JP3707511B2 - Optical scanning device - Google Patents

Optical scanning device Download PDF

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JP3707511B2
JP3707511B2 JP04645397A JP4645397A JP3707511B2 JP 3707511 B2 JP3707511 B2 JP 3707511B2 JP 04645397 A JP04645397 A JP 04645397A JP 4645397 A JP4645397 A JP 4645397A JP 3707511 B2 JP3707511 B2 JP 3707511B2
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Prior art keywords
light beam
optical system
scanning
optical
polygon mirror
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JPH10239621A (en
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望 井上
高志 ▲浜▼
球 高田
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Seiko Epson Corp
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Seiko Epson Corp
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Description

【０００１】
【発明の属する技術分野】
本発明はレーザービームプリンターなどに用いられる光走査装置に関するもので、特に回転多面鏡の反射面に光ビームが２度入射する光学系を用いた光走査装置の構造に関する。
【０００２】
【従来の技術】
レーザービームプリンターなど画像記録装置や、各種画像読込み、測定装置に用いられる光走査装置においては、光ビームを偏向走査する偏向器として回転多面鏡が多く用いられてきた。
【０００３】
これらの装置においては光ビームを被走査面上において、直線あるいは曲線上を光走査装置によって繰り返し走査し、被走査面に位置する被走査媒体を前記の走査方向とはおおむね直交方向に相対移動させ２次元の走査を行う。なお、前者の光走査装置による走査方向を「主走査方向」とし、後者の被走査媒体の相対移動方向を「副走査方向」と定義する。
【０００４】
近年、上記の装置においては解像度や処理速度の向上のため、より高速の光走査装置が求められるようになってきている。光ビームの偏向に回転多面鏡を用いた光走査装置では、走査速度（走査周波数）を上げるためには、
（１）回転多面鏡の回転数を上げる
（２）回転多面鏡の面数を増加させる
の２つの方法が考えられる。
【０００５】
回転多面鏡の回転数を上げるためには、高速回転可能な軸受が必要になるが、現在最も多く用いられているボールベアリングでは毎分２００００回転程度が上限となる。エアベアリングを用いれば毎分３００００回転以上の回転数で使用可能であるが、軸受が高価なため使用できる装置が限られる。特に、一般消費者向けの安価なレーザービームプリンターなどには使えない。
【０００６】
一方、回転多面鏡の面数を増加させると、１つの反射面当りの回転角度が小さくなってしまう。また、個々の反射面の大きさを一定以上確保しようとすると、回転多面鏡の直径が大きくなってしまう。
【０００７】
光走査装置では被走査面上に光ビームを結像させて用いるが、レーザービームを走査する場合、小さなスポットに結像させるには、光ビームの拡がり角に応じて回転多面鏡の反射面は主走査方向にある一定の大きさが必要である。ところが、回転多面鏡の面数を増加させた場合、１つの反射面での回転角度が小さいため光ビームの走査角も小さくなる。光ビームの走査角が小さいと、所定の走査幅を得るためには走査光学系の焦点距離が長くなり、回転多面鏡から被走査面までの光路長も伸びる。このため、回転多面鏡の反射面上での光ビームの主走査方向の直径も大きくなり、面数が少ない場合に比べてより反射面が大きくなり、さらに一層回転多面鏡の大きさが増加する。
【０００８】
すなわち回転多面鏡の面数が増加するに従って、必要な反射面の大きさは面数の少ない場合に比べてより大きくなるという矛盾した特性をもつため、回転多面鏡の大きさ（内接円筒の大きさ）が決まれば、面数の上限が決まる。例えば、レーザービームプリンターに用いる光走査装置において、所要走査幅３５０ｍｍ、波長７８０ｎｍ、回転多面鏡の内接円筒の半径を２５ｍｍ、被走査面での主走査方向のスポット直径を５０μｍ以下にする場合、面数はおおむね７面が上限となる。
【０００９】
そこで、面数を多く取るために、回転多面鏡の直径を大きくすると、回転多面鏡の重量や慣性２次モーメントが増加し、回転に伴う空気抵抗（風損）も増加するので、回転数が低く制限される。
【００１０】
このように回転多面鏡の面数、回転数とも上限があり、かつ各々が矛盾する特性を有するので、それを越える走査速度を得るために様々な走査装置が考案されてきた。
【００１１】
例えば、特開昭５１−１００７４２号公報記載の技術では、光源に半導体レーザーアレーを用い、同時に複数のレーザービームで被走査面を走査することで、走査速度を向上させている。この方法によれば、回転多面鏡の回転数を上げることなく、素子に集積されたレーザーの個数だけ走査速度を早めることができる。
【００１２】
一方、特開昭５１−３２３４０号公報では、光源から射出された光ビームを主走査方向に非常に直径の小さい状態で回転多面鏡に入射させ、偏向された光ビームを伝達光学系を介して再び回転多面鏡に入射させる方法が開示されている。２回目に回転多面鏡に入射した後に、光ビームは走査光学系によって被走査面上にスポットとして結像する。すなわち、回転多面鏡に光ビームを２度入射させている。
【００１３】
この後者の方法においては、光ビームが最初に回転多面鏡に入射するときの主走査方向の光ビームの直径を２回目に入射する場合に比べて極めて小さくし、かつ２回目に回転多面鏡に入射する光ビームが回転する反射面の主走査方向の中心点を追従するように伝達光学系を構成している。
【００１４】
このように構成することで、光ビームが最初に回転多面鏡に入射する際には、光ビームの直径を極端に小さくできるので、回転多面鏡の分割角度一杯まで走査可能となる。第１の反射面で偏向された光ビームが伝達光学系を経由して、２回目に回転多面鏡に入射する際には、光ビームの直径は被走査面上で所定のスポットを得るのに必要な大きさに拡大されるものの、反射面の回転に追従するため、回転多面鏡の回転角度とは無関係に光ビームの大きさを設定できる。従って、回転多面鏡の反射面の主走査方向の大きさを小さくすることが可能となり、小径で面数の多い回転多面鏡が使用可能となる。
【００１５】
【発明が解決しようとする課題】
このように回転多面鏡に光ビームが２度入射する光走査装置では、伝達光学系を構成するレンズや反射鏡を高精度に取り付ける必要があるので、高精度の加工や成形技術が要求される。たとえば収縮の少ないプラスチックの射出成形や、ダイキャストの鋳物に対してさらに必要な部分に切削加工を行なうなどの方法で製作される。ところが、このような方法で製作された部品は、一般的なプラスチックの射出成形部品や板金部品に比べて高価なものとなるという課題を有していた。
【００１６】
上記の課題に鑑み本発明では、回転多面鏡に光ビームを２度入射させて光ビームの偏向・走査を行なう光走査装置において、伝達光学系を構成するレンズや反射鏡などを高精度に取り付けることが可能あって、かつ光走査装置全体を収納する光学ケースを安価に製造することを目的とする。
【００１７】
上記の課題に鑑み本発明の走査装置では、光源と、前記光源からの光ビームを所定の特性の整形光ビームに変換するビーム整形光学系と、前記整形光ビームを第１の反射面で偏向し、少なくとも前記第１の反射面と第２の反射面を有する回転多面鏡と、前記回転多面鏡を駆動する偏向モーターと、前記回転多面鏡の前記第１の反射面により偏向された光ビームを前記回転多面鏡の前記第２の反射面に入射させる伝達光学系と、前記回転多面鏡の前記第２の反射面で偏向された走査光ビームを所定の被走査面に結像させる走査光学系を有し、前記走査光ビームで前記被走査面を走査する光走査装置において、前記伝達光学系と前記伝達光学系内に配置された折り返し鏡及び前記偏向モーターを支持するベース部材を前記光走査装置のケースとは異なる部材で構成し、前記光走査装置の光軸を折り曲げる前記走査光学系を構成する全ての折り返し鏡を前記光走査装置のケースに配列したことを特徴とする。
【００１８】
【発明の実施の形態】
図１、図２は本発明による光走査装置の実施例の概観を示す斜視図であって、図２は図１より補正レンズ６２及び第３の折り返し鏡９３を取り除いた状態を示す斜視図である。また、図３、図４は本発明による光走査装置の実施例の主走査断面での平面図を示す。図３、図４において回転多面鏡３０の第１の反射面３１以降の光ビームについては、ビーム検出位置、走査開始位置、走査光学系の光軸位置、走査終了位置の４ヵ所での光ビーム位置を示している。図３は走査光学系及び光ビーム検出光学系とその中を通過する光ビームを示し、図４は伝達光学系とビーム整形光学系とその中を通過する光ビームを示している。さらに、図５には本発明による光走査装置の実施例のビーム整形光学系を含んだ副走査面内の断面図を示し、図６には本発明による光走査装置の実施例の走査光学系を含んだ副走査面内の断面図を示す。
【００１９】
光源には半導体レーザー１１が用いられており、発散光として射出されたレーザービームはコリメータレンズ２１で緩やかな集束角を持つ集束光ビームに整形される。コリメータレンズ２１の射出面は、球面収差を減ずるために光軸に回転対称な非球面形状に形成されている。
【００２０】
コリメータレンズ２１を射出した光ビームは、入射側が平面で射出側が凹のシリンドリカル面である整形レンズ２２に入射する。整形レンズ２２は主走査方向にのみ負の屈折力を有しており、入射した集束光ビームは主走査方向には比較的小さな直径の平行な光ビームに変換される。一方、副走査方向においては、コリメータレンズ２１によって変換された集束光ビームのままである。以上に述べたコリメータレンズ２１と整形レンズ２２とでビーム整形光学系を構成している。
【００２１】
すなわち、図４に示すように回転多面鏡３０の第１の反射面３１に入射する光ビームは、主走査方向には通常の光走査装置に比べて小さい直径を有する平行光ビームで、副走査方向には第１の反射面３１上に結像するような集束光ビームである。なお、回転多面鏡３０については後ほど説明する。
【００２２】
上記のように本発明の実施例においては、半導体レーザー１１から射出した光ビームの直径がある程度広がった位置で、コリメータレンズ２１で緩い集束光ビームに変換し、さらにこのコリメータレンズ２１から距離をおいて凹のシリンドリカルレンズである整形レンズ２２を配して、主走査方向にのみ平行光ビームに変換する。このため、コリメータレンズ２１の焦点距離を比較的大きくでき、そのことによってコリメータレンズ２１のレンズ面の曲率半径も大きくでき、レンズ面あるいはそれを成形する金型の加工が容易になる。また、レンズ面の大きさが大きくなることで、収差上レンズ面に要求される精度が緩和され製造が容易となると同時に、被走査面への結像性能も向上することが期待できる。
【００２３】
また、本発明の実施例においては、図４に示すように、光源である半導体レーザー１１から回転多面鏡３０の第１の反射面３１に入射するまでの光路を長く取れるので、主走査面内で見た場合の第１の反射面３１から後で述べる伝達光学系の第１の反射鏡５１までの距離より、第１の反射面３１から光源部までの距離を長くなる。そのため、図５に示すように、光源部の上下方向の空間的な制約がなく、特に半導体レーザー１１の駆動回路基板の大きさを任意に設定できる。そのため、半導体レーザー１１の高度な制御、特に階調制御を行なうための電子回路を半導体レーザー１１の直近に集積することができる。
【００２４】
整形レンズ２２を出た光ビームは、回転多面鏡３０の第１の反射面３１に入射する。第１の反射面３１に入射する光ビームが通過するビーム整形光学系の光軸と、反射された光ビームが通過する伝達光学系の光軸は、図４に示すように主走査面内では重なっている。一方、図５に示すように、副走査面内において第１の反射面３１の垂線とは角度γ１を有している、すなわち副走査面内で入射角γ１で入射している。従って、第１の反射面３１で反射され偏向される光ビームと入射光ビームは副走査面内において角度２・γ１をなしており、互いに干渉することがない。本実施例ではγ１を６゜としている。
【００２５】
第１の反射面３１で反射かつ偏向された光ビームは、伝達光学系を構成する伝達レンズ第１群４１に入射する。伝達レンズ第１群４１は入射側から順に、平面と凸のシリンドリカル面からなる第１伝達レンズ、凸のシリンドリカル面と平面からなる第２伝達レンズ、凹のシリンドリカル面と平面からなる第３伝達レンズの３枚で構成され、いずれのレンズも主走査方向にのみ屈折力を有する。
【００２６】
伝達レンズ第１群４１を出た光ビームは、主走査方向に関しては集束光ビームとなり、伝達レンズ第１群４１の後ろ側焦点に一旦結像する。一旦結像した光ビームは発散光ビームとなり、反射鏡５１で反射されて伝達レンズ第２群４２に向かう。伝達レンズ第２群４２は、入射側が凸のシリンドリカル面で射出側が平面の第４伝達レンズ１枚で構成されている。伝達レンズ第２群４２は副走査方向にのみ屈折力を有する。
【００２７】
伝達レンズ第２群４２を出た光ビームは、伝達レンズ第３群４３に入射する。伝達レンズ第３群４３は、入射側が平面で、射出側が凸のシリンドリカル面の第５伝達レンズ１枚で構成されている。伝達レンズ第３群４３は主走査方向にのみ屈折力を有する。
【００２８】
伝達レンズ第３群４３を出た光ビームは、主走査方向に関してはほぼ平行な光ビームとなる。この平行光ビームは反射鏡５２で光軸の向きを変えられて、回転多面鏡３０の第２の反射面３２に入射する。第２の反射面３２に入射する光ビームは第１の反射面３１での偏向にともない、第２の反射面３２の中心に追従するよう光ビームの中心が移動する。これらの伝達レンズ第１群４１から第３群４３までの３群のレンズで伝達光学系を構成している。
【００２９】
第２の反射面３２に入射する平行光ビームの主走査方向の直径は、第１の反射面３１に入射する平行光ビームの直径に比べて数倍大きくなるが、第２の反射面３２の回転移動に追従して光ビームが移動するので、反射面の大きさをはみ出ることはない。
【００３０】
また、第２の反射面３２に入射する光ビームが通過する伝達光学系の光軸と、偏向された光ビームのが通過する走査光学系の光軸は、図４に示すように主走査面内では重なっている。一方、図６に示すように回転多面鏡３０の回転軸を含む面内すなわち副走査面内では、第２の反射面３２に対して垂直とは異なる斜め方向に配置されている。この実施例においては、副走査面内での第２の反射面３２に入射する光ビームが反射面の垂線に対する角度、すなわち入射角γ２を６゜としている。
【００３１】
伝達光学系に置かれている反射鏡５１、反射鏡５２には、フロートガラスの表面に反射膜を蒸着したミラーを用いている。連続的に生産されるフロートガラスは、製造工程の進行方向とその直交方向で平面度が異なる。本発明の実施例では、その平面度の良好な方向を主走査方向に一致させることで、安価な反射鏡が利用可能にしている。なお、ガラスの平面度を維持させるには所定の厚みが必要なことは、研磨ガラスでもフロートガラスでも同様であり、本実施例でも反射鏡５１、５２には厚み５ｍｍのガラスを用いて十分な平面度を得ている。
【００３２】
また、伝達光学系に限らずビーム整形光学系に反射鏡を介在させる場合も上記と全く同様に、主走査方向に平面度の良好な方向を一致させることで、安価なフロートガラスが使用可能となる。さらに、このようなビーム整形光学系に介在する反射鏡は、本発明の実施例のような回転多面鏡の反射面に光ビームが２度入射するような光学系のみならず、一般の走査光学系において、回転多面鏡に光源からの光ビームを導く光学系に広く適用できる。
【００３３】
本発明の実施例の伝達光学系を副走査断面内で見ると、伝達レンズ第２群４２のみが光学的に屈折力を有しており、第１の反射面３１と第２の反射面３２が光学的な共役関係になるように配置されている。このため、回転多面鏡３０の第１の反射面３１の各々が副走査方向に倒れ誤差をもっていても、反射された光ビームは第２の反射面３２上では副走査方向に同じ位置に入射する。すなわち倒れ補正機能を有している。
【００３４】
次に、第２の反射面３２で偏向された光ビームは結像レンズ６１、補正レンズ６２に入射して集束光ビームに整形された後に被走査面７１上に結像する。結像レンズ６１と補正レンズ６２とで、走査光学系を構成しており、一定速度で回転する回転多面鏡３０の回転に伴って、等角速度で走査される光ビームを等線速で被走査面上７１を走査させる。
【００３５】
図６に示すように、結像レンズ６１を出た光ビームは、第１の折り返し鏡９１で、回転多面鏡３０の上方に折り返される。この折り返された光ビームはさらに第２の折り返し鏡９２で折り返され、補正レンズ６２に入射する。補正レンズ６２を出た光ビームは最後に第３の折り返し鏡９３で折り返されて、被走査面７０に向かう。これら３つの折り返し鏡は光走査装置の容器となる光学ケース８２に取り付けられている。
【００３６】
このように、走査光学系の光軸を含む副走査面内で見ると、後で述べるベース部材８１あるいは光学ケース８２の上に、（Ａ）伝達光学系の第２の反射鏡５２から回転多面鏡３０の第２の反射面３２に至る部分、（Ｂ）走査光学系の回転多面鏡３０の第２の反射面３２から、結像レンズ６１を含み第１の折り返し鏡９１に至る部分、（Ｃ）第１の折り返し鏡９１から第２の折り返し鏡９２に至る部分、（Ｄ）第２の折り返し鏡９３から、補正レンズ６２と経由して第３の折り返し鏡９３に至る部分、の４段に光路が折り重なっている。
【００３７】
本発明の実施例においては、このような構造をとることで、走査光学系全体の光路長にかかわらず、光走査装置の走査光学系の光軸方向の長さを短縮できる。
【００３８】
また、走査光学系内においては、光ビームが回転偏向するので、回転多面鏡３０の第２の反射面３２から離れるに従って、走査される光ビームの振れ幅が増加し、必要な折り返し鏡の幅も増加していく。これに対して上記のような構造の場合、光学ケース８２の底面から離れるに従って折り返し鏡の幅も増加するので、折り返し鏡の両側にその保持部分を設けた場合に、下方（光学ケース８２の底面側）に位置するレンズや、走査される光ビームに干渉することが避けられる。
【００３９】
また、光学ケースの表面側、すなわち回転多面鏡や走査光学系を構成するレンズ群が載置されている側に全ての折り返し鏡を配置しているので、組立・調整・検査作業が容易なため製造費用が低下するとともに、装置の信頼性も増す。
【００４０】
特に本発明の実施例のように、光学ケース８２の底面に近い側に、伝達光学系が位置する場合には、伝達光学系を構成する各伝達レンズや反射鏡を避けて、折り返し鏡の支持部を設けることが容易となる。
【００４１】
被走査面上７１に光ビームが結像して得られるスポットは、回転多面鏡３０の回転に応じた方向に直線状に移動して走査線を形成する。本発明の実施例においては、既に述べたように副走査面内おいて、回転多面鏡３０の回転軸に対して直角とは異なる方向で光ビームが入射し、得られる偏向光ビームも回転多面鏡３０の回転軸に直角な方向とは異なる角度をもって偏向されるので、偏向光ビームが掃引してできる面は平面ではなく円錐面となる。従って、結像レンズ６１や補正レンズ６２に入射する光ビームの軌跡も湾曲しているが、被走査面上７１で得られる走査線は直線となるように、走査光学系が構成されている。
【００４２】
被走査面７１には走査対象物が設置される。本発明の光走査装置は主走査方向一方向にしか光ビームを走査しないので、２次元走査を実現させるためには走査対象物を主走査方向とは直交する副走査方向に移動させる必要がある。この副走査方向の移動は、平板状の媒体を直線状に移動させてもよいし、走査線の方向に平行な回転軸を持つ円筒状の媒体を回転移動させてもよい。例えば本発明の光走査装置をレーザービームプリンターに用いる場合には、秘走査面７１には感光体が置かれ、光ビームの走査によって静電潜像を形成する。
【００４３】
ここで本発明の実施例の伝達光学系の光路の配置の特徴について説明する。ここまでで述べたように、本発明の実施例では、主走査面内で光走査装置の走査範囲の中央付近を走査する時点での回転多面鏡３０の位置において、ビーム整形光学系の光軸と第１の反射面３１、あるいは回転多面鏡３０の第２の反射面３２に入射する伝達光学系の光軸と回転多面鏡３０の第２の反射面３２との位置関係は、各光学系の光軸が各反射面に対してほぼ垂直になるように配置されている。
【００４４】
別の言い方をすると、回転多面鏡の２箇所の反射面へ光ビームを導く各光学系の光軸が、回転多面鏡の回転軸に対して、空間的な「ねじれの位置」になく、ほぼ交差する状態である。光学系の光軸と反射面のこのような位置関係を以後「正面入射」状態と定義する。
【００４５】
本発明の実施例では、このように「正面入射」の配置をとることで、光ビームの断面直径に対して、回転多面鏡３０の第２の反射面３２の大きさを最も有効に使用している。また、回転多面鏡３０の第１の反射面３１に対して、ビーム整形光学系から入射する光ビームは相対的に移動するが、反射点は入射する光ビームの対してほぼ垂直な方向に移動するので、移動に対する反射面の大きさも最小限ですむ。
【００４６】
このように各反射面の大きさを小さくできるので、回転多面鏡３０の大きさを最小にできる。従って、回転多面鏡の慣性２次モーメント、重量、反射面に働く遠心力を小さくでき、より高い回転数まで回転させることが可能となった。
【００４７】
また、図６に示すように伝達光学系を構成する各レンズや反射鏡と、走査光学系を構成するレンズを副走査面内において分離して配置できるので、これらのレンズや反射鏡が主走査面内において互いに干渉することがないので、レンズの大きさに制約がなく、良好な光学特性を得ることができる。
【００４８】
次に伝達光学系の２つの反射鏡と各レンズの位置関係について考察する。上記のように本発明の実施例では、図５、図６に示すように、伝達光学系の内で第２の反射鏡５２以降の部分の光軸と、走査光学系の光軸は副走査面内で角度をもって配置されているので、主走査面内ではレンズの大きさに制約がない。
【００４９】
さらに本発明の実施例では、回転多面鏡の第１の反射面３１と第１の反射鏡５１の間に、伝達レンズ第１群４１が位置しており、第２の反射鏡５２と第２の反射面３２の間には、伝達レンズ第２群４２、及び伝達レンズ第３群４３が位置している。すなわち、第２の反射鏡５２以降の伝達光学系の光軸上にはレンズが存在しないので、伝達光学系のレンズと走査光学系のレンズが主走査面で見ても重なることがない。このため、走査光学系のレンズ、特に結像レンズ６１の大きさや取り付け方法に制約がなくなり、光学的に最適な位置、大きさの結像レンズを用いることが可能となる。
【００５０】
次に本発明の実施例の伝達光学系とビーム整形光学系あるいは走査光学系の位置関係について説明する。
【００５１】
また図５あるいは図６でわかるように、伝達光学系とビーム整形光学系あるいは走査光学系が主走査面内で重なっている部分において、各レンズやミラーを支えるベース部材８１に対する光軸の上下関係を見ると、伝達光学系の上あるいはベース部材８１の底面から遠い側にビーム整形光学系あるいは走査光学系が重なる構造となっている。
【００５２】
本発明の実施例においては、このような構造をとることで、ベース部材８１から一体に成形されていて伝達光学系を構成するレンズや反射鏡を支持する部分のベース部材８１からの突出高さを低く押さえることが可能となり、これらのレンズや反射鏡を精度よくベース部材８１に取り付けることができる。
【００５３】
これに対して、走査光学系を構成する結像レンズ６１、あるいは補正レンズ６２の取り付け精度は伝達光学系に比べればさほど高くなくてもよいので、ベース部材８１から高い位置に支持しても問題とならない。一方、ビーム整形光学系のレンズや光源の位置精度は非常に厳しいが、あまりに要求精度が厳しいために調整せざるを得ない。このため、ビーム整形光学系のレンズなどを支持する部材自身の位置精度はさほど高くなくてもよく、むしろ調整の容易な構造が望まれる。この観点においても、ビーム整形光学系が伝達光学系の上に位置するほうが、調整作業が容易になり好ましい。
【００５４】
本発明においては、図８に示すように伝達光学系の各レンズと２枚の反射鏡及び回転多面鏡を一体の高精度の加工方向で製造されたベース部材８１に取り付け、他の部分は一般的な製造方法で製作される光学ケース８２に取り付けている。
【００５５】
例えば、ベース部材８１の製造には、金属をダイキャストで鋳造したものをレンズや反射鏡の取付面のように精度の必要な部分のみ機械加工を施す方法が好適である。また、プラスチックの射出成形方法を用いる場合でも、最近開発されている成形後の収縮の小さい特殊な成形方法等を用いれば所期の精度が得られる。
【００５６】
これに対して、光学ケース８２は一般的な加工方法で製作可能で、例えばガラス繊維入りのポリカーボネイド樹脂を射出成形することで安価に製造できる。また、形状の工夫によっては板金のプレス加工によっても製作できる。
【００５７】
このように本発明においては、精度の必要なベース部材８１を必要最小限の大きさにとどめ、それ以外の光学ケース８２を比較的安価な製造方法で製作することで、装置全体の製造コストを削減できる。
【００５８】
なお、この実施例においては平面的に見て伝達光学系の上方に位置する結像レンズ６１及び整形レンズ２２は、わざわざ光学ケース８２に取り付けるより、ベース部材８１に取り付ける方が構造が簡単で、そのことによりベース部材８１の大きさが増加することもないので、ベース部材８１に取り付けてある。
【００５９】
次に、本発明の光走査装置の実施例の伝達光学系の回転多面鏡３０の反射面に対する追従作用を詳しく説明する。図７は図４で説明した本発明の光走査装置の伝達光学系を反射鏡５１、反射鏡５２について折り返さずに引伸ばして主走査断面について示した図である。但し、伝達レンズ第２群４２は、主走査方向には屈折力を持たないので省略してある。
【００６０】
伝達光学系を主走査方向について見ると、伝達レンズ第１群４１の後側焦点位置Ｐに、伝達レンズ第３群４３の前側焦点が一致するように置かれており、これら２群のレンズ群でアフォーカル光学系を構成している。従って伝達レンズ第３群４３を通過した光ビームは再び平行光ビームとなり、反射鏡５２で光軸の向きを変えられて、回転多面鏡３０の第２の反射面３２に入射する。
【００６１】
いま、第１の反射面３１に入射する平行光ビームのこの反射面の位置での直径ｗｉとする。伝達光学系はアフォーカル光学系を構成しているので、第２の反射面３２の位置では直径ｗｏの平行な光ビームに変換される。ここで伝達レンズ第１群４１の焦点距離をｆ１、伝達レンズ第３群４３の焦点距離をｆ２とすると、ｗｏをｗｉで除した光ビームの直径の比の値は、ｆ２をｆ１で除した値に等しい。
【００６２】
ここで、回転多面鏡３０がθ１だけ回転すると、第１の反射面３１で光ビームは２・θ１だけ偏向される。偏向された光ビームは伝達レンズ第１群４１、同第３群４３を通過して、角度θ２で偏向される。この光ビームは点Ｑで光軸と交差する。交差した後に第２の反射面３２に入射する位置において、偏向された光ビームと光軸との距離はδとなり、このδは回転多面鏡３がθ１回転したときの反射面の移動量に等しい。
【００６３】
このとき、偏向された光ビームは第２の反射面３２に対して角度θ２だけ入射角度が増大する側に偏向するので、第２の反射面で反射された光ビームの走査角θｓは、θｓ＝２・θ１＋θ２とあらわされる。すなわち、通常の１度しか回転多面鏡に入射しない方式、あるいは第２の反射面３２に対して光ビームが平行移動しながら追従する方式に比べて光ビームの偏向角をθ２だけ増大させることができる。
【００６４】
ところで、上記のように回転多面鏡の第１の反射面３１で偏向された光ビームの中心光線が伝達光学系の光軸と交差する場所が回数がＱ点のみの１箇所である場合には、伝達光学系の途中にある光路折り返しのための反射鏡の数が偶数であると、第２の反射面３２の回転移動方向と光ビームが移動する方向が一致する。
【００６５】
より一般的に検討すると、偏向された光ビームが光軸と交差する回数が奇数回のときは、折り返しの反射鏡の数を偶数にすればいいことがわかる。伝達光学系の折り返しの反射鏡は、その平面度が被走査面への結像性能に影響を及ぼし、かつ反射率によって光学系のパワー効率が低下させるので、なるべく数が少ない方がよい。しかし、少なくとも１枚の反射鏡がないと、同一の回転多面鏡に光ビームを戻すことができないので、最小値は１となる。
【００６６】
また、回転多面鏡の第１の反射面から第２の反射面までの距離を短くするためには、偏向された光ビームが光軸と交差する回数も少ないほうがよく、現実的にはまったく交差しないか、１回だけ交差するように設定するのが望ましい。
【００６７】
これらの条件を考え合わせると、以下の４つの組み合わせが現実的な選択肢である。
（１）偏向された光ビームが光軸と交差する回数が０回で、折り返しの反射鏡の数が１枚。
（２）偏向された光ビームが光軸と交差する回数が０回で、折り返しの反射鏡の数が３枚。
（３）偏向された光ビームが光軸と交差する回数が１回で、折り返しの反射鏡の数が２枚。
（４）偏向された光ビームが光軸と交差する回数が１回で、折り返しの反射鏡の数が４枚。
【００６８】
ところが（１）の場合では、反射鏡の数が１であって、本発明のように回転多面鏡の２つの異なる反射面に対して同時に「正面入射」状態を実現することができないので採用できない。
【００６９】
また、（２）の場合は反射鏡の数が多いため、反射鏡の平面度の影響により結像性能が劣化する危険性が増す。また、１つの反射鏡あたりの反射率を８５％とすると、反射鏡３面を経由した場合の光パワーの効率は６１％になってしまう。さらに、各反射面の取り付け角度精度がそれぞれ光軸の方向に影響を与えるので、光ビームが通過する位置精度を確保する上でも好ましくない。同様に（４）の場合はもう１枚反射鏡の数が増加するので、上記（２）の課題はより厳しくなる。
【００７０】
従って、本発明に実施例では、図４に示すように、上記の（３）に相当する伝達光学系の光路の折り返しの反射鏡の数を２とし、伝達光学系の中を偏向されて移動する光ビームと伝達光学系の光軸との交差個所を１ヵ所にすることで、回転多面鏡３０への光ビームの入射を正面入射とした上で、反射鏡の数を最小にして光パワーの減衰を小さくすると同時に、伝達光学系の光路長も短縮することが可能となった。
【００７１】
次に回転多面鏡３０の反射面数について説明する。本発明の実施例においては、回転多面鏡３０の面数を４の倍数である１２としている。回転多面鏡３０の面数を４の倍数とすることで、回転多面鏡３０の同時に使用する２つの反射面のなす角度を９０度とすることが可能である。回転多面鏡３０の回転軸に対する反射面の倒れ誤差や位置誤差の内、１回転の中で緩やかに（おおむね正弦波状に）変化する成分については、２つの反射面の位相が９０度ずれているため、第１の反射面３１、第２の反射面３２の両方が同時に最悪の値となる場合がないので、反射面の倒れ誤差や位置誤差の影響を緩和できる。また、この効果は本発明の実施例のように正面入射する構成をとる光学系のみならず、同一の回転多面鏡に光ビームが２度入射する光走査装置に広くあてはまるものである。
【００７２】
また、図４に示すように主走査面内において第１の反射面３１に入射する光ビームと、伝達光学系を経由して第２の反射面３２に入射する光ビームのなす角度ηを９０度とすることが可能となった。このように配置することで、第１の反射面３１から第２の反射面３２に至る光軸上の距離を適切に確保でき、最適な構成の伝達光学系を得ることができる。
【００７３】
さらに、光走査装置の機構的な設計を考えると、ビーム整形光学系の光軸と、走査光学系の光軸が直交している方が、各要素をレイアウトするのが容易であるというで利点もある。
【００７４】
一方、回転多面鏡の加工方法を考察すると、反射面の加工機械における割り出し角度が整数に限定されることが多い。つまり隣接反射面の角度が３６０の約数となる。従って、回転多面鏡の形状を正多角形（正多面体）にするためには、１０面、１２面、１５面、１８面等の面数の多面鏡は加工できるが、１１面、１３面、１４面、１６面、１７面は加工できない場合がある。この条件と上記に述べた４の倍数である条件とを考慮すると、本発明の実施例に示すごとく回転多面鏡３０の面数Ｎは１２面であるのが、装置の設計上も、多面鏡の加工上も好適である。
【００７５】
もちろん、回転多面鏡の各反射面のなす角度を均等ではないようにすれば上記の制約はないが、各反射面の大きさが不同になり、小さい反射面にあわせて光学系を設計せねばならぬため多面鏡の大きさには無駄が生ずる。
【００７６】
次に本発明の実施例の光ビーム検出方法について説明する。一般に光走査装置を画像記録装置や画像入力装置に応用する場合には、各走査の基点となる同期信号を発生させる手段が必要になる。本発明の光走査装置の実施例においては、被走査面上の有効走査領域を走査する手前の位置で、光ビームを光ビーム検出器６３に導き、光ビームの到達を電気信号に変換することで同期信号を得ている。この光ビーム検出器６３は必ずしも被走査面上７１になくてもよい。しかし、光走査装置としては、この光ビーム検出器６３の位置から有効走査領域の後端までが所要の走査範囲となる。
【００７７】
より詳しく説明すると、回転多面鏡３０で偏向された光ビームは、結像レンズ６１で主走査方向に集束光ビームに変換された後に、第１の折り返し鏡９１、第２の折り返し鏡９２で折り返され、図９に示すように補正レンズの直前に設けられた分離鏡６４で本来の被走査面７１へ向かう光路とは分離された後に、再び第２の折り返し鏡９２を経て、光ビーム検出レンズ６５で副走査方向に集束する光ビームに変換された後に、光ビーム検出器６３に入射する。図９では光ビーム検出器６３に入射する光ビームをＬｓという記号で示している。
【００７８】
このように、折り返し鏡を何枚も用いて走査光学系の光路を複雑に折り返したような光走査装置においても、検出用の光ビームを検出器に導く反射鏡を新たに設ける必要がないため、走査光学系の構成が非常にシンプルになる。
【００７９】
回転多面鏡３０の第２の反射面３２を基準とすると、光ビーム検出器６３は走査光学系の光軸上においては被走査面７１と同じ距離にある。また、副走査面内でみると、光ビーム検出器６３の位置は、被走査面７１と同様に回転多面鏡３０の第２の反射面３２に対して光学的に共役となるように、光ビーム検出レンズ６５が設けられている。
【００８０】
光ビームの偏向の周期の中で、光ビームが分離鏡６４を横切る間は被走査面７１には光ビームは到達しない。光ビーム検出器６３で、光ビームの到達を検出するためには、光ビームが光ビーム検出器６３に達する直前に、光源を点灯させる必要がある。この点灯期間における光ビームが、補正レンズ６２に入射しないように、分離鏡６４の取付部の走査上流に位置する部分には、遮蔽板６６が設けられている。
【００８１】
また、本発明の実施例においては、図８に示すように、主走査面内において、光ビーム検出器６３の表面は入射してくる光ビームに対して傾斜しており、光ビーム検出器６３の素子を封入してあるパッケージの表面、あるいは素子自体の表面で反射される反射光Ｌｇは、第２の折り返し鏡９２で反射されて上記の遮蔽板６６に向かうため、補正レンズ６２を通過して被走査面７１に達してしまうことを防止している。
【００８２】
次に本発明の実施例の光走査装置のゴースト像の発生を防止する構造について説明する。本発明の実施例においては、図１０に示すように反射面３３と結像レンズ６１の間に遮蔽板３４を設けて、平面である伝達レンズ第１群の第１伝達レンズの入射面で反射された光ビームが、結像レンズ６１に入射するのを防止している。また遮蔽板３４は、回転多面鏡３０の第２の反射面３２で偏向される本来の走査光ビームを遮らない位置に置かれていることは言うまでもない。
【００８３】
なお、光学系の構成によっては、ゴースト像を生じさせる光ビームは第１の反射面３１に隣接する反射面３３ではなくさらに隣の反射面である場合も有り得る。そのような場合でも問題となる反射面と結像レンズ３１の間に遮蔽板３４を置くことで全く同様な効果を有する。
【００８４】
次に以上に述べた実施例の光学系の調整方法について図２、図４を用いて説明する。ビーム整形光学系から出た整形光ビームは回転多面鏡３０の第１の反射面３１に入射するが、その光軸の延長線上に、副走査方向に平行なエッジを持つナイフエッジ（Ｍ）８３、主走査方向に平行なエッジを持つナイフエッジ（Ｓ）８４が光学ケース８２と一体に設けられている。またこれらのナイフエッジの先端がビーム整形光学系の光軸Ｌ１と一致している。なお、本実施例では光学ケース８２の側壁の下部を切り欠いてナイフエッジ（Ｓ）８４を設けている。
【００８５】
この２つのナイフエッジの周辺には、図４に示すように前記のビーム整形光学系の光軸上において、ナイフヘッジ（Ｍ）８３の手前に切り欠き部Ａ、ナイフエッジ（Ｍ）８３とナイフエッジ（Ｓ）８４の間に切り欠き部Ｂが設けられており、ナイフエッジの通過前後の光パワーを検出するためのセンサが進入できるようになっている。
【００８６】
実際の調整作業は、回転多面鏡３０を取り外した状態で、ビーム整形光学系を通過した光ビームを上記の２つのナイフエッジに照射することで行なう。ビーム整形光学系を通過した光ビームは、主走査方向においては平行な光ビームである。一方、副走査方向においては回転多面鏡３０の第１の反射面３１に結像するような集束光ビームである。従って、ナイフエッジの位置においては、光ビームは副走査方向にはある程度広がっている。
【００８７】
まず、上記の切り欠き部Ａに光パワーを検出するセンサを挿入し、光ビームのパワーを測定する。次に切り欠き部Ｂにセンサを挿入し、ナイフエッジ（Ｍ）８３を通過する光ビームの光パワーを測定する。このときナイフエッジ（Ｍ）８３の先端はビーム整形光学系の光軸に一致しているので、切り欠き部Ｂでの光パワーを切り欠き部Ａで計った光パワーのちょうど半分になるように半導体レーザー１１あるいはコリメータレンズ２１を主走査方向に調整すれば、ビーム整形光学系の主走査方向の調整が正しく行われたことになる。
【００８８】
同様に切り欠き部Ｂの光パワーとナイフエッジ（Ｓ）８４の後ろ側、すなわち光学ケース８１の外側の光パワーを比較し、ちょうど半分の光パワーにるように半導体レーザー１１あるいはコリメータレンズ２１を副走査方向に調整すれば、ビーム整形光学系の副走査方向の調整が終わる。既に述べたようにナイフエッジの位置では副走査方向には光ビームが広がっているので、検出精度は低下するが実用上は十分な精度であり問題はない。
【００８９】
このような調整方法を用いることで、光学ケース８２に半導体レーザー１１とビーム整形光学系を取り付けただけで他の光学素子を取り付けない状態で調整作業が可能となるので、回転多面鏡３０の反射面３１以降に位置する光学素子の誤差の影響を受けずに正確な調整が可能となる。
【００９０】
また、光走査装置の組立工程の中間ステップでの光学特性の確認が可能であるので、段階的な品質保証が可能となり、製品の品質確保作業が容易になる。
【００９１】
さらに、ナイフエッジを通過する光パワーを比較するだけで調整作業が行えるので、被走査面７１上で結像性能を測定する場合に必要となるような大がかりな測定装置が不要となる。
【００９２】
その上、２つのナイフエッジは光学ベース８２に一体に成形されているので、別部材で構成された治具を使用する場合に比べて、光ビームの位置を正確に調整することが可能となる。
【００９３】
このようなビーム整形光学系の光軸と直交方向への光ビームの位置の調整作業は、半導体レーザー１１を移動させて行うか、あるいはコリメータレンズ２１を移動させても行える。本実施例では半導体レーザー１１をその駆動回路を実装した回路基板と一体で、光軸と直交方向の上下左右に移動させて調整しているが、コリメータレンズ２１を移動させても同様の効果が発揮される。
【００９４】
このように、調整されたビーム整形光学系を射出した光ビームも、伝達光学形に存在する反射鏡５１、反射鏡５２や、走査光学系の３つの折り返し鏡を通過することで、各ミラーの副走査方向の取付角度精度の影響を受け、補正レンズ６２に副走査方向に入射する位置が変動する。
【００９５】
本発明の実施例においては、伝達光学系の第１の反射鏡５１あるいは第２の反射鏡５２、さらに走査光学系内の第１の折り返し鏡９１、第２の折り返し鏡９２、第３の折り返し鏡９３の５箇所の反射ミラーのうちのいずれかを副走査面内に回転させることで、補正レンズ６２に入射する光ビームの位置を調整している。
【００９６】
例えば第１の反射鏡５１を副走査面内で回転させて調整することで、他の反射ミラーの調整は不要になる。特に第１の反射鏡５１は上記の５つの反射ミラーの中で最も光源に近いので、それより下流にある反射ミラーを調整する場合に比べて、光路の途中の誤差を小さくできる。
【００９７】
このように補正レンズ６２に対する光ビームの副走査方向の位置を基準に、上記の５箇所の反射ミラーの内の１つの副走査方向の角度を調整することで、他の４箇所の反射ミラーを調整する必要はなくなる。さらに、１箇所の反射ミラーを調整するだけで、補正レンズ６２に対して光ビームを副走査方向において正確な位置に入射させることが可能になり、光ビームの被走査面上での良好な結像性能を得ることができる。
【００９８】
また、補正レンズ６２上において副走査方向に光ビームの入射位置が所定の範囲に入るように調整されるので、補正レンズ６２の直後にある被走査面７１上に結像するスポット、あるいはその軌跡として形成される走査線の副走査方向の位置もおおむね正規の位置におかれる。
【００９９】
あるいは本発明の実施例においては、回転多面鏡の第１の反射面３１以降にある５箇所の反射ミラーの調整は一切行わず、第１の補正レンズ６２を副走査方向に変位させることで、補正レンズ６１に入射する光ビームに対する副走査方向の相対位置を所定の範囲にしている。そして、このような調整を補正レンズ６２の左右、すなわち走査の開始端、終了端で独立して行うことができるので、開始側、終了側それぞれ独立して最適な結像性能をうることができる。
【０１００】
【発明の効果】
以上で述べたように本発明の光走査装置では、伝達光学系を構成するレンズ群及び反射鏡、回転多面鏡を高精度なベース部材に取り付けて、他の光学素子を比較的精度の低い加工方法で製造される光学ケースに取り付けることで、装置全体の製造費用を削減できるという効果を有する。また、光学ケースの表面側、すなわち回転多面鏡や走査光学系を構成するレンズ群が載置されている側に全ての折り返し鏡を配置しているので、組立・調整・検査作業が容易なため製造費用が低下するとともに、装置の信頼性も増す。特に本発明のように、光学ケースの底面に近い側に、伝達光学系が位置する場合には、伝達光学系を構成する各伝達レンズや反射鏡を避けて、折り返し鏡の支持部を設けることが容易となる。
【図面の簡単な説明】
【図１】本発明の実施例における光走査装置の全体の概観を示す斜視図である。
【図２】本発明の実施例における光走査装置において長尺レンズ及び第３の折り返し鏡を除いて描いた全体の概観を示す斜視図である。
【図３】本発明の実施例における光走査装置の走査光学系を含む主走査面内での平面図である。
【図４】本発明の実施例における光走査装置の伝達光学系を含む主走査面内での平面図である。
【図５】本発明の実施例における光走査装置のビーム整形光学系を含む副走査面内での断面図である。
【図６】本発明の実施例における光走査装置の走査光学系を含む副走査面内での断面図である。
【図７】本発明の実施例における光走査装置の伝達光学系の主走査面内における展開図である。
【図８】本発明の実施例における光走査装置の光学ベースと光学ケースの関係を示す斜視図である。
【図９】本発明の実施例における光走査装置の光ビーム検出器に光ビームを導く光学系の斜視図である。
【図１０】本発明の実施例における光走査装置の回転多面鏡の周囲と遮蔽板を示す平面図である。
【符号の説明】
１１ ・・・・ 半導体レーザー
２１ ・・・・ コリメータレンズ
２２ ・・・・ 整形レンズ
３０ ・・・・ 回転多面鏡
４１、４２、４３・・・ 伝達レンズ
５１、５２ ・・・・ 反射鏡
６１ ・・・・ 結像レンズ
６２ ・・・・ 補正レンズ
６３ ・・・・ 光ビーム検出器
７１ ・・・・ 被走査面
８１ ・・・・ 光学ベース
８２ ・・・・ 光学ケース
９１、９２、９３ ・・・・ 折り返し鏡[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 the structure of an optical scanning device using an optical system in which a light beam is incident twice on a reflecting surface of a rotary polygon mirror.
[0002]
[Prior art]
In an image recording apparatus such as a laser beam printer and an optical scanning apparatus used in various image reading and measuring apparatuses, a rotating polygon mirror has been often used as a deflector for deflecting and scanning a light beam.
[0003]
In these apparatuses, a light beam is repeatedly scanned on a surface to be scanned on a straight line or a curved line by an optical scanning device, and a scanning medium positioned on the surface to be scanned is relatively moved in a direction substantially orthogonal to the scanning direction. Two-dimensional scanning is performed. Note that the scanning direction of the former optical scanning device is defined as “main scanning direction”, and the relative movement direction of the latter scanning medium is defined as “sub-scanning direction”.
[0004]
In recent years, higher speed optical scanning devices have been required for the above-described devices in order to improve resolution and processing speed. In an optical scanning device using a rotating polygon mirror for deflecting a light beam, in order to increase the scanning speed (scanning frequency),
(1) Increasing the number of rotations of the rotating polygon mirror (2) Two methods of increasing the number of surfaces of the rotating polygon mirror can be considered.
[0005]
In order to increase the rotational speed of the rotary polygon mirror, a bearing capable of high-speed rotation is required. However, the maximum number of ball bearings currently used is about 20,000 revolutions per minute. If an air bearing is used, it can be used at a rotational speed of 30000 revolutions per minute or more, but the apparatus that can be used is limited because the bearing is expensive. In particular, it cannot be used for inexpensive laser beam printers for general consumers.
[0006]
On the other hand, when the number of surfaces of the rotating polygon mirror is increased, the rotation angle per one reflecting surface is decreased. Also, if the size of each reflecting surface is to be secured above a certain level, the diameter of the rotating polygon mirror will increase.
[0007]
In an optical scanning device, a light beam is imaged on a surface to be scanned, but when a laser beam is scanned, in order to form an image on a small spot, the reflecting surface of the rotating polygon mirror depends on the divergence angle of the light beam. A certain size in the main scanning direction is required. However, when the number of surfaces of the rotary polygon mirror is increased, the scanning angle of the light beam is also reduced because the rotation angle on one reflecting surface is small. If the scanning angle of the light beam is small, the focal length of the scanning optical system becomes long to obtain a predetermined scanning width, and the optical path length from the rotary polygon mirror to the surface to be scanned also increases. For this reason, the diameter of the light beam in the main scanning direction on the reflecting surface of the rotating polygon mirror also increases, the reflecting surface becomes larger than when the number of surfaces is small, and the size of the rotating polygon mirror further increases. .
[0008]
In other words, as the number of rotating polygonal mirrors increases, the size of the reflecting polygonal mirror (the size of the inscribed cylinder) has the contradictory characteristic that the required size of the reflecting surface becomes larger than when the number of rotating polygons is small. If the size is determined, the upper limit of the number of faces is determined. For example, in an optical scanning device used for a laser beam printer, when the required scanning width is 350 mm, the wavelength is 780 nm, the radius of the inscribed cylinder of the rotary polygon mirror is 25 mm, and the spot diameter in the main scanning direction on the surface to be scanned is 50 μm or less, The upper limit of the number of faces is generally seven.
[0009]
Therefore, increasing the diameter of the rotating polygon mirror to increase the number of surfaces increases the weight and inertial moment of inertia of the rotating polygon mirror, and increases the air resistance (windage loss) associated with the rotation. Limited to low.
[0010]
As described above, since the number of surfaces and the number of rotations of the rotary polygon mirror have upper limits, and each has contradictory characteristics, various scanning devices have been devised in order to obtain a scanning speed exceeding that.
[0011]
For example, in the technique described in JP-A-51-100742, the scanning speed is improved by using a semiconductor laser array as a light source and simultaneously scanning the surface to be scanned with a plurality of laser beams. According to this method, the scanning speed can be increased by the number of lasers integrated in the element without increasing the rotational speed of the rotary polygon mirror.
[0012]
On the other hand, in Japanese Patent Application Laid-Open No. 51-32340, a light beam emitted from a light source is incident on a rotating polygon mirror in a main scanning direction with a very small diameter, and the deflected light beam is transmitted through a transmission optical system. A method of making it incident on a rotating polygon mirror again is disclosed. After entering the rotary polygon mirror for the second time, the light beam is imaged as a spot on the surface to be scanned by the scanning optical system. That is, the light beam is incident twice on the rotating polygon mirror.
[0013]
In this latter method, the diameter of the light beam in the main scanning direction when the light beam first enters the rotating polygon mirror is made extremely small compared to the case where it enters the second time, and the second time the rotating polygon mirror is applied to the rotating polygon mirror. The transmission optical system is configured so that the incident light beam follows the center point in the main scanning direction of the rotating reflecting surface.
[0014]
With this configuration, when the light beam first enters the rotating polygon mirror, the diameter of the light beam can be made extremely small, so that the scanning can be performed up to the full dividing angle of the rotating polygon mirror. When the light beam deflected by the first reflecting surface enters the rotary polygon mirror for the second time via the transmission optical system, the diameter of the light beam is such that a predetermined spot is obtained on the surface to be scanned. Although it is enlarged to a required size, the size of the light beam can be set regardless of the rotation angle of the rotary polygon mirror in order to follow the rotation of the reflecting surface. Accordingly, the size of the reflecting surface of the rotating polygon mirror in the main scanning direction can be reduced, and a rotating polygon mirror having a small diameter and a large number of surfaces can be used.
[0015]
[Problems to be solved by the invention]
As described above, in an optical scanning device in which a light beam is incident twice on a rotating polygon mirror, it is necessary to attach a lens and a reflecting mirror constituting a transmission optical system with high accuracy, and thus high-precision processing and molding techniques are required. . For example, it is manufactured by a method such as injection molding of plastic with less shrinkage or cutting a further necessary portion of a die-cast casting. However, the parts manufactured by such a method have a problem that they are more expensive than general plastic injection-molded parts and sheet metal parts.
[0016]
In view of the above problems, in the present invention, in an optical scanning device that deflects and scans a light beam by making the light beam incident twice on the rotary polygon mirror, a lens, a reflecting mirror, and the like constituting the transmission optical system are attached with high accuracy. It is possible to manufacture an optical case that can accommodate the entire optical scanning device at a low cost.
[0017]
In view of the above problems, in the scanning device of the present invention, a light source, a beam shaping optical system that converts a light beam from the light source into a shaped light beam having a predetermined characteristic, and the shaped light beam are deflected by a first reflecting surface. And a rotating polygon mirror having at least the first reflecting surface and the second reflecting surface, a deflection motor for driving the rotating polygon mirror, and a light beam deflected by the first reflecting surface of the rotating polygon mirror. Is transmitted to the second reflecting surface of the rotating polygonal mirror, and scanning optics is used to form an image of the scanning light beam deflected by the second reflecting surface of the rotating polygonal mirror on a predetermined surface to be scanned. In the optical scanning device having a system and scanning the surface to be scanned with the scanning light beam, the transmission optical system, a folding mirror disposed in the transmission optical system, and a base member that supports the deflection motor are disposed on the light beam. What is a scanning device case? Becomes constituted by members, characterized in that all the folding mirror constituting the scanning optical system for bending the optical axis of the optical scanning device arranged in the case of the optical scanning device.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
1 and 2 are perspective views showing an overview of an embodiment of an optical scanning device according to the present invention. FIG. 2 is a perspective view showing a state in which the correction lens 62 and the third folding mirror 93 are removed from FIG. is there. FIGS. 3 and 4 are plan views of main scanning sections of the embodiment of the optical scanning device according to the present invention. 3 and 4, the light beam after the first reflecting surface 31 of the rotary polygon mirror 30 is a light beam at four positions: a beam detection position, a scanning start position, an optical axis position of the scanning optical system, and a scanning end position. Indicates the position. FIG. 3 shows a scanning optical system and a light beam detecting optical system and a light beam passing therethrough, and FIG. 4 shows a transmission optical system, a beam shaping optical system, and a light beam passing therethrough. Further, FIG. 5 shows a sectional view in the sub-scanning plane including the beam shaping optical system of the embodiment of the optical scanning device according to the present invention, and FIG. 6 shows the scanning optical system of the embodiment of the optical scanning device according to the present invention. Sectional drawing in the sub-scanning surface containing is shown.
[0019]
A semiconductor laser 11 is used as a light source, and a laser beam emitted as divergent light is shaped by a collimator lens 21 into a focused light beam having a gentle focusing angle. The exit surface of the collimator lens 21 is formed in an aspherical shape that is rotationally symmetric with respect to the optical axis in order to reduce spherical aberration.
[0020]
The light beam emitted from the collimator lens 21 is incident on a shaping lens 22 that is a cylindrical surface having a flat incident surface and a concave emission side. The shaping lens 22 has a negative refractive power only in the main scanning direction, and the incident focused light beam is converted into a parallel light beam having a relatively small diameter in the main scanning direction. On the other hand, in the sub-scanning direction, the focused light beam converted by the collimator lens 21 remains. The collimator lens 21 and the shaping lens 22 described above constitute a beam shaping optical system.
[0021]
That is, as shown in FIG. 4, the light beam incident on the first reflecting surface 31 of the rotary polygon mirror 30 is a parallel light beam having a smaller diameter in the main scanning direction than that of an ordinary optical scanning device, and is sub-scanned. In the direction, the focused light beam forms an image on the first reflecting surface 31. The rotary polygon mirror 30 will be described later.
[0022]
As described above, in the embodiment of the present invention, the collimator lens 21 converts the light beam emitted from the semiconductor laser 11 into a loose focused light beam at a position where the diameter of the light beam has spread to some extent, and further increases the distance from the collimator lens 21. In addition, a shaping lens 22 that is a concave cylindrical lens is arranged to convert it into a parallel light beam only in the main scanning direction. For this reason, the focal length of the collimator lens 21 can be made relatively large, thereby the radius of curvature of the lens surface of the collimator lens 21 can also be made large, and the processing of the lens surface or a mold for molding the lens surface becomes easy. Further, since the size of the lens surface is increased, the accuracy required for the lens surface due to aberrations is eased and the manufacture is facilitated, and at the same time, the imaging performance on the surface to be scanned can be expected to be improved.
[0023]
Further, in the embodiment of the present invention, as shown in FIG. 4, the optical path from the semiconductor laser 11 serving as the light source to the first reflecting surface 31 of the rotary polygon mirror 30 can be made long, so that it is within the main scanning plane. The distance from the first reflecting surface 31 to the light source unit becomes longer than the distance from the first reflecting surface 31 to the first reflecting mirror 51 of the transmission optical system described later. Therefore, as shown in FIG. 5, there is no spatial restriction in the vertical direction of the light source unit, and in particular, the size of the drive circuit board of the semiconductor laser 11 can be arbitrarily set. Therefore, it is possible to integrate an electronic circuit for performing advanced control of the semiconductor laser 11, particularly gradation control, in the immediate vicinity of the semiconductor laser 11.
[0024]
The light beam exiting the shaping lens 22 is incident on the first reflecting surface 31 of the rotary polygon mirror 30. The optical axis of the beam shaping optical system through which the light beam incident on the first reflecting surface 31 passes and the optical axis of the transmission optical system through which the reflected light beam passes are within the main scanning plane as shown in FIG. overlapping. On the other hand, as shown in FIG. 5, it has an angle γ1 with respect to the perpendicular of the first reflecting surface 31 in the sub-scanning plane, that is, it is incident at an incident angle γ1 in the sub-scanning plane. Therefore, the light beam reflected and deflected by the first reflecting surface 31 and the incident light beam form an angle 2 · γ1 in the sub-scanning surface and do not interfere with each other. In this embodiment, γ1 is set to 6 °.
[0025]
The light beam reflected and deflected by the first reflecting surface 31 enters the transmission lens first group 41 constituting the transmission optical system. The transmission lens first group 41 includes, in order from the incident side, a first transmission lens composed of a plane and a convex cylindrical surface, a second transmission lens composed of a convex cylindrical surface and a plane, and a third transmission lens composed of a concave cylindrical surface and a plane. These lenses have a refractive power only in the main scanning direction.
[0026]
The light beam exiting the transfer lens first group 41 becomes a focused light beam in the main scanning direction, and once forms an image at the rear focal point of the transfer lens first group 41. The once-formed light beam becomes a divergent light beam, is reflected by the reflecting mirror 51, and travels toward the transfer lens second group 42. The second transmission lens group 42 is composed of a fourth transmission lens having a convex cylindrical surface on the incident side and a flat surface on the emission side. The transmission lens second group 42 has refractive power only in the sub-scanning direction.
[0027]
The light beam exiting the transfer lens second group 42 enters the transfer lens third group 43. The third transmission lens group 43 is composed of one fifth transmission lens having a cylindrical surface with a flat incident surface and a convex exit surface. The third transmission lens group 43 has refractive power only in the main scanning direction.
[0028]
The light beam that has exited the third transmission lens group 43 becomes a substantially parallel light beam in the main scanning direction. The direction of the optical axis is changed by the reflecting mirror 52 and the parallel light beam enters the second reflecting surface 32 of the rotating polygon mirror 30. As the light beam incident on the second reflecting surface 32 is deflected by the first reflecting surface 31, the center of the light beam moves so as to follow the center of the second reflecting surface 32. These transfer lens first group 41 to third group 43 constitute a transfer optical system.
[0029]
The diameter of the parallel light beam incident on the second reflection surface 32 in the main scanning direction is several times larger than the diameter of the parallel light beam incident on the first reflection surface 31. Since the light beam moves following the rotational movement, the size of the reflecting surface does not protrude.
[0030]
Further, the optical axis of the transmission optical system through which the light beam incident on the second reflecting surface 32 passes and the optical axis of the scanning optical system through which the deflected light beam passes are as shown in FIG. It overlaps inside. On the other hand, as shown in FIG. 6, in the plane including the rotation axis of the rotary polygon mirror 30, that is, in the sub-scanning plane, it is arranged in an oblique direction different from perpendicular to the second reflecting surface 32. In this embodiment, the angle of the light beam incident on the second reflecting surface 32 in the sub-scanning plane with respect to the normal of the reflecting surface, that is, the incident angle γ2 is 6 °.
[0031]
As the reflecting mirror 51 and the reflecting mirror 52 placed in the transmission optical system, a mirror having a reflective film deposited on the surface of float glass is used. The float glass produced continuously has a different flatness in the direction in which the manufacturing process proceeds and in the direction perpendicular thereto. In the embodiment of the present invention, an inexpensive reflecting mirror can be used by matching the direction of good flatness with the main scanning direction. It should be noted that a predetermined thickness is required to maintain the flatness of the glass, which is the same for both polished glass and float glass. In this embodiment, a glass having a thickness of 5 mm is sufficient for the reflecting mirrors 51 and 52. Flatness is obtained.
[0032]
Also, when a reflecting mirror is interposed in the beam shaping optical system as well as the transmission optical system, it is possible to use an inexpensive float glass by matching the direction of good flatness with the main scanning direction in exactly the same manner as described above. Become. Further, the reflecting mirror interposed in such a beam shaping optical system is not only an optical system in which a light beam is incident twice on the reflecting surface of the rotary polygon mirror as in the embodiment of the present invention, but also general scanning optics. The system can be widely applied to an optical system that guides a light beam from a light source to a rotating polygon mirror.
[0033]
When the transmission optical system of the embodiment of the present invention is viewed in the sub-scan section, only the transmission lens second group 42 has optical refractive power, and the first reflection surface 31 and the second reflection surface 32. Are arranged in an optically conjugate relationship. For this reason, even if each of the first reflecting surfaces 31 of the rotating polygon mirror 30 is tilted in the sub-scanning direction and has an error, the reflected light beam is incident on the second reflecting surface 32 at the same position in the sub-scanning direction. . That is, it has a tilt correction function.
[0034]
Next, the light beam deflected by the second reflecting surface 32 enters the imaging lens 61 and the correction lens 62, is shaped into a focused light beam, and then forms an image on the scanned surface 71. The imaging lens 61 and the correction lens 62 constitute a scanning optical system, and a light beam scanned at a constant angular speed is scanned at a constant linear speed as the rotary polygon mirror 30 that rotates at a constant speed rotates. The surface 71 is scanned.
[0035]
As shown in FIG. 6, the light beam exiting the imaging lens 61 is folded back above the rotary polygon mirror 30 by the first folding mirror 91. The folded light beam is further folded by the second folding mirror 92 and enters the correction lens 62. The light beam exiting from the correction lens 62 is finally folded back by the third folding mirror 93 and travels toward the surface to be scanned 70. These three folding mirrors are attached to an optical case 82 serving as a container for the optical scanning device.
[0036]
In this way, when viewed in the sub-scanning plane including the optical axis of the scanning optical system, (A) a rotating polygonal surface from the second reflecting mirror 52 of the transmission optical system on the base member 81 or the optical case 82 described later. A part reaching the second reflecting surface 32 of the mirror 30, (B) a part reaching the first folding mirror 91 including the imaging lens 61 from the second reflecting surface 32 of the rotary polygon mirror 30 of the scanning optical system; C) Four stages of a part from the first folding mirror 91 to the second folding mirror 92, and (D) a part from the second folding mirror 93 to the third folding mirror 93 via the correction lens 62. The optical path is folded.
[0037]
In the embodiment of the present invention, the length in the optical axis direction of the scanning optical system of the optical scanning device can be shortened regardless of the optical path length of the entire scanning optical system by adopting such a structure.
[0038]
In the scanning optical system, since the light beam is rotationally deflected, as the distance from the second reflecting surface 32 of the rotary polygon mirror 30 increases, the swing width of the scanned light beam increases, and the required width of the folding mirror is increased. Will also increase. In contrast, in the case of the structure as described above, the width of the folding mirror increases as the distance from the bottom surface of the optical case 82 increases. Therefore, when the holding portions are provided on both sides of the folding mirror, the lower side (the bottom surface of the optical case 82). Interference with the lens located on the side) and the scanned light beam.
[0039]
In addition, since all the folding mirrors are arranged on the surface side of the optical case, that is, the side on which the lens group constituting the rotating polygon mirror and the scanning optical system is placed, it is easy to assemble, adjust, and inspect. The manufacturing cost is reduced and the reliability of the device is increased.
[0040]
In particular, when the transmission optical system is located on the side close to the bottom surface of the optical case 82 as in the embodiment of the present invention, support of the folding mirror is avoided by avoiding each transmission lens and reflecting mirror constituting the transmission optical system. It becomes easy to provide the part.
[0041]
A spot obtained by forming an image of a light beam on the surface to be scanned 71 moves linearly in a direction corresponding to the rotation of the rotary polygon mirror 30 to form a scanning line. In the embodiment of the present invention, as already described, a light beam is incident in a direction different from a right angle with respect to the rotation axis of the rotary polygon mirror 30 in the sub-scanning plane, and the resulting deflected light beam is also a rotary polygon. Since the light is deflected at an angle different from the direction perpendicular to the rotation axis of the mirror 30, the surface formed by sweeping the deflected light beam is not a flat surface but a conical surface. Accordingly, the trajectory of the light beam incident on the imaging lens 61 and the correction lens 62 is also curved, but the scanning optical system is configured so that the scanning line obtained on the scanned surface 71 is a straight line.
[0042]
A scanning object is placed on the scanned surface 71. Since the optical scanning device of the present invention scans the light beam only in one direction in the main scanning direction, it is necessary to move the scanning object in the sub-scanning direction orthogonal to the main scanning direction in order to realize two-dimensional scanning. . The movement in the sub-scanning direction may move the flat plate-like medium linearly, or may rotate the cylindrical medium having a rotation axis parallel to the scanning line direction. For example, when the optical scanning device of the present invention is used in a laser beam printer, a photosensitive member is placed on the secret scanning surface 71 and an electrostatic latent image is formed by scanning the light beam.
[0043]
Here, the characteristics of the optical path arrangement of the transmission optical system according to the embodiment of the present invention will be described. As described so far, in the embodiment of the present invention, the optical axis of the beam shaping optical system at the position of the rotary polygon mirror 30 at the time of scanning near the center of the scanning range of the optical scanning device within the main scanning plane. The positional relationship between the optical axis of the transmission optical system incident on the first reflecting surface 31 or the second reflecting surface 32 of the rotating polygon mirror 30 and the second reflecting surface 32 of the rotating polygon mirror 30 depends on each optical system. Are arranged such that their optical axes are substantially perpendicular to the respective reflecting surfaces.
[0044]
In other words, the optical axis of each optical system that guides the light beam to the two reflecting surfaces of the rotary polygon mirror is not at a spatial “twist position” with respect to the rotation axis of the rotary polygon mirror. It is in a state of crossing. Such a positional relationship between the optical axis of the optical system and the reflecting surface is hereinafter defined as a “front incidence” state.
[0045]
In the embodiment of the present invention, the size of the second reflecting surface 32 of the rotary polygon mirror 30 is most effectively used with respect to the cross-sectional diameter of the light beam by adopting the “front incidence” arrangement. ing. In addition, the light beam incident from the beam shaping optical system moves relative to the first reflecting surface 31 of the rotary polygon mirror 30, but the reflection point moves in a direction substantially perpendicular to the incident light beam. Therefore, the size of the reflective surface for movement is also minimized.
[0046]
Thus, since the size of each reflecting surface can be reduced, the size of the rotary polygon mirror 30 can be minimized. Accordingly, the inertial moment of inertia, weight, and centrifugal force acting on the reflecting surface of the rotating polygon mirror can be reduced, and the rotating polygon mirror can be rotated to a higher rotational speed.
[0047]
Further, as shown in FIG. 6, the lenses and reflecting mirrors constituting the transmission optical system and the lenses constituting the scanning optical system can be arranged separately in the sub-scanning plane, so that these lenses and reflecting mirrors are used for the main scanning. Since they do not interfere with each other in the plane, there is no restriction on the size of the lens, and good optical characteristics can be obtained.
[0048]
Next, the positional relationship between the two reflecting mirrors of the transmission optical system and each lens will be considered. As described above, in the embodiment of the present invention, as shown in FIGS. 5 and 6, the optical axis of the transmission optical system after the second reflecting mirror 52 and the optical axis of the scanning optical system are sub-scanned. Since they are arranged at an angle in the plane, there is no restriction on the size of the lens in the main scanning plane.
[0049]
Further, in the embodiment of the present invention, the transmission lens first group 41 is located between the first reflecting surface 31 and the first reflecting mirror 51 of the rotary polygon mirror, and the second reflecting mirror 52 and the second reflecting mirror 52 are connected to the second reflecting mirror 52. Between the reflecting surfaces 32, the transmission lens second group 42 and the transmission lens third group 43 are located. That is, since there is no lens on the optical axis of the transmission optical system after the second reflecting mirror 52, the transmission optical system lens and the scanning optical system lens do not overlap even when viewed on the main scanning plane. For this reason, there are no restrictions on the size and mounting method of the scanning optical system lens, particularly the imaging lens 61, and it is possible to use an imaging lens having an optically optimal position and size.
[0050]
Next, the positional relationship between the transmission optical system and the beam shaping optical system or the scanning optical system according to the embodiment of the present invention will be described.
[0051]
Further, as can be seen from FIG. 5 or FIG. 6, in the portion where the transmission optical system and the beam shaping optical system or the scanning optical system overlap in the main scanning plane, the vertical relationship of the optical axis with respect to the base member 81 that supports each lens and mirror. , The beam shaping optical system or the scanning optical system overlaps on the transmission optical system or on the side far from the bottom surface of the base member 81.
[0052]
In the embodiment of the present invention, by adopting such a structure, the protruding height from the base member 81 of the portion that is integrally molded from the base member 81 and that supports the lens and the reflecting mirror constituting the transmission optical system. Can be kept low, and these lenses and reflecting mirrors can be attached to the base member 81 with high accuracy.
[0053]
On the other hand, the mounting accuracy of the imaging lens 61 or the correction lens 62 constituting the scanning optical system may not be so high as compared with the transmission optical system. Not. On the other hand, the position accuracy of the lens and light source of the beam shaping optical system is very strict, but because the required accuracy is too strict, it must be adjusted. For this reason, the positional accuracy of the member itself that supports the lens of the beam shaping optical system does not have to be so high, but rather a structure that is easy to adjust is desired. Also in this viewpoint, it is preferable that the beam shaping optical system is positioned on the transmission optical system because the adjustment work is facilitated.
[0054]
In the present invention, as shown in FIG. 8, each lens of the transmission optical system, two reflecting mirrors, and a rotating polygon mirror are attached to a base member 81 manufactured in an integrated high-precision processing direction, and the other parts are general. It is attached to an optical case 82 manufactured by a typical manufacturing method.
[0055]
For example, for the production of the base member 81, a method in which a metal cast by die-casting is machined only on a portion requiring accuracy, such as a lens or reflector mounting surface. Even when a plastic injection molding method is used, the desired accuracy can be obtained by using a special molding method or the like that has been developed recently and has small shrinkage after molding.
[0056]
On the other hand, the optical case 82 can be manufactured by a general processing method, and can be manufactured at low cost by, for example, injection-molding a polycarbonate resin containing glass fiber. In addition, depending on the shape, it can be manufactured by pressing a sheet metal.
[0057]
As described above, in the present invention, the base member 81 that requires accuracy is kept to the minimum necessary size, and the other optical case 82 is manufactured by a relatively inexpensive manufacturing method, thereby reducing the manufacturing cost of the entire apparatus. Can be reduced.
[0058]
In this embodiment, the imaging lens 61 and the shaping lens 22 positioned above the transmission optical system in plan view have a simpler structure when attached to the base member 81 than to be attached to the optical case 82. As a result, the size of the base member 81 does not increase, so that the base member 81 is attached.
[0059]
Next, the following operation of the transmission optical system according to the embodiment of the optical scanning device of the present invention with respect to the reflecting surface of the rotary polygon mirror 30 will be described in detail. FIG. 7 is a diagram showing the main scanning section of the transmission optical system of the optical scanning apparatus according to the present invention described with reference to FIG. 4 without extending the reflecting mirror 51 and the reflecting mirror 52. However, the transmission lens second group 42 is omitted because it has no refractive power in the main scanning direction.
[0060]
When the transmission optical system is viewed in the main scanning direction, the transmission lens first group 41 is placed such that the front focal point of the transmission lens third group 43 coincides with the rear focal position P of the transmission lens first group 41. Constitutes an afocal optical system. Accordingly, the light beam that has passed through the third transmission lens group 43 becomes a parallel light beam again, the direction of the optical axis is changed by the reflecting mirror 52, and is incident on the second reflecting surface 32 of the rotating polygon mirror 30.
[0061]
Now, the diameter wi of the parallel light beam incident on the first reflecting surface 31 at the position of the reflecting surface is set. Since the transmission optical system constitutes an afocal optical system, it is converted into a parallel light beam having a diameter wo at the position of the second reflecting surface 32. Here, assuming that the focal length of the transmission lens first group 41 is f1, and the focal length of the transmission lens third group 43 is f2, the value of the ratio of the diameter of the light beam obtained by dividing wo by wi is obtained by dividing f2 by f1. Equal to the value.
[0062]
Here, when the rotary polygon mirror 30 is rotated by θ1, the light beam is deflected by 2 · θ1 on the first reflecting surface 31. The deflected light beam passes through the transmission lens first group 41 and the third group 43 and is deflected at an angle θ2. This light beam intersects the optical axis at point Q. The distance between the deflected light beam and the optical axis is δ at the position where the light enters the second reflecting surface 32 after intersecting, and δ is equal to the amount of movement of the reflecting surface when the rotary polygon mirror 3 rotates θ1. .
[0063]
At this time, the deflected light beam is deflected to the side where the incident angle increases by an angle θ2 with respect to the second reflecting surface 32, so that the scanning angle θs of the light beam reflected by the second reflecting surface is θs. = 2 · θ1 + θ2. That is, the deflection angle of the light beam can be increased by θ2 as compared with a method in which the light beam is incident on the rotary polygon mirror only once or a method in which the light beam follows the second reflecting surface 32 while moving in parallel. it can.
[0064]
By the way, when the central ray of the light beam deflected by the first reflecting surface 31 of the rotating polygon mirror intersects the optical axis of the transmission optical system as described above, the number of times is only Q point. If the number of reflecting mirrors for turning back the optical path in the middle of the transmission optical system is an even number, the rotational movement direction of the second reflecting surface 32 coincides with the direction in which the light beam moves.
[0065]
More generally, it can be seen that when the number of times the deflected light beam intersects the optical axis is an odd number, the number of folding reflectors should be an even number. The number of reflecting mirrors in the transmission optical system should be as small as possible because the flatness affects the imaging performance on the surface to be scanned and the power efficiency of the optical system is reduced by the reflectivity. However, if there is not at least one reflecting mirror, the light beam cannot be returned to the same rotating polygonal mirror, so the minimum value is 1.
[0066]
In addition, in order to shorten the distance from the first reflecting surface to the second reflecting surface of the rotary polygon mirror, it is better that the number of times the deflected light beam intersects the optical axis is smaller, and in reality, it does not intersect at all. It is desirable not to set it so that it intersects only once.
[0067]
Considering these conditions, the following four combinations are realistic options.
(1) The number of times the deflected light beam intersects the optical axis is zero, and the number of reflecting mirrors is one.
(2) The number of times the deflected light beam intersects the optical axis is zero, and the number of folding reflectors is three.
(3) The number of times the deflected light beam intersects the optical axis is one, and the number of folding reflectors is two.
(4) The number of times the deflected light beam intersects the optical axis is one, and the number of folding reflectors is four.
[0068]
However, in the case of (1), the number of reflecting mirrors is 1, and it cannot be adopted because the “front incidence” state cannot be realized simultaneously with respect to two different reflecting surfaces of the rotating polygon mirror as in the present invention. .
[0069]
In the case of (2), since the number of reflecting mirrors is large, there is an increased risk that the imaging performance deteriorates due to the flatness of the reflecting mirrors. If the reflectance per one reflecting mirror is 85%, the optical power efficiency when passing through the reflecting mirror 3 surface is 61%. Furthermore, since the mounting angle accuracy of each reflecting surface affects the direction of the optical axis, it is not preferable for ensuring the positional accuracy through which the light beam passes. Similarly, in the case of (4), the number of another reflecting mirror increases, so the problem of (2) becomes more severe.
[0070]
Therefore, in the embodiment of the present invention, as shown in FIG. 4, the number of reflecting mirrors of the optical path of the transmission optical system corresponding to the above (3) is set to 2, and it is deflected and moved in the transmission optical system. By making the intersection of the light beam to be transmitted and the optical axis of the transmission optical system one place, the light beam is incident on the rotary polygon mirror 30 as front incidence, and the number of reflecting mirrors is minimized to reduce the optical power. At the same time, the optical path length of the transmission optical system can be shortened.
[0071]
Next, the number of reflecting surfaces of the rotary polygon mirror 30 will be described. In the embodiment of the present invention, the number of surfaces of the rotary polygon mirror 30 is 12 which is a multiple of four. By making the number of surfaces of the rotating polygon mirror 30 a multiple of 4, the angle formed by the two reflecting surfaces simultaneously used by the rotating polygon mirror 30 can be set to 90 degrees. Of the tilting error and position error of the reflecting surface with respect to the rotation axis of the rotary polygon mirror 30, the phase of the two reflecting surfaces is shifted by 90 degrees for a component that changes gently (generally in a sine wave shape) in one rotation. Therefore, there is no case where both the first reflecting surface 31 and the second reflecting surface 32 have the worst values at the same time, so that the influence of the tilting error and the position error of the reflecting surface can be reduced. In addition, this effect is widely applied not only to an optical system having a configuration of front incidence as in the embodiment of the present invention, but also to an optical scanning device in which a light beam is incident twice on the same rotary polygon mirror.
[0072]
Further, as shown in FIG. 4, an angle η formed by the light beam incident on the first reflecting surface 31 and the light beam incident on the second reflecting surface 32 via the transmission optical system in the main scanning plane is set to 90. It became possible to make it. By arranging in this way, the distance on the optical axis from the first reflecting surface 31 to the second reflecting surface 32 can be appropriately ensured, and an optimally configured transmission optical system can be obtained.
[0073]
Furthermore, considering the mechanical design of the optical scanning device, it is advantageous that each element is easier to lay out if the optical axis of the beam shaping optical system and the optical axis of the scanning optical system are orthogonal. There is also.
[0074]
On the other hand, when considering the processing method of the rotary polygon mirror, the index angle in the processing machine of the reflecting surface is often limited to an integer. That is, the angle of the adjacent reflecting surface is a divisor of 360. Therefore, in order to change the shape of the rotating polygon mirror to a regular polygon (regular polyhedron), a polygon mirror having the number of surfaces such as 10, 12, 15, and 18 surfaces can be processed. The 14th, 16th, and 17th surfaces may not be processed. Considering this condition and the condition that is a multiple of 4 described above, the number N of surfaces of the rotary polygon mirror 30 is 12 as shown in the embodiment of the present invention. This is also suitable for processing.
[0075]
Of course, if the angles formed by the reflecting surfaces of the rotating polygon mirror are not uniform, there will be no restriction as described above, but the size of each reflecting surface will be the same, and the optical system must be designed to match the small reflecting surface. Therefore, the size of the polygon mirror is wasted.
[0076]
Next, a light beam detection method according to an embodiment of the present invention will be described. In general, when the optical scanning device is applied to an image recording device or an image input device, a means for generating a synchronization signal as a base point of each scanning is required. In the embodiment of the optical scanning device of the present invention, the light beam is guided to the light beam detector 63 at a position before scanning the effective scanning area on the surface to be scanned, and the arrival of the light beam is converted into an electrical signal. The sync signal is obtained. The light beam detector 63 does not necessarily have to be on the surface to be scanned 71. However, as the optical scanning device, the required scanning range is from the position of the light beam detector 63 to the rear end of the effective scanning area.
[0077]
More specifically, the light beam deflected by the rotary polygon mirror 30 is converted into a focused light beam in the main scanning direction by the imaging lens 61 and then folded by the first folding mirror 91 and the second folding mirror 92. As shown in FIG. 9, after being separated from the optical path toward the original scanned surface 71 by the separation mirror 64 provided immediately before the correction lens, the light beam detection lens passes through the second folding mirror 92 again. The light beam is converted into a light beam focused in the sub-scanning direction at 65 and then enters the light beam detector 63. In FIG. 9, the light beam incident on the light beam detector 63 is indicated by a symbol Ls.
[0078]
As described above, even in an optical scanning device in which the optical path of the scanning optical system is complicatedly folded using a plurality of folding mirrors, there is no need to newly provide a reflecting mirror for guiding the detection light beam to the detector. The configuration of the scanning optical system becomes very simple.
[0079]
When the second reflecting surface 32 of the rotary polygon mirror 30 is used as a reference, the light beam detector 63 is at the same distance as the scanned surface 71 on the optical axis of the scanning optical system. Further, when viewed in the sub-scanning plane, the position of the light beam detector 63 is optically conjugated with respect to the second reflecting surface 32 of the rotary polygon mirror 30 in the same manner as the scanned surface 71. A beam detection lens 65 is provided.
[0080]
During the light beam deflection period, the light beam does not reach the scanned surface 71 while the light beam crosses the separation mirror 64. In order for the light beam detector 63 to detect the arrival of the light beam, it is necessary to turn on the light source immediately before the light beam reaches the light beam detector 63. A shielding plate 66 is provided at a portion located upstream of the scanning of the attachment portion of the separation mirror 64 so that the light beam during this lighting period does not enter the correction lens 62.
[0081]
In the embodiment of the present invention, as shown in FIG. 8, the surface of the light beam detector 63 is inclined with respect to the incident light beam in the main scanning plane, and the light beam detector 63. The reflected light Lg reflected on the surface of the package encapsulating the element or on the surface of the element itself is reflected by the second folding mirror 92 and travels toward the shielding plate 66, and thus passes through the correction lens 62. This prevents the surface 71 from being scanned.
[0082]
Next, a structure for preventing the generation of a ghost image in the optical scanning device according to the embodiment of the present invention will be described. In the embodiment of the present invention, as shown in FIG. 10, a shielding plate 34 is provided between the reflecting surface 33 and the imaging lens 61, and reflected by the incident surface of the first transmitting lens of the first group of transmitting lenses which is a plane. The incident light beam is prevented from entering the imaging lens 61. Needless to say, the shielding plate 34 is placed at a position that does not block the original scanning light beam deflected by the second reflecting surface 32 of the rotary polygon mirror 30.
[0083]
Note that, depending on the configuration of the optical system, the light beam that generates the ghost image may be a reflective surface adjacent to the first reflective surface 31 instead of the reflective surface 33 adjacent thereto. Even in such a case, the same effect can be obtained by placing the shielding plate 34 between the reflecting surface in question and the imaging lens 31.
[0084]
Next, a method for adjusting the optical system of the embodiment described above will be described with reference to FIGS. The shaped light beam emitted from the beam shaping optical system is incident on the first reflecting surface 31 of the rotary polygon mirror 30, and a knife edge (M) 83 having an edge parallel to the sub-scanning direction on the extension line of the optical axis. A knife edge (S) 84 having an edge parallel to the main scanning direction is provided integrally with the optical case 82. The tips of these knife edges coincide with the optical axis L1 of the beam shaping optical system. In this embodiment, a knife edge (S) 84 is provided by cutting out the lower part of the side wall of the optical case 82.
[0085]
Around the two knife edges, as shown in FIG. 4, on the optical axis of the beam shaping optical system, a notch A, a knife edge (M) 83 and a knife are placed in front of the knife hedge (M) 83. A notch B is provided between the edges (S) 84 so that a sensor for detecting the optical power before and after passing through the knife edge can enter.
[0086]
The actual adjustment work is performed by irradiating the two knife edges with the light beam that has passed through the beam shaping optical system with the rotary polygon mirror 30 removed. The light beam that has passed through the beam shaping optical system is a parallel light beam in the main scanning direction. On the other hand, in the sub-scanning direction, the focused light beam forms an image on the first reflecting surface 31 of the rotary polygon mirror 30. Therefore, at the position of the knife edge, the light beam spreads to some extent in the sub-scanning direction.
[0087]
First, a sensor for detecting optical power is inserted into the notch A, and the power of the light beam is measured. Next, a sensor is inserted into the notch B, and the optical power of the light beam passing through the knife edge (M) 83 is measured. At this time, the tip of the knife edge (M) 83 coincides with the optical axis of the beam shaping optical system, so that the optical power at the notch B is exactly half of the optical power measured at the notch A. If the semiconductor laser 11 or the collimator lens 21 is adjusted in the main scanning direction, the beam shaping optical system is correctly adjusted in the main scanning direction.
[0088]
Similarly, the optical power at the notch B is compared with the optical power behind the knife edge (S) 84, that is, outside the optical case 81, and the semiconductor laser 11 or the collimator lens 21 is adjusted so that the optical power is exactly half. If the adjustment is made in the sub-scanning direction, the adjustment of the beam shaping optical system in the sub-scanning direction is completed. As described above, since the light beam spreads in the sub-scanning direction at the knife edge position, the detection accuracy is lowered, but the accuracy is practically sufficient and there is no problem.
[0089]
By using such an adjustment method, it is possible to perform the adjustment work without attaching other optical elements only by attaching the semiconductor laser 11 and the beam shaping optical system to the optical case 82. Therefore, the reflection of the rotary polygon mirror 30 is possible. Accurate adjustment is possible without being affected by the error of the optical element located after the surface 31.
[0090]
Further, since it is possible to confirm the optical characteristics at an intermediate step of the assembly process of the optical scanning device, it is possible to guarantee the quality step by step and facilitate the work of ensuring the quality of the product.
[0091]
Furthermore, since the adjustment operation can be performed only by comparing the optical power passing through the knife edge, a large-scale measuring device that is necessary for measuring the imaging performance on the scanned surface 71 is not necessary.
[0092]
In addition, since the two knife edges are formed integrally with the optical base 82, the position of the light beam can be accurately adjusted as compared with the case where a jig made of different members is used. .
[0093]
Such adjustment of the position of the light beam in the direction orthogonal to the optical axis of the beam shaping optical system can be performed by moving the semiconductor laser 11 or by moving the collimator lens 21. In this embodiment, the semiconductor laser 11 is integrated with the circuit board on which the drive circuit is mounted, and is adjusted by moving it vertically and horizontally in the direction orthogonal to the optical axis. However, the same effect can be obtained by moving the collimator lens 21. Demonstrated.
[0094]
In this way, the light beam emitted from the adjusted beam shaping optical system also passes through the reflecting mirror 51, the reflecting mirror 52, and the three folding mirrors of the scanning optical system, which are present in the transmission optical form. Under the influence of the mounting angle accuracy in the sub-scanning direction, the position of incidence on the correction lens 62 in the sub-scanning direction varies.
[0095]
In the embodiment of the present invention, the first reflecting mirror 51 or the second reflecting mirror 52 of the transmission optical system, the first folding mirror 91, the second folding mirror 92, and the third folding mirror in the scanning optical system are provided. The position of the light beam incident on the correction lens 62 is adjusted by rotating any one of the five reflecting mirrors of the mirror 93 within the sub-scanning plane.
[0096]
For example, by adjusting the first reflecting mirror 51 by rotating it in the sub-scanning plane, it is not necessary to adjust other reflecting mirrors. In particular, since the first reflecting mirror 51 is closest to the light source among the above five reflecting mirrors, an error in the middle of the optical path can be reduced as compared with the case where the reflecting mirror downstream thereof is adjusted.
[0097]
In this way, by adjusting the angle of one of the five reflecting mirrors in the sub-scanning direction with respect to the position of the correction lens 62 in the sub-scanning direction, the other four reflecting mirrors can be adjusted. No need to adjust. Furthermore, it is possible to allow the light beam to be incident on the correction lens 62 at an accurate position in the sub-scanning direction by adjusting only one reflection mirror. Image performance can be obtained.
[0098]
Further, since the incident position of the light beam is adjusted in the sub-scanning direction on the correction lens 62 so as to fall within a predetermined range, the spot formed on the scanned surface 71 immediately after the correction lens 62 or its locus The position of the scanning line formed in the sub-scanning direction is also generally set to the normal position.
[0099]
Alternatively, in the embodiment of the present invention, the five reflecting mirrors after the first reflecting surface 31 of the rotary polygon mirror are not adjusted at all, and the first correction lens 62 is displaced in the sub-scanning direction, The relative position in the sub-scanning direction with respect to the light beam incident on the correction lens 61 is set within a predetermined range. Since such adjustment can be performed independently at the left and right sides of the correction lens 62, that is, at the start and end of scanning, optimum imaging performance can be obtained independently at each of the start and end sides. .
[0100]
【The invention's effect】
As described above, in the optical scanning device of the present invention, the lens group, the reflecting mirror, and the rotating polygon mirror constituting the transmission optical system are attached to a highly accurate base member, and other optical elements are processed with relatively low accuracy. By attaching to the optical case manufactured by the method, the manufacturing cost of the entire apparatus can be reduced. In addition, since all the folding mirrors are arranged on the surface side of the optical case, that is, the side on which the lens group constituting the rotating polygon mirror and the scanning optical system is placed, it is easy to assemble, adjust, and inspect. The manufacturing cost is reduced and the reliability of the device is increased. In particular, when the transmission optical system is located on the side close to the bottom surface of the optical case as in the present invention, a support portion for the folding mirror is provided by avoiding each transmission lens and reflecting mirror constituting the transmission optical system. Becomes easier.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an overall view of an optical scanning device according to an embodiment of the present invention.
FIG. 2 is a perspective view showing the overall appearance of the optical scanning device according to the embodiment of the present invention, excluding a long lens and a third folding mirror.
FIG. 3 is a plan view in a main scanning plane including a scanning optical system of an optical scanning device according to an embodiment of the present invention.
FIG. 4 is a plan view in a main scanning plane including a transmission optical system of an optical scanning device according to an embodiment of the present invention.
FIG. 5 is a cross-sectional view in the sub-scanning plane including the beam shaping optical system of the optical scanning device according to the embodiment of the present invention.
FIG. 6 is a cross-sectional view in the sub-scanning plane including the scanning optical system of the optical scanning device according to the embodiment of the present invention.
FIG. 7 is a development view in the main scanning plane of the transmission optical system of the optical scanning device in the embodiment of the present invention.
FIG. 8 is a perspective view showing a relationship between an optical base and an optical case of the optical scanning device according to the embodiment of the present invention.
FIG. 9 is a perspective view of an optical system for guiding a light beam to a light beam detector of an optical scanning device according to an embodiment of the present invention.
FIG. 10 is a plan view showing the periphery of the rotary polygon mirror and the shielding plate of the optical scanning device according to the embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Semiconductor laser 21 ... Collimator lens 22 ... Shaping lens 30 ... Revolving polygon mirror 41, 42, 43 ... Transmission lens 51, 52 ... Reflecting mirror 61 Image forming lens 62 ... Correction lens 63 ... Light beam detector 71 ... Scanned surface 81 ... Optical base 82 ... Optical cases 91, 92, 93 ... Folding mirror

Claims (1)

光源と、前記光源からの光ビームを所定の特性の整形光ビームに変換するビーム整形光学系と、前記整形光ビームを第１の反射面で偏向し、少なくとも前記第１の反射面と第２の反射面を有する回転多面鏡と、前記回転多面鏡を駆動する偏向モーターと、前記回転多面鏡の前記第１の反射面により偏向された光ビームを前記回転多面鏡の前記第２の反射面に入射させる伝達光学系と、前記回転多面鏡の前記第２の反射面で偏向された走査光ビームを所定の被走査面に結像させる走査光学系を有し、前記走査光ビームで前記被走査面を走査する光走査装置において、前記伝達光学系と前記伝達光学系内に配置された折り返し鏡及び前記偏向モーターを支持するベース部材を前記光走査装置のケースとは異なる部材で構成し、前記光走査装置の光軸を折り曲げる前記走査光学系を構成する全ての折り返し鏡を前記光走査装置のケースに配列したことを特徴とする光走査装置。A light source, a beam shaping optical system for converting a light beam from the light source into a shaped light beam having a predetermined characteristic, and deflecting the shaped light beam by a first reflecting surface, and at least the first reflecting surface and the second reflecting surface. A rotary polygon mirror having a reflective surface; a deflection motor that drives the rotary polygon mirror; and a light beam deflected by the first reflective surface of the rotary polygon mirror, the second reflective surface of the rotary polygon mirror. And a scanning optical system that forms an image of a scanning light beam deflected by the second reflecting surface of the rotary polygon mirror on a predetermined surface to be scanned. In the optical scanning device that scans a scanning surface, the transmission optical system, a folding mirror disposed in the transmission optical system, and a base member that supports the deflection motor are configured by members different from the case of the optical scanning device, Light of the optical scanning device An optical scanning device, characterized in that arranged in the case of the optical scanning device all folding mirror constituting the scanning optical system for bending the.
JP04645397A 1997-02-28 1997-02-28 Optical scanning device Expired - Fee Related JP3707511B2 (en)

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