JP3630732B2 - Optical scanning device - Google Patents

Description

【００３８】
【表２】

【００３９】
図３によれば、レーザ素子３Ｙから出射されたレーザビームＬＹは、有限焦点レンズ９Ｙにより、おおむね、像面Ｓに集光するレーザビームに変換される。レンズ９Ｙを通過されたレーザビームＬＹは、副走査方向のみにパワーを持つハイブリッドシリンダレンズ１１Ｙにより、副走査方向では、おおむね、光偏向装置５の各反射面５αないし５εおよび５κないし５μ上に集光される。
【００４０】
ハイブリッドシリンダレンズ１１Ｙは、副走査方向に対して実質的に等しい曲率を持つＰＭＭＡのシリンダレンズ１７Ｙとガラスのシリンダレンズ１９Ｙとによって形成されている。ＰＭＭＡのシリンダレンズ１７Ｙは、空気と接する面がほぼ平面に形成される。それぞれのシリンダレンズ１７Ｙとシリンダレンズ１９Ｙとは、シリンダレンズ１７Ｙの出射面とシリンダレンズ１９Ｙの入射面で接着され、あるいは、シリンダレンズ１９Ｙの入射面にシリンダレンズ１７Ｙが一体に成型されることで、提供される。また、シリンダレンズ１９Ｙとシリンダレンズ１７Ｙとは、図示しない位置決め部材に所定の方向から押圧されてもよい。なお、シリンダレンズ１７Ｙの材質、ＰＭＭＡは、偏向後光学系２１に利用される第１ないし第３の結像レンズ２７，２９および３１と実質的に光学特性が等しい材質によって形成される。
【００４１】
次に、ハイブリッドシリンダレンズ１１Ｙの光学特性を詳細に説明する。
偏向後光学系２１すなわち第１ないし第３の結像レンズ２７，２９および３１は、プラスチック、たとえば、ＰＭＭＡにより形成されることから、 （光偏向装置の） 周辺温度が、たとえば、０°Ｃから５０°Ｃの間で変化することにより、屈折率ｎが、１．４８７６から１．４７８９まで変化することが知られている。この場合、第１ないし第３の結像レンズ２７，２９および３１を通過されたレーザビームＬ （Ｙ，Ｍ，ＣおよびＢ） が実際に集光される結像面すなわち副走査方向結像位置は、±１２ｍｍ程度変動してしまう。ここで、偏向後光学系２１に利用されるレンズの材質と同一の材質のレンズを、曲率を最適化した状態で偏向前光学系７に組み込むことによって、温度変化による屈折率ｎの変動に伴って発生する結像面の変動を±０．５ｍｍ程度に抑えることができる。すなわち、偏向前光学系７がガラスレンズで、偏向後光学系２１がＰＭＭＡで形成されたレンズにより構成される従来の光学系に比較して、偏向後光学系２１のレンズの温度変化による屈折率の変化に起因して発生する副走査方向の色収差が補正できる。
【００４２】
なお、図３から明らかなように、それぞれのレーザビームＬＹ，ＬＭ，ＬＣおよびＬＢは、副走査方向で、光偏向装置１の光軸 （系の光軸） に対して対称に入射されている。すなわち、レーザビームＬＹおよびＬＢは、光軸Ｏを挟んで対称に、多面鏡５ａに入射される。また、レーザビームＬＭおよびＬＣは、同様に、光軸Ｏを挟んで対称に、かつ、レーザビームＬＹおよびＬＢよりも光軸Ｏ側を、多面鏡５ａに案内される。このことは、それぞれのレーザビームＬ （Ｙ，Ｍ，ＣおよびＢ） に関し、偏向後光学系２１を、副走査方向の２箇所で最適化できることを示している。従って、各レーザビームＬ （Ｙ，Ｍ，ＣおよびＢ） の像面湾曲および非点収差などの特性をより向上させたり、偏向後光学系２１のレンズ枚数を低減できる。
【００４３】
図４によれば、ミラーブロック１３は、第１ないし第４のレーザビームＬＹ，ＬＭ，ＬＣおよびＬＢを、１つの束のレーザビームＬｏとして光偏向装置５の各反射面５αないし５εおよび５κないし５μに案内するために利用される。詳細には、ミラーブロック１３は、入射させるためにレーザ素子３Ｙから出射されたレーザビームＬＹを折り返して光偏向装置５の各反射面５αないし５εおよび５κないし５μに案内する第１の反射面１３Ｙ、レーザ素子３ＭからのレーザビームＬＭおよびレーザ素子３ＣからのレーザビームＬＣを、それぞれ、光偏向装置５の各反射面５αないし５εおよび５κないし５μに向かって折り返す第２および第３の反射面１３Ｍおよび１３Ｃ、及び、レーザ素子３ＢからのレーザビームＬＢをそのまま光偏向装置５の各反射面５αないし５εおよび５κないし５μに案内する通過領域１３Ｂを有している。
【００４４】
それぞれの反射面１３Ｙ，１３Ｍおよび１３Ｃは、ブロック本体１３ａの各反射面に対応する位置が所定の角度に切り出されたのち、切削面に、たとえば、アルミニウムなどの反射率の高い材質がが塗布または蒸着されることにより提供される。なお、ブロック本体１３ａの各反射面に対応する位置は、切削後、研磨により鏡面加工されてもよい。
【００４５】
図４に示したミラーブロックによれば、各反射面１３Ｙ，１３Ｍおよび１３Ｃは、１つのブロック本体１３ａから切り出されることから、各ミラーごとの相対的な傾き誤差が低減される。また、ブロック本体１３ａを、たとえば、ダイカストにより製造することで、精度の高いミラーブロックが提供できる。
【００４６】
なお、レーザ素子３ＢからのレーザビームＬＢは、すでに説明したように、ミラーブロック１３と交わることなく、ブロック本体１３ａ上の通過領域１３Ｂを通過されて、光偏向装置５の各反射面５αないし５εおよび５κないし５μに直接案内される。
【００４７】
ここで、ミラーブロック１３により反射されて光偏向装置５に案内される各レーザビームＬ （Ｙ，ＭおよびＣ） ならびに光偏向装置５に直接案内されるレーザビームＬＢの強度 （光量） について考察する。
【００４８】
従来技術の項ですでに説明したように、特開平５−３４６１２号公報には、２以上のレーザビームを１つの束のレーザビームとして光偏向装置の反射面に入射させる方法として、ハーフミーラにより、レーザビームを、順に、重ねる方法が示されている。しかしながら、複数のハーフミラーが利用されることで、１回の反射および透過 （ハーフミラーを１回通過するごとに） に対し、各レーザから出射されたレーザビームの光量の５０％は無駄となってしまうことは公知である。この場合、ハーフミラーの透過率と反射率を、それぞれ、各レーザビームごとに最適化したとしても、すべてのハーフミラーを通過されるいづれか１つのレーザビームの強度 （光量） は、レーザ素子から出力された光量の約２５％まで低減されてしまう。また、光路中にハーフミラーが光路に傾いて存在すること、及び、各レーザビームが通過するハーフミラーの枚数が異なること、などに起因して、像面湾曲あるいは非点収差など代表される光学特性に、各レーザビームごとに差が生じることが知られている。各レーザビームごとに像面湾曲および非点収差などの特性が異なることは、全てのレーザビームを、同一の有限焦点レンズおよびシリンダレンズのみにより像面に結像させることを困難にする。
【００４９】
これに対して、図４に示されているミラーブロック１３によれば、それぞれのレーザビームＬＹ，ＬＭおよびＬＣは、光偏向装置５の多面鏡５ａに入射する前段であって、各レーザビームＬＹ，ＬＭおよびＬＣが副走査方向に分離している領域 （図３に網かけで示されている） で、通常のミラーによって折り返される。従って、多面鏡５ａにより像面Ｓに向かって供給 （反射） される各レーザビームＬ （Ｙ，Ｍ，ＣおよびＢ） の光量は、出射光量のおおむね９０％以上に維持できる。このことは、各レーザの出力を低減できるばかりでなく、像面Ｓに到達される光の収差を均一に補正できるため、レーザビームを小さく絞り、高精細化への対応を可能とする。なお、Ｂ （ブラック） に対応するレーザ素子３Ｂは、ミラーブロック１３の通過領域１３Ｂを通過されて多面鏡５ａに案内されることから、レーザの出力容量が低減できるばかりでなく、反射面で反射されることによる多面鏡５ａへの入射角の誤差が除去される。
【００５０】
次に、図５ないし図７を参照して、光偏向装置５の多面鏡５ａで反射された１束のレーザビームＬｏと偏向後光学系２１との関係について説明する。
なお、表３には、偏向後光学系２１の各レンズすなわち第１ないし第３のプラスチックレンズ２７，２９および３１のレンズデータが示されている。
【００５１】
【表３】

【００５２】
なお、副走査の曲率が“−”の面は、これを光軸に関して回転した形状がレンズ形状、曲率が示されている面は、その局所座標のｚ軸方向に１／トーリック回転対象軸の欄に示された方向の曲率分だけ離れた平面内の、トーリック回転対象軸の欄に示された方向に平行な軸を中心として回転した形状を示している。 （以下、表４に、比較例として従来から利用されている光学系のレンズデータの一例を、同様の方法で示す。）
【００５３】
【表４】

【００５４】
表３および表４におけるエラー関数 （後述、表９参照） は、像面Ｓに導かれる各レーザビームＬの計算上 （コンピュータシミュレート） の結像特性と、理想的な結像特性の偏差を求めた数値であって、数値が小さいほど、理想に近い結像特性が得られることを示している。なお、表３ならびに表４に示されている偏向後光学系は、第１ないし第３のプラスチックレンズ２７，２９および３１のどの面についても、非球面係数を「０」とした光学系であって、特に、表４に示した光学系は、トーリック面の入射面と出射面の回転対称軸が全て同じ方向のものを示している。
【００５５】
表３および表４から明らかなように、表１に示した偏向前光学系と表３に示した偏向後光学系とを組み合わせることで、エラー関数 （表９参照） の小さい、理想条件に比較的近い光学特性を有する光走査装置が提供される。
【００５６】
図５は、図１および図２で説明した光走査装置を光軸Ｏに沿って切断した光路展開図である。なお、図５では、１つのレーザビームＬＹ （Ｙ＝イエロー画像に対応） に対する光学部品のみが代表して示され、残りのレーザビームＬＭ，ＬＣおよびＬＢに対しては、各レーザビームＬ （Ｍ，ＣおよびＢ） の最外殻とそれぞれの光軸のみを示している。また、第１ないし第３の折り返しミラー３３Ｂ，３５Ｙ，３５Ｍ，３５Ｃ，３７Ｙ，３７Ｍおよび３７Ｃは、省略されている。図６は、図５に示されている光路中の第１ないし第３の結像レンズのトーリック面の回転軸を示す概略斜視図である。なお、図６によれば、各レンズを通過されるレーザビームＬ （Ｙ，Ｍ，ＣおよびＢ） は、省略されている。図７は、図５に示されている光路展開図を、光偏向装置５の各反射面において副走査方向に直交する方向から見た光路展開図である。
【００５７】
図５ないし図７によれば、偏向後光学系２１は、第１ないし第３のプラスチックトーリックレンズ２７，２９および３１、及び、各レーザビームＬ （Ｙ，Ｍ，ＣおよびＢ） のそれぞれに対応して配置される防塵ガラス３９Ｙ，３９Ｍ，３９Ｃおよび３９Ｂを含んでいる。
【００５８】
第１ないし第３のプラスチックトーリックレンズ２７，２９および３１は、偏向前光学系７ （Ｙ，Ｍ，ＣおよびＢ） に関して既に説明したように、それぞれ、ハイブリッドシリンダレンズ１１ （Ｙ，Ｍ，ＣおよびＢ） に利用されているプラスチックシリンダレンズ１７ （Ｙ，Ｍ，ＣおよびＢ） と実質的に等しい材質、たとえば、ＰＭＭＡ （ポリメチルメタクリル） などにより形成される。なお、光偏向装置５の前段で１束のレーザビームＬｏに束ねられた各レーザビームＬＹ，ＬＭ，ＬＣおよびＬＢは、それぞれ、おおむね、同一の束の状態で、第１ないし第３のプラスチックトーリックレンズ２７，２９および３１を通過される。
【００５９】
第１のプラスチックトーリックレンズ２７は、入射面 （光偏向装置５側） ２７_ｉｎおよび出射面 （像面Ｓ側） ２７_ｒａの双方ともにトーリック面に形成されたトーリックレンズである。レンズ２７の各面のトーリック回転対称軸は、入射面２７_ｉｎに関し主走査方向 （図６、Ｒ２７_ｉｎ） に、また、出射面２７_ｒａに関し副走査方向 （図６、Ｒ２７_ｒａ） に、すなわち、入射面２７_ｉｎのトーリック回転対称軸と出射面２７_ｒａのトーリック回転対称面とが互いに直交するように延出されている。なお、入射面２７_ｉｎおよび出射面２７_ｒａによる副走査方向の合成パワーは、負に規定される。
【００６０】
第２のプラスチックトーリックレンズ２９は、入射面 （光偏向装置５側） ２９_ｉｎおよび出射面 （像面Ｓ側） ２９_ｒａの双方ともにトーリック面に形成されたトーリックレンズである。レンズ２９の各面のトーリック回転対称軸は、入射面２９_ｉｎに関し主走査方向 （図６、Ｒ２９_ｉｎ） に、また、出射面２９_ｒａに関し副走査方向 （図６、Ｒ２９_ｒａ） に、すなわち、入射面２９_ｉｎのトーリック回転対称軸と出射面２７_ｒａのトーリック回転対称面とが互いに直交するように延出されている。なお、入射面２９_ｉｎおよび出射面２９_ｒａによる副走査方向の合成パワーは、正に規定される。
【００６１】
第３のプラスチックトーリックレンズ （最終レンズ） ３１は、入射面 （光偏向装置５側） ３１_ｉｎがトーリック面、及び、出射面 （像面Ｓ側） ３１_ｒａが回転対称非球面に形成された片面トーリックレンズである。レンズ３１の入射面３１_ｉｎのトーリック回転対称軸は、主走査方向 （図６、Ｒ３１_ｉｎ） に延出されている。なお、出射面３１_ｒａは、光軸Ｏを中心として回転されることはいうまでもない。また、入射面３１_ｉｎおよび出射面３１_ｒａによる副走査方向の合成パワーは、正に規定される。
【００６２】
次に、第１ないし第３のプラスチックレンズのトーリック軸と、結像面の変動および収差特性について考察する。
従来から利用されている光走査装置では、全てのトーリックレンズのトーリック軸は、主走査方向に沿って規定される。この場合、結像面における球面収差、コマ収差、像面湾曲あるいは倍率誤差などの収差特性は、副走査方向に関し、独立に設定できないことは、すでに説明した通りである。
【００６３】
これに対して、第１のプラスチックレンズ２７および第２のプラスチックレンズのトーリック回転対称軸をそれぞれ独立に規定することで、副走査方向の球面収差、コマ収差、像面湾曲あるいは倍率誤差などを、第１ないし第３のプラスチックレンズ２７，２９および３１により独立に最適化することができる。なお、第３のトーリックレンズ３１の出射面 （回転非球面） ３１_ｒａは、副走査方向の特性への影響を抑えるとともに、主走査方向のさまざまな特性の微妙な調整のために利用される。また、第１のプラスチックレンズ２７、第２のプラスチックレンズ２９および第３のプラスチックレンズ３１のそれぞれの副走査方向の合成パワーを、順に、負、正および正とした場合に、光偏向装置５の各反射面で反射されるレーザビームの反射角を最大にできる。
図５によれば、さらに、光偏向装置５の多面鏡５ａで反射されたそれぞれのレーザビームＬＹ，ＬＭ，ＬＣおよびＬＢは、偏向後光学系２１の各レンズ２７，２９および３１の素材であるＰＭＭＡの温度変化による屈折率変化あるいは熱膨張による像面Ｓでの副走査方向の位置ずれを低減させるために、光軸上では、偏向後光学系２１の合成節点位置よりも像面Ｓ側に僅かにシフトした位置を通過され、像面Ｓに案内される。すなわち、多面鏡５ａで反射されたそれぞれのレーザビームＬＹ，ＬＭ，ＬＣおよびＬＢの副走査方向でのレンズ面通過位置は、第１のレンズ２７の入射面２７_ｉｎと第３のレンズ３１の出射面３１_ｒａとの間で、光軸を挟んで逆方向に規程される。一例として、レーザビームＬＣを参照すれば、レーザ素子３Ｃは、光軸Ｏに対し所定の角度で、光軸Ｏの上方に配置される。レーザ素子３ＣからのレーザビームＬＣは、多面鏡５ａで光軸Ｏの上方を通過され、第１のトーリックレンズ２７の入射面２７_ｉｎで光軸Ｏの上方かつ光軸Ｏの直近を通過され、第１のトーリックレンズ２７の出射面２７_ｒａと第２のトーリックレンズ２９の入射面２９_ｉｎで光軸Ｏの直近かつ光軸Ｏの下方を通過され、第３のトーリックレンズ３１に案内される。このレンズ２７とレンズ３１との副走査方向の通過位置は、偏向前光学系７Ｙ，７Ｍ，７Ｃおよび７Ｂの有限焦点レンズ９Ｙ，９Ｍ，９Ｃおよび９Ｂ、及び、ハイブリッドシリンダレンズ１１Ｙ，１１Ｍ，１１Ｃおよび１１Ｂの、それぞれの光軸を最適に配置することによって、容易に達成される。
【００６４】
図７によれば、各レーザ素子３Ｙ，３Ｍ，３Ｃおよび３Ｂから出射されたレーザビームＬＹ，ＬＭ，ＬＣおよびＬＢは、それぞれ、対応する偏向前光学系を通過され、所定の速度で回転されている多面鏡５ａを介して偏向後光学系に向かって偏向 （連続的に反射） される。すでに説明したように、多面鏡５ａに入射される各レーザビームＬ （Ｙ，Ｍ，ＣおよびＢ） は、偏向前光学系７ （Ｙ，Ｍ，ＣおよびＢ） と多面鏡５ａ （光偏向装置５） との間に配置されているミラーブロック１３により、主走査方向に関しては、１束のレーザビームＬｏとして多面鏡５ａに案内される。
【００６５】
また、光偏向装置５の多面鏡５ａで反射され、偏向後光学系２１すなわち第１ないし第３のトーリックレンズ２７，２９および３１を通過された各レーザビームＬ （Ｙ，Ｍ，ＣおよびＢ） の一部であって、像面Ｓの画像領域外に対応する各レーザビームＬ （Ｙ，Ｍ，ＣおよびＢ） は、 （ただ１つの） 水平同期用折り返しミラー２５を介して （ただ１つの） 水平同期検出器２３に反射される。
【００６６】
図８ （ａ） および図８ （ｂ） は、図７に示した光路を通って像面Ｓに偏向される各レーザビームＬＹ，ＬＭ，ＬＣおよびＬＢを、ただ１つの水平同期検出器に案内できる水平同期用折り返しミラーを示している。
【００６７】
図８ （ａ） によれば、水平同期用折り返しミラー２５は、それぞれのレーザビームＬＹ，ＬＭ，ＬＣおよびＬＢを、主走査方向には水平同期検出器２３に異なるタイミングで反射させるとともに、副走査方向には水平同期検出器２３上で実質的に同一の高さを提供できるよう、主走査方向および副走査方向ともに異なる角度に形成された第１ないし第４の折り返しミラー面２５Ｙ，２５Ｍ，２５Ｃおよび２５Ｂ、及び、それぞれのミラー２５ （Ｙ，Ｍ，ＣおよびＢ） を一体に保持するミラーブロック２５ａを有している。
【００６８】
ミラーブロック２５ａは、たとえば、ガラス入りＰＣ （ポリカーボネイト） などにより成型される。また、各ミラー２５ （Ｙ，Ｍ，ＣおよびＢ） は、所定の角度で成型されたブロック２５ａの対応する位置に、たとえば、アルミニウムなどの金属が蒸着されて形成される。
【００６９】
このようにして、光偏向装置５で偏向された各レーザビームＬＹ，ＬＭ，ＬＣおよびＬＢを、１つの検出器２３に入射させることが可能となるばかりでなく、たとえば、検出器が複数個配置される際に問題となる各検出器の感度あるいは位置ずれに起因する水平同期信号のずれが除去できる。なお、水平同期検出器２３には、水平同期用折り返しミラー２５により主走査方向１ラインあたりレーザビームＬＹ，ＬＭ，ＬＣおよびＬＢが合計４回入射されることはいうまでもない。また、ミラーブロック２５ａは、型のミラー面が１つにブロックから切削加工により作成可能に設計され、アンダーカットを必要とせずに、型から抜けるよう工夫されている。
【００７０】
図８ （ｂ） には、図８ （ａ） に示した水平同期用折り返しミラー２５の変形例が示されている。
水平同期用折り返しミラー２６ （識別のため２６とする） は、図８ （ｂ） に示されるように、中間ベース１ａの所定の位置に一体的に形成された固定部材１ｂに、４枚のミラー２６Ｙ，２６Ｍ，２６Ｃおよび２６Ｂが順に貼り合わせられてもよい。この場合も、ミラー保持面の形状が工夫されることで、アンダーカットが不要に形成されている。
【００７１】
図８ （ａ） および図８ （ｂ） に示した水平同期検出用折り返しミラー２５ （あるいは２６） が利用されることで、水平同期信号を検出するために必要とされる電気部品の数が低減できる。なお、検出器２３には、それぞれのレーザビームＬＹ，ＬＭ，ＬＣおよびＬＢが１本ずつ入射される。従って、検出器２３は、各レーザビームＬ （Ｙ，Ｍ，Ｃおよびが入射されたことが検出できればよい。このことは、光偏向装置５の各反射面５αないし５εおよび５κないし５μの副走査方向の平面度が不十分であっても、各レーザビームＬ （Ｙ，Ｍ，ＣおよびＢ） の書き出し位置を正確に検知できることを示している。
【００７２】
次に、再び、図２を参照して、光偏向装置５の多面鏡５ａで反射されたレーザビームＬ （Ｙ，Ｍ，ＣおよびＢ） と偏向後光学系２１を通って光走査装置１の外部へ出射される各レーザビームＬＹ，ＬＭ，ＬＣおよびＬＢの傾きと折り返しミラー３３Ｂ，３７Ｙ，３７Ｍおよび３７Ｃとの関係について説明する。
【００７３】
既に説明したように、光偏向装置５の多面鏡５ａで反射され、第１ないし第３のプラスチックレンズ２７，２９および３１により所定の収差特性が与えられた各レーザビームＬＹ，ＬＭ，ＬＣおよびＬＢは、それぞれ、第１の折り返しミラー３３Ｙ，３３Ｍ，３３Ｃおよび３３Ｂを介して所定の方向に折り返される。
【００７４】
このとき、レーザビームＬＢは、第１の折り返しミラー３３Ｂで反射されたのち、そのまま防塵ガラス３９Ｂを通って像面Ｓに案内される。これに対し、残りのレーザビームＬＹ，ＬＭおよびＬＣは、それぞれ、第２の折り返しミラー３５Ｙ，３５Ｍおよび３５Ｃに案内され、第２の折り返しミラー３５Ｙ，３５Ｍおよび３５Ｃによって、第３の折り返しミラー３７Ｙ，３７Ｍおよび３７Ｃに向かって反射され、さらに、第３の折り返しミラー３７Ｙ，３７Ｍおよび３７Ｃで反射されたのち、それぞれ、防塵ガラス３９Ｙ，３９Ｍおよび３９Ｃにより、おおむね等間隔で像面Ｓに結像される。この場合、第１の折り返しミラー３３Ｂで出射されたレーザビームＬＢとレーザビームＬＢに隣り合うレーザビームＬＣも、おおむね等間隔で像面Ｓに結像される。
【００７５】
ところで、レーザビームＬＢは、レーザ素子３Ｂを出射されたのち、多面鏡５ａと折り返しミラー３３Ｂで反射されるのみで光走査装置１から像面Ｓに向かって出射される。このことから、実質的に折り返しミラー３３Ｂ１枚のみで案内されるレーザビームＬＢが確保できる。
【００７６】
このレーザビームＬＢは、光路中に複数のミラーが存在する場合に、ミラーの数に従って増大 （逓倍） される結像面での像のさまざまな収差特性の変動あるいは主走査線曲がりなどに関し、残りのレーザビームＬ （Ｙ，ＭおよびＣ） を相対的に補正する際の基準光線として有益である。
【００７７】
なお、光路中に複数のミラーが存在する場合には、それぞれのレーザビームＬＹ，ＬＭ，ＬＣおよびＬＢごとに利用されるミラーの枚数を奇数または偶数に揃えることが好ましい。すなわち、図２によれば、レーザビームＬＢに関与するミラーの枚数は、光偏向装置５の多面鏡５ａを除いて１枚 （奇数） 、レーザビームＬＣ，ＬＭおよびＬＹに関与するミラーの枚数は、それぞれ、３枚 （奇数） である。ここで、いづれか１つのレーザビームＬＣ，ＬＭおよびＬＹに関し、第２のミラー３５が省略されたと仮定すれば、第２のミラー３５が省略された光路 （ミラーの枚数は偶数） を通るレーザビームのレンズなどの傾きなどによる主走査線曲がりの方向は、他のレーザビームすなわちミラーの枚数が奇数のレンズなど傾きなどによる主走査線曲がりの方向と逆になり、所定の色を再現する際に有害な問題である色ズレを引き起こす。
【００７８】
従って、４本のレーザビームＬＹ，ＬＭ，ＬＣおよびＬＢを重ねて所定の色を再現する際には、各レーザビームＬＹ，ＬＭ，ＬＣおよびＬＢの光路中に配置されるミラーの枚数は、実質的に、奇数または偶数に統一される。
【００７９】
図９は、第３の折り返しミラー３７Ｙ，３７Ｍおよび３７Ｃの支持機構を示す概略斜視図である。
図９によれば、第３の折り返しミラー３７ （Ｙ，ＭおよびＣ） は、それぞれ、光走査装置１の中間ベース１ａの所定の位置に、中間ベース１ａと一体的に形成された固定部４１ （Ｙ，ＭおよびＣ） 、及び、固定部４１ （Ｙ，ＭおよびＣ） に対し、対応するミラーを挟んで対向されるミラー押さえ板ばね４３ （Ｙ，ＭおよびＣ） により保持される。
【００８０】
固定部４１ （Ｙ，ＭおよびＣ） は、各ミラー３７ （Ｙ，ＭおよびＣ） の両端部 （主走査方向） に一対形成されている。一方の固定部４１ （Ｙ，ＭおよびＣ） には、それぞれ、ミラー３７ （Ｙ，ＭおよびＣ） を２点で保持するための２つの突起４５ （Ｙ，ＭおよびＣ） が形成されている。なお、２つの突起４５ （Ｙ，ＭおよびＣ） は、図９に点線で示すように、リブ４６ （Ｙ，ＭおよびＣ） であってもよい。
【００８１】
残りの固定部４１ （Ｙ，ＭおよびＣ） には、突起４５ （Ｙ，ＭおよびＣ） で保持されているミラーを、光軸に沿って移動可能に支持する止めねじ４７ （Ｙ，ＭおよびＣ） が配置されている。
【００８２】
図９から明らかなように、各ミラー３７ （Ｙ，ＭおよびＣ） は、止めねじ４７ （Ｙ，ＭおよびＣ） が前後進されることで、突起４５ （Ｙ，ＭおよびＣ） を支点として、光軸方向に移動される。
【００８３】
次に、図１ないし図９に示した光走査装置１の偏向前光学系７すなわち有限焦点レンズ９、プラスチックシリンダレンズ１７とガラスシリンダレンズ１９ （ハイブリッドシリンダレンズ１１） 、及び、偏向後光学系２１すなわち第１ないし第３のプラスチックレンズ２７，２９および３１の各レンズ （表１および表３にレンズデータとして示されている） に関し、像面Ｓに走査される各レーザビームＬＹ，ＬＭ，ＬＣおよびＬＢの球面収差、コマ収差、像面湾曲あるいは倍率誤差などをより最適なレベルに整えることのできる例について説明する。
【００８４】
表５ （偏向前光学系） および表７ （偏向後光学系） は、別の実施例に関するレンズデータを示している。なお、表６ （偏向前光学系） および表８ （偏向後光学系） に、比較例として従来から利用されている光学系のレンズデータの一例を、同様の方法で示す。
【００８５】
【表５】

【００８６】
【表６】

【００８７】
【表７】

【００８８】
【表８】

【００８９】
表９は、表１および表３の光学系の組み合わせ、 （比較例としての） 表２および表４の光学系の組み合わせ、表５および表７の光学系の組み合わせ、 （比較例としての） 表６および表８の光学系の組み合わせ、のそれぞれの結像特性を、数値的に示すエラー関数として評価したものである。
【００９０】
【表９】

【００９１】
表９に示したエラー関数は、既に説明したように、像面Ｓに導かれる各レーザビームＬの計算上の結像特性と理想的な結像特性の偏差を求めた数値であって、数値が小さいほど、理想に近い結像特性が得られることを示している。なお、表７に示されている偏向後光学系は、第１のプラスチックレンズ２７の入射面、第２のプラスチックレンズ２９の入射面、第３のプラスチックレンズ３１の入射面および出射面の合計４面の非球面係数を、４次の項まで求めた （補正した） 光学系である。また、表８に示されている偏向後光学系は、第１ないし第３のプラスチックレンズ２７，２９および３１の全ての面の非球面係数を、４次の項まで求めた （補正した） 光学系である。
【００９２】
表９から明らかなように、表５に示した偏向前光学系と表７に示した偏向後光学系とを組み合わせることで、エラー関数が最も小さい、理想条件に近い光学特性を有する光走査装置が提供される。
【００９３】
図１０ないし図１２には、図５および図７に示した偏向後光学系２１とは異なる偏向後光学系の例を示す概略図である。
図１０ないし図１２を参照すれば、偏向後光学系１２１は、第１ないし第３のプラスチックレンズ１２７，１２９および１３１を含み、図５ないし図７に示した例に比較して、各レンズの曲率あるいはトーリック面の回転対称軸の方向が、それぞれ、変更されている。
【００９４】
【発明の効果】
以上説明したように、この発明の光走査装置は、複数の光を、その回転軸方向に異なる所定の位置で反射して所定の方向に走査するただ１つの光走査手段により走査された光が入射される所定の１枚のレンズの入射面およびこの入射面に入射された光が出射される出射面のそれぞれがトーリック面を有し、上記入射面のトーリック回転対称軸と光軸を含む面と上記出射面のトーリック回転対称軸と光軸を含む面とが直交するとともに、それぞれの面のトーリック回転対称軸が相互に直交されている両面トーリックレンズを含むことから、所定の位置に結像される光の理論上の結像位置との偏差を低減できる。
【００９５】
また、この発明の光走査装置によれば、レンズの入射面の回転対称軸と出射面の回転対称軸は、相互に直交するよう、規定される。
これにより、副走査方向の全域における色消し、像面湾曲、像面歪曲および横倍率などの結像特性が改善される。
【００９６】
従って、色ずれのないカラー画像を低コストで提供できる画像形成装置およびその画像形成装置に適したマルチビーム光走査装置が提供される。
このことから、マルチビーム多色画像形成装置のコストが提供される。
【図面の簡単な説明】
【図１】この発明の実施例である光走査装置の部分平面図。
【図２】図１に示した光走査装置を光偏向装置から像面に向かう光軸に沿って切断した断面図。
【図３】図１に示した光走査装置の偏向前光学系部分を展開した光路図。
【図４】図１に示した光走査装置の偏向前折り返しミラーブロックの概略斜視図。
【図５】図１に示した光走査装置の折り返しミラーなどを省略した状態の光路図。
【図６】図１に示した光走査装置の偏向後光学系部分の各レンズのトーリック面の回転軸を示す概略斜視図。
【図７】図１に示した光走査装置の各光学部材の配置を示す概略平面図。
【図８】図１に示した光走査装置の水平同期検出用折り返しミラーの概略斜視図。
【図９】図１に示した光走査装置の出射ミラーの調整機構を示す概略斜視図。
【図１０】図５に示した光走査装置の変形例を示す光路図。
【図１１】図６に示した光走査装置の偏向後光学系部分の各レンズのトーリック面の回転軸を示す概略斜視図。
【図１２】図１０に示した光走査装置の各光学部材の配置を示す概略平面図。
【符号の説明】
１…マルチビーム光走査装置、 ３…半導体レーザ素子、
５…光偏向装置、 ７…偏向前光学系、
９…有限焦点レンズ、 １１…ハイブリッドシリンダレンズ、
１３…ミラーブロック、 １５…保持部材、
１７…プラスチックシリンダレンズ、 １９…ガラスシリンダレンズ、
２１…偏向後光学系、 ２３…水平同期検出器、
２５…水平同期用折り返しミラー、 ２７…第１の結像レンズ、
２９…第２の結像レンズ、 ３１…第３の結像レンズ、
３３…第１の折り返しミラー、 ３５…第２の折り返しミラー、
３７…第３の折り返しミラー、 ３９…防塵ガラス、
４１…固定部、 ４３…ミラー押さえ板ばね、
４５…突起、 ４７…止めねじ。[0001]
[Industrial application fields]
The present invention relates to a multi-beam optical scanning device that scans a plurality of laser beams, and a multi-beam optical scanning device that can be used for a multi-drum color printer, a multi-drum color copying machine, a high-speed laser printer, a digital copying machine, and the like. The present invention relates to an image forming apparatus used.
[0002]
[Prior art]
For example, in an image forming apparatus such as a multi-drum type color printer or a multi-drum type color copier, a plurality of image forming units corresponding to the color components subjected to color separation, and an image corresponding to the color component in the image forming unit An optical scanning device (laser exposure device) that provides data, that is, a plurality of laser beams, is used.
[0003]
In this type of image forming apparatus, an example in which a plurality of optical scanning devices are arranged corresponding to each of the image forming units, and a multi-beam optical scanning device formed so as to be able to provide a plurality of laser beams are arranged. Examples are known.
[0004]
A conventional multi-beam optical scanning device has N sets of semiconductor laser elements, cylinder lenses, and glass fθ lens groups as light sources, where N is the number of multi-beams, as seen in Japanese Patent Laid-Open No. 5-83485. There is an example in which N / 2 polygon mirrors are used. Accordingly, in the case of four laser beams, four sets of laser elements, cylinder lenses and glass fθ lens groups and two polygon mirrors are used. An example in which some lenses of the fθ lens group are used in common is also widely known.
[0005]
Japanese Patent Laid-Open No. 62-232344 shows an example in which a lens in which at least a part of the fθ lens has a toric surface is used in common. Japanese Patent Application Laid-Open No. 62-232344 proposes that some fθ lenses are made of plastic to improve the degree of design freedom of each lens surface and to improve the aberration characteristics at the imaging position. This publication also shows a method of allowing all laser beams to pass through each lens by using each lens in common.
Japanese Patent Laid-Open No. 5-34612 discloses a method in which laser beams from a plurality of light sources are incident on one polygon mirror using a half mirror.
[0006]
[Problems to be solved by the invention]
When the multi-beam optical scanning device shown in Japanese Patent Laid-Open No. 5-83485 is used, the size of the space occupied by the optical scanning device is reduced compared to the case where a plurality of optical scanning devices are used. However, as an optical scanning device alone, there are an increase in parts cost and assembly cost due to an increase in the number of lenses or mirrors, or an increase in size and weight of the optical scanning device alone. In addition, the deviation of the aberration characteristic on the imaging surface represented by the curvature of the main scanning line of the laser beam for each color component or the fθ characteristic due to the shape error or solid error or mounting error of the fθ lens is non-uniform. It is known to be.
[0007]
On the other hand, in the example in which the first fθ lens is commonly used for each laser beam, the second fθ lens arranged for each laser beam is shown. However, the shape error or the solid error of the second fθ lens is shown. Alternatively, the same inconvenience as in the example disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 5-83485 occurs due to an attachment error.
[0008]
Further, in the example shown in Japanese Patent Laid-Open No. 62-232344, only a toric surface whose shape is not optimized is arranged, so that the main scanning line curve is applied to any one of a plurality of laser beams. There is a problem that occurs. In connection with the above Japanese Patent Laid-Open No. 62-232344, an example of controlling a part of the laser beam directed to the scanning device in the optical axis direction has been proposed. Is difficult to correct.
[0009]
Furthermore, in the example shown in the above Japanese Patent Laid-Open No. 62-232344, since the amount of change in the refractive index of a lens formed of plastic due to a change in temperature is relatively large, a wide range of environmental conditions (especially temperature conditions) ), There is a problem that characteristics such as field curvature, main scanning line bending, or fθ characteristics vary greatly. However, this example has a problem that the number of lenses is increased because various conditions such as achromaticity, field curvature, field curvature, and lateral magnification must be satisfied, particularly in the entire region in the sub-scanning direction. At the same time, in order to ensure the parallelism of the main scanning lines of each laser beam, the accuracy of the housing must be very high, resulting in an increase in cost.
[0010]
On the other hand, in the example shown in Japanese Patent Laid-Open No. 5-34612, the light intensity (light quantity) of the laser beam that passes through the most half mirrors must be sufficiently secured, and the light source becomes large. become. In this type of optical scanning device, there is a problem that an optical system in the subsequent stage of the scanning device for separating the laser beam scanned by one scanning device is likely to be enlarged.
[0011]
An object of the present invention is to provide an image forming apparatus capable of providing a color image without color misregistration at a low cost and a multi-beam optical scanning apparatus suitable for the image forming apparatus.
[0012]
[Means for Solving the Problems]
The present invention has been made on the basis of the above problems, and a plurality of lights are Reflected at different predetermined positions in the direction of the rotation axis Scan in a predetermined direction Just one Optical scanning means and this Just one Each of an incident surface of a predetermined lens on which light scanned by the optical scanning unit is incident and an exit surface from which the light incident on the incident surface is emitted have a toric surface, and the toric of the incident surface is provided. A double-sided toric lens in which the surface including the rotational symmetry axis and the optical axis, the toric rotational symmetry axis of the exit surface and the surface including the optical axis are orthogonal to each other, and the toric rotational symmetry axes of the respective surfaces are orthogonal to each other ,the above Just one Imaging optical means for imaging light scanned by the optical scanning means at a predetermined imaging position;
An optical scanning device having the above is provided.
[0013]
Further, according to the present invention, the optical scanning means for scanning a plurality of lights in a predetermined direction and the rotation of the surface on which the light scanned by the optical scanning means is incident in order from the side close to the optical scanning means The optical scanning means scans the first double-sided toric lens in which the symmetry axis is defined in the main scanning direction and the rotational symmetry axis of the exit surface from which the incident light is emitted is defined in the sub-scanning direction. A second double-sided toric lens in which a rotationally symmetric axis of a surface on which light is incident is defined in the main scanning direction and a rotationally symmetric axis of an outgoing surface from which incident light is emitted is defined in the sub-scanning direction; A single-sided toric lens in which the surface on which the light scanned by the means is incident is a toric surface, the rotational symmetry axis is in the main scanning direction, and the exit surface from which the incident light is emitted is defined as a rotationally symmetric surface. The above optical scanning hand An optical scanning device having an imaging optical means for applying a predetermined image formation characteristic in each of the light scanning is provided by.
[0014]
Furthermore, according to the present invention, the optical scanning means for scanning a plurality of lights in a predetermined direction, and the rotation of the surface on which the light scanned by the optical scanning means is incident in order from the side close to the optical scanning means The optical scanning means scans the first double-sided toric lens in which the symmetry axis is defined in the main scanning direction and the rotational symmetry axis of the exit surface from which the incident light is emitted is defined in the sub-scanning direction. A second double-sided toric lens in which a rotationally symmetric axis of a surface on which light is incident is defined in the main scanning direction and a rotationally symmetric axis of an exit surface from which incident light is emitted is defined in the main scanning direction; A single-sided toric lens in which the surface on which the light scanned by the optical scanning means is incident is a toric surface, the axis of rotational symmetry is defined in the main scanning direction and the rotationally symmetric surface of the outgoing surface from which the incident light is emitted; Including, above An optical scanning device having an imaging optical means for applying a predetermined image formation characteristic in each of the light scanned by the scanning means.
Still further, according to the present invention, a plurality of light sources, a first optical means for grouping a plurality of lights from the plurality of light sources into a light beam group that can be regarded as a bundle of light beams, and the first optical means. And a first to third lens arrayed in order from the side closer to the scanning means, and the shapes of the entrance surface and the exit surface are toric. The rotational symmetry axis of the incident surface is defined in the main scanning direction in which the light beam is scanned by the scanning means, and the rotational symmetry axis of the exit surface is defined in the sub-scanning direction orthogonal to the main scanning direction. The first lens, the entrance surface and the exit surface are each formed in a toric shape, the rotational symmetry axis of the entrance surface is defined in the main scanning direction, and the rotational symmetry axis of the exit surface is defined in the sub-scanning direction. Is A second lens, a third lens in which the shape of the incident surface is toric, the shape of the exit surface is a rotationally symmetric surface, and the rotational symmetry axis of the incident surface is such that the ray group is defined in the main scanning direction; And a second optical means for separating the light beam grouped by the first optical means into the original number of lights, and forming each light in a substantially linear form at a predetermined position, and There is provided an optical scanning device having third optical means for guiding the light beam group having passed through at least a part of the second optical means to approximately one point.
[0015]
Furthermore, according to the present invention, a plurality of light sources, a first optical means for grouping a plurality of lights from the plurality of light sources into a light beam group that can be regarded as a bundle of light beams, and the first optical means. And a first to third lens arrayed in order from the side closer to the scanning means, and the shapes of the entrance surface and the exit surface are toric. The rotational symmetry axis of the incident surface is defined in the main scanning direction orthogonal to the main scanning direction in which the light beam is scanned by the scanning means, and the rotational symmetry axis of the exit surface is defined in the sub-scanning direction. The first lens, the entrance surface and the exit surface are each formed in a toric shape, the rotational symmetry axis of the entrance surface is defined in the main scanning direction, and the rotational symmetry axis of the exit surface is defined in the main scanning direction. Is A second lens, a third lens in which the shape of the incident surface is toric, the shape of the exit surface is a rotationally symmetric surface, and the rotational symmetry axis of the incident surface is such that the ray group is defined in the main scanning direction; And a second optical means for separating the light beam grouped by the first optical means into the original number of lights, and forming each light in a substantially linear form at a predetermined position, and There is provided an optical scanning device having third optical means for guiding the light beam group having passed through at least a part of the second optical means to approximately one point.
[0016]
[Action]
In the optical scanning device of the present invention, each of the incident surface on which the light scanned by the optical scanning means is incident and the exit surface from which the light incident on the incident surface is emitted have a toric surface. The toric rotational symmetry axis is orthogonal to the plane including the optical axis from the incident surface to the exit surface, and further includes a double-sided toric lens that is orthogonal to each other. The deviation from the theoretical imaging position can be reduced.
[0017]
Further, according to the optical scanning device of the present invention, the rotational symmetry axis of the entrance surface of the first lens and the rotational symmetry axis of the exit surface are defined to be orthogonal to each other.
Thereby, image forming characteristics such as achromaticity, field curvature, field distortion, and lateral magnification in the entire region in the sub-scanning direction are improved.
[0018]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
1 and 2 are a schematic plan view and a schematic cross-sectional view of a multi-beam optical scanning apparatus which is an embodiment of the present invention. In a color laser beam printer, normally, four types of image data obtained by color separation for each color component of yellow = Y, magenta = M, cyan = C, and black = B, and Y, M, C, and B are used. Since four sets of various apparatuses for forming an image for each color component corresponding to each are used, by adding Y, M, C and B to each reference symbol, image data for each color component and each The device corresponding to is identified.
[0019]
1 and 2, the multi-beam optical scanning device 1 includes first to fourth semiconductor lasers that generate laser beams (light beams) LY, LM, LC, and LB corresponding to image data for each color component. (Ie, light source, hereinafter referred to as a laser element) 3Y, 3M, 3C and 3B and laser beams L (Y, M, C and B) emitted from the respective laser elements 3 (Y, M, C and B) ) Is scanned (deflected) at a predetermined linear velocity toward an image plane (an imaging target disposed at a predetermined position, for example, the surface of a photosensitive drum) S (only one) optical deflector (scanning means) ) 5 etc.
[0020]
The respective laser elements 3Y, 3M, 3C and 3B are arranged at a predetermined angle with respect to the optical deflecting device 5 in the order of 3Y, 3M, 3C and 3B. Note that the laser element corresponding to the laser element 3B, that is, the B (black) image, allows the laser beam LB directed toward the reflection surface of the optical deflector 5 to be directly incident on the optical deflector 5 (without being reflected). Be placed.
[0021]
Between each laser element 3 (Y, M, C and B) and the optical deflecting device 5, a laser beam L (Y, M, C and B) from the laser element 3 (Y, M, C and B) is provided. The light source side optical system, that is, the pre-deflection optical systems 7Y, 7M, 7C and 7B for arranging the cross-sectional beam spot shape into a predetermined shape is disposed.
[0022]
For example, the light deflecting device 5 includes a polygon mirror body 5a in which eight plane reflecting mirrors (surfaces) 5α to 5ε and 5κ to 5μ are arranged in a regular polygon shape, and a polygon mirror body 5a at a predetermined speed. The motor 5m is rotated in the direction. The polygon mirror body 5a is formed of, for example, an aluminum alloy. Further, the reflecting surfaces 5α to 5ε and 5κ to 5μ of the polygon mirror 5a are cut out along a plane perpendicular to the plane including the direction in which the polygon mirror body 5a is rotated, and then, for example, S _i O ₂ It is provided that a surface reflective layer such as is deposited.
[0023]
The pre-deflection optical system 7 (Y, M, C, and B) is optically deflected with respect to the laser beams L (Y, M, C, and B) from the respective laser elements 3 (Y, M, C, and B). A direction in which the laser beam L 1 (Y, M, C and B) is deflected by the device 5 (that is, a first direction, hereinafter referred to as a main scanning direction) and a second direction orthogonal to the first direction (hereinafter, referred to as “first direction”) The finite focal lenses 9Y, 9M, 9C and 9B which give a predetermined convergence with respect to both the sub-scanning direction) and the laser beam L (Y which has passed through the respective finite focal lenses 9 (Y, M, C and B). , M, C, and B) and the hybrid cylinder lenses 11Y, 11M, 11C, and 11B that give further convergence only in the sub-scanning direction, and the respective hybrid cylinder lenses 11 (Y, M, C). And B) the four laser beams L (Y, M, C, and B) that have passed through are bent toward the respective deflection surfaces (reflection surfaces) 5α to 5ε and 5κ to 5μ of the optical deflection device 5 (only one ) Pre-deflection folding mirror block (multi-stage reflection means) 13 and the like. The laser element 3 (Y, M, C and B), the finite focal lens 9 (Y, M, C and B), the hybrid cylinder lens 11 (Y, M, C and B), and the mirror block (folding mirror) 13 is integrally disposed on a holding member 15 formed of, for example, an aluminum alloy.
[0024]
Each of the finite focal lenses 9 (Y, M, C, and B) is formed of an aspheric glass lens or a spherical glass lens bonded with an aspheric surface using UV curable plastic. Each lens is fixed on the holding member 15 via a lens barrel (lens holding ring) (not shown) formed of a material having substantially the same coefficient of thermal expansion as that of the holding member 15.
[0025]
The hybrid cylinder lens 11 (Y, M, C and B) includes plastic cylinder lenses 17Y, 17M, 17C and 17B and glass cylinder lenses 19Y, 19M, 19C and 19B, respectively (see FIGS. 3 and 5). Details are shown).
[0026]
Each plastic cylinder lens 17 (Y, M, C, and B) and glass cylinder lens 19 (Y, M, C, and B) have substantially the same curvature in the sub-scanning direction. Each plastic cylinder lens 17 (Y, M, C and B) is formed of a material such as PMMA (polymethylmethacryl). The glass cylinder lens 19 (Y, M, C, and B) is formed of a material such as SFS1. The cylinder lenses 17 and 19 are fixed on the holding member 15 via a lens barrel (lens holding ring) (not shown) formed of a material having a coefficient of thermal expansion substantially equal to that of the holding member 15. The finite focal lens 9 (Y, M, C, and B) and the hybrid cylinder lens 11 (Y, M, C, and B) may be held by the same lens barrel.
[0027]
The mirror block 13 includes a block main body 13a formed of a material having a low coefficient of thermal expansion, for example, an aluminum alloy, and a predetermined surface of the block main body 13a. The number of reflection surfaces 13Y, 13M, and 13C arranged by a number smaller by “1” than the number of (see FIG. 4 to be described later).
[0028]
Between the optical deflecting device 5 and the image plane S, the laser beams L (Y, M, C and B) deflected by the reflecting surfaces 5α to 5ε and 5κ to 5μ of the optical deflecting device 5 are applied to the image plane S. Each of the laser beams L (Y, M, C, and B) that have passed through the image plane side optical system, that is, the post-deflection optical system 21 and the post-deflection optical system 21 for forming a substantially linear image at a predetermined position. The (only one) horizontal synchronization detector 23 for detecting a part, and the four pieces of light that are disposed between the post-deflection optical system 21 and the horizontal synchronization detector 23 and passed through the post-deflection optical system 21 A (only one) horizontal synchronization folding mirror 25 is disposed to reflect a part of the laser beam L (Y, M, C and B) toward the horizontal synchronization detector 23.
[0029]
The post-deflection optical system 21 has a wide deflection width (that is, the length in the main scanning direction on the image plane S of the laser beam L (Y, M, C, and B) deflected to the image plane by the optical deflector 5). The four laser beams L (Y, M, C, and B) deflected by the respective reflecting surfaces 5α to 5ε and 5κ to 5μ of the optical deflecting device 5 are given predetermined aberration characteristics, and the respective laser beams L First to third imaging lenses 27, 29, and 31 are provided for suppressing fluctuations in the imaging plane (Y, M, C, and B) within a certain range.
[0030]
Between the third imaging lens (lens closest to the image plane) 31 and the image plane S of the post-deflection optical system 21, four laser beams LY, LM, LC, and LB that have passed through the lens 31 are transmitted. First folding mirrors 33Y, 33M, 33C and 33B that are folded toward the image plane S, and second folding mirrors that further fold the laser beams LY, LM, and LC that are folded by the first folding mirrors 33Y, 33M, and 33C. 35Y, 35M and 35C and third folding mirrors 37Y, 37M and 37C are arranged. As is apparent from FIG. 2, the laser beam LB corresponding to the B (black) image is folded back by the first folding mirror 33B and then guided to the image plane S without passing through another mirror. . That is, the second folding mirrors 35Y, 35M, and 35C and the third folding mirrors 37Y, 37M, and 37C are arranged for four laser beams, respectively.
[0031]
The first, second and third imaging lenses 27, 29 and 31, the first folding mirror 33 (Y, M, C and B) and the second folding mirror 35 (Y, M and C) are These are fixed to a plurality of fixing members (not shown) formed by integral molding or the like on the intermediate base 1a of the light deflection apparatus 1 by bonding or the like. Further, the third folding mirror 37 (Y, M, and C) is moved in at least one direction related to the sub-scanning direction by a fixing rib and an inclination adjusting mechanism that are formed integrally with the intermediate base 1a. (See FIG. 9).
[0032]
Third lasers 37Y, 37M, and 37C, and four lasers reflected between the first mirror 35B and the image plane S through the mirrors 33B, 37Y, 37M, and 37C, respectively. Further, dust-proof glasses 39Y, 39M, 39C and 39B for dust-proofing the inside of the light deflecting device 1 are arranged at positions where the beam L (Y, M, C and B) is emitted from the light deflecting device 1. .
[0033]
Referring to FIG. 2, each of the laser beams LY, LM, LC, and LB is approximately equally spaced by the third folding mirrors 37Y, 37M, and 37C and the first folding mirror 33B. To the outside. That is, the laser beam LB (black) is emitted from the optical deflection apparatus 1 through an optical path including the first folding mirror 33B (only one). The laser beams LY, LM, and LC are emitted from the optical deflecting device 1 through optical paths including the third folding mirrors 37Y, 37M, and 37C (each of the three mirrors). Since the number of mirrors in each optical path is one and three, they are unified to an odd number. This can provide the same phase (directionality) in the direction of bending of the main scanning line of each laser beam L (Y, M and C) reaching the image plane due to the inclination of the lens.
[0034]
Next, the pre-deflection optical system will be described in detail.
FIG. 3 is a partial cross-sectional view in which the folding mirror of the pre-deflection optical system 7 is omitted. Table 1 shows lens data of each lens of the pre-deflection optical system 7. In FIG. 3, only optical components for one laser beam LY (Y = corresponding to a yellow image) are shown as representatives. For the remaining laser beams LM, LC and LB, the outermost shell of the laser beam L (M, C and B) after passing through the last optical component of the pre-deflection optical system 7 and the optical system Only the optical axis is shown. Each of the pre-deflection optical systems 7Y and 7B, 7M and 7C includes the same finite lens 9 and the same hybrid cylinder lens 11, the distances from the laser elements 3 to the polygon mirrors are equal, and the optical axis O Are formed symmetrically with respect to each other.
[0035]
Here, the distance between the finite focus lens 9Y and the hybrid cylinder lens 11Y and the distance between the finite focus lens 9B and the hybrid cylinder lens 11B are formed to be the same. Further, the distance between the finite focus lens 9M and the hybrid cylinder lens 11M and the distance between the finite focus lens 9C and the hybrid cylinder lens 11C are formed to be the same. In this case, the distance between the lens 9Y and the lens 11Y is defined to be slightly longer than the distance between the lens 9M and the lens 11M.
[0036]
On the other hand, the distance between the hybrid cylinder lens 11Y and the reflecting surface of the light deflecting device 5 and the distance between the hybrid cylinder lens 11B and the reflecting surface of the light deflecting device 5 are formed to be the same. Further, the distance between the hybrid cylinder lens 11M and the reflecting surface of the light deflecting device 5 and the distance between the hybrid cylinder lens 11C and the reflecting surface of the light deflecting device 5 are formed to be the same. In this case, the distance between the lens 11Y and the light deflecting device 5 is defined to be slightly longer than the distance between the lens 11M and the light deflecting device 5. Note that the distances between the light emitting point 3 and the finite focal length lens 9 are equally formed in all of Y, M, C, and B. (Hereinafter, Table 1 shows lens data of the pre-deflection optical system, and Table 2 shows lens data of the optical system conventionally used as a comparative example in a similar manner.)
[0037]
[Table 1]

[0038]
[Table 2]

[0039]
According to FIG. 3, the laser beam LY emitted from the laser element 3Y is converted into a laser beam that is generally focused on the image plane S by the finite focus lens 9Y. The laser beam LY having passed through the lens 9Y is collected on the reflecting surfaces 5α to 5ε and 5κ to 5μ of the optical deflector 5 in the sub-scanning direction by the hybrid cylinder lens 11Y having power only in the sub-scanning direction. Lighted.
[0040]
The hybrid cylinder lens 11Y is formed by a PMMA cylinder lens 17Y and a glass cylinder lens 19Y having substantially the same curvature in the sub-scanning direction. The cylinder lens 17Y of PMMA has a substantially flat surface in contact with air. The cylinder lens 17Y and the cylinder lens 19Y are bonded to each other at the exit surface of the cylinder lens 17Y and the entrance surface of the cylinder lens 19Y, or the cylinder lens 17Y is integrally molded on the entrance surface of the cylinder lens 19Y. Provided. Further, the cylinder lens 19Y and the cylinder lens 17Y may be pressed from a predetermined direction by a positioning member (not shown). The material of the cylinder lens 17Y, PMMA, is formed of a material having substantially the same optical characteristics as the first to third imaging lenses 27, 29, and 31 used in the post-deflection optical system 21.
[0041]
Next, the optical characteristics of the hybrid cylinder lens 11Y will be described in detail.
Since the post-deflection optical system 21, that is, the first to third imaging lenses 27, 29, and 31 are formed of plastic, for example, PMMA, the ambient temperature (of the optical deflection device) is, for example, from 0 ° C. It is known that the refractive index n changes from 1.4876 to 1.4789 by changing between 50 ° C. In this case, an imaging plane on which the laser beam L (Y, M, C and B) that has passed through the first to third imaging lenses 27, 29 and 31 is actually condensed, that is, an imaging position in the sub-scanning direction. Fluctuates by about ± 12 mm. Here, by incorporating a lens made of the same material as that of the lens used for the post-deflection optical system 21 into the pre-deflection optical system 7 with the curvature optimized, the refractive index n varies with changes in temperature. The fluctuation of the image plane that occurs can be suppressed to about ± 0.5 mm. That is, as compared with a conventional optical system in which the pre-deflection optical system 7 is a glass lens and the post-deflection optical system 21 is a lens formed of PMMA, the refractive index due to the temperature change of the lens of the post-deflection optical system 21. It is possible to correct the chromatic aberration in the sub-scanning direction that is caused by the change in the sub-scanning direction.
[0042]
As is clear from FIG. 3, the respective laser beams LY, LM, LC, and LB are incident symmetrically with respect to the optical axis (system optical axis) of the optical deflector 1 in the sub-scanning direction. . That is, the laser beams LY and LB are incident on the polygonal mirror 5a symmetrically with respect to the optical axis O. Similarly, the laser beams LM and LC are guided to the polygon mirror 5a symmetrically with respect to the optical axis O and on the optical axis O side of the laser beams LY and LB. This indicates that the post-deflection optical system 21 can be optimized at two locations in the sub-scanning direction for each laser beam L (Y, M, C and B). Therefore, characteristics such as field curvature and astigmatism of each laser beam L (Y, M, C, and B) can be further improved, and the number of lenses in the post-deflection optical system 21 can be reduced.
[0043]
According to FIG. 4, the mirror block 13 uses the first to fourth laser beams LY, LM, LC and LB as one bundle of laser beams Lo as the reflecting surfaces 5α to 5ε and 5κ to Used to guide to 5μ. Specifically, the mirror block 13 folds the laser beam LY emitted from the laser element 3Y so as to be incident, and guides the laser beam LY to the respective reflecting surfaces 5α to 5ε and 5κ to 5μ of the light deflector 5. The second and third reflecting surfaces 13M that fold the laser beam LM from the laser element 3M and the laser beam LC from the laser element 3C toward the reflecting surfaces 5α to 5ε and 5κ to 5μ of the optical deflector 5, respectively. And 13C, and a passing region 13B for guiding the laser beam LB from the laser element 3B to the reflecting surfaces 5α to 5ε and 5κ to 5μ of the optical deflector 5 as they are.
[0044]
Each of the reflecting surfaces 13Y, 13M, and 13C is cut or cut at a predetermined angle at a position corresponding to each reflecting surface of the block main body 13a, and then, for example, a highly reflective material such as aluminum is applied to the cutting surface. Provided by being deposited. In addition, the position corresponding to each reflective surface of the block main body 13a may be mirror-finished by polishing after cutting.
[0045]
According to the mirror block shown in FIG. 4, each of the reflecting surfaces 13Y, 13M and 13C is cut out from one block body 13a, so that a relative tilt error for each mirror is reduced. Moreover, a mirror block with high accuracy can be provided by manufacturing the block body 13a by, for example, die casting.
[0046]
As described above, the laser beam LB from the laser element 3B passes through the passage region 13B on the block body 13a without intersecting with the mirror block 13, and is reflected on each reflecting surface 5α to 5ε of the light deflector 5. And guided directly to 5κ to 5μ.
[0047]
Here, the laser beam L (Y, M and C) reflected by the mirror block 13 and guided to the optical deflecting device 5 and the intensity (light quantity) of the laser beam LB directly guided to the optical deflecting device 5 will be considered. .
[0048]
As already described in the section of the prior art, Japanese Patent Application Laid-Open No. 5-34612 discloses a method of causing two or more laser beams to be incident on the reflecting surface of the optical deflector as a single bundle of laser beams. A method of overlapping laser beams in order is shown. However, by using a plurality of half mirrors, 50% of the light amount of the laser beam emitted from each laser is wasted for one reflection and transmission (each time passing through the half mirror). It is well known. In this case, even if the transmittance and reflectance of the half mirror are optimized for each laser beam, the intensity (light quantity) of one laser beam that passes through all the half mirrors is output from the laser element. It is reduced to about 25% of the emitted light amount. In addition, due to the fact that the half mirror is inclined in the optical path in the optical path and the number of half mirrors through which each laser beam passes are different, such as field curvature or astigmatism. It is known that there is a difference in characteristics for each laser beam. Different characteristics such as field curvature and astigmatism for each laser beam make it difficult to form all the laser beams on the image plane only by the same finite focal lens and cylinder lens.
[0049]
On the other hand, according to the mirror block 13 shown in FIG. 4, the laser beams LY, LM, and LC are in the previous stage that are incident on the polygonal mirror 5a of the optical deflector 5, and each laser beam LY. , LM and LC are separated in the sub-scanning direction (shown by shading in FIG. 3) and are folded by a normal mirror. Accordingly, the light quantity of each laser beam L (Y, M, C and B) supplied (reflected) toward the image plane S by the polygon mirror 5a can be maintained at 90% or more of the emitted light quantity. This not only can reduce the output of each laser, but also can uniformly correct the aberration of light reaching the image plane S, so that the laser beam can be narrowed down to cope with high definition. The laser element 3B corresponding to B (black) is guided by the polygon mirror 5a through the passage area 13B of the mirror block 13, so that not only the output capacity of the laser can be reduced but also reflected by the reflecting surface. As a result, the error of the incident angle to the polygonal mirror 5a is removed.
[0050]
Next, the relationship between the bundle of laser beams Lo reflected by the polygonal mirror 5a of the optical deflector 5 and the post-deflection optical system 21 will be described with reference to FIGS.
Table 3 shows lens data of each lens of the post-deflection optical system 21, that is, the first to third plastic lenses 27, 29, and 31.
[0051]
[Table 3]

[0052]
It should be noted that the surface of which the sub-scanning curvature is “−” is the lens shape when the surface is rotated with respect to the optical axis, and the surface where the curvature is indicated is the 1 / toric rotation target axis in the z-axis direction of the local coordinates. A shape rotated about an axis parallel to the direction shown in the column of the toric rotation target axis in a plane separated by the curvature in the direction shown in the column is shown. (Hereinafter, Table 4 shows an example of lens data of an optical system conventionally used as a comparative example in the same manner.)
[0053]
[Table 4]

[0054]
The error functions in Tables 3 and 4 (see Table 9 described later) are the calculation (computer simulation) imaging characteristics of each laser beam L guided to the image plane S and the deviation between the ideal imaging characteristics. The obtained numerical value indicates that the smaller the numerical value, the closer to ideal imaging characteristics can be obtained. The post-deflection optical system shown in Table 3 and Table 4 is an optical system in which the aspheric coefficient is “0” for any of the first to third plastic lenses 27, 29 and 31. In particular, in the optical system shown in Table 4, the rotational symmetry axes of the entrance surface and the exit surface of the toric surface are all in the same direction.
[0055]
As is clear from Tables 3 and 4, by combining the pre-deflection optical system shown in Table 1 and the post-deflection optical system shown in Table 3, the error function (see Table 9) is small and compared to ideal conditions. An optical scanning device having near-optimal optical characteristics is provided.
[0056]
FIG. 5 is an optical path development view in which the optical scanning device described in FIGS. 1 and 2 is cut along the optical axis O. FIG. In FIG. 5, only optical components for one laser beam LY (Y = corresponding to a yellow image) are representatively shown, and the remaining laser beams LM, LC and LB are represented by respective laser beams L (M , C and B) only the outermost shells and the respective optical axes are shown. The first to third folding mirrors 33B, 35Y, 35M, 35C, 37Y, 37M, and 37C are omitted. FIG. 6 is a schematic perspective view showing the rotation axis of the toric surface of the first to third imaging lenses in the optical path shown in FIG. In FIG. 6, the laser beam L (Y, M, C, and B) that passes through each lens is omitted. FIG. 7 is an optical path development view of the optical path development view shown in FIG. 5 as viewed from the direction orthogonal to the sub-scanning direction on each reflection surface of the optical deflector 5.
[0057]
According to FIGS. 5 to 7, the post-deflection optical system 21 corresponds to each of the first to third plastic toric lenses 27, 29 and 31, and each of the laser beams L (Y, M, C and B). The dustproof glass 39Y, 39M, 39C and 39B are arranged.
[0058]
The first to third plastic toric lenses 27, 29, and 31 are respectively connected to the hybrid cylinder lens 11 (Y, M, C, and C) as described above with respect to the pre-deflection optical system 7 (Y, M, C, and B). B) is formed of a material substantially the same as the plastic cylinder lens 17 (Y, M, C and B) used for B, for example, PMMA (polymethylmethacryl). Note that the laser beams LY, LM, LC, and LB bundled in one bundle of laser beams Lo at the front stage of the optical deflecting device 5 are generally in the same bundle state, and the first to third plastic torics. Passed through lenses 27, 29 and 31.
[0059]
The first plastic toric lens 27 has an incident surface (on the optical deflector 5 side) 27 _in And exit surface (image surface S side) 27 _ra Both are toric lenses formed on a toric surface. The toric rotational symmetry axis of each surface of the lens 27 is the incident surface 27. _in In the main scanning direction (FIG. 6, R27 _in In addition, the emission surface 27 _ra With respect to the sub-scanning direction (FIG. 6, R27 _ra ), That is, the entrance surface 27. _in Toric rotational symmetry axis and exit surface 27 _ra Are extended so as to be orthogonal to each other. The incident surface 27 _in And exit surface 27 _ra The combined power in the sub-scanning direction is defined as negative.
[0060]
The second plastic toric lens 29 has an incident surface (on the optical deflection device 5 side) 29 _in And exit surface (image surface S side) 29 _ra Both are toric lenses formed on a toric surface. The toric rotational symmetry axis of each surface of the lens 29 is the incident surface 29. _in In the main scanning direction (FIG. 6, R29 _in In addition, the emission surface 29 _ra With respect to the sub-scanning direction (FIG. 6, R29 _ra ), That is, the incident surface 29 _in Toric rotational symmetry axis and exit surface 27 _ra Are extended so as to be orthogonal to each other. The incident surface 29 _in And exit surface 29 _ra The combined power in the sub-scanning direction is defined positively.
[0061]
A third plastic toric lens (final lens) 31 is an incident surface (on the optical deflector 5 side) 31 _in Is the toric surface and the exit surface (image surface S side) 31 _ra Is a one-sided toric lens formed on a rotationally symmetric aspherical surface. Incident surface 31 of lens 31 _in The toric rotational symmetry axis of the main scanning direction (FIG. 6, R31 _in ). The exit surface 31 _ra Needless to say, is rotated around the optical axis O. Further, the incident surface 31 _in And emission surface 31 _ra The combined power in the sub-scanning direction is defined positively.
[0062]
Next, the toric axis of the first to third plastic lenses, the fluctuation of the image plane, and the aberration characteristics will be considered.
In a conventionally used optical scanning device, the toric axes of all toric lenses are defined along the main scanning direction. In this case, as already described, aberration characteristics such as spherical aberration, coma aberration, field curvature, or magnification error on the imaging surface cannot be set independently in the sub-scanning direction.
[0063]
On the other hand, by defining independently the toric rotational symmetry axes of the first plastic lens 27 and the second plastic lens, spherical aberration, coma aberration, field curvature, magnification error, etc. in the sub-scanning direction, The first to third plastic lenses 27, 29 and 31 can be optimized independently. The exit surface (rotating aspheric surface) 31 of the third toric lens 31 _ra Is used for suppressing the influence on the characteristics in the sub-scanning direction and finely adjusting various characteristics in the main scanning direction. Further, when the combined powers of the first plastic lens 27, the second plastic lens 29, and the third plastic lens 31 in the sub-scanning direction are sequentially set to negative, positive, and positive, the optical deflector 5 The reflection angle of the laser beam reflected by each reflecting surface can be maximized.
According to FIG. 5, the respective laser beams LY, LM, LC and LB reflected by the polygonal mirror 5 a of the optical deflecting device 5 are the materials of the lenses 27, 29 and 31 of the post-deflection optical system 21. In order to reduce the positional deviation in the sub-scanning direction on the image plane S due to the refractive index change due to the temperature change of PMMA or the thermal expansion, on the optical axis, the image plane S side is closer to the combined node position of the post-deflection optical system 21 It is passed through a slightly shifted position and guided to the image plane S. That is, the lens surface passing position of each laser beam LY, LM, LC, and LB reflected by the polygon mirror 5 a in the sub-scanning direction is the incident surface 27 of the first lens 27. _in And the exit surface 31 of the third lens 31 _ra And in the opposite direction across the optical axis. As an example, referring to the laser beam LC, the laser element 3C is disposed above the optical axis O at a predetermined angle with respect to the optical axis O. The laser beam LC from the laser element 3 </ b> C is passed above the optical axis O by the polygon mirror 5 a and is incident on the incident surface 27 of the first toric lens 27. _in Is passed above the optical axis O and in the immediate vicinity of the optical axis O, and the emission surface 27 of the first toric lens 27 _ra And the incident surface 29 of the second toric lens 29 _in Then, the light passes through the vicinity of the optical axis O and below the optical axis O and is guided to the third toric lens 31. The passing positions of the lens 27 and the lens 31 in the sub-scanning direction are the finite focus lenses 9Y, 9M, 9C and 9B of the pre-deflection optical systems 7Y, 7M, 7C and 7B, and the hybrid cylinder lenses 11Y, 11M, 11C and This is easily achieved by optimally arranging the respective optical axes of 11B.
[0064]
According to FIG. 7, the laser beams LY, LM, LC, and LB emitted from the laser elements 3Y, 3M, 3C, and 3B are respectively passed through the corresponding pre-deflection optical system and rotated at a predetermined speed. The light is deflected (continuously reflected) toward the post-deflection optical system through the polygonal mirror 5a. As already described, each laser beam L (Y, M, C and B) incident on the polygonal mirror 5a is transmitted to the pre-deflection optical system 7 (Y, M, C and B) and the polygonal mirror 5a (optical deflecting device). 5) is guided to the polygonal mirror 5a as a bundle of laser beams Lo in the main scanning direction by the mirror block 13 disposed between.
[0065]
Each laser beam L (Y, M, C, and B) reflected by the polygon mirror 5a of the light deflecting device 5 and passed through the post-deflection optical system 21, that is, the first to third toric lenses 27, 29, and 31. Each laser beam L (Y, M, C, and B) corresponding to outside the image area of the image plane S passes through (only one) the horizontal synchronization folding mirror 25 (only one ) Reflected by the horizontal synchronization detector 23.
[0066]
8 (a) and 8 (b) guide each laser beam LY, LM, LC and LB deflected to the image plane S through the optical path shown in FIG. 7 to only one horizontal synchronization detector. A horizontal synchronization folding mirror is shown.
[0067]
According to FIG. 8A, the horizontal synchronization folding mirror 25 reflects the respective laser beams LY, LM, LC, and LB to the horizontal synchronization detector 23 at different timings in the main scanning direction, and performs sub-scanning. The first to fourth folding mirror surfaces 25Y, 25M, and 25C formed at different angles in both the main scanning direction and the sub-scanning direction so that substantially the same height can be provided on the horizontal synchronization detector 23 in the direction. And 25B and a mirror block 25a for holding the respective mirrors 25 (Y, M, C, and B) integrally.
[0068]
The mirror block 25a is molded by, for example, glass-filled PC (polycarbonate). Each mirror 25 (Y, M, C and B) is formed by evaporating a metal such as aluminum at a corresponding position of the block 25a formed at a predetermined angle.
[0069]
Thus, not only can each laser beam LY, LM, LC and LB deflected by the optical deflecting device 5 be made incident on one detector 23, but also, for example, a plurality of detectors are arranged. In this case, it is possible to remove the horizontal synchronization signal shift caused by the sensitivity or position shift of each detector, which is a problem when the detection is performed. It goes without saying that the laser beam LY, LM, LC and LB are incident on the horizontal synchronization detector 23 a total of four times per line in the main scanning direction by the horizontal synchronization folding mirror 25. The mirror block 25a is designed so that a single mirror surface of the mold can be formed by cutting from the block, and is designed to come out of the mold without requiring an undercut.
[0070]
FIG. 8B shows a modification of the horizontal synchronization folding mirror 25 shown in FIG.
As shown in FIG. 8B, the horizontal synchronization folding mirror 26 (denoted 26 for identification) includes four mirrors on a fixing member 1b integrally formed at a predetermined position of the intermediate base 1a. 26Y, 26M, 26C, and 26B may be bonded in order. Also in this case, the undercut is unnecessary because the shape of the mirror holding surface is devised.
[0071]
By using the horizontal synchronization detecting folding mirror 25 (or 26) shown in FIGS. 8A and 8B, the number of electrical components required to detect the horizontal synchronization signal is reduced. it can. Each of the laser beams LY, LM, LC, and LB is incident on the detector 23 one by one. Therefore, the detector 23 only needs to be able to detect that each laser beam L (Y, M, C, and the incident light is incident. This shows that even if the directional flatness is insufficient, the writing position of each laser beam L (Y, M, C and B) can be detected accurately.
[0072]
Next, referring again to FIG. 2, the laser beam L (Y, M, C, and B) reflected by the polygon mirror 5 a of the optical deflecting device 5 and the post-deflection optical system 21 pass through the optical scanning device 1. The relationship between the inclination of each laser beam LY, LM, LC and LB emitted to the outside and the folding mirrors 33B, 37Y, 37M and 37C will be described.
[0073]
As already described, the laser beams LY, LM, LC, and LB reflected by the polygon mirror 5a of the optical deflector 5 and given predetermined aberration characteristics by the first to third plastic lenses 27, 29, and 31 are provided. Are folded in a predetermined direction via the first folding mirrors 33Y, 33M, 33C and 33B, respectively.
[0074]
At this time, the laser beam LB is reflected by the first folding mirror 33B and then guided to the image plane S as it is through the dust-proof glass 39B. In contrast, the remaining laser beams LY, LM, and LC are guided to the second folding mirrors 35Y, 35M, and 35C, respectively, and the third folding mirrors 37Y, 37M, 35C are guided by the second folding mirrors 35Y, 35M, and 35C. After being reflected toward 37M and 37C and further reflected by the third folding mirrors 37Y, 37M and 37C, the images are formed on the image plane S at approximately equal intervals by the dustproof glasses 39Y, 39M and 39C, respectively. . In this case, the laser beam LB emitted from the first folding mirror 33B and the laser beam LC adjacent to the laser beam LB are also formed on the image plane S at approximately equal intervals.
[0075]
By the way, the laser beam LB is emitted from the optical scanning device 1 toward the image plane S after being emitted from the laser element 3B and only reflected by the polygon mirror 5a and the folding mirror 33B. Thus, the laser beam LB guided by substantially only the folding mirror 33B1 can be secured.
[0076]
This laser beam LB remains with respect to fluctuations in various aberration characteristics of the image on the image plane that are increased (multiplied) according to the number of mirrors when there are a plurality of mirrors in the optical path, or bending of the main scanning line. This is useful as a reference beam when the laser beam L (Y, M and C) is relatively corrected.
[0077]
When there are a plurality of mirrors in the optical path, the number of mirrors used for each of the laser beams LY, LM, LC, and LB is preferably set to an odd number or an even number. That is, according to FIG. 2, the number of mirrors involved in the laser beam LB is one (odd number) except for the polygon mirror 5a of the optical deflector 5, and the number of mirrors involved in the laser beams LC, LM and LY is , Respectively, 3 (odd). Here, with respect to any one of the laser beams LC, LM, and LY, assuming that the second mirror 35 is omitted, the laser beam passing through the optical path (the number of mirrors is an even number) where the second mirror 35 is omitted. The direction of main scanning line bending due to tilting of the lens etc. is opposite to the direction of main scanning line bending due to tilting of other laser beams, that is, lenses with an odd number of mirrors, etc., which is harmful when reproducing a predetermined color Cause color misregistration.
[0078]
Therefore, when a predetermined color is reproduced by superimposing the four laser beams LY, LM, LC, and LB, the number of mirrors arranged in the optical paths of the laser beams LY, LM, LC, and LB is substantially equal. Therefore, it is unified to odd or even.
[0079]
FIG. 9 is a schematic perspective view showing a support mechanism for the third folding mirrors 37Y, 37M and 37C.
According to FIG. 9, the third folding mirror 37 (Y, M, and C) is fixed at a predetermined position of the intermediate base 1 a of the optical scanning device 1 and formed integrally with the intermediate base 1 a. (Y, M, and C) and the fixed portion 41 (Y, M, and C) are held by mirror pressing leaf springs 43 (Y, M, and C) that are opposed to each other with the corresponding mirror interposed therebetween.
[0080]
A pair of fixed portions 41 (Y, M and C) are formed at both ends (main scanning direction) of each mirror 37 (Y, M and C). On one fixing part 41 (Y, M and C), two protrusions 45 (Y, M and C) for holding the mirror 37 (Y, M and C) at two points are formed. . The two protrusions 45 (Y, M, and C) may be ribs 46 (Y, M, and C) as shown by dotted lines in FIG.
[0081]
The remaining fixing portion 41 (Y, M, and C) has a set screw 47 (Y, M, and C) that supports the mirror held by the protrusion 45 (Y, M, and C) so as to be movable along the optical axis. C) is arranged.
[0082]
As is clear from FIG. 9, each mirror 37 (Y, M, and C) has the projection 45 (Y, M, and C) as a fulcrum by moving the set screw 47 (Y, M, and C) back and forth. , Moved in the optical axis direction.
[0083]
Next, the pre-deflection optical system 7 of the optical scanning device 1 shown in FIGS. 1 to 9, that is, the finite focal lens 9, the plastic cylinder lens 17 and the glass cylinder lens 19 (hybrid cylinder lens 11), and the post-deflection optical system 21 That is, for each of the first to third plastic lenses 27, 29 and 31 (shown as lens data in Tables 1 and 3), the laser beams LY, LM, LC scanned on the image plane S and An example in which LB spherical aberration, coma aberration, field curvature, or magnification error can be adjusted to a more optimal level will be described.
[0084]
Table 5 (pre-deflection optical system) and Table 7 (post-deflection optical system) show lens data for another example. Table 6 (pre-deflection optical system) and Table 8 (post-deflection optical system) show an example of lens data of an optical system conventionally used as a comparative example by the same method.
[0085]
[Table 5]

[0086]
[Table 6]

[0087]
[Table 7]

[0088]
[Table 8]

[0089]
Table 9 is a combination of optical systems of Table 1 and Table 3, a combination of optical systems of Table 2 and Table 4 (as a comparative example), a combination of optical systems of Table 5 and Table 7, and (as a comparative example) 6 and the optical system combinations shown in Table 8 are evaluated as error functions numerically.
[0090]
[Table 9]

[0091]
The error function shown in Table 9 is a numerical value obtained by calculating a deviation between the calculated imaging characteristic and the ideal imaging characteristic of each laser beam L guided to the image plane S as described above. This indicates that the smaller the is, the closer to ideal imaging characteristics can be obtained. The post-deflection optical system shown in Table 7 is a total of 4 of the incident surface of the first plastic lens 27, the incident surface of the second plastic lens 29, the incident surface and the exit surface of the third plastic lens 31. This is an optical system that calculates (corrects) the aspherical coefficient of the surface up to the fourth-order term. The post-deflection optical system shown in Table 8 calculated (corrected) the aspheric coefficients of all surfaces of the first to third plastic lenses 27, 29, and 31 up to the fourth order term. It is a system.
[0092]
As is apparent from Table 9, by combining the pre-deflection optical system shown in Table 5 and the post-deflection optical system shown in Table 7, an optical scanning device having an optical characteristic close to ideal conditions with the smallest error function Is provided.
[0093]
10 to 12 are schematic diagrams showing examples of post-deflection optical systems different from the post-deflection optical system 21 shown in FIGS. 5 and 7.
Referring to FIGS. 10 to 12, the post-deflection optical system 121 includes first to third plastic lenses 127, 129, and 131. Compared to the examples shown in FIGS. The curvature or the direction of the rotational symmetry axis of the toric surface has been changed.
[0094]
【The invention's effect】
As described above, the present invention of The optical scanning device A plurality of lights are reflected at a predetermined position different in the rotation axis direction and scanned in a predetermined direction. Each of an incident surface of a predetermined lens on which light scanned by the optical scanning unit is incident and an exit surface from which the light incident on the incident surface is emitted have a toric surface, and the toric of the incident surface is provided. A double-sided toric lens in which the plane including the rotational symmetry axis and the optical axis, the toric rotational symmetry axis of the exit surface and the plane including the optical axis are orthogonal, and the toric rotational symmetry axes of the respective planes are orthogonal to each other Therefore, the deviation of the light imaged at a predetermined position from the theoretical image formation position can be reduced.
[0095]
Further, according to the optical scanning device of the present invention, the rotational symmetry axis of the entrance surface of the lens and the rotational symmetry axis of the exit surface are defined so as to be orthogonal to each other.
Thereby, image forming characteristics such as achromaticity, field curvature, field distortion, and lateral magnification in the entire region in the sub-scanning direction are improved.
[0096]
Therefore, an image forming apparatus capable of providing a color image free from color misregistration at low cost and a multi-beam optical scanning apparatus suitable for the image forming apparatus are provided.
This provides the cost of the multi-beam multicolor image forming apparatus.
[Brief description of the drawings]
FIG. 1 is a partial plan view of an optical scanning device according to an embodiment of the present invention.
2 is a cross-sectional view of the optical scanning device shown in FIG. 1 cut along the optical axis from the optical deflection device toward the image plane.
3 is an optical path diagram in which a pre-deflection optical system portion of the optical scanning device shown in FIG. 1 is developed.
4 is a schematic perspective view of a pre-deflection folding mirror block of the optical scanning device shown in FIG. 1. FIG.
5 is an optical path diagram in a state where a folding mirror and the like of the optical scanning device shown in FIG. 1 are omitted.
6 is a schematic perspective view showing a rotation axis of a toric surface of each lens in a post-deflection optical system portion of the optical scanning device shown in FIG. 1. FIG.
7 is a schematic plan view showing the arrangement of optical members of the optical scanning device shown in FIG.
8 is a schematic perspective view of a folding mirror for horizontal synchronization detection of the optical scanning device shown in FIG.
9 is a schematic perspective view showing an adjustment mechanism of an output mirror of the optical scanning device shown in FIG.
10 is an optical path diagram showing a modification of the optical scanning device shown in FIG.
11 is a schematic perspective view showing a rotation axis of a toric surface of each lens in a post-deflection optical system portion of the optical scanning device shown in FIG. 6;
12 is a schematic plan view showing the arrangement of optical members of the optical scanning device shown in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Multi-beam optical scanning device, 3 ... Semiconductor laser element,
5 ... Optical deflection device, 7 ... Optical system before deflection,
9 ... finite focus lens, 11 ... hybrid cylinder lens,
13 ... Mirror block, 15 ... Holding member,
17 ... Plastic cylinder lens, 19 ... Glass cylinder lens,
21: post-deflection optical system, 23 ... horizontal synchronization detector,
25 ... Horizontal mirror folding mirror, 27 ... First imaging lens,
29 ... Second imaging lens, 31 ... Third imaging lens,
33 ... 1st folding mirror, 35 ... 2nd folding mirror,
37 ... Third folding mirror, 39 ... Dust-proof glass,
41 ... fixed part, 43 ... mirror holding leaf spring,
45 ... projection, 47 ... set screw.

Claims (5)

A single light scanning means for reflecting a plurality of lights at a predetermined position different in the rotation axis direction and scanning in a predetermined direction;
Each of an incident surface of a predetermined lens on which light scanned by the single light scanning unit is incident and an emission surface from which light incident on the incident surface is emitted have a toric surface, and Both the surface including the toric rotation symmetry axis and the optical axis of the incident surface are orthogonal to the surface including the toric rotation symmetry axis and the optical axis of the exit surface, and the toric rotation symmetry axes of the respective surfaces are orthogonal to each other. An imaging optical unit that includes a toric lens and forms an image of light scanned by the single optical scanning unit at a predetermined imaging position;
An optical scanning device. Optical scanning means for scanning a plurality of lights in a predetermined direction;
Rotation of an exit surface arranged in order from the side closer to the optical scanning means, the rotational symmetry axis of the surface on which the light scanned by the optical scanning means is incident is defined in the main scanning direction, and the incident light is emitted The first double-sided toric lens whose symmetry axis is defined in the sub-scanning direction and the rotational symmetry axis of the surface on which the light scanned by the optical scanning means is incident are emitted in the main scanning direction. A second double-sided toric lens in which the rotational symmetry axis of the outgoing surface is defined in the sub-scanning direction, the surface on which the light scanned by the optical scanning means is incident, and the rotational symmetry axis is the main scanning direction And a single-sided toric lens in which the exit surface from which the incident light is emitted is defined as a rotationally symmetric surface, and imaging optics that gives predetermined imaging characteristics to each light scanned by the optical scanning means Means and
An optical scanning device. Optical scanning means for scanning a plurality of lights in a predetermined direction;
Rotation of an exit surface arranged in order from the side closer to the optical scanning means, the rotational symmetry axis of the surface on which the light scanned by the optical scanning means is incident is defined in the main scanning direction, and the incident light is emitted The first double-sided toric lens whose symmetry axis is defined in the sub-scanning direction and the rotational symmetry axis of the surface on which the light scanned by the optical scanning means is incident are defined in the main scanning direction and the incident light is The second double-sided toric lens in which the rotational symmetry axis of the outgoing exit surface is defined in the main scanning direction and the surface on which the light scanned by the optical scanning means is incident are the toric surfaces and the rotational symmetry axis is the main symmetry axis. A single-sided toric lens defined on the rotationally symmetric surface of the exit surface from which the incident light is emitted in the scanning direction, and providing predetermined imaging characteristics to each light scanned by the optical scanning means Optical And the stage,
An optical scanning device. Multiple light sources;
A first optical means for grouping a plurality of lights from the plurality of light sources into a light beam group that can be regarded as a bundle of light beams;
Scanning means for scanning the light beam grouped by the first optical means in a predetermined direction;
The first to third lenses are arranged in order from the side close to the scanning means, and the shapes of the entrance surface and the exit surface are formed in a toric shape, and the rotational symmetry axis of the entrance surface is the light beam group is the scanning means. The shape of the first lens, the incident surface, and the exit surface are toric, respectively, in the main scanning direction scanned in accordance with the above and in the sub-scanning direction in which the rotational symmetry axis of the exit surface is orthogonal to the main scan direction. A second lens that is formed, the rotational symmetry axis of the entrance surface is defined in the main scanning direction, and the rotational symmetry axis of the exit surface is defined in the sub-scanning direction, the shape of the entrance surface is toric, and The shape of the exit surface is formed on a rotationally symmetric surface, the rotationally symmetric axis of the incident surface includes the third lens in which the light beam group is defined in the main scanning direction, and the light beam group collected by the first optical means. The original number Thereby separating the light, a second optical means for focusing the respective light substantially linearly in a predetermined position,
Third optical means for guiding the light beam group having passed through at least a part of the second optical means to approximately one point;
An optical scanning device. Multiple light sources;
A first optical means for grouping a plurality of lights from the plurality of light sources into a light beam group that can be regarded as a bundle of light beams;
Scanning means for scanning the light beam grouped by the first optical means in a predetermined direction;
The first to third lenses are arranged in order from the side close to the scanning means, and the shapes of the entrance surface and the exit surface are formed in a toric shape, and the rotational symmetry axis of the entrance surface is the light beam group is the scanning means. In the main scanning direction orthogonal to the main scanning direction scanned by the lens, the rotational symmetry axis of the exit surface is in the sub-scanning direction, and the shapes of the first lens, the entrance surface, and the exit surface are respectively toric. A second lens that is formed, the rotational symmetry axis of the entrance surface is defined in the main scanning direction, and the rotational symmetry axis of the exit surface is defined in the main scanning direction, respectively, and the shape of the entrance surface is toric, and The shape of the exit surface is formed on a rotationally symmetric surface, the rotationally symmetric axis of the incident surface includes the third lens in which the light beam group is defined in the main scanning direction, and the light beam group collected by the first optical means. The original number Thereby separating the light, a second optical means for focusing the respective light substantially linearly in a predetermined position,
Third optical means for guiding the light beam group having passed through at least a part of the second optical means to approximately one point;
An optical scanning device.

Images