095]
From equation (18), to reduce V,
(I) w / d
(Ii) m
(Iii) 1 / q
(Iv) √ (v_z ²) Or head pressure P
It can be seen that it is necessary to reduce the value.
[0096]
The following implementation measures can be considered for each.
[0097]
(I) Shutter size d / W ≧ 1
(Ii) Reduce the mass of gaseous ink particles
(Iii) Increase the charge amount
(Iv) Suppressing the increase in the internal pressure of the head (lowering the ink heating temperature, that is, using ink with a low sublimation temperature)
Among such implementation measures, the present invention adopts the implementation measure (i), specifically, the image recording apparatus described in claim 1.
[0098]
Here, the advantage of being able to reduce the voltage applied to the electric field shutter 8 is to first ensure the insulation between the control electrodes 8b. Second, since the power supply scale can be reduced and the noise divergence to the surroundings can be reduced correspondingly, the reliability of the image recording apparatus can be improved.
[0099]
Next, the configuration of the control system and the printing operation of the image recording apparatus according to the first embodiment will be described with reference to FIGS. The CPU 20 serves as a control center of the image recording apparatus. As shown in FIG. 7, the CPU 20 controls the heating of the heating device 2, controls the energization of the discharge device composed of the charging electrode 4 and the back electrode 11, and controls it. The ejection control device including the unit 9 and the electric field shutter 8 is controlled, and the printing operation of the print head 1 is controlled according to these control contents. Details will be described below.
[0100]
When the head control signal having the waveform shown in FIG. 8A is given from the CPU 20 to the print head 1, as shown in FIG. 8B, the heating device 2 causes the head control signal to rise (point A). As a trigger, the electric heater 13 is driven at a point B after a predetermined time has elapsed from the point A. At this time, a voltage of +2 to 5 kV is applied to the charging electrode 4 (see FIG. 5C).
[0101]
When the heating device 2 is driven, the solid or liquid ink 3 is heated and the sublimation temperature T of the ink 3 is increased._gWhen the above is reached, the ink 3 is vaporized to become a gaseous ink 3 ″. Then, the ink 3 ″ increases as time passes, and reaches a threshold value at a point C (see FIG. 4D). Here, the threshold value means a gaseous ink amount sufficient for ejection, and when the threshold value is exceeded, printing becomes possible. This state means that the inside of the print head 1 is filled with the high-pressure ink 3 ″.
[0102]
Note that the heating device 2 uses an ink sublimation temperature T._gConstant control is performed so that the above temperature T is reached. For this reason, T = T_gThe relationship + ΔT is established. For example, T_g= 140 ° C, T = 155 ° C.
[0103]
Also, the drive disclosure time of the heating device 2 does not have to be the same as the above point B. For example, at B ′ before the point C (see FIG. 5F), all the control electrodes 8b of the electric field shutter 8 have 50˜ A voltage of about 1 kV may be applied to turn on the electric field shutter 8. That is, in this state, the ejection of the ink 3 ″ is prevented.
[0104]
As shown in FIG. 4E, a print start / end signal is output from the CPU 20 to the control unit 9 at a point D when the print is ready. In the first embodiment, the determination as to whether or not the ink 3 ″ has exceeded the threshold value is not directly measured, so the time after heating the electric heater 13 or the temperature of the print head 1 is measured. The CPU 20 estimates and compares the indirect data obtained in this way with the time or temperature data previously input as the target value, so that the CPU 20 generates a print start / end signal.
The control unit 9 requests the transmission of image data from an image memory (not shown) using the rise of the print start / end signal as a trigger, and D ′ shown in FIG. The ON / OFF signal corresponding to the image data is output at the point. The electric field shutter 8 is connected to a power supply device (not shown) that supplies a voltage of 500 V, and 500 V is turned ON / OFF according to the image data.
[0105]
Further, a voltage of −1 kV is applied to the back electrode 11 at a point D ′ where the electric field shutter 8 starts to turn on / off (see FIG. 5G). During printing, the print start / end signal is maintained at the “H” level.
[0106]
When the printing operation is completed, the printing start / end signal falls to the “L” level at the point E shown in FIG. 4E, and the heating device 2, the charging electrode 4 and the back electrode 11 are triggered by this falling. All are OFF. Even when the heating device 2 stops energizing the electric heater 13, the ink 3 "is not immediately cooled and remains in the print head 1, so that after the printing is finished, the electric field is applied to the point E 'after the threshold F point. The shutter 8 is forcibly turned on to prevent the ink 3 "from leaking to the outside (see (f) in the figure). After the point E ′, the electric field shutter 8 is turned off until the next printing operation is started.
[0107]
(Embodiment 2)
Next, a second embodiment of the image recording apparatus of the present invention will be described. In the second embodiment, attention is paid to the relationship between the applied voltage V to the electric field shutter (hereinafter referred to as the electric field shutter voltage V) and the ink heating temperature T, and the electric field shutter voltage V is controlled based on the relational expression therebetween. Ink 3 ″ is prevented from leaking out.
[0108]
First, the relationship between the electric field shutter voltage V and the ink heating temperature T is obtained.
[0109]
In the above equation (18), considering the case where the left side is the right side, the following equation (19) is established.
[0110]

However,
[0111]
## EQU11 ##

[0112]
It was.
[0113]
If you square both sides of equation (19),
V_EQUAL= (W / d)²・ B²・ T ... (20)
It becomes.
[0114]
Here, the electric field shutter voltage V is V> V_EQUALTherefore, it can be expressed by the following equation (21).
[0115]

Here, ΔV is a positive constant, and is determined in consideration of variations in environmental temperature, charge amount q, and the like. Also,
[0116]
[Expression 12]

[0117]
It was.
[0118]
From the above equation, it can be seen that there is a linear relationship between the electric field shutter voltage V and the ink heating temperature T.
[0119]
Here, the ink heating temperature T is the sublimation temperature T of the ink._gBased on the above, it is represented by the following formula (22).
[0120]
T = T_g+ ΔT (22)
For example, T_gWhen ΔT = 140 ° C., ΔT = 15 ° C. and T = 155 ° C. Therefore, the heating device 2 is T_gThe electric power applied to the electric heater 13 is controlled so that = 140 ° C. = constant.
[0121]
At this time, the ink heating temperature T may fluctuate due to the stability of the control device and the influence of disturbance, the change in the consumption of the gaseous ink 3 ″ due to the difference in ambient temperature and printing density, etc. If it is known that it is small, the amount is included in ΔV, and control is performed so that V = constant, and q, and hence constant a, may fluctuate due to fluctuations in the charge amount. In this case, if the value is small, it may be included in ΔV and V = constant.
[0122]
However, when the variation in the ink heating temperature T is large, control is performed to adjust V based on the equation (21).
[0123]
The control method will be described below with reference to FIG. 9 and FIG. FIG. 9 shows the configuration of the control system of the image recording apparatus according to the second embodiment. This control system includes the ink discriminating device 21, and the control system of the image recording apparatus of the first embodiment described above. It has the same configuration as
[0124]
Here, the ink discriminating device 21 reads the ink information displayed on the ink cartridge containing the ink 3 and gives an ink discrimination signal to the CPU 20. Then, the CPU 20 determines the ink sublimation temperature T from the ink discrimination signal._gAnd the control described later is performed. In addition, the same code | symbol is attached | subjected to the part corresponding to Embodiment 1, and description is abbreviate | omitted.
[0125]
In the above equation (21), ΔV is a known amount (in the second embodiment, for example, set to 45 V), and as is apparent from FIG. 10, the electric field shutter voltage V is V1 at a certain ink heating temperature T1. If it is known, since the constant a can be obtained, the electric field shutter voltage V2 when the ink heating temperature T is T2 is obtained according to the equation (21). For example, when T1 = 155 ° C., V1 = 200V, and ΔV = 45V, if these values are substituted into equation (21), a = 1 (V / ° C.), so when T2 = 140 ° C. The electric field shutter voltage V is controlled so that V2 = 185V. In addition to the above case, such a situation may occur, for example, when the ink is improved and the sublimation temperature is lowered, or when ink of a different manufacturer is used, or between colors in color printing. This occurs when the ink sublimation temperature is different. Therefore, for a plurality of inks having different thermophysical property values, the sublimation temperature T_gWhen the electric field shutter voltage is controlled according to the equation (21), an appropriate electric field shutter voltage can be applied to each ink. In this case, the heating device 2 uses the ink sublimation temperature T._gNeedless to say, the ink heating temperature T is controlled to change according to the above. That is, with ΔT = 15 ° C. = constant, the relational expression T = T_gThe ink heating temperature T is given by + ΔT, that is, the above equation (22).
[0126]
Here, the ink 3 is generally stored in a container called a cartridge, and the ink can be identified if the cartridge has information indicating the type of ink. That is, although the method of identifying information differs depending on the method of entering information into the ink cartridge, a mechanical mechanism such as a lever can be used for information on physical unevenness, and the barcode With such printing information, an optical element such as a photo interrupter can be used. Specifically, when physical unevenness information is used, for example, two unevennesses are selectively formed, and the lever is in contact with each position. Each lever works as a binary switch. When there is no unevenness, the lever switch is OFF, and if there is a convex part or concave part, it is ON.²= Since it is possible to have four pieces of information, each piece of information_g= 140 ° C., 145 ° C., 150 ° C., 155 ° C., information on four types of ink can be provided. In addition, if 3 irregularities can be selectively formed, 2^Three= 8 ink information can be held.
[0127]
Similarly, two bar codes are selectively formed, and a reflection type photo interrupter is arranged at each position. When there is no barcode, the photo interrupter output is OFF, and when there is a barcode, it is ON.²= Four types of ink can be handled.
[0128]
When the ink cartridge filled with the ink information as described above is attached to the print head 1, the ink discriminating device 21 reads the ink information and outputs an ink discrimination signal to the CPU 20. The CPU 20 determines the ink sublimation temperature T of the ink 3 stored in the ink cartridge based on the ink determination signal._gAnd T = T in equation (22) above_gThe ink heating temperature T is determined by + ΔT. Further, the voltage V to be applied to the control electrode 8b of the electric field shutter 8 is determined by V = a · T + ΔV in the above equation (21). ΔT is, for example, 15 ° C.
[0129]
In the second embodiment, the ink heating temperature T is obtained by the equation (22) with ΔT = constant, but the ink sublimation temperature T is previously determined._gInk heating temperature T may be created as a look-up table (LUT), and ink heating temperature T may be determined with reference to this LUT. Further, when determining the voltage V applied to the control electrode 8b of the electric field shutter 8, the ink sublimation temperature T is also determined._gAlternatively, the LUT of the electric field shutter voltage V may be prepared and determined with reference to this.
[0130]
After determining the ink heating temperature T and the electric field shutter voltage V in the above procedure, the CPU 20 outputs a print start signal to each device of the print head 1. This start signal gives the timing of voltage application / release. In FIG. 9, this print start signal is indicated by a dotted line.
[0131]
The CPU 20 inputs a heating control signal to heat the ink 3 at the determined ink heating temperature T in the heating device 2. Thus, the electric heater 13 is driven so that the heating device 2 has the above temperature. Further, the CPU 20 inputs a charging start signal to the charging electrode 4. As a result, a voltage of 2 to 5 kV is applied to the charging electrode 4 and the ink 3 ″ is charged. At a time before the gaseous ink amount exceeds the threshold value, an electric field shutter voltage control signal is sent to the control unit 9. As a result, a voltage is applied to all the control electrodes 8b of the electric field shutter 8, that is, the electric field shutter 8 is turned ON to prevent ink leakage. A voltage application start signal is output to the electrode 11, and a voltage of -1 kV is applied to the back electrode 11. At the same time, the electric field shutter 8 is turned ON / OFF according to the image data, and the printing operation is started. Is done.
[0132]
When the printing operation is completed, the CPU 20 outputs a control signal to each of the above devices. That is, a release signal is output to the heating device 2, the charging electrode 4, and the back electrode 11 to complete the voltage application at the same time, and the generation and ejection of the gaseous ink 3 ″ are suppressed. 8, a voltage is applied to all the control electrodes 8b immediately after the printing is completed to prevent the ink 3 ″ from leaking. The electric field shutter voltage V is finally released at an arbitrary point in time when the amount of gaseous charged ink falls below the threshold value.
[0133]
As described above, by recording or forming ink information in an ink cartridge containing ink, the optimum ink heating temperature T and electric field shutter voltage V are supplied to each ink 3 having a plurality of physical property values. can do.
[0134]
The reason will be described below.
[0135]
For convenience of explanation, two types of ink, that is, the ink sublimation temperature is T_g1And T_g2(T_g1> T_g2) Is the optimum heating temperature for each ink.₁= T_g1+ ΔT, T₂= T_g2+ ΔT (hence T₁> T₂), And the optimum electric field shutter voltage V is V₁, V₂(V₁> V₂). However, the electric field shutter voltage V is given by the above equation (21).
[0136]
Sublimation temperature T_g1In an image recording device optimized for ink 3 having a lower sublimation temperature T₂The same heating temperature T₁Since the ink is heated, the ink is excessively heated, and power is wasted. In the worst case, the ink is decomposed.
[0137]
Also, sublimation temperature T_g2In an image recording device optimized for ink having a higher sublimation temperature T_g1When the ink having an ink is used and the ink discrimination device 21 is not provided, the optimum heating temperature T₁Lower temperature T₂Since the ink is heated, the ink does not sublime sufficiently.
[0138]
Therefore, it becomes necessary to appropriately control the heating device 2 in accordance with the sublimation temperature of the ink to change the ink heating temperature. However, if only the heating device 2 is controlled, another problem occurs for the following reason.
[0139]
That is, sublimation temperature T_g1In an image recording device optimized for ink 3 having a lower sublimation temperature T_g2In order to eliminate the above problems, the heating temperature is set to T.₁To T₂When changed to V₂Where V is sufficient, V₁> V₂An extra voltage is applied. This is a disadvantage when considering low power consumption of the apparatus.
[0140]
Also, sublimation temperature T_g2In an image recording device optimized for ink having a higher sublimation temperature T_g1In order to eliminate the above problems, the heating temperature is set to T.₂To T₁Since the pressure in the head increases, the electric field shutter 8 has the same voltage V as in the conventional case.₂(<V₁) Is applied, the electric field shutter 8 does not operate completely, which may cause ink leakage.
[0141]
However, in the image recording apparatus according to the present invention, since both the ink heating temperature and the electric field shutter voltage are controlled to be optimal according to the type of ink, the ink is overheated or insufficiently heated, and the power consumption There is no worry about an increase in ink or ink leakage.
[0142]
That is, according to the ink sublimation temperature, the ink heating temperature T is T = T_gThe heating device is controlled so as to be + ΔT, and the control is performed so that the applied voltage V when the electric field shutter is ON is V = a · T + ΔV, so that each device is always driven under optimum driving conditions. can do.
[0143]
(Other embodiments)
Embodiments to which the image recording apparatus of the present invention is applied are not limited to those of the first and second embodiments, and various modifications can be made as described below.
That is, the present invention can be similarly applied to an image recording apparatus of the type that generates gaseous ink 3 ″ by vaporizing charged ink 3 ′ as shown in FIG. 12 can be similarly applied to a type having a plurality of ejection holes 14 as shown in Fig. 12. Furthermore, the present invention can be similarly applied to an image recording apparatus employing a frictional charging method.
[0144]
【The invention's effect】
According to the above-described image recording apparatus of the present invention, printing is performed by intermittently discharging gaseous ink, so that it is possible to perform printing with a necessary and sufficient discharge amount, thereby reducing running costs. There are advantages you can do. In addition, because it is composed of a print head in which the heating device, charging electrode, and electric field shutter are integrated, the degree of ink clogging due to adhesion of the ink blocked by the electric field shutter to the electric field shutter can be reduced and adhered. Since an ink recovery device and a cleaning device are not required, there is an advantage that the device configuration can be greatly reduced in size.
[0145]
In addition to the above effects,
In particular, according to the image recording apparatus of the first aspect, the value of the voltage V applied to the electric field shutter can be made as small as possible. Since the scale can be reduced, it is possible to reduce the influence of noise on peripheral devices and to improve the reliability.
[0146]
In particular, according to the image recording apparatus of the second aspect, it is possible to reliably prevent the gaseous ink in the heated state from leaking out of the print head, so that the printing efficiency can be further improved.
[0147]
In particular, according to the image recording apparatus of claims 3 to 5, it is possible to reliably prevent the gaseous ink that is always in a heated state from unexpectedly leaking from the print head regardless of the type of ink. Therefore, even when the ink to be used is different and the thermal characteristics of the ink are different, it is possible to cope flexibly. Therefore, the present invention is particularly effective when applied to an image recording apparatus that performs color printing.
[Brief description of the drawings]
FIG. 1 is a schematic front view showing a part of an image recording apparatus of the present invention according to a first embodiment.
FIG. 2 is a perspective view showing details of an electric field shutter unit of the image recording apparatus of the present invention according to Embodiment 1. FIG.
FIG. 3 is an explanatory diagram showing forces acting on charged ink particles in an electric field shutter unit.
FIG. 4 is an explanatory diagram showing a force in an ink discharge direction that acts on charged ink particles in an electric field shutter unit.
FIG. 5 is an explanatory diagram showing electric field direction forces acting on charged ink particles in an electric field shutter unit.
FIG. 6 is a graph showing the relationship between the electric field shutter voltage and the vertical velocity component of ink particles.
7 is a block diagram showing a control system of the image recording apparatus of the present invention according to Embodiment 1. FIG.
FIG. 8 is a timing chart showing a printing operation of the image recording apparatus of the present invention according to Embodiment 1.
FIG. 9 is a block diagram showing a control system of the image recording apparatus according to the second embodiment of the present invention.
FIG. 10 is a graph showing the relationship between the electric field shutter voltage and the ink heating temperature.
FIG. 11 is a partially cutaway schematic front view showing another embodiment of an image recording apparatus to which the present invention is applied.
FIG. 12 is a perspective view showing another embodiment of the electric field shutter.
FIG. 13 is a cross-sectional view showing a conventional example of an image recording apparatus.
[Explanation of symbols]
1 Print head
2 Heating device
3 Powder ink
3 "gaseous ink
4 Charging electrodes
8 Electric field shutter
8a Common electrode
8b Control electrode
9 Control part
11 Back electrode
12 Recording media
14 Discharge hole
20 CPU
  21 Ink discrimination device
d Length of electric field shutter along the ink ejection direction
V Electric field shutter voltage
w Width between electric field shutters separated by discharge holes

Claims (5)

In an image recording apparatus that controls discharge of charged ink particles by the action of an electric field,
A charging electrode for charging the ink particles;
The direction of the main electric field is perpendicular to the discharge direction of the charged ink particles, and the relationship between the width w of the control electrode separated by the discharge holes and the length d along the discharge direction of the charged ink particles is d / an electric field shutter configured to satisfy w ≧ 1,
A print head containing the charged ink particles and having a space in which the pressure is increased by the charged ink particles;
A back electrode provided facing the print head and forming an electric field in a direction in which the charged ink particles are ejected from the print head;
An image recording apparatus comprising: A heating device that heats and vaporizes solid or liquid ink, an ejection device that ejects the vaporized gaseous ink from ejection holes formed in the print head, and an electrical signal corresponding to the image data to be recorded A discharge control device that controls the discharge device so that the gaseous ink is discharged intermittently, and the discharge device is disposed on a back surface of the recording medium, a charging electrode unit that charges the gaseous ink, A back electrode unit that guides the charged gaseous ink onto the recording medium, and the discharge control device includes an electric field shutter unit that electrically controls the discharge of the gaseous ink. The part is an image recording apparatus whose main electric field direction is perpendicular to the discharge direction of the gaseous ink,
The applied voltage of the electric field shutter unit satisfies the relationship of the following formula (1):
√V> (w / d) · √ [2C / (q · N)] · √T (1)
Where w: width between the separated electric field shutters d: length of the electric field shutter portion along the ejection direction of the gaseous ink T: ink heating temperature q: charge amount of the gaseous ink N: number of particles of the gaseous ink C: Gas constant An image recording apparatus characterized by being set. A heating device that heats and vaporizes solid or liquid ink, an ejection device that ejects the vaporized gaseous ink from ejection holes formed in the print head, and an electrical signal corresponding to the image data to be recorded A discharge control device that controls the discharge device so that the gaseous ink is discharged intermittently, and the discharge device is disposed on a back surface of the recording medium, a charging electrode unit that charges the gaseous ink, A back electrode unit that guides the charged gaseous ink onto the recording medium, and the discharge control device includes an electric field shutter unit that electrically controls the discharge of the gaseous ink. The part is an image recording apparatus whose main electric field direction is perpendicular to the discharge direction of the gaseous ink,
The solid or liquid ink is stored in an ink cartridge, the ink cartridge is detachably attached to the apparatus main body, and information indicating the sublimation temperature of the ink is recorded on the ink cartridge. Image recording device.   4. The image recording apparatus according to claim 3, further comprising an ink discriminating device that reads information on an ink sublimation temperature recorded on the ink cartridge. On the basis of a signal from the ink determination device, to determine the sublimation temperature of the set ink, the ink heating temperature T for ink sublimation temperature T _g is, so as to satisfy the following relationship (2),
T = T _g + ΔT (2)
While driving and controlling the heating device, the applied voltage V when the electric field shutter unit is ON satisfies the relationship of the following expression (3):
V = a · T + ΔV (3)
However,
[Expression 1]
w: Width between the separated electric field shutters d: Length of the electric field shutter portion along the ejection direction of the gaseous ink T: Heating temperature of the ink q: Charge amount of the gaseous ink N: Number of particles of the gaseous ink C 5. The image recording apparatus according to claim 4, wherein the gas constant is controlled.

Images