JP3719301B2 - Optical scanning device - Google Patents

Description

【００１５】
第１整形レンズ２および第１伝達レンズ７の非球面の数式は次の数１に示すとおりであり、その非球面係数を次の表２に示す。
【００１６】
【数１】

【００１７】
【表２】

【００１８】
上記表１に示す実施例では、１走査の走査開始から走査終了までの回転多面鏡３の回転角は２ω＝２４°である。また、回転多面鏡３への光ビームａの第１反射面４での副走査方向の入射角αと光ビームｂの第２反射面５での副走査方向の入射角βはともに６°であり、回転多面鏡３の面数は１２面、回転多面鏡３の内接円半径は１７ｍｍ、第１反射面４と第２反射面５のなす角度は９０°、光源１の光ビームであるレーザー光の波長は６７０ｎｍである。
【００１９】
この実施例において、光ビームａは、副走査方向では回転多面鏡３の第１反射面４の近傍と、回転多面鏡３の第２反射面５の近傍においてそれぞれ結像するように構成している。言い換えれば、伝達光学系（第１伝達レンズ７、第２伝達レンズ９および第３伝達レンズ１０）により第１反射面４と第２反射面５が幾何光学的にほぼ共役関係にあり、また、走査光学系（第１走査レンズ１２および第２走査レンズ１３）により第２反射面５と被走査面１４がほぼ共役関係にあるように構成される。従って、回転多面鏡３の第１反射面４および第２反射面５の面倒れが良く補正され、しかも副走査方向の走査位置が一定となる。以下、この点を図面を参照してさらに詳細に説明する。
【００２０】
図２（ａ）〜（ｅ）は、回転多面鏡３の第１反射面４と第２反射面５との間の副走査方向における展開図である。本実施例の場合は、回転多面鏡３の第１反射面４の近傍の結像点Ｐは、図２（ａ）に示すように厳密には第１反射面４から僅かにずれており、第１反射面４と第１伝達レンズ７ａとの間に存在する。ここでは光源１からの光ビームａの主走査方向、副走査方向ともにこの結像点Ｐに結像させるように構成されている。
【００２１】
回転多面鏡３の第１反射面４からの結像点Ｐのずれの量ｌが大きすぎると、第１反射面４の面倒れによる被走査面１４上の走査線のずれが大きくなり問題となる。逆に、このずれの量ｌが小さいと、第１反射面４上での光ビームａの大きさが小さすぎて回転多面鏡３の第１反射面４に存在する傷、埃の影響を受けて光ビームａが散乱され、被走査面１４上に小さなビームスポットを形成することができない。また、傷、埃により光ビームａが遮られて、光パワーが低下する。従って、この結像点Ｐのずれの量ｌは適正な値が存在する。この例では、このずれの量ｌを１１ｍｍとしている。これは回転多面鏡３の第１反射面４から第２反射面５までの伝達光学系の光路長３００ｍｍに比べれば十分に小さい値であるため、面倒れの補正の効果は十分に得られる。
【００２２】
次に、具体的な計算例を示す。即ち、整形光学系による結像点Ｐの回転多面鏡３の第１反射面４からのずれの量ｌ＝１１ｍｍ、伝達光学系の副走査方向の光学倍率βｄ＝１．５７、走査光学系の副走査方向の光学倍率βｓ＝０．４１８である。これは、回転多面鏡３の第１反射面４の面倒れθ＝３ｅ−４〔ｒａｄ〕（０．０１７２°）とすると、被走査面１４上での走査線のずれδ＝２・ｌ・θ・βｄ・βｓ＝０．００４３３〔ｍｍ〕であり、この程度なら問題ない。また、本実施例での第１反射面４に入射する光ビームａの直径は、主走査方向で０．８４ｍｍ、副走査方向で０．１３ｍｍである。従って、第１反射面４での光ビームａの大きさが十分に大きく、第１反射面４による傷や埃の影響を受けることがない。一般に、主走査方向、副走査方向の少なくとも一方向の光ビームの直径が０．５ｍｍ程度あれば回転多面鏡３の反射面での傷や埃の影響を受けることがない。
【００２３】
この実施例では、第２反射面５の近傍の結像点Ｑは、丁度第２反射面５上に位置させている。ただし、これは第２反射面５からずれていても有効である。このことについてさらに詳しく説明する。図２（ａ）の伝達光学系７ａは仮の存在であるが、第１反射面４と第２反射面５が共役となる屈折力を有している。第１反射面４からｌだけずれた位置Ｐに結像する光ビームａが、光ビームｂとして仮の伝達光学系７ａにより第２反射面５の近傍に再び結像する位置をＱとする。実際の第２反射面５近傍の結像点は第２反射面５と再び結像する位置Ｑを含め、これらの間に存在することが望ましい。
【００２４】
まず、第２反射面５近傍の光ビームｂの結像点Ｑが、上記の範囲の両端にある場合について説明する。図２（ｂ）、（ｃ）は、伝達光学系７ｂにより第１反射面４と第２反射面５とが完全に共役で、伝達光学系７ｂによる結像点がＱに一致し、これに続く走査光学系１２ａによる第２反射面５と被走査面１４との関係は若干共役からずれており、光ビームｃが被走査面１４に結像する場合である。この場合は、図２（ｃ）に示すように第１反射面４の面倒れ４´は完全に補正され、第２反射面５の面倒れ５´によるずれが被走査面１４にΔとして生じる。図２（ｄ）、（ｅ）は、伝達光学系７ｃによる第１反射面４と第２反射面５との関係は若干共役からずれて構成されている場合で、伝達光学系７ｃによる結像点が第２反射面５に一致し、走査光学系１２ｂにより第２反射面５と被走査面１４とが完全に共役で、光ビームｂが光ビームｃとして被走査面１４上に結像する場合である。この場合は、図２（ｅ）に示すように、逆に第２反射面５の面倒れ５´は完全に補正され、第１反射面４による面倒れ４´が被走査面１４上にずれΔ´として生じる。なお、主光線を破線で示している。従って、第２反射面５近傍の結像点が第２反射面５と結像点Ｑとの間にあれば第１反射面４と第２反射面５の面倒れ４´、５´が逆方向の場合、面倒れ４´、５´によるずれが打ち消されて被走査面１４上の走査線の位置ずれが小さくなる。例え同方向であっても、このずれ量は図２（ｃ）、（ｅ）に示す場合と同じか良くなるわけで、少なくとも悪くなることはない。
【００２５】
次に、伝達光学系の構成について説明する。光ビームの主走査方向において、伝達光学系に必要な機能は、第１反射面４近傍のＰ点に結像する光ビームａを、平行ビームにして第２反射面５に導くこと、回転多面鏡３の回転に伴って第２反射面５上を移動する光ビームｂの移動が第２反射面５の移動に追従することの二つである。
【００２６】
図３は、伝達光学系の一例を示す主走査方向の断面展開図で、この発明の実施例を示す図ではないが、光ビームの主走査方向の機能からすれば、この図に示すように近軸的には伝達光学系のレンズ枚数はレンズ２０１の１枚だけあればよい。しかし、１枚のレンズ２０１で伝達光学系を構成すると、レンズ２０１の口径が大きくなりすぎ実用的ではない。そのため、図４の主走査方向の断面展開図に示すように、２枚のレンズ２０２、２０３で伝達光学系を構成すればレンズ口径を小さくすることができて実用的である。従って、伝達光学系に主走査方向の機能を持たせるためには、主走査方向に屈折力を有するレンズを２枚以上で構成することが望ましいことになる。一方、副走査方向おいて伝達光学系に必要な機能は、第１反射面４近傍の結像点Ｑに結像する光ビームａを光ビームｂとして第２反射面５の近傍に結像させることのみである。図５に伝達光学系の副走査方向の断面展開図を示す。副走査方向の機能からすれば、伝達光学系のレンズ枚数はレンズ２０４の１枚あればよい。以上のことから、伝達光学系に主走査方向の機能と副走査方向の機能を両方持たせるためには、３枚のレンズで構成することがよいことになる。また、この伝達光学系は、副走査方向に屈折力を有するレンズと、主走査方向に屈折力を有するレンズを組み合わせて１枚にすれば、伝達光学系のレンズ枚数を２枚にすることも可能である。この実施例では以上のことから第１伝達レンズ７、第２伝達レンズ９および第３伝達レンズ１０の３枚のレンズで伝達光学系を構成している。
【００２７】
次に、図６を参照して光ビームの光軸との交差について説明する。図６は実施例の伝達光学系の主走査方向の断面展開図であり、第１伝達ミラー８および第２伝達ミラー１１について展開した断面図である（図１参照）。即ち、回転多面鏡３は走査の期間、図示の位置を中心にして角度θ1 だけ回転する。従って、回転多面鏡３の第１反射面４では角度θ1 の２倍の２θ1 だけ光ビームａは偏向される。偏向された光ビームｂは伝達光学系である第１伝達レンズ７、第２伝達レンズ９および第３伝達レンズ１０を通過して、角度θ2 だけ偏向される。この光ビームｂは点Ｒで光軸Ｏと交差する。そして、交差した後に回転多面鏡３の第２反射面５に入射する位置において、偏向された光ビームｂと光軸Ｏとの距離は回転多面鏡３が角度θ1 だけ回転したときの反射面の移動量δに等しくなる。
【００２８】
このとき、偏向された光ビームｂは回転多面鏡３の第２反射面５に対して角度θ2 だけ入射角度が増大する側に偏向されるので、第２反射面５で反射された光ビームｃは２・θ1 ＋θ2 だけ偏向されることになる。即ち、通常の一度きり回転多面鏡に入射させて偏向する方式の光走査装置に比べて光ビームの偏向角度をθ2 だけ増大させることができる。従って、伝達光学系で走査領域の走査端を走査する光ビームｂが光軸Ｏと交差すると、第２反射面５で偏向した光ビームｃの偏向角を２・θ1 ＋θ2 だけ増大させることができる。
【００２９】
次に、図７および図８に基づいて伝達光学系のミラー枚数と光ビームの光軸との交差回数の関係を説明する。伝達光学系のミラー枚数から、走査端を走査する光ビームが光軸と交差する回数を引いた数が奇数である。即ち、図７（ａ）に示す場合は、ミラー枚数、交差回数に関して本実施例と同じ構成である。伝達光学系に使用されるミラー枚数は第１伝達ミラー８と第２伝達ミラー１１の２枚である。図８（ａ）にその展開図を示すように、この場合には光軸Ｏとの交差回数は破線の主光線で示されるように１回である。また、図７（ｂ）で示す例では、ミラー枚数は第１伝達ミラー８、第２伝達ミラー１１および第３伝達ミラー１５の３枚である。図８（ｂ）に示すその展開図から分かるように、この場合の光軸Ｏとの交差回数は２回である。従って、図７（ａ）に示す本実施例においては、二度目の偏向で回転多面鏡３が回転したときの第２反射面５上での光ビームｂの移動方向、移動量が、第２反射面５の移動方向、移動量と同じになり、第２反射面５に入射する光ビームｂが第２反射面５からはみ出すことなく追従させることができる。
【００３０】
次に、図９から図１５に基づいてこの発明の特徴である伝達光学系で発生する光ビームの回転の補正について詳しく説明する。整形光学系を介して光源１からの光ビームａが副走査方向に角度を持って下方から回転多面鏡３の第１反射面４に入射され、一度目の偏向が行われる。この一度目の偏向から光ビームｂとして二度目の偏向の間の光路が副走査方向に角度を持っているため、第２反射面５上の光ビームｂの座標系が回転してしまう。即ち、主走査方向をｙ、副走査方向をｘ、光軸方向をｚとする座標系を有する光ビームａが、副走査方向に角度をもって第１反射面４で反射され、さらに、第１伝達ミラー８で反射されると、図９に示されるように反射後の光ビームｂの座標系が回転してしまう。この光ビームｂはさらに第２伝達ミラー１１で反射され、回転多面鏡３の第２反射面５に入射されるときには、図１０に示されるように光ビームｂの座標系が回転してしまう。即ち、光ビームｂのｙ方向と主走査方向や、光ビームｂのｘ方向と副走査方向が所定の角度θだけずれてしまうことになる。
【００３１】
このように、光ビームｂが回転多面鏡３の第２反射面５で二度目の偏向が行われ、光ビームｃとなるときには、図１１に示されるように偏向された光ビームｃの座標系は常に角度θ傾いている。角度θ傾いた光ビームｃは、アナモフィックな走査光学系で被走査面１４上に結像させても一点に結像されず、ビームスポットの形状が崩れてしまう。このような場合、図１２に示すように副走査方向に屈折力を有するシリンドリカルレンズ２１１を光ビームｃの傾きθに沿ように傾けて配置すれば、被走査面１４上に結像する光ビームｃの結像特性は良好となるが、シリンドリカルレンズ２１１の副走査方向の有効径を大きくする必要がある。また、被走査面１４上での走査線がシリンドリカルレンズ２１１の傾きに応じて傾いてしまうという問題点を有する。
【００３２】
図１３は伝達光学系の光路を主走査方向に投影した図である。回転多面鏡３の第１反射面４による一度目の偏向後の光軸Ｏ₁ と回転多面鏡３の第２反射面５による二度目の偏向前の光軸Ｏ₂ とのなす角度をγとする。第１反射面４および第２反射面５への光ビームａおよび光ビームｂの副走査方向の入射角をそれぞれα、βとする。図１４に光ビームｂの回転角度を計算した結果を示す。回転角度θは反時計回りが正である。ただし、次の条件に基づく。
【００３３】
▲１▼ 回転多面鏡３の大きさに対して、第１反射面４から第２反射面５までの光路長が十分に大きい。
【００３４】
▲２▼ １度目の偏向後の光軸Ｏ₁ と２度目の偏向前の光軸Ｏ₂ の２等分線に関して、第１反射面４から第２反射面５までの光路が対称である。
【００３５】
図１４に示されるように、副走査方向における第１反射面４および第２反射面５への入射角αおよび入射角βが同じ場合と、γが１８０°の場合に回転角度θがゼロになる。なお、上記条件▲１▼、▲２▼とは異なり、光路長に対して回転多面鏡３の大きさが無視できない場合には、第１反射面４および第２反射面５への入射角αおよび入射角βが異なれば、回転角度θの値は回転多面鏡３の大きさに若干依存する。また、光路が対称でない場合にも、入射角αと入射角βが異なれば回転角度θの値は若干変動する。ただし、入射角α＝入射角βであれば、常に回転角度θ＝０となる。
【００３６】
本実施例において、第１反射面４および第２反射面５への光ビームａの入射角αおよび光ビームｂの入射角βのみを変更し、仮に光ビームａの第１反射面４への入射角α＝３°、光ビームｂの第２反射面への入射角β＝６°とすると、走査端を走査する光ビームｃによるビームスポット形状は、図１５に示すように崩れた形状となる。この図はビームスポットの等強度線図である。なお、ビームスポットの形状の崩れはビームスポットの大きさに依存し、より小さいビームスポットを形成しようとすると形状の崩れはいっそう悪くなってしまう。
【００３７】
そこで、入射角α＝入射角βとすれば、図１４に示されるように回転角度θ＝０となり、ビームスポットの形状が良好となる。本実施例では入射角α＝入射角β＝６°であり、走査端を走査する光ビームｃ１、ｃ２によるビームスポット形状は図１６に示すようになり良好である。また、γ＝１８０°であっても回転角度θ＝０となるので、この場合にもビームスポット形状は良好となる。
【００３８】
次に、γ＝１８０°、即ち、第１反射面４と第２反射面５が平行な場合について説明する。図１３において、光軸Ｏ₁ と光軸Ｏ₂ のなす角度がγであるが、この角度は第１反射面４と第２反射面５とのなす角度に等しい。本実施例の場合、γ＝９０°であるが、本実施例とは別に、第１反射面４と第２反射面５が平行である場合には、γ＝１８０°となり、図１４のグラフから光ビームの回転角度θ＝０となる。この場合の光路図を図２５に示す。即ち、回転多面鏡３の第１反射面４で上方に偏向された光ビームｂは第１伝達ミラー８で反射され、回転多面鏡３の直上を通過し回転軸６と交差し、第２伝達ミラー１１で反射されて回転多面鏡３の第２反射面５に上方から入射し、ここで下方に偏向されて光ビームｃとなる。
【００３９】
次に、偏向で発生する光ビームの回転補正について図１７から図２２に基づいて説明する。副走査方向において角度を有して走査器の反射面に入射させるタイプの光走査装置では、図１７（ａ）に示すように主走査方向ｙ、副走査方向ｘ、光軸方向ｚの座標系を有する光ビームｂが副走査方向に角度をもって回転多面鏡３の第２反射面５に入射すると、ここで偏向された光ビームｃは湾曲し、光ビームｃの座標系が回転してしまう。このとき、走査中心の光ビームｃ₀ は回転しないが、走査端を走査する光ビームｃ₁ 、ｃ₂ は図１７（ｂ）に示すように両走査端で互いに異なる方向に回転される。この走査端を走査する傾いた光ビームｃ₁ 、ｃ₂ は、アナモフィックな走査光学系で被走査面１４上に結像しても一点に結像されず、ビームスポット形状が崩れてしまい、被走査面１４上で良好な結像とはならない。
【００４０】
本実施例においては、第２走査レンズ１３を偏心させて配置しており、しかも図１９に示すように、第２走査レンズ１３に入射する光ビームの軌跡Ｃは湾曲するため、走査端を走査する光ビームｃ₁、ｃ₂は第２走査レンズ１３の中心軸Ｎから離れた位置に入射する。なお、第２走査レンズ１３の中心軸Ｎは、第２走査レンズ１３の光軸を通り、主走査方向に平行な軸である。ここで、仮に、走査端を走査する光ビームｃ₁、ｃ₂を第２走査レンズ１３の中心軸Ｎを透過させるように構成すると、走査端を走査する光ビームｃ₁、ｃ₂によるビームスポット形状は図１８に示すような崩れた形状となる。ビームスポットの形状の崩れはレンズで絞り込む前の光ビームの大きさに依存し、より小さいビームスポットを形成しようとすると、形状の崩れはいっそう悪くなる。なお、本実施例においては整形光学系の第１整形レンズ２は光軸回りに回転対称なレンズなので、回転多面鏡３の第１反射面４に入射する光ビームａの結像は、主走査方向、副走査方向とで区別がない。従って、第１反射面４により偏向された光ビームｂの回転は問題とならない。
【００４１】
このビームスポット形状の崩れを、本実施例においては、走査端を走査する光ビームｃ₁、ｃ₂を第２走査レンズ１３の中心軸Ｎから離れた位置に入射させて補正している。図２０に回転多面鏡３から第２走査レンズ１３までの光路の副走査方向の断面を示す。図示されている光ビームｃ₁、ｃ₂は走査端を走査する光ビームである。図２０において、回転多面鏡３の第２反射面５に入射する光ビームｃ₁、ｃ₂に対して、射出する光ビームは下側に位置する。さらに光ビームｃ₁、ｃ₂は、第１走査レンズ１２を透過後、第２走査レンズ１３の光軸Ｏから下側に離れた位置で、第２走査レンズ１３を透過する。なお、第２走査レンズ１３の光軸Ｏと第２走査レンズ１３に入射する光ビームとはほぼ平行である。
【００４２】
本実施例では、第２走査レンズ１３は、走査中心を走査する光ビームｃ₀に対して、副走査方向で、かつ図２０の矢印Ｅの方向に２．６７ｍｍ偏心させて配置している。すなわち、走査中心を走査する光ビームｃ₀は、第２走査レンズ１３の光軸から２．６７ｍｍ離れた位置に入射する。また、走査端を走査する光ビームｃ₁、ｃ₂は、第２走査レンズ１３の光軸から７．０２ｍｍ離れた位置に入射する。その結果、走査端を走査する光ビームｃ₁ 、ｃ₂ によるビームスポット形状は図１６に示すように良好となる。
【００４３】
本発明者が行なったシミュレーションによると、このように、走査端を走査する光ビームｃ₁、ｃ₂が、第２走査レンズ１３のようなアナモフィックレンズの光軸から、副走査方向に隔離した位置を透過するように構成すると、光ビームの回転を補正し、ビームスポット形状の崩れを補正することができる。特に、上記したように、回転多面鏡３の反射面に入射する光ビームに対して、回転多面鏡３から射出する光ビームが存在する側（図２０では下側）と、第２走査レンズ１３の光軸に対して、第２走査レンズ１３に入射する光ビームが存在する側（図２０では下側）が一致すれば、ビームスポット形状を補正する効果を有する。
【００４４】
本実施例の第２走査レンズ１３は入射面が正の屈折力を有しているが、逆に、射出面が正の屈折力を有するレンズであっても、同様の効果が得られる。さらに、第２走査レンズ１３が副走査方向において負の屈折力を有するレンズである場合には、回転多面鏡３の反射面に入射する光ビームに対して、回転多面鏡３から射出する光ビームが存在する側と、アナモフィックレンズの光軸に対して、アナモフィックレンズに入射する光ビームが存在する側を逆にすれば、同様の効果が得られる。
【００４５】
なお、走査中心を走査する光ビームｃ₀は、偏向による座標系の回転が生じていないため、元々ビームスポット形状が崩れるという問題を生ぜず、第２走査レンズ１３が偏心してもビームスポット形状に影響を及ぼさない。従って、ビームスポット形状はやはり良好である。また、偏心によりわずかな球面収差が生じるが、実質的に問題とならない。
【００４６】
次に、第２走査レンズ１３の別の配置を図２１に示す。走査端を走査する光ビームｃ₁、ｃ₂に対して第２走査レンズ１３の光軸Ｏが傾いており、しかも光ビームｃ₁、ｃ₂は、第２走査レンズ１３の光軸Ｏから離れた位置に入射する。この構成でも、やはりビームスポット形状の崩れを補正する効果を有する。
【００４７】
図２０、図２１に示した第２走査レンズ１３の副走査方向の断面形状は、第２走査レンズ１３の光軸Ｏに関して対称な形状となっている。ところが、第２走査レンズ１３を光ビームが透過する位置は、光軸Ｏに関して片側に寄っている。そこで、光ビームが透過する範囲だけでレンズを構成するようにしてもよく、副走査方向の断面を図２２（ａ）、（ｂ）のようにしてもよい。図２２（ａ）では、レンズの厚みが一端と他端とで異なっている。このような形状のレンズを作る際には、まず光軸を含み主走査方向に平行な面に関して対称にレンズを作り、次に光軸を含み主走査方向に平行な面で切断すれば、１度のレンズ加工で２個のレンズを得ることが可能となり、コストを半減できる。
【００４８】
第２走査レンズ１３のような複雑な面形状のレンズは、樹脂成形により製造することがしばしばある。樹脂成形により製造した第２走査レンズ１３の副走査方向の断面形状は、図２２（ｂ）のようにリブ２３、２４が形成されている。図２２（ｂ）で、リブ２３、２４を除いたレンズ有効部において、やはりレンズの厚みが一端と他端とで異なっている。なお、図２２（ａ）、（ｂ）のようなレンズ形状の場合は、レンズの光軸がレンズの外側に位置することもあるが、光軸はレンズの入射面と射出面との両方に垂直な軸であると定義する。第２走査レンズ１３の副走査方向の断面形状を図２２（ａ）、（ｂ）のようにすると、第２走査レンズ１３のレンズ面の面積や、特にレンズ面の副走査方向の幅を小さくすることができるために、レンズ面の面精度を高くすることができる。このことは、特に本実施例のように、第２走査レンズ１３がトーリック面を有している場合に有効である。
【００４９】
一般に、トーリック面は、主走査方向の加工と副走査方向の加工を独立した送り運動で加工するため、主走査方向の面精度と副走査方向の面精度を両立させることが難しい。一方向の面精度を上げようとすると、他方向の面精度が悪化してしまう。特に、工具の磨耗のために取りしろにむらを生じ、面精度が悪くなるため、レンズ面の面積が大きければより磨耗量が多くなり、いっそう面精度が悪くなる。従って、図２２（ａ）、（ｂ）のようにレンズ面の面積を小さくすれば、高い面精度を得ることができる。
【００５０】
また、図２２（ａ）、（ｂ）のようにすることにより、第２走査レンズ１３の大きさを小さくすることができ、光走査装置全体の大きさを小型化することができ、またコストダウンもできる。
【００５１】
次に、走査線の湾曲補正について説明する。図２６に示すように回転多面鏡３の第２反射面５に副走査方向に角度を有して光ビームｂが入射すると、反射されて偏向した光ビームｃは湾曲し、走査中心では実線のような光ビームｃ０となるが、走査端では破線のような光ビームｃ１、ｃ２となる。ところが、副走査方向において、回転多面鏡３の第２反射面５と被走査面１４が幾何光学的に共役関係にあると、走査中心の光ビームｃ０も走査端を走査する光ビームｃ１、ｃ２も被走査面１４上では副走査方向において同じ位置に到達し、被走査面１４上での走査線は直線となる。
【００５２】
また、この実施例では、第１伝達レンズ７および第１走査レンズ１２に主走査方向の長さに対して副走査方向の長さが短い形状のレンズを使用している。これらのレンズは、副走査方向の長さが極めて短く、光ビームが透過するために必要な最小限の長さとなっている。従って、回転多面鏡３へ入射する光ビームａは第１伝導レンズ７に干渉せず、光ビームｂも第１走査レンズ１２に干渉しない。また、光ビームとレンズが干渉しないため、回転多面鏡３への光ビームａおよび光ビームｂの副走査方向の入射角を小さくすることができ、それぞれの反射面で偏向された光ビームｂおよび光ビームｃの湾曲が小さくなり、第２伝達レンズ９、第３伝達レンズ１０、第２走査レンズ１３の副走査方向の口径を小さくすることが可能である。さらに、本実施例では、第１伝達レンズ７および第１走査レンズ１２の入射面の副走査方向の口径が、それぞれの反射面の位置における回転多面鏡３へ入射する光ビームａおよび光ビームｂと偏向された光ビームｂおよび光ビームｃとの距離が一致する。図２３において、実線は、ずれのない走査中心の光ビームｂ₀、ｃ₀であり、破線で示された副走査方向のずれが最大となる走査端を走査する光ビームｂ₁、ｃ₁とｂ₂、ｃ₂について、レンズ口径がこれより大きいと入射光ビームｂおよび光ビームｃがレンズと干渉してしまう。逆にレンズ口径がこれより小さいと反射光ビームｂおよび光ビームｃがレンズ外側を通過してしまう。従って、上記構成にすると、光ビームｂおよび光ビームｃの副走査方向へのずれの許容値が最大になる。
【００５３】
次に、図２４に基づいて走査領域のシフトについて説明する。従来の光走査装置においては、走査光学系の光軸に関して走査開始位置と走査終了位置が対称であり、水平同期信号検出位置はその外側に設けられる。このような構成であると、走査レンズ系の利用領域を水平同期信号検出側にのみ大きくとる必要があるが、製造上では一般的にレンズは光軸に関して対称であることが望ましいため、このような場合にはレンズの口径を大きく形成しなければならなかった。特に走査レンズのような正レンズでは、口径が大きくなるとレンズ外周の厚みを確保するために光軸方向のレンズの厚さもそれだけ大きくしなければならない。本発明では、水平同期信号検出位置と走査終了位置が走査光学系の光軸に関して対称であるように配置している。従って、第１走査レンズ１２の主走査方向の口径を小さくすることができる。
【００５４】
次に、水平同期レンズを傾けることについて説明する。上述した偏向で発生する光ビームの回転補正で説明したとおり、副走査方向に角度を有して入射させる光走査装置においては、主走査方向ｙ、副走査方向ｘ、光軸方向ｚの座標系を有する光ビームｂが副走査方向に角度をもって回転多面鏡３の第２反射面５に入射し、偏向された光ビームｃは湾曲して偏向され、そのため光ビームｃの座標系が回転してしまう（図１７参照）。回転多面鏡３の第２反射面５の偏向により光ビームｄが回転すると、水平同期信号光ビームｄによるビームスポットが一点に結像されず、そのビームスポット形状が崩れ、検出精度が悪くなる。このため、この実施例では図１に示されるように水平同期レンズ８２がビーム進行方向に向かって見て、光軸を回転軸として矢印Ｃで示すように時計回りに２．４°傾けて配置している。従って、回転した光ビームｄの座標系と水平同期レンズ８２の母線方向、周方向の座標系とが一致し、ビームスポットの形状が良好となって水平同期センサー８３に導入され、検出精度が向上したものとなる。
【００５５】
次に、水平同期センサー８３を傾けることについて説明する。この実施例では、上記水平同期レンズ８２を傾けると同時に、水平同期センサー８３も水平同期レンズ８２と同じ角度２．４°だけ矢印Ｄ方向に傾けて配置している。従って、水平同期レンズ８２が傾いている場合、水平同期センサー８３上をビームスポットが走査する方向も同じ角度だけ傾くことになる。そこで、水平同期センサー８３上を水平同期信号光ビームｄが垂直に走査するため、さらに、検出感度が向上したものとなる。
【００５６】
次に、図２７に基づいてこの発明の第２実施例を説明する。先の実施例では走査器である回転多面鏡の回転軸に垂直な走査面に角度を有して二度入射させて偏向するように構成した光走査装置であるが、この例では回転多面鏡の回転軸に垂直な走査面に角度を有して入射する光ビームを一度だけ偏向させて走査する光走査装置である。即ち、光源として半導体レーザー１から射出された光ビームａは第１整形レンズ５１および第２整形レンズ５２からなる整形光学系を透過し、集束光ビームａとして回転多面鏡３の反射面６１に下方から入射させる。この反射面６１から上方に反射され偏向された光ビームｂは、第１走査レンズ７１および第２走査レンズ７２からなる走査光学系を透過して被走査面１４上にビームスポットを形成し走査線を形成する。また、反射面６１からの光ビームｂの走査端において、水平同期ミラー１０１で分離された光ビームｄは、水平同期信号用のもので、水平同期レンズ１０２により水平同期センサー１０３上に結像される。
【００５７】
上記第１整形レンズ５１は光軸の回りに回転対称な非球面レンズであり、第２整形レンズ５２は副走査方向のみ屈折力を有するシリンドリカルレンズである。また、第１走査レンズ７１は球面レンズであり、第２走査レンズ７２はプラスチックス製レンズであり、その入射面は主走査方向で曲率半径の大きな凹形状となっており、副走査方向は曲率半径の小さな凸形状となっている。また、主走査方向の断面曲線を入射面よりも被走査面１４側にある主走査方向に平行な軸の回りに回転させることにより形成された鞍型トーリック面で、射出面は主走査方向で曲率半径の大きな非円弧で、副走査方向の断面は直線の非円弧シリンドリカル面である。
【００５８】
次に、このように構成された具体的な数値例を表３に示す。この表では、アナモフィック面は副走査方向、主走査方向の曲率半径をｒｉｘ、ｒｉｙとしている。また、非球面である面については、曲率半径は光軸上の値を示している。
【００５９】
【表３】

【００６０】
第１整形レンズ５１の非球面係数の数式は先の例の数１に示すものと同じであり、非球面係数は次の表４に示す。
【００６１】
【表４】

【００６２】
この数値例においては、１走査の走査開始から走査終了までの回転多面鏡３の回転角２ωが３１．７°であり、回転多面鏡３への光ビームａの副走査方向の入射角は６°である。回転多面鏡３の面数は６面であり、回転多面鏡３の内接円半径は１７ｍｍ、半導体レーザー１からの光ビームａの波長は８００ｎｍである。従って、先の第１実施例と同様に回転多面鏡３の反射面６１に入射する光ビームａの入射角は上方に斜めに副走査方向で角度をもって入射するようになっているので、偏向前の光ビームａと偏向後の光ビームｂは分離され、回転多面鏡３の回転軸方向の上下に隔離され、何ら干渉することがない。
【００６３】
そして、回転多面鏡３の反射面６１に副走査方向で角度をもって入射させているので、先の実施例と同様に偏向された光ビームｂが湾曲し、光ビームｂが回転してしまう。即ち、図９に示すように光ビームｂの座標系は同様に回転し、このため、先の実施例と同様に、走査端を走査する光ビームの回転を補正し、ビームスポット形状の崩れを補正する。このことについて図２８を用いて説明する。
【００６４】
回転多面鏡３の反射面６１に入射する光ビームｃ₁、ｃ₂に対して、射出する光ビームは下側に位置する。さらに光ビームｃ₁、ｃ₂は、第１走査レンズ７１を透過後、第２走査レンズ７２の光軸Ｏから下側に離れた位置で、第２走査レンズ７２を透過する。なお、第２走査レンズ７２の光軸Ｏと第２走査レンズ７２に入射する光ビームとはほぼ平行である。
【００６５】
本実施例では、第２走査レンズ７２は、走査中心を走査する光ビームｃ₀に対して、副走査方向で、かつ図２８の矢印Ｅの方向に２．２５ｍｍ偏心させて配置している。すなわち、走査中心を走査する光ビームｃ₀は、第２走査レンズ７２の光軸から２．２５ｍｍ離れた位置に入射する。また、走査端を走査する光ビームｃ₁、ｃ₂は、第２走査レンズ７２の光軸から５．５４ｍｍ離れた点Ａに入射する。このように構成すると、先の実施例と同様に、光ビームの回転を補正し、ビームスポット形状の崩れを補正することができる。
【００６６】
次に、水平同期レンズを傾けることについて説明する。先の例の偏向で発生する光ビームの回転補正で説明したとおり、副走査方向に角度を有して入射させる光走査装置においては、主走査方向ｙ、副走査方向ｘ、光軸方向ｚの座標系を有する光ビームｂが副走査方向に角度をもって回転多面鏡３の反射面６１に入射されると、偏向された光ビームｃは湾曲して偏向され、そのため光ビームｃの座標系が回転してしまう（図１７参照）。回転多面鏡３の反射面６１の偏向によりビームｃが回転すると、水平同期信号ビームｄによるビームスポットが一点に結像されず、そのビームスポット形状が崩れ、検出精度が悪くなる。このため、この実施例では、図２７に示されるように水平同期レンズ１０２がビーム進行方向に向かって見て、光軸を回転軸として矢印Ｃで示すように時計回りに傾けて配置している。従って、回転したビームｄの座標系と水平同期レンズ８２の母線方向、周方向の座標系とが一致し、ビームスポット形状の崩れがなくなって水平同期センサー１０３に導入され、検出精度が向上したものとなる。
【００６７】
次に、水平同期センサー１０３を傾けることについて説明する。この実施例では、上記水平同期レンズ１０２を傾けると同時に、水平同期センサー１０３も水平同期レンズ１０２と同じ角度だけ矢印Ｄ方向に傾けて配置している。従って、水平同期レンズ１０２が傾いている場合、水平同期センサー１０３上をビームスポットが走査する方向も同じ角度だけ傾くことになる。そこで、水平同期センサー１０３上を水平同期信号光ビームｄが垂直に走査するため、さらに、検出感度が向上したものとなる。
【００６８】
これらの実施例では、走査器として回転多面鏡を使用するものについて説明したが、これは回転多面鏡に限らず少なくとも２面以上の反射面を有すればよく、回転多面鏡の他に回転２面鏡、回動軸を中心に正弦振動を行なうガルバノミラーの表裏両面を使用するものでもよい。また、レーザープリンタに用いられると特に有効であるが、その他デジタル複写機、ファクシミリ、レーザー走査ディスプレイなどの画像形成装置や、スキャナなどの画像入力装置、あるいは光学マーク読取用レーザー装置、表面検査用レーザー走査装置などにも適用することができることは勿論である。
【００６９】
【発明の効果】
以上説明したように、本発明の光走査装置によれば、以下のような効果を有する。
【００７０】
まず、請求項１、２記載の発明によれば、走査端を走査する光ビームが、走査光学系のアナモフィックなレンズの入射面を透過する点における入射面の法線と、走査端を走査する光ビームが、アナモフィックレンズの射出面を透過する点における射出面の法線とが、互いに副走査方向に角度を有する構成とすることにより、走査器で偏向された光ビームの回転によるビームスポット形状の崩れを防止することが可能となり、画像の良好な光走査装置を提供することが可能となる。また、アナモフィックレンズの副走査方向の断面形状において、レンズの厚みが、副走査方向の一端と他端とで異ならせることにより、高い面精度のアナモフィックレンズを得ることができ、画像の良好な光走査装置を提供することが可能となるばかりでなく、光走査装置の小型化、コストダウンも可能となる。
【００７１】
さらに、請求項１記載の発明によれば、水平同期レンズをその光軸に関して回転させて配置することにより、走査開始点の位置を高精度に揃えることができるようになる。
【００７２】
また、請求項２記載の発明によれば、水平同期センサーをその光軸に関して回転させて配置することにより、走査開始点の位置さらに高精度に揃えることができるようになる。
【図面の簡単な説明】
【図１】一実施例の光走査装置の構成を示す斜視図。
【図２】（ａ）、（ｂ）、（ｃ）、（ｄ）、（ｅ）は、副走査方向の面倒れと走査位置が一定となることを説明するための展開図。
【図３】伝達光学系の主走査方向の展開図。
【図４】伝達光学系の主走査方向の展開図。
【図５】伝達光学系の副走査方向の展開図。
【図６】光ビームの交差を説明するための伝達光学系の主走査方向の展開図。
【図７】（ａ）、（ｂ）は、伝達光学系のミラー枚数と光ビームの交差を説明するための平面図。
【図８】（ａ）、（ｂ）は、図７の伝達光学系の主走査方向の展開図。
【図９】伝達光学系で発生する光ビームの回転を説明するための側面図。
【図１０】光ビームの回転を説明するための回転多面鏡の側面図。
【図１１】光ビームの回転を説明するための回転多面鏡の側面図。
【図１２】傾けて配置したシリンドリカルレンズの正面図。
【図１３】伝達光学系の光路を主走査方向に投影した光路図。
【図１４】回転角度と第１反射面と第２反射面の光軸のなす角との関係を示すグラフ。
【図１５】ビームスポットの等強度線図。
【図１６】ビームスポットの等強度線図。
【図１７】（ａ）、（ｂ）は、偏向で発生する光ビームの回転を説明するための斜視図、および座標系を示す説明図。
【図１８】ビームスポットの等強度線図。
【図１９】第２走査レンズの正面図。
【図２０】走査光学系の副走査方向の断面図。
【図２１】他の配置の第２走査レンズの副走査方向の断面図。
【図２２】他の断面形状の第２走査レンズの副走査方向の断面図。
【図２３】走査レンズと走査レンズ付近の光路を示す副走査方向の断面図。
【図２４】走査領域のシフトを説明するための説明図。
【図２５】変形例の光路を示す光走査装置の側面図。
【図２６】走査線の湾曲補正を説明するための説明図。
【図２７】第２実施例の光走査装置の構成を示す斜視図。
【図２８】走査光学系の副走査方向の断面図。
【符号の説明】
１ 光源（半導体レーザー）
２ 整形レンズ
３ 回転多面鏡
４ 第１反射面
５ 第２反射面
６ 回転軸
７ 第１伝達レンズ
８ 第１伝達ミラー
９ 第２伝達レンズ
１０ 第３伝達レンズ
１１ 第２伝達ミラー
１２ 第１走査レンズ
１３ 第２走査レンズ
１４ 被走査面
８１ 水平同期ミラー
８２ 水平同期レンズ
８３ 水平同期センサー[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical scanning device used in a laser beam printer or the like, and more particularly to an optical scanning device that makes a light beam incident at an angle with respect to a scanning surface perpendicular to the rotation axis of the scanner, and is deflected by the scanning surface. The present invention relates to an optical scanning apparatus configured to correct a tilted light beam that is bent and the light beam rotates to break a beam spot.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an optical scanning device used in a laser beam printer or the like generally deflects a light beam emitted from a light source such as a semiconductor laser through a shaping optical system by a scanner such as a rotary polygon mirror that is a deflecting unit. The formed light beam is scanned by forming a beam spot on the surface to be scanned by an imaging lens system that is an f · θ lens. In such an optical scanning device, since a light beam is incident on the scanning plane and deflected, there is no particular problem. For example, a multicolor printing laser printer described in Japanese Patent Application Laid-Open No. 56-161666 is disclosed. As described above, in an optical scanning apparatus that deflects light beams of a plurality of colors simultaneously incident on the same scanning surface of a rotary polygon mirror that is a scanner, in order to separate the light beams of these colors, Need to be deflected by making them incident at different angles to the scanning plane perpendicular to the rotation axis of the rotary polygon mirror. An optical scanning apparatus that deflects a light beam incident on a rotary polygon mirror of a scanner is also known. Also in the case of this optical scanning device, in order to reduce the size of the device, in order to separate the optical path for performing the first deflection and the optical path for performing the second deflection, the scanning surface is perpendicular to the rotation axis of the rotary polygon mirror. On the other hand, there has been a case in which it is necessary to configure each light beam to be incident and deflected at an angle.
[0003]
[Problems to be solved by the invention]
As described above, when the light beam is incident on the scanning surface of the rotary polygon mirror of the scanner with an angle and deflected, the light beam deflected on the scanning surface of the rotary polygon mirror is curved, and the trajectory of the conical scanning line is changed. As a result, the light beam that scans the scanning end rotates, the shape of the beam spot on the surface to be scanned collapses, and it is difficult to form a clear image.
[0004]
In the above multicolor printer, the light beam deflected on the scanning surface is curved and the scanning line on the surface to be scanned does not become a straight line. Therefore, an optical scanning device that scans this through a cylindrical lens is disclosed. Yes. By the way, even in such an optical scanning device, the light beam that scans the scanning end of the deflected light beam rotates, and the scanning line on the surface to be scanned becomes linear, but the shape of the beam spot is destroyed. As a result, a good image could not be formed.
[0005]
Further, in order to align the position of the scanning start point, the horizontal synchronizing signal light beam is detected. If the light beam is incident at an angle on the scanning surface of the rotary polygon mirror of the scanner and deflected, the horizontal scanning signal light beam is detected. There is a problem in that the shape of the beam spot formed by the synchronization signal light beam is deformed and the detection accuracy is deteriorated.
[0006]
Accordingly, the present invention solves the above-described problems, and the invention according to claim 1 is directed so that the light beam incident on the reflection surface of the scanner is at an angle with respect to the reflection surface perpendicular to the rotation axis of the scanner. The incident surface at the point where the light beam that scans the scanning end passes through the incident surface of the anamorphic lens of the scanning optical system, because the deflected light beam is bent and the shape of the beam spot is destroyed. And the normal of the exit surface at the point where the light beam that scans the scanning end passes through the exit surface of the anamorphic lens is arranged so that the beam spot of the beam spot is at an angle in the sub-scanning direction. It is an object of the present invention to provide an optical scanning device capable of obtaining a good image in which shape deformation is corrected. It is another object of the present invention to obtain an anamorphic lens with high surface accuracy and to reduce the size of the anamorphic lens. It is an object of the present invention to align the position of the scanning start point with high accuracy.
[0007]
[Means for Solving the Problems]
The optical scanning device of the present invention is a light source that generates a light beam, a scanner that deflects a light beam incident from the light source at an angle in the sub-scanning direction, and a light reflected by the reflecting surface of the scanner. In an optical scanning device that scans a light beam by forming a beam spot on a surface to be scanned by a scanning optical system,
The light beam deflected by the reflecting surface of the scanner is transmitted at a scanning end through a position separated from the optical axis of the anamorphic lens of the scanning optical system in the sub-scanning direction, and the anamorphic In the cross-sectional shape of the lens in the sub-scanning direction, the thickness of the lens is different at one end and the other end in the sub-scanning direction, and
The horizontal synchronization lens is characterized in that it is arranged with its optical axis as a rotation axis so as to correspond to the rotation of the coordinate system of the deflected light beam.
Another optical scanning device includes a light source that generates a light beam, a scanner that deflects the light beam incident from the light source at an angle in the sub-scanning direction, and the light reflected by the reflecting surface of the scanner. In an optical scanning device that scans a light beam by forming a beam spot on a surface to be scanned by a scanning optical system,
The light beam deflected by the reflecting surface of the scanner is transmitted at a scanning end through a position separated from the optical axis of the anamorphic lens of the scanning optical system in the sub-scanning direction, and the anamorphic In the cross-sectional shape of the lens in the sub-scanning direction, the thickness of the lens is different at one end and the other end in the sub-scanning direction, and
The horizontal synchronization sensor is characterized in that it is arranged with its optical axis as a rotation axis so as to correspond to the rotation of the coordinate system of the deflected light beam.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing a configuration of an optical scanning device according to an embodiment. Hereinafter, in the present invention, a rotary polygon mirror is used as the scanner, the direction orthogonal to the rotation axis of the rotary polygon mirror, which is the rotation axis of the scanner, is set as the main scanning direction, and the direction parallel to the rotation axis of the rotary polygon mirror is set. It is defined as the sub-scanning direction. An optical system provided between the light source 1 and the first reflecting surface that performs the first deflection of the rotating polygon mirror is called a shaping optical system, and the first reflecting surface that performs the first deflection of the rotating polygon mirror and the second reflecting surface. The optical system provided between the second reflecting surface for deflecting the light beam is referred to as a transmission optical system, and the optical system provided between the second reflecting surface and the surface to be scanned is referred to as a scanning optical system. Deflection is defined as performing a deflection by causing a light beam to enter twice.
[0009]
In FIG. 1, a light beam a emitted from a semiconductor laser 1 as a light source passes through a first shaping lens 2 and is shaped, and is applied to a first reflecting surface 4 of a rotary polygon mirror 3 as a scanner from below in the sub-scanning direction. Incident with an angle and the first deflection is made. The light beam b reflected from the first reflecting surface 4 with an angle upward in the sub-scanning direction passes through the first transmission lens 7 and is reflected by the first transmission mirror 8. 3 is transmitted through the transmission lens 10, reflected by the second transmission mirror 11, and incident again on the second reflection surface 5 of the rotary polygon mirror 3 with an angle from above in the sub-scanning direction to be deflected a second time. The light beam c deflected at an angle downward from the second reflecting surface 5 in the sub-scanning direction forms an image as a beam spot on the scanned surface 14 by the first scanning lens 12 and the plastic second scanning lens 13. And configured to scan. The light beam d is for a horizontal synchronizing signal, and is separated at the scanning end of the light beam c and is introduced into the horizontal synchronizing sensor 83 via a horizontal synchronizing mirror 81 and a horizontal synchronizing lens 82.
[0010]
The shaping lens 2 and the first transmission lens 7 are aspherical lenses that are rotationally symmetric about the optical axis, the second transmission lens 9 is a cylindrical lens having power only in the sub-scanning direction, and the third transmission lens 10 is It is a cylindrical lens having power only in the main scanning direction. The first scanning lens 12 is a spherical lens. The second scanning lens 13 is a plastic lens, and its incident surface has a concave shape with a large radius of curvature in the main scanning direction, and has a convex shape with a small radius of curvature in the sub-scanning direction. Further, it is a surface formed by rotating a cross-sectional curve in the main scanning direction around an axis parallel to the main scanning direction that is closer to the surface to be scanned 14 than the incident surface. Such a surface is called a saddle type toric surface. The exit surface is a convex non-arc having a large curvature radius in the main scanning direction (referred to as a non-arc because it is aspheric only in the main scanning direction). The cross section in the sub-scanning direction is a straight line. Such a surface is called a non-circular cylindrical surface. The second scanning lens 13 is an anamorphic lens whose refractive power in the sub-scanning direction is larger than that in the main scanning direction and whose refractive power in the sub-scanning direction is positive.
[0011]
The light beam a and the light beam b incident on the first reflecting surface 4 and the second reflecting surface 5 of the rotary polygon mirror 3 serving as a scanner are perpendicular to the first reflecting surface 4 and the second reflecting surface 5 in the main scanning direction, respectively. It is comprised so that it may inject into. In the conventional optical scanning device that deflects only once on the reflecting surface of the rotating polygon mirror, the size of the light beam incident in the main scanning direction on the reflecting surface of the rotating polygon mirror is equal to the twice-deflecting object of the present invention. When the rotating polygon mirror is rotated by an angle that is larger than the case of the optical scanning device and obtains a required scanning angle, if the entire light beam is always put on the same reflecting surface, the size of the reflecting surface is somewhat The above-mentioned size is necessary, and the number of reflecting surfaces of the rotary polygon mirror cannot be formed so much. On the other hand, in the two-deflection type optical scanning device of the present invention, a light beam is imaged in both the main and sub-scanning directions in the vicinity of the first reflecting surface 4 that performs the first deflection. In order to obtain a necessary scanning angle even if the size of the first reflecting surface 4 of the rotary polygon mirror 3 is small, since the size of the light beam a is extremely smaller than that of the once deflected optical scanning device. When the rotary polygon mirror 3 is rotated by this angle, the entire light beam can always enter the first reflecting surface. Therefore, the reflecting surface of the rotary polygon mirror 3 can be made small. Further, in the second deflection, although the size of the light beam b incident on the second reflecting surface 5 of the rotary polygon mirror 3 is large, the movement of the light beam b when the rotary polygon mirror 3 is rotated. The movement of the second reflecting surface coincides. For this reason, the size of the second reflecting surface 5 in the main scanning direction need only be the same as the size of the incident light beam b, and the second reflecting surface 5 can also be made small. Accordingly, since the size of the reflecting surface of the rotary polygon mirror 3 can be reduced as compared with the optical scanning device of the deflection type once, the number of reflecting surfaces can be increased, and the scanning speed can be increased accordingly.
[0012]
Further, the light beam a and the light beam b incident on the first reflecting surface 4 and the second reflecting surface 5 of the rotating polygon mirror 3, and the light beam b deflected from the first reflecting surface 4 and the second reflecting surface 5. The light beam a and the light beam b are incident on the first reflecting surface 4 and the second reflecting surface 5 of the rotary polygon mirror 3 at an angle in the sub-scanning direction, respectively. ing. As a result, the shaping optical system (first shaping lens 2) and the transmission optical system (first transmission lens 7, second transmission lens 9, and third transmission lens 10), and the transmission optical system and the scanning optical system (first optical system). The scanning lens 12 and the second scanning lens 13) can be spaced apart upward and downward in the direction of the rotational axis 6 of the rotary polygon mirror 3, and the respective light beams a, b, c interfere with each other. And the arrangement of the optical system can be freely selected.
[0013]
Next, Table 1 shows specific numerical examples of the optical scanning apparatus configured as described above. In this table, the curvature radius of the anamorphic surface in the sub-scanning direction and the main scanning direction is set to rix and riy, respectively. In addition, for a surface that is an aspherical surface, the radius of curvature indicates a value on the optical axis.
[0014]
[Table 1]

[0015]
Formulas of aspherical surfaces of the first shaping lens 2 and the first transmission lens 7 are as shown in the following Equation 1, and the aspherical coefficients are shown in Table 2 below.
[0016]
[Expression 1]

[0017]
[Table 2]

[0018]
In the embodiment shown in Table 1 above, the rotation angle of the rotary polygon mirror 3 from the start of scanning to the end of scanning is 2ω = 24 °. Further, the incident angle α of the light beam a on the first reflecting surface 4 of the light beam a to the rotary polygon mirror 3 and the incident angle β of the light beam b on the second reflecting surface 5 in the sub-scanning direction are both 6 °. The rotating polygon mirror 3 has 12 surfaces, the inscribed circle radius of the rotating polygon mirror 3 is 17 mm, the angle formed by the first reflecting surface 4 and the second reflecting surface 5 is 90 °, and the light beam of the light source 1. The wavelength of the laser beam is 670 nm.
[0019]
In this embodiment, the light beam a is configured to form an image in the sub-scanning direction in the vicinity of the first reflecting surface 4 of the rotating polygon mirror 3 and in the vicinity of the second reflecting surface 5 of the rotating polygon mirror 3. Yes. In other words, the first reflective surface 4 and the second reflective surface 5 are geometrically optically conjugate with the transmission optical system (the first transmission lens 7, the second transmission lens 9, and the third transmission lens 10), and The scanning optical system (the first scanning lens 12 and the second scanning lens 13) is configured so that the second reflecting surface 5 and the surface to be scanned 14 are substantially in a conjugate relationship. Accordingly, the tilting of the first reflecting surface 4 and the second reflecting surface 5 of the rotary polygon mirror 3 is well corrected, and the scanning position in the sub-scanning direction becomes constant. Hereinafter, this point will be described in more detail with reference to the drawings.
[0020]
2A to 2E are development views in the sub-scanning direction between the first reflecting surface 4 and the second reflecting surface 5 of the rotary polygon mirror 3. In the case of the present embodiment, the imaging point P in the vicinity of the first reflecting surface 4 of the rotating polygon mirror 3 is slightly shifted from the first reflecting surface 4 as shown in FIG. It exists between the 1st reflective surface 4 and the 1st transmission lens 7a. Here, the light beam a from the light source 1 is configured to form an image at this image point P in both the main scanning direction and the sub-scanning direction.
[0021]
If the amount of displacement l of the imaging point P from the first reflecting surface 4 of the rotary polygon mirror 3 is too large, the displacement of the scanning line on the scanned surface 14 due to the tilting of the first reflecting surface 4 becomes large. Become. Conversely, if the amount of deviation l is small, the size of the light beam a on the first reflecting surface 4 is too small and is affected by scratches and dust present on the first reflecting surface 4 of the rotary polygon mirror 3. As a result, the light beam a is scattered, and a small beam spot cannot be formed on the scanned surface 14. Further, the light beam a is blocked by scratches and dust, and the optical power is reduced. Accordingly, there is an appropriate value for the amount l of deviation of the image point P. In this example, the amount of deviation l is 11 mm. This is a sufficiently small value as compared with the optical path length of 300 mm of the transmission optical system from the first reflecting surface 4 to the second reflecting surface 5 of the rotary polygon mirror 3, so that the effect of correcting the surface tilt is sufficiently obtained.
[0022]
Next, a specific calculation example is shown. That is, the amount of displacement l of the imaging point P by the shaping optical system from the first reflecting surface 4 of the rotary polygon mirror 3 is 11 mm, the optical magnification βd of the transmission optical system in the sub-scanning direction is 1.57, and the scanning optical system The optical magnification βs in the sub-scanning direction is 0.418. This is because when the surface tilt of the first reflecting surface 4 of the rotary polygon mirror 3 is θ = 3e−4 [rad] (0.0172 °), the scanning line deviation δ = 2 · l · θ · βd · βs = 0.00433 [mm]. The diameter of the light beam a incident on the first reflecting surface 4 in this embodiment is 0.84 mm in the main scanning direction and 0.13 mm in the sub-scanning direction. Accordingly, the size of the light beam a on the first reflecting surface 4 is sufficiently large, and the first reflecting surface 4 is not affected by scratches or dust. In general, if the diameter of the light beam in at least one direction of the main scanning direction and the sub-scanning direction is about 0.5 mm, it is not affected by scratches or dust on the reflecting surface of the rotary polygon mirror 3.
[0023]
In this embodiment, the image forming point Q in the vicinity of the second reflecting surface 5 is located just on the second reflecting surface 5. However, this is effective even if it deviates from the second reflecting surface 5. This will be described in more detail. Although the transmission optical system 7a in FIG. 2A is temporarily present, the first reflecting surface 4 and the second reflecting surface 5 have a refractive power that is conjugate. Let Q be the position at which the light beam a that forms an image at a position P deviated by 1 from the first reflecting surface 4 is imaged again near the second reflecting surface 5 by the provisional transmission optical system 7a as the light beam b. It is desirable that the actual image forming point in the vicinity of the second reflecting surface 5 exists between the second reflecting surface 5 and the position Q where the image is formed again.
[0024]
First, the case where the image forming points Q of the light beam b near the second reflecting surface 5 are at both ends of the above range will be described. 2B and 2C, the first reflecting surface 4 and the second reflecting surface 5 are completely conjugate by the transmission optical system 7b, and the image forming point by the transmission optical system 7b coincides with Q. The relationship between the second reflecting surface 5 and the scanned surface 14 by the subsequent scanning optical system 12 a is slightly deviated from the conjugate, and the light beam c forms an image on the scanned surface 14. In this case, as shown in FIG. 2C, the surface tilt 4 ′ of the first reflecting surface 4 is completely corrected, and a displacement due to the surface tilt 5 ′ of the second reflecting surface 5 occurs as Δ on the scanned surface 14. . 2D and 2E show a case where the relationship between the first reflecting surface 4 and the second reflecting surface 5 by the transfer optical system 7c is slightly deviated from the conjugate, and the image is formed by the transfer optical system 7c. The point coincides with the second reflecting surface 5, the second reflecting surface 5 and the scanned surface 14 are completely conjugate by the scanning optical system 12b, and the light beam b forms an image on the scanned surface 14 as the light beam c. Is the case. In this case, as shown in FIG. 2 (e), the surface tilt 5 ′ of the second reflecting surface 5 is completely corrected, and the surface tilt 4 ′ due to the first reflecting surface 4 is shifted on the scanned surface 14. It occurs as Δ ′. The principal ray is indicated by a broken line. Therefore, if the image forming point in the vicinity of the second reflecting surface 5 is between the second reflecting surface 5 and the image forming point Q, the surface tilts 4 ′ and 5 ′ of the first reflecting surface 4 and the second reflecting surface 5 are reversed. In the case of the direction, the displacement due to the surface tilts 4 ′ and 5 ′ is cancelled, and the positional deviation of the scanning lines on the scanned surface 14 is reduced. Even in the same direction, the amount of deviation is the same as or better than that shown in FIGS. 2C and 2E, and at least does not worsen.
[0025]
Next, the configuration of the transmission optical system will be described. In the main scanning direction of the light beam, the necessary functions of the transmission optical system are to guide the light beam a imaged at the point P near the first reflecting surface 4 to the second reflecting surface 5 as a parallel beam, The movement of the light beam b moving on the second reflecting surface 5 with the rotation of the mirror 3 follows the movement of the second reflecting surface 5.
[0026]
FIG. 3 is a developed sectional view in the main scanning direction showing an example of the transmission optical system, and is not a diagram showing an embodiment of the present invention. However, in terms of the function of the light beam in the main scanning direction, as shown in FIG. Paraxially, only one lens 201 is required for the number of lenses in the transmission optical system. However, if the transmission optical system is constituted by a single lens 201, the diameter of the lens 201 becomes too large to be practical. Therefore, as shown in the developed sectional view in the main scanning direction of FIG. 4, if the transmission optical system is constituted by the two lenses 202 and 203, the lens aperture can be reduced, which is practical. Therefore, in order to provide the transmission optical system with a function in the main scanning direction, it is desirable to configure two or more lenses having refractive power in the main scanning direction. On the other hand, a function necessary for the transmission optical system in the sub-scanning direction is to form an image in the vicinity of the second reflecting surface 5 by using the light beam a imaged at the imaging point Q in the vicinity of the first reflecting surface 4 as the light beam b. It is only that. FIG. 5 shows a developed sectional view of the transmission optical system in the sub-scanning direction. In terms of the function in the sub-scanning direction, the number of lenses in the transmission optical system may be one of the lenses 204. From the above, in order for the transmission optical system to have both the function in the main scanning direction and the function in the sub-scanning direction, it is preferable to use three lenses. In addition, if this transfer optical system is combined with a lens having refractive power in the sub-scanning direction and a lens having refractive power in the main scanning direction, the number of lenses in the transfer optical system can be reduced to two. Is possible. In this embodiment, the transmission optical system is constituted by the three lenses of the first transmission lens 7, the second transmission lens 9, and the third transmission lens 10 from the above.
[0027]
Next, the intersection with the optical axis of the light beam will be described with reference to FIG. FIG. 6 is a developed sectional view in the main scanning direction of the transmission optical system of the embodiment, and is a developed sectional view of the first transmission mirror 8 and the second transmission mirror 11 (see FIG. 1). That is, the rotary polygon mirror 3 rotates by an angle θ1 around the position shown in the figure during the scanning period. Therefore, the light beam a is deflected by 2θ1 which is twice the angle θ1 on the first reflecting surface 4 of the rotary polygon mirror 3. The deflected light beam b passes through the first transmission lens 7, the second transmission lens 9, and the third transmission lens 10 which are transmission optical systems, and is deflected by an angle θ2. This light beam b intersects the optical axis O at point R. The distance between the deflected light beam b and the optical axis O at the position where the light enters the second reflecting surface 5 of the rotating polygon mirror 3 after intersecting is the distance of the reflecting surface when the rotating polygon mirror 3 is rotated by the angle θ1. It becomes equal to the movement amount δ.
[0028]
At this time, the deflected light beam b is deflected to the side where the incident angle is increased by the angle θ 2 with respect to the second reflecting surface 5 of the rotary polygon mirror 3, so that the light beam c reflected by the second reflecting surface 5 is. Is deflected by 2 · θ1 + θ2. In other words, the deflection angle of the light beam can be increased by .theta.2 as compared with an optical scanning device that deflects light by being incident on a normal once-turned polygonal mirror. Therefore, when the light beam b that scans the scanning end of the scanning region by the transmission optical system intersects the optical axis O, the deflection angle of the light beam c deflected by the second reflecting surface 5 can be increased by 2 · θ1 + θ2. .
[0029]
Next, the relationship between the number of mirrors of the transmission optical system and the number of intersections of the optical axis of the light beam will be described with reference to FIGS. The number obtained by subtracting the number of times the light beam that scans the scanning end intersects the optical axis from the number of mirrors of the transmission optical system is an odd number. That is, in the case shown in FIG. 7A, the configuration is the same as that of this embodiment with respect to the number of mirrors and the number of crossings. The number of mirrors used in the transmission optical system is the first transmission mirror 8 and the second transmission mirror 11. As shown in the developed view in FIG. 8A, in this case, the number of intersections with the optical axis O is one as indicated by the broken principal ray. In the example shown in FIG. 7B, the number of mirrors is three, that is, the first transmission mirror 8, the second transmission mirror 11, and the third transmission mirror 15. As can be seen from the developed view shown in FIG. 8B, the number of intersections with the optical axis O in this case is two. Therefore, in this embodiment shown in FIG. 7A, the moving direction and moving amount of the light beam b on the second reflecting surface 5 when the rotary polygon mirror 3 is rotated by the second deflection are the second values. The moving direction and the moving amount of the reflecting surface 5 are the same, and the light beam b incident on the second reflecting surface 5 can be caused to follow without protruding from the second reflecting surface 5.
[0030]
Next, the correction of the rotation of the light beam generated in the transmission optical system, which is a feature of the present invention, will be described in detail with reference to FIGS. The light beam a from the light source 1 is incident on the first reflecting surface 4 of the rotary polygon mirror 3 from below with an angle in the sub-scanning direction via the shaping optical system, and the first deflection is performed. Since the optical path between the first deflection and the second deflection as the light beam b has an angle in the sub-scanning direction, the coordinate system of the light beam b on the second reflecting surface 5 rotates. That is, a light beam a having a coordinate system in which the main scanning direction is y, the sub-scanning direction is x, and the optical axis direction is z is reflected by the first reflecting surface 4 at an angle in the sub-scanning direction, and further the first transmission is performed. When reflected by the mirror 8, the coordinate system of the reflected light beam b is rotated as shown in FIG. When the light beam b is further reflected by the second transmission mirror 11 and is incident on the second reflecting surface 5 of the rotary polygon mirror 3, the coordinate system of the light beam b is rotated as shown in FIG. That is, the y direction and the main scanning direction of the light beam b, and the x direction and the sub scanning direction of the light beam b are shifted by a predetermined angle θ.
[0031]
In this way, when the light beam b is deflected a second time on the second reflecting surface 5 of the rotary polygon mirror 3 and becomes the light beam c, the coordinate system of the deflected light beam c as shown in FIG. Is always inclined at an angle θ. Even if the light beam c inclined by the angle θ is formed on the scanning surface 14 by an anamorphic scanning optical system, it is not formed at one point, and the shape of the beam spot is destroyed. In such a case, as shown in FIG. 12, if a cylindrical lens 211 having a refractive power in the sub-scanning direction is tilted along the inclination θ of the light beam c, the light beam that forms an image on the scanned surface 14 Although the imaging characteristic of c is good, it is necessary to increase the effective diameter of the cylindrical lens 211 in the sub-scanning direction. Further, there is a problem that the scanning line on the surface to be scanned 14 is inclined according to the inclination of the cylindrical lens 211.
[0032]
FIG. 13 is a diagram in which the optical path of the transmission optical system is projected in the main scanning direction. Optical axis O after the first deflection by the first reflecting surface 4 of the rotary polygon mirror 3 ₁ And the optical axis O before the second deflection by the second reflecting surface 5 of the rotary polygon mirror 3. ₂ Let γ be the angle formed by. The incident angles of the light beam a and the light beam b on the first reflecting surface 4 and the second reflecting surface 5 in the sub-scanning direction are α and β, respectively. FIG. 14 shows the calculation result of the rotation angle of the light beam b. The rotation angle θ is positive counterclockwise. However, it is based on the following conditions.
[0033]
(1) The optical path length from the first reflecting surface 4 to the second reflecting surface 5 is sufficiently larger than the size of the rotating polygon mirror 3.
[0034]
(2) Optical axis O after the first deflection ₁ And the optical axis O before the second deflection ₂ , The optical path from the first reflecting surface 4 to the second reflecting surface 5 is symmetric.
[0035]
As shown in FIG. 14, the rotation angle θ is zero when the incident angle α and the incident angle β on the first reflecting surface 4 and the second reflecting surface 5 in the sub-scanning direction are the same and when γ is 180 °. Become. Unlike the above conditions (1) and (2), when the size of the rotary polygon mirror 3 is not negligible with respect to the optical path length, the incident angle α to the first reflecting surface 4 and the second reflecting surface 5 is determined. If the incident angle β is different, the value of the rotation angle θ slightly depends on the size of the rotary polygon mirror 3. Even when the optical path is not symmetric, the value of the rotation angle θ slightly varies if the incident angle α and the incident angle β are different. However, if the incident angle α is equal to the incident angle β, the rotation angle θ is always zero.
[0036]
In this embodiment, only the incident angle α of the light beam a and the incident angle β of the light beam b on the first reflecting surface 4 and the second reflecting surface 5 are changed, and the light beam a is incident on the first reflecting surface 4. Assuming that the incident angle α = 3 ° and the incident angle β of the light beam b on the second reflecting surface = 6 °, the beam spot shape by the light beam c scanning the scanning end is a collapsed shape as shown in FIG. Become. This figure is an isointensity diagram of a beam spot. Note that the collapse of the shape of the beam spot depends on the size of the beam spot, and if a smaller beam spot is formed, the shape of the beam spot becomes worse.
[0037]
Therefore, if the incident angle α = the incident angle β, the rotation angle θ = 0 as shown in FIG. 14, and the beam spot shape is good. In this embodiment, the incident angle α = incident angle β = 6 °, and the beam spot shape by the light beams c1 and c2 scanning the scanning end is good as shown in FIG. Further, even if γ = 180 °, the rotation angle θ = 0, so that the beam spot shape is also good in this case.
[0038]
Next, the case where γ = 180 °, that is, the first reflecting surface 4 and the second reflecting surface 5 are parallel will be described. In FIG. 13, the optical axis O ₁ And optical axis O ₂ Is equal to the angle formed by the first reflecting surface 4 and the second reflecting surface 5. In the present embodiment, γ = 90 °, but separately from the present embodiment, when the first reflecting surface 4 and the second reflecting surface 5 are parallel, γ = 180 °, and the graph of FIG. Therefore, the rotation angle θ of the light beam becomes 0. An optical path diagram in this case is shown in FIG. That is, the light beam b deflected upward by the first reflecting surface 4 of the rotary polygon mirror 3 is reflected by the first transmission mirror 8, passes directly above the rotary polygon mirror 3, intersects the rotation axis 6, and is transmitted by the second transmission mirror 8. Reflected by the mirror 11 and incident on the second reflecting surface 5 of the rotary polygon mirror 3 from above, where it is deflected downward to become a light beam c.
[0039]
Next, rotation correction of a light beam generated by deflection will be described with reference to FIGS. In the type of optical scanning device that is incident on the reflecting surface of the scanner with an angle in the sub-scanning direction, as shown in FIG. 17A, the coordinate system of the main scanning direction y, the sub-scanning direction x, and the optical axis direction z Is incident on the second reflecting surface 5 of the rotary polygon mirror 3 at an angle in the sub-scanning direction, the light beam c deflected here is curved and the coordinate system of the light beam c is rotated. At this time, the light beam c at the scanning center ₀ Does not rotate, but the light beam c scans the scanning end. ₁ , C ₂ Are rotated in different directions at both scanning ends as shown in FIG. An inclined light beam c that scans the scanning end ₁ , C ₂ Even if an image is formed on the scanned surface 14 by an anamorphic scanning optical system, the image is not formed at one point, the beam spot shape is destroyed, and the image is not favorably formed on the scanned surface 14.
[0040]
In the present embodiment, the second scanning lens 13 is arranged eccentrically, and the trajectory C of the light beam incident on the second scanning lens 13 is curved as shown in FIG. Light beam c ₁ , C ₂ Is incident on a position away from the central axis N of the second scanning lens 13. The central axis N of the second scanning lens 13 is an axis that passes through the optical axis of the second scanning lens 13 and is parallel to the main scanning direction. Here, it is assumed that the light beam c scans the scanning end. ₁ , C ₂ Is configured to transmit the central axis N of the second scanning lens 13, the light beam c for scanning the scanning end. ₁ , C ₂ The beam spot shape due to is a collapsed shape as shown in FIG. The collapse of the shape of the beam spot depends on the size of the light beam before being narrowed down by the lens, and the collapse of the shape becomes worse when an attempt is made to form a smaller beam spot. In the present embodiment, the first shaping lens 2 of the shaping optical system is a rotationally symmetric lens around the optical axis, so that the image of the light beam a incident on the first reflecting surface 4 of the rotary polygon mirror 3 is the main scanning. There is no distinction between the direction and the sub-scanning direction. Therefore, the rotation of the light beam b deflected by the first reflecting surface 4 is not a problem.
[0041]
In this embodiment, the beam spot shape collapses in the light beam c that scans the scanning end. ₁ , C ₂ Is incident on a position away from the central axis N of the second scanning lens 13 for correction. FIG. 20 shows a cross section in the sub-scanning direction of the optical path from the rotary polygon mirror 3 to the second scanning lens 13. Illustrated light beam c ₁ , C ₂ Is a light beam that scans the scanning end. In FIG. 20, the light beam c incident on the second reflecting surface 5 of the rotary polygon mirror 3. ₁ , C ₂ On the other hand, the emitted light beam is located on the lower side. Further light beam c ₁ , C ₂ Passes through the second scanning lens 13 at a position away from the optical axis O of the second scanning lens 13 after passing through the first scanning lens 12. The optical axis O of the second scanning lens 13 and the light beam incident on the second scanning lens 13 are substantially parallel.
[0042]
In this embodiment, the second scanning lens 13 is a light beam c that scans the scanning center. ₀ On the other hand, they are arranged eccentrically by 2.67 mm in the sub-scanning direction and in the direction of arrow E in FIG. That is, the light beam c that scans the scanning center. ₀ Is incident at a position 2.67 mm away from the optical axis of the second scanning lens 13. Further, the light beam c that scans the scanning end ₁ , C ₂ Is incident at a position away from the optical axis of the second scanning lens 13 by 7.02 mm. As a result, the light beam c that scans the scanning end. ₁ , C ₂ As shown in FIG. 16, the beam spot shape by is good.
[0043]
According to the simulation performed by the present inventor, the light beam c for scanning the scanning end is thus obtained. ₁ , C ₂ However, if the optical axis of the anamorphic lens such as the second scanning lens 13 is configured to pass through a position separated in the sub-scanning direction, the rotation of the light beam can be corrected and the collapse of the beam spot shape can be corrected. it can. In particular, as described above, with respect to the light beam incident on the reflecting surface of the rotating polygon mirror 3, the side where the light beam emitted from the rotating polygon mirror 3 exists (the lower side in FIG. 20) and the second scanning lens 13 are provided. If the side where the light beam incident on the second scanning lens 13 is present (the lower side in FIG. 20) coincides with the optical axis, the beam spot shape is corrected.
[0044]
The second scanning lens 13 of the present embodiment has a positive refractive power at the incident surface, but the same effect can be obtained even when the lens has a positive refractive power at the exit surface. Further, when the second scanning lens 13 is a lens having a negative refractive power in the sub-scanning direction, a light beam emitted from the rotating polygon mirror 3 with respect to a light beam incident on the reflecting surface of the rotating polygon mirror 3. If the side where the light beam is present and the side where the light beam incident on the anamorphic lens is present are reversed with respect to the optical axis of the anamorphic lens, the same effect can be obtained.
[0045]
A light beam c that scans the scanning center. ₀ Since the rotation of the coordinate system due to deflection does not occur, the beam spot shape is not originally lost, and even if the second scanning lens 13 is decentered, the beam spot shape is not affected. Therefore, the beam spot shape is still good. In addition, slight spherical aberration occurs due to decentration, but this is not substantially a problem.
[0046]
Next, another arrangement of the second scanning lens 13 is shown in FIG. Light beam c for scanning the scanning end ₁ , C ₂ The optical axis O of the second scanning lens 13 is inclined with respect to the light beam c. ₁ , C ₂ Is incident on a position away from the optical axis O of the second scanning lens 13. This configuration also has an effect of correcting the collapse of the beam spot shape.
[0047]
The cross-sectional shape of the second scanning lens 13 shown in FIGS. 20 and 21 in the sub-scanning direction is symmetrical with respect to the optical axis O of the second scanning lens 13. However, the position where the light beam passes through the second scanning lens 13 is shifted to one side with respect to the optical axis O. Therefore, the lens may be configured only in the range through which the light beam is transmitted, and the cross section in the sub-scanning direction may be as shown in FIGS. 22 (a) and 22 (b). In FIG. 22A, the thickness of the lens is different at one end and the other end. When manufacturing a lens having such a shape, first, a lens is formed symmetrically with respect to a plane including the optical axis and parallel to the main scanning direction, and then cut along a plane including the optical axis and parallel to the main scanning direction. It becomes possible to obtain two lenses by the lens processing of the degree, and the cost can be halved.
[0048]
A lens having a complicated surface shape such as the second scanning lens 13 is often manufactured by resin molding. The cross-sectional shape in the sub-scanning direction of the second scanning lens 13 manufactured by resin molding is formed with ribs 23 and 24 as shown in FIG. In FIG. 22B, in the lens effective portion excluding the ribs 23 and 24, the lens thickness is also different between one end and the other end. In the case of the lens shape as shown in FIGS. 22A and 22B, the optical axis of the lens may be located outside the lens, but the optical axis is on both the entrance surface and the exit surface of the lens. Defined as a vertical axis. When the cross-sectional shape of the second scanning lens 13 in the sub-scanning direction is as shown in FIGS. 22A and 22B, the area of the lens surface of the second scanning lens 13 and particularly the width of the lens surface in the sub-scanning direction is reduced. Therefore, the surface accuracy of the lens surface can be increased. This is particularly effective when the second scanning lens 13 has a toric surface as in this embodiment.
[0049]
In general, the toric surface is processed by independent feed movements in the main scanning direction and the sub-scanning direction, so it is difficult to achieve both surface accuracy in the main scanning direction and surface accuracy in the sub-scanning direction. When trying to increase the surface accuracy in one direction, the surface accuracy in the other direction will deteriorate. In particular, due to wear of the tool, unevenness is caused and the surface accuracy is deteriorated. Therefore, if the area of the lens surface is large, the amount of wear increases and the surface accuracy is further deteriorated. Therefore, if the area of the lens surface is reduced as shown in FIGS. 22A and 22B, high surface accuracy can be obtained.
[0050]
22A and 22B, the size of the second scanning lens 13 can be reduced, the overall size of the optical scanning device can be reduced, and the cost can be reduced. You can also go down.
[0051]
Next, scanning line curvature correction will be described. As shown in FIG. 26, when the light beam b is incident on the second reflecting surface 5 of the rotary polygon mirror 3 at an angle in the sub-scanning direction, the reflected and deflected light beam c is curved, and a solid line is formed at the scanning center. The light beam c0 becomes like this, but becomes light beams c1 and c2 as shown by broken lines at the scanning end. However, if the second reflecting surface 5 of the rotary polygon mirror 3 and the scanned surface 14 are geometrically conjugate in the sub-scanning direction, the light beam c0 at the scanning center also scans the scanning end with the light beams c1 and c2. Also, the same position is reached on the scanned surface 14 in the sub-scanning direction, and the scanning line on the scanned surface 14 becomes a straight line.
[0052]
In this embodiment, the first transmission lens 7 and the first scanning lens 12 are lenses having a shape whose length in the sub-scanning direction is shorter than the length in the main scanning direction. These lenses have a very short length in the sub-scanning direction, and are the minimum length necessary for transmitting the light beam. Therefore, the light beam a incident on the rotary polygon mirror 3 does not interfere with the first conductive lens 7, and the light beam b does not interfere with the first scanning lens 12. Further, since the light beam and the lens do not interfere with each other, the incident angles of the light beam a and the light beam b on the rotary polygon mirror 3 in the sub-scanning direction can be reduced, and the light beam b deflected by the respective reflecting surfaces and The curvature of the light beam c is reduced, and the apertures of the second transmission lens 9, the third transmission lens 10, and the second scanning lens 13 in the sub-scanning direction can be reduced. Furthermore, in this embodiment, the apertures in the sub-scanning direction of the incident surfaces of the first transmission lens 7 and the first scanning lens 12 are the light beam a and the light beam b incident on the rotary polygon mirror 3 at the positions of the respective reflecting surfaces. And the deflected light beam b and the light beam c coincide with each other. In FIG. 23, the solid line indicates the light beam b at the scanning center without deviation. ₀ , C ₀ The light beam b that scans the scanning end where the deviation in the sub-scanning direction indicated by the broken line is maximum ₁ , C ₁ And b ₂ , C ₂ When the lens aperture is larger than this, the incident light beam b and the light beam c interfere with the lens. Conversely, if the lens diameter is smaller than this, the reflected light beam b and the light beam c will pass outside the lens. Therefore, with the above configuration, the allowable value of the deviation of the light beam b and the light beam c in the sub-scanning direction is maximized.
[0053]
Next, the scanning area shift will be described with reference to FIG. In the conventional optical scanning device, the scanning start position and the scanning end position are symmetric with respect to the optical axis of the scanning optical system, and the horizontal synchronization signal detection position is provided outside thereof. In such a configuration, it is necessary to make the use area of the scanning lens system large only on the horizontal synchronization signal detection side. However, in general, it is desirable that the lens is symmetric with respect to the optical axis in manufacturing. In some cases, the aperture of the lens had to be made large. In particular, in a positive lens such as a scanning lens, when the aperture is increased, the thickness of the lens in the optical axis direction must be increased accordingly in order to ensure the thickness of the outer periphery of the lens. In the present invention, the horizontal synchronizing signal detection position and the scanning end position are arranged symmetrically with respect to the optical axis of the scanning optical system. Therefore, the aperture of the first scanning lens 12 in the main scanning direction can be reduced.
[0054]
Next, the tilting of the horizontal synchronization lens will be described. As described in the above-described correction of the rotation of the light beam generated by the deflection, in the optical scanning device that is incident at an angle in the sub-scanning direction, the coordinate system of the main scanning direction y, the sub-scanning direction x, and the optical axis direction z Is incident on the second reflecting surface 5 of the rotary polygon mirror 3 at an angle in the sub-scanning direction, and the deflected light beam c is bent and deflected, so that the coordinate system of the light beam c is rotated. (See FIG. 17). When the light beam d is rotated by the deflection of the second reflecting surface 5 of the rotary polygon mirror 3, the beam spot formed by the horizontal synchronizing signal light beam d is not imaged at one point, and the shape of the beam spot is destroyed, and the detection accuracy is deteriorated. For this reason, in this embodiment, as shown in FIG. 1, the horizontal synchronizing lens 82 is tilted 2.4 ° clockwise as indicated by an arrow C with the optical axis as the rotation axis when viewed in the beam traveling direction. doing. Accordingly, the coordinate system of the rotated light beam d coincides with the coordinate system in the generatrix direction and the circumferential direction of the horizontal synchronization lens 82, and the shape of the beam spot is improved and introduced into the horizontal synchronization sensor 83, thereby improving detection accuracy. Will be.
[0055]
Next, the tilting of the horizontal synchronization sensor 83 will be described. In this embodiment, the horizontal synchronization lens 82 is tilted, and at the same time, the horizontal synchronization sensor 83 is also tilted in the direction of arrow D by the same angle 2.4 ° as the horizontal synchronization lens 82. Therefore, when the horizontal synchronization lens 82 is tilted, the beam spot scanning direction on the horizontal synchronization sensor 83 is also tilted by the same angle. Therefore, since the horizontal synchronizing signal light beam d scans vertically on the horizontal synchronizing sensor 83, the detection sensitivity is further improved.
[0056]
Next, a second embodiment of the present invention will be described with reference to FIG. In the previous embodiment, the optical scanning device is configured to be incident and deflected twice at an angle to the scanning plane perpendicular to the rotation axis of the rotary polygon mirror that is a scanner. This is an optical scanning device that scans by deflecting a light beam incident at an angle on a scanning plane perpendicular to the rotation axis of the optical axis. In other words, the light beam a emitted from the semiconductor laser 1 as a light source passes through the shaping optical system including the first shaping lens 51 and the second shaping lens 52 and passes down to the reflecting surface 61 of the rotary polygon mirror 3 as a focused light beam a. Incident from. The light beam b reflected and deflected upward from the reflecting surface 61 is transmitted through a scanning optical system including the first scanning lens 71 and the second scanning lens 72 to form a beam spot on the surface 14 to be scanned, thereby scanning lines. Form. The light beam d separated by the horizontal synchronization mirror 101 at the scanning end of the light beam b from the reflecting surface 61 is for a horizontal synchronization signal, and is imaged on the horizontal synchronization sensor 103 by the horizontal synchronization lens 102. The
[0057]
The first shaping lens 51 is an aspherical lens that is rotationally symmetric about the optical axis, and the second shaping lens 52 is a cylindrical lens having refractive power only in the sub-scanning direction. The first scanning lens 71 is a spherical lens, the second scanning lens 72 is a plastic lens, and its incident surface has a concave shape with a large curvature radius in the main scanning direction, and the curvature in the sub-scanning direction. It has a convex shape with a small radius. Further, a vertical toric surface formed by rotating a cross-sectional curve in the main scanning direction around an axis parallel to the main scanning direction on the scanned surface 14 side with respect to the incident surface, and an exit surface in the main scanning direction. A non-arc having a large radius of curvature, and the cross section in the sub-scanning direction is a straight non-arc cylindrical surface.
[0058]
Next, specific numerical examples configured in this way are shown in Table 3. In this table, the curvature radius of the anamorphic surface in the sub-scanning direction and the main scanning direction is set to rix and riy. In addition, for a surface that is an aspherical surface, the radius of curvature indicates a value on the optical axis.
[0059]
[Table 3]

[0060]
The formula of the aspheric coefficient of the first shaping lens 51 is the same as that shown in Equation 1 of the previous example, and the aspheric coefficient is shown in Table 4 below.
[0061]
[Table 4]

[0062]
In this numerical example, the rotation angle 2ω of the rotary polygon mirror 3 from the start of scanning to the end of scanning is 31.7 °, and the incident angle of the light beam a on the rotary polygon mirror 3 in the sub-scanning direction is 6 °. The number of surfaces of the rotating polygon mirror 3 is 6, the inscribed circle radius of the rotating polygon mirror 3 is 17 mm, and the wavelength of the light beam a from the semiconductor laser 1 is 800 nm. Accordingly, as in the first embodiment, the incident angle of the light beam a incident on the reflecting surface 61 of the rotary polygon mirror 3 is inclined obliquely upward in the sub-scanning direction. The light beam a and the deflected light beam b are separated and separated vertically in the direction of the rotation axis of the rotary polygon mirror 3 and do not interfere at all.
[0063]
Then, since the light is incident on the reflecting surface 61 of the rotary polygon mirror 3 at an angle in the sub-scanning direction, the deflected light beam b is curved and the light beam b is rotated as in the previous embodiment. That is, as shown in FIG. 9, the coordinate system of the light beam b rotates in the same manner. Therefore, as in the previous embodiment, the rotation of the light beam that scans the scanning end is corrected, and the beam spot shape is not deformed. to correct. This will be described with reference to FIG.
[0064]
Light beam c incident on the reflecting surface 61 of the rotary polygon mirror 3 ₁ , C ₂ On the other hand, the emitted light beam is located on the lower side. Further light beam c ₁ , C ₂ Passes through the first scanning lens 71 and then passes through the second scanning lens 72 at a position away from the optical axis O of the second scanning lens 72. The optical axis O of the second scanning lens 72 and the light beam incident on the second scanning lens 72 are substantially parallel.
[0065]
In this embodiment, the second scanning lens 72 is a light beam c that scans the scanning center. ₀ On the other hand, they are arranged eccentrically by 2.25 mm in the sub-scanning direction and in the direction of arrow E in FIG. That is, the light beam c that scans the scanning center. ₀ Is incident at a position 2.25 mm away from the optical axis of the second scanning lens 72. Further, the light beam c that scans the scanning end ₁ , C ₂ Enters the point A which is 5.54 mm away from the optical axis of the second scanning lens 72. With this configuration, as in the previous embodiment, the rotation of the light beam can be corrected and the collapse of the beam spot shape can be corrected.
[0066]
Next, the tilting of the horizontal synchronization lens will be described. As described in the above-described correction of the rotation of the light beam generated by the deflection, in the optical scanning device that is incident at an angle in the sub-scanning direction, the main scanning direction y, the sub-scanning direction x, and the optical axis direction z When the light beam b having the coordinate system is incident on the reflecting surface 61 of the rotary polygon mirror 3 with an angle in the sub-scanning direction, the deflected light beam c is bent and deflected, and therefore the coordinate system of the light beam c is rotated. (See FIG. 17). When the beam c is rotated by the deflection of the reflecting surface 61 of the rotary polygon mirror 3, the beam spot formed by the horizontal synchronizing signal beam d is not imaged at one point, and the shape of the beam spot is broken and the detection accuracy is deteriorated. For this reason, in this embodiment, as shown in FIG. 27, the horizontal synchronization lens 102 is tilted clockwise as indicated by an arrow C with the optical axis as the rotation axis when viewed in the beam traveling direction. . Therefore, the coordinate system of the rotated beam d is coincident with the generatrix and circumferential coordinate systems of the horizontal synchronization lens 82, and the beam spot shape is not destroyed and introduced into the horizontal synchronization sensor 103, thereby improving the detection accuracy. It becomes.
[0067]
Next, the tilting of the horizontal synchronization sensor 103 will be described. In this embodiment, at the same time that the horizontal sync lens 102 is tilted, the horizontal sync sensor 103 is also tilted in the direction of arrow D by the same angle as the horizontal sync lens 102. Accordingly, when the horizontal synchronization lens 102 is tilted, the beam spot scanning direction on the horizontal synchronization sensor 103 is also tilted by the same angle. Therefore, since the horizontal synchronization signal light beam d vertically scans on the horizontal synchronization sensor 103, the detection sensitivity is further improved.
[0068]
In these embodiments, the rotating polygon mirror is used as the scanner. However, this is not limited to the rotating polygon mirror, and it is sufficient that the scanner has at least two reflecting surfaces. The front and back surfaces of a galvano mirror that performs sinusoidal vibration about a surface mirror and a rotation axis may be used. In addition, it is particularly effective when used in laser printers. Other image forming apparatuses such as digital copying machines, facsimiles, and laser scanning displays, image input apparatuses such as scanners, optical mark reading laser apparatuses, and surface inspection lasers. Of course, the present invention can also be applied to a scanning device or the like.
[0069]
【The invention's effect】
As described above, the optical scanning device of the present invention has the following effects.
[0070]
First, according to the first and second aspects of the invention, the light beam that scans the scanning end scans the normal of the incident surface at the point where the light beam passes through the incident surface of the anamorphic lens of the scanning optical system and the scanning end. The beam spot shape by the rotation of the light beam deflected by the scanner is such that the normal of the exit surface at the point where the light beam passes through the exit surface of the anamorphic lens has an angle in the sub-scanning direction. Can be prevented, and an optical scanning device with good image quality can be provided. In addition, in the cross-sectional shape of the anamorphic lens in the sub-scanning direction, the thickness of the lens is made different between one end and the other end in the sub-scanning direction, whereby an anamorphic lens with high surface accuracy can be obtained, and the image has good light Not only can the scanning device be provided, but also the optical scanning device can be reduced in size and cost.
[0071]
Furthermore, according to the first aspect of the present invention, the position of the scanning start point can be aligned with high accuracy by arranging the horizontal synchronizing lens so as to rotate with respect to the optical axis thereof.
[0072]
According to the second aspect of the present invention, the position of the scanning start point can be more accurately aligned by rotating the horizontal synchronization sensor with respect to its optical axis.
[Brief description of the drawings]
FIG. 1 is a perspective view illustrating a configuration of an optical scanning device according to an embodiment.
FIGS. 2A, 2B, 2C, 2D, and 2E are development views for explaining that the surface tilt in the sub-scanning direction and the scanning position are constant.
FIG. 3 is a development view of the transmission optical system in the main scanning direction.
FIG. 4 is a development view of the transmission optical system in the main scanning direction.
FIG. 5 is a development view of the transmission optical system in the sub-scanning direction.
FIG. 6 is a development view of a transmission optical system in the main scanning direction for explaining the intersection of light beams.
FIGS. 7A and 7B are plan views for explaining the intersection of the number of mirrors of a transmission optical system and a light beam. FIGS.
8A and 8B are development views in the main scanning direction of the transmission optical system in FIG.
FIG. 9 is a side view for explaining rotation of a light beam generated in a transmission optical system.
FIG. 10 is a side view of a rotating polygon mirror for explaining rotation of a light beam.
FIG. 11 is a side view of a rotating polygon mirror for explaining rotation of a light beam.
FIG. 12 is a front view of a cylindrical lens arranged at an angle.
FIG. 13 is an optical path diagram obtained by projecting the optical path of the transmission optical system in the main scanning direction.
FIG. 14 is a graph showing the relationship between the rotation angle and the angle formed by the optical axes of the first reflecting surface and the second reflecting surface.
FIG. 15 is an isointensity diagram of a beam spot.
FIG. 16 is an isointensity diagram of a beam spot.
FIGS. 17A and 17B are a perspective view for explaining rotation of a light beam generated by deflection, and an explanatory diagram showing a coordinate system. FIGS.
FIG. 18 is an isointensity diagram of a beam spot.
FIG. 19 is a front view of a second scanning lens.
FIG. 20 is a sectional view of the scanning optical system in the sub-scanning direction.
FIG. 21 is a cross-sectional view in the sub-scanning direction of a second scanning lens having another arrangement.
FIG. 22 is a cross-sectional view in the sub-scanning direction of a second scanning lens having another cross-sectional shape.
FIG. 23 is a cross-sectional view in the sub-scanning direction showing a scanning lens and an optical path near the scanning lens.
FIG. 24 is an explanatory diagram for explaining scanning area shift;
FIG. 25 is a side view of an optical scanning device showing an optical path of a modified example.
FIG. 26 is an explanatory diagram for explaining scanning line curvature correction;
FIG. 27 is a perspective view illustrating a configuration of an optical scanning device according to a second embodiment.
FIG. 28 is a sectional view of the scanning optical system in the sub-scanning direction.
[Explanation of symbols]
1 Light source (semiconductor laser)
2 shaping lens
3 Rotating polygon mirror
4 First reflective surface
5 Second reflective surface
6 Rotating shaft
7 First transmission lens
8 First transmission mirror
9 Second transmission lens
10 Third transmission lens
11 Second transmission mirror
12 First scanning lens
13 Second scanning lens
14 Scanned surface
81 Horizontal synchronous mirror
82 Horizontal synchronization lens
83 Horizontal sync sensor

Claims (2)

A light source for generating a light beam, a scanner for deflecting a light beam incident at an angle in the sub-scanning direction from the light source, and a light beam reflected and deflected by the reflecting surface of the scanner by a scanning optical system In an optical scanning device that scans by forming a beam spot on a surface to be scanned,
The light beam deflected by the reflecting surface of the scanner is transmitted at a scanning end from a position separated from the optical axis of the anamorphic lens of the scanning optical system in the sub-scanning direction, and the anamorphic In the cross-sectional shape of the lens in the sub-scanning direction, the thickness of the lens is different at one end and the other end in the sub-scanning direction, and
The horizontal synchronizing lens, the optical axis as a rotation axis, the optical scanning device you characterized in that arranged rotated so as to correspond to a rotation of the coordinate system of the deflected light beam. A light source for generating a light beam, a scanner for deflecting a light beam incident at an angle in the sub-scanning direction from the light source, and a light beam reflected and deflected by the reflecting surface of the scanner by a scanning optical system In an optical scanning device that scans by forming a beam spot on a surface to be scanned,
The light beam deflected by the reflecting surface of the scanner is transmitted at a scanning end from a position separated from the optical axis of the anamorphic lens of the scanning optical system in the sub-scanning direction, and the anamorphic In the cross-sectional shape of the lens in the sub-scanning direction, the thickness of the lens is different at one end and the other end in the sub-scanning direction, and
The horizontal synchronization sensor, the optical axis as a rotation axis, the optical scanning device you characterized in that arranged rotated so as to correspond to a rotation of the coordinate system of the deflected light beam.

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