JP3787877B2 - Optical scanning device - Google Patents

Description

【００４０】
但し、ｔは短期往復時間、Ｂは実効偏向角、Ｃは前記光ビーム検出手段に光ビームが入射するときの、前記偏向面で反射された光ビームの進行方向を示す直線と前記偏向面の振動の中心線とがなす角度、ｆは前記偏向面が正弦揺動するときの偏向周波数、Ｔは走査時間である。かかる請求項４記載の光走査装置によれば、請求項１と同様の効果が得られる。
【００４１】
請求項５記載の発明は、請求項４に記載の光走査装置であって、前記全偏向角調整手段は、前記往復時間比較手段の結果、実際の短期往復時間の方が適正な短期往復時間よりも小さいときには全偏向角が大きくなるように調整し、実際の短期往復時間の方が適正な短期往復時間よりも大きいときには全偏向角が小さくなるように調整することを特徴とする。
【００４２】
かかる請求項５記載の光走査装置では、実際の短期往復時間の方が適正な短期往復時間よりも小さい場合には、上記式（２）より、全偏向角Ａを大きくすれば実際の走査時間は小さくなり、所望の走査時間に近づく。また、実際の短期往復時間の方が適正な短期往復時間よりも大きい場合には、上記式（２）より、全偏向角Ａを小さくすれば実際の走査時間は大きくなり、所望の走査時間に近づく。このように、短期往復時間比較手段の比較結果に基づき全偏向角が増加又は減少する方向に光偏向手段の偏向面の正弦揺動を微調整してフィードバック制御することにより、実際の走査時間を所望の走査時間に一致させる。かかる請求項５記載の光走査装置によれば、請求項１と同様の効果が得られる。
【００４３】
【００４４】
【００４５】
【００４６】
請求項６記載の発明は、請求項１から３のいずれかに記載の光走査装置であって、前記往復時間算出手段は、下記式（３）に基づいて、前記往復時間のうち長い方の往復時間（即ち長期往復時間）の適正時間を算出することを特徴とする。
【００４７】
【数４】

【００４８】
但し、ｔ２は長期往復時間、Ｂは実効偏向角、Ｃは前記光ビーム検出手段に光ビームが入射するときの、前記偏向面で反射された光ビームの進行方向を示す直線と前記偏向面の振動の中心線とがなす角度、ｆは前記偏向面が正弦揺動するときの偏向周波数、Ｔは走査時間である。かかる請求項６記載の光走査装置によれば、請求項１と同様の効果を得ることができる。
【００４９】
請求項７記載の発明は、請求項６記載の光走査装置であって、前記全偏向角調整手段は、前記往復時間比較手段の結果、実際の長期往復時間の方が適正な長期往復時間よりも大きいときには全偏向角が大きくなるように調整し、実際の長期往復時間の方が適正な長期往復時間よりも小さいときには全偏向角が小さくなるように調整することを特徴とする。
【００５０】
かかる請求項７記載の光走査装置では、実際の長期往復時間の方が適正な長期往復時間よりも大きい場合には、上記式（３）より、全偏向角Ａを大きくすれば実際の走査時間は小さくなり、所望の走査時間に近づく。また、実際の長期往復時間の方が適正な長期往復時間よりも小さい場合には、上記式（３）より、全偏向角Ａを小さくすれば実際の走査時間は大きくなり、所望の走査時間に近づく。このように、長期往復時間比較手段の比較結果に基づき全偏向角が増加又は減少する方向に光偏向手段の偏向面の正弦揺動を微調整してフィードバック制御することにより、実際の走査時間を所望の走査時間に一致させる。かかる請求項７記載の光走査装置によれば、請求項１と同様の効果が得られる。
【００５１】
請求項８記載の発明は、請求項１〜７のいずれかに記載の光走査装置であって、前記光ビーム検出手段は、前記被走査媒体上を走査される光ビームの水平同期をとるための検出器を利用したことを特徴とする。かかる請求項８記載の光走査装置では、光ビーム検出手段として、走査開始位置を揃えるために一般的な光走査装置に装備されている検出器、即ち被走査媒体上を走査される光ビームの水平同期をとるための検出器、を利用している。このため、別途光ビーム検出手段を設ける必要がなく、部品点数が削減され、コストが低減されるという効果が得られる。
【００５２】
【００５３】
【００５４】
【００５５】
【００５６】
【００５７】
【００５８】
【００５９】
【００６０】
【００６１】
請求項９記載の発明は、請求項１〜８のいずれかに記載の光走査装置であって、前記光偏向手段は、単一の絶縁基板をエッチングすることによって作製した光偏向素子と該光偏向素子を正弦揺動させる駆動部とを含んでなることを特徴とする。
【００６２】
かかる請求項９記載の光走査装置に用いられる光偏向素子は、単一の絶縁基板（例えば単結晶水晶基板など）をエッチングすることにより作製したものであるため、絶縁基板の厚みや、材質の不均衡、あるいはエッチングプロセスの誤差により、通常その偏向周波数の誤差は±３％程度となる。このため、大量生産時には個々の光偏向素子による偏向周波数のばらつきが大きい。従って、このような光偏向素子を用いる従来の光走査装置は偏向面が正弦揺動して走査を行う際に出力画像の位置ズレを生じるおそれが大きいものである。このような光走査装置に請求項１〜８記載の発明の構成を採用した場合には、その効果が顕著に発揮される。
【００６３】
【発明の実施の形態】
以下に、本発明の好適な実施例を図面に基づいて説明する。尚、本発明の実施の形態は、下記の実施例に何ら限定されるものではなく、本発明の技術的範囲に属する限り種々の形態を採り得ることはいうまでもない。
はじめに、本発明を説明する上での前提となる参考例を説明する。
［第１参考例］
図１は第１参考例の光走査装置の概略説明図、図２は光偏向素子の斜視図である。
【００６４】
光走査装置１の筐体２には、被走査媒体である感光ドラム３を照射するに必要なレーザビームを形成する全ての部材、即ちレーザユニット２５（本発明の光ビーム出射手段）、偏向器１０（本発明の光偏向手段）、ビーム検出器１４、制御ユニット５０（本発明の出射制御手段）が備えられている。
【００６５】
レーザユニット２５は、筐体２の一部位である円筒開口部６に一体化されて固定され、半導体レーザ４とコリメータレンズ５と鏡筒７とから構成されている。このうち、半導体レーザ４は、外部から入力される画像信号に従って強弱に変調されたレーザビームを出射し、コリメータレンズ５に入射させる。また、コリメータレンズ５は、円筒形状のガラスレンズからなり、半導体レーザ４から出射されたレーザビームを受けて平行なレーザ光として鏡筒７の開口から出射させるものである。このような円筒形状のレンズとしては、円筒軸垂直方向に屈折率分布を持ったＧＲＩＮレンズが知られている。鏡筒７は、樹脂成型品からなり、コリメータレンズ５を、鏡筒７の外形円筒面の中心軸と、コリメータレンズ５の光軸がほぼ一致するように保持するものである。半導体レーザ４とコリメータレンズ５は、半導体レーザ４の発光点がコリメータレンズ５の光軸に略一致し、また半導体レーザ４の発光点がコリメータレンズ５の焦点に一致するように調整される。これらを調整することにより半導体レーザ４より放射されたレーザビームはコリメータレンズ５を通過後、コリメータレンズ５の光軸と略一致した平行ビームとなり、鏡筒７の開口により平行ビームの断面形状が所定の形状となるべく規制されて出射される。
【００６６】
偏向器１０は、光偏向素子９とその光偏向素子９を正弦振動させるための駆動部１１とからなり、筐体２に配設されている。この光偏向素子９の構成について、図２を参照して説明する。光偏向素子９を構成するフレーム４１には、上部及び下部に一体形成されたバネ部４２、４３を介して可動部４４が支持されている。これら、フレーム４１、バネ部４２、４３及び可動部４４は単一の絶縁基板によって構成されており、またこれらの形状は、フォトリソグラフィ及びエッチングの技術を利用して形成される。ここで、絶縁基板としては、例えば厚さが５×１０-5ｍ程度の水晶基板が使用可能である。なお、フレーム４１は必ずしも必要ではない。また、可動部４４には反射鏡４５とコイルパターン４６とがフォトリソグラフィ及びエッチングの技術を利用して形成されている。この反射鏡４５の表面精度は、結像時のビーム形状を乱さないようにするために、半導体レーザ４より出射されるレーザビームの波長の１／４程度とされる。また、上部及び下部のバネ部４２、４３にはそれぞれコイルパターン４６への導通のためのリード線４７、４８が設けられており、上部側のリード線４７にはコイルパターン４６を飛び越して接続されるジャンパ線４９が設けられている。尚、上述したフレーム４１、バネ部４２，４３及び可動部４４の形成方法や反射鏡４５及びコイルパターン４６の形成方法については、特公昭６０−５７０５２号公報に詳細に記載されているので、ここでの説明を省略する。また、偏向器１０の駆動部１１としては、例えば永久磁石が用いられ、所定のバイアス磁界を形成するように配置されている。
【００６７】
このように構成された本実施例の偏向器１０では、光偏向素子９のコイルパターン４６を駆動部１１により与えられるバイアス磁界中に配置させ、リード線４７、４８及びジャンパ線４９を介してコイルパターン４６に電流を流すことにより、可動部４４が上部及び下部のバネ部４２、４３を軸として正弦的に往復揺動運動する。そして、可動部４４がこのような往復揺動をすることにより、反射鏡４５にて反射されるレーザビームが偏向作用を受けて水平に掃引されるのである。
【００６８】
ここで、可動部４４の往復揺動によって、レーザビームが偏向される最大角度を全偏向角Ａ（図１参照）と呼ぶ。また、実際に画像の書き込みに利用される角度、すなわち走査開始位置へレーザビームが入射する時点での偏向角から走査終了位置へレーザビームが入射する時点での偏向角に至る角度を、実効偏向角（図１参照）と呼ぶ。全偏向角Ａは、例えば１００゜程度であるが、実効偏向角はこれより小さく８０゜程度となる。
【００６９】
筐体２には偏向器１０の駆動をコントロールするための偏向器ドライバ２１が設置されており、偏向器ドライバ２１は、全偏向角Ａを調整可能な全偏向角調整トリマ２２を備えている。結像レンズ１２は、１枚玉のプラスチックレンズからなり、偏向器１０による偏向作用を受けたレーザビームを感光ドラム３上に結像させ、更に感光ドラム３上にてレーザビームによる走査線が略等速で主走査方向に移動するようにＦ・ａｒｃｓｉｎθ特性を有している。ところで一般の結像レンズでは、光線のレンズへの入射角がθの時、像面上での結像する位置ｒについて、ｒ＝Ｆ・ｔａｎθ（Ｆは結像レンズの焦点距離）となる関係がある。しかし、本実施例のように、正弦揺動する偏向器１０により反射されるレーザビームは結像レンズ１２への入射角が、時間と共に三角関数的に変化する。従って、一般の結像レンズを用いると共に一定時間間隔で半導体レーザ４をＯＮすることにより間欠的にレーザビームを出射させて、そのビームスポット列を感光ドラム３上に結像させると、それらビームスポット列の間隔は等間隔とはならなくなる。よって、本実施例のように正弦揺動する偏向器１０を用いる光走査装置１においては、上述のような現象を避けるために、結像レンズ１２として、ｒ＝Ｆ・ａｒｃｓｉｎθなる特性を有するものが用いられる。このような結像レンズ１２をＦアークサインθレンズと称する。
【００７０】
そして、結像レンズ１２より出射されたレーザビームは、感光ドラム３上への照射を妨げない領域内でかつ往路の走査開始側に設けられた導光ミラー１３にて光路を折り返されて、筐体２の一部分として形成されているナイフエッジ２０を通過してビーム検出器１４に導かれる。
【００７１】
ビーム検出器１４は、ｐｉｎフォトダイオード等の光電変換素子からなり、掃引されるレーザビームを検出するものである。このビーム検出器１４は、往路における画像情報を半導体レーザ４へ入力するスタートタイミングを制御するための検出信号を制御ユニット５０に出力する。これにより、偏向器１０の可動部４４が正弦揺動する際の偏向角速度のムラによる水平方向の信号の同期ズレを大幅に軽減でき、質のよい画像が得られると共に偏向器１０に要求される偏向角速度の精度の許容範囲を大きくすることができる。
【００７２】
また、ビーム検出器１４は、半導体レーザ４と同一の一枚の基板１７平面上に配設されている。このため、ビーム検出器１４と半導体レーザ４を駆動するための駆動回路との間の電気信号の経路を短くすることができるので、回路系が周囲電気ノイズによって誤動作を起こす可能性を低くすることができる。さらに、ビーム検出器１４と半導体レーザ４とが同一の一枚の基板１７平面上に配設されており、両者の駆動回路が基板１７上に共存しているため、基板１７の枚数が低減でき、基板間を結線するハーネス１８の本数を同時に低減することもできるという効果を合わせもっている。
【００７３】
基板１７は、ネジにより筐体２に固定されており、ハーネス１８伝い、または、直接の外力により、基板１７が力を受けて半導体レーザ４が筐体２から抜けてしまったり、その位置がずれてしまったりするのを防ぐという効果を持っている。
【００７４】
ナイフエッジ２０は筐体２の一部分として設けられている。なお、従来は、薄い金属を打ち抜き加工した矩形スリット状の部品を位置調整して筐体２にネジ等で固定して配設されていた。従って、本実施例のように、ナイフエッジ２０を筐体２の一部分として形成したことにより、部品点数を低減できるという効果が得られる。
【００７５】
筐体２は一般に広く用いられているガラス繊維入りポリカーボネートにて形成されている。このため、各構成要素を位置精度よく担持し、振動による歪が小さい。制御ユニット５０は、周知のＣＰＵ５１、ＲＯＭ５２、ＲＡＭ５３、タイマカウンタ５４及び入出力ポート５６を備え、これらがバス５７で接続されたものである。この制御ユニット５０には、入出力ポート５６を介して、ビーム検出器１４からの検出信号が入力可能に接続され、レーザユニット２５に制御信号（出射信号、停射信号）を出力可能に接続され、偏向器１０に電流を流すための信号を出力可能に接続されている。
【００７６】
次に、上記光走査装置１を組立、調整する工程における全偏向角調整処理について図３に基づいて説明する。図３は第１参考例の全偏向角調整処理のフローチャートである。まず、所定の走査開始位置に相当する位置に走査開始時期検出センサ２６を設置し、所定の走査終了位置に相当する位置に走査終了時期検出センサ２７を設置する。これらのセンサ２６、２７は制御ユニット５０に検出信号を出力するように接続されている。
【００７７】
この状態で光走査装置１のスイッチがオンされると、制御ユニット５０は、光偏向素子９のコイルパターン４６に所定の電流を流し、また、レーザユニット２５に出射信号を出力する（Ｓ１０）。これにより、光偏向素子９の反射鏡４５は正弦揺動を開始し、レーザユニット２５はレーザビームを出射する。尚、制御ユニット５０のＲＯＭ５２には、予め設定された所望の走査時間Tobj が記憶されている。
【００７８】
制御ユニット５０は、光偏向素子９の反射鏡４５が安定して正弦揺動するまでの準備時間が経過したか否かを判断し（Ｓ１１）、この準備時間が経過していなければ（Ｓ１１でＮＯ）、この準備時間が経過するまで待機する。この準備時間が経過したならば（Ｓ１１でＹＥＳ）、実際の走査時間Ｔを測定する（Ｓ１２）。この実際の走査時間Ｔの測定は、走査開始時期検出センサ２６の検出信号が入力された時点から走査終了時期検出センサ２７の検出信号が入力された時点までの時間を測定することにより行う。
【００７９】
実際の走査時間Ｔの測定終了後、この走査時間Ｔと所望の走査時間Ｔobj との差の絶対値が許容範囲内か否かを判定する（Ｓ１３）。両者の差の絶対値が許容範囲内でなければ（Ｓ１３でＮＯ）、続いてＳ１４で両者の大小関係を判定する。
【００８０】
Ｓ１４で実際の走査時間Ｔが所望の走査時間Ｔobj よりも大きければ（Ｓ１４でＹＥＳ）、全偏向角Ａが大きくなるように全偏向角調整トリマ２２を回転させて光偏向素子９のコイルパターン４６に流れる電流量を調整する（Ｓ１５）。即ち、全偏向角Ａと走査時間Ｔの関係は、
【００８１】
【数５】

【００８２】
で表されるため、実際の走査時間Ｔが所望の走査時間Ｔobj よりも大きいときには全偏向角Ａが大きくなるように調整すれば、実際の走査時間Ｔは小さくなり所望の走査時間Ｔobj に近づく。即ち、上記式（１）より、偏向周波数ｆにばらつきがあったとしても、偏向周波数ｆを測定することなく、実際の走査時間Ｔが所望の走査時間Ｔobj に一致するように全偏向角Ａの微調整を繰り返し行えば、実際の走査時間Ｔを所望の走査時間Ｔobj に一致させることができることがわかる。
【００８３】
Ｓ１４で実際の走査時間Ｔが所望の走査時間Ｔobjが小さければ（Ｓ１４でＮＯ）、全偏向角Ａが小さくなるように全偏向角調整トリマ２２を回転させて光偏向素子９のコイルパターン４６に流れる電流量を調整する（Ｓ１６）。このように調整することで、実際の走査時間Ｔは大きくなり所望の走査時間Ｔobj に近づく。
【００８４】
そして、Ｓ１５又はＳ１６で全偏向角調整トリマ２２を回転させてコイルパターン４６に流れる電流量を調整した後、再びＳ１２以下の処理を繰り返す。そして、Ｓ１３で走査時間Ｔと所望の走査時間Ｔobj との差の絶対値が許容範囲内となった時点で（Ｓ１３でＹＥＳ）、この処理を終える。
【００８５】
その後、走査開始時期検出センサ２６、走査終了時期検出センサ２７を取り外す。このように、第１参考例の光走査装置１は、組立、調整する工程において実際の走査時間Ｔがスペックの範囲内になるように全偏向角調整トリマ２２を調整してあるため、反射鏡４５の偏向周波数が設計値通りでない場合でも、出力画像の位置ズレを生じることがないという効果が得られる。特に、光偏向素子９のように、単結晶水晶基板をエッチングプロセスとフォトリソグラフィプロセルにより加工したものは、水晶基板の厚みや材質の不均衡、あるいはエッチングプロセスの誤差により、大量生産時に偏向周波数のばらつきが大きいので、本実施例の上記効果が際立って発揮される。また、全偏向角調整トリマ２２を回転させることで光偏向素子９のコイルパターン４６に供給する電流量を変化させて全偏向角Ａを調整するため、調整を迅速に行うことができる。
【００８６】
尚、制御ユニット５０が本発明の走査時間記憶手段、全偏向角調整手段に相当する。また、Ｓ１５及びＳ１６が全偏向角調整手段の処理に相当する。
［第２参考例］
第２参考例の光走査装置は、リアルタイムで走査時間を測定し制御するものである。図４は第２参考例の光走査装置の概略説明図である。
【００８７】
第２参考例の光走査装置は、走査開始時期検出センサ２６が筺体２における感光ドラム３の所定の走査開始位置に相当する位置に設けられ、走査終了時期検出センサ２７が筺体２における感光ドラム３の所定の走査終了位置に相当する位置に設けられている点を除いては、第１参考例と同様であるため、同じ構成要素については同じ符号を付し、その説明を省略する。尚、両検出センサ２６、２７は、検出信号を制御ユニット５０に出力可能に接続されている。
【００８８】
第２参考例の光走査装置は、第１参考例の全偏向角調整処理と同様の処理を１頁分の画像を出力する前に行う。そして、この全偏向角調整処理が終了した後、１頁分の画像を出力する。画像を出力する場合、制御ユニット５０は、レーザユニット２５が画像情報に基づいて点滅するレーザビームを出射するように制御する。これを受けた感光ドラム３は公知の電子写真プロセス等により顕像化された後、普通紙または特殊紙より成る転写材上に周知の転写機構及び定着機構により転写・定着されハードコピーとして出力される。
【００８９】
第２参考例では１頁分の画像を出力する前に全偏向角調整処理を行うため、光偏向素子９の個体差を補正できるだけでなく、偏向周波数の温度、湿度等による変動や経時的に変動した場合にも、実際の走査時間Ｔが常にスペックの範囲内に収まるように制御できる。このため、出力画像の位置ズレを生じることがないという効果が得られる。
【００９０】
尚、第２参考例につき、走査開始時期検出センサ２６の検出信号を利用して偏向周期を測定し該偏向周期から偏向周波数ｆを求めて、この偏向周波数ｆと所望の走査時間を上記式（１）に代入して目標とする全偏向角Ａの値を算出し、直接全偏向角Ａを例えば角度センサでモニターしながら、全偏向角調整トリマ２２の回転を調整してもよい。この場合にも、上記と同様の効果が得られる。
［第１実施例］
第１実施例の光走査装置の構成は、走査開始時期検出センサ２６及び走査終了時期検出センサ２７を備えていない点を除いては第１参考例と同様の構成であるため、その説明を省略する。
【００９１】
光偏向素子９の反射鏡４５は正弦揺動するため、この反射鏡４５によって偏向されるレーザビームは往復運動する。このため、ビーム検出器１４には往復それぞれ１回づつ、つまり１周期で２回づつレーザビームが入射する。このときのタイムチャートを図５に示す。ビーム検出器１４は前述のように、感光ドラム３上への照射を妨げない領域に設置された導光ミラー１３で折り返されたレーザビームが入射する位置に設置されており、感光ドラム３側をレーザビームが往復する長期往復時間ｔ’と、感光ドラム３の反対側をレーザビームが往復する短期往復時間ｔが交互に発生する。この長期往復時間ｔ’と短期往復時間ｔの和が偏向周期である。
【００９２】
この偏向周期から偏向周波数ｆを求めれば、短期往復時間ｔと、所定の走査開始位置から所定の走査終了位置までに要する時間即ち走査時間Ｔとは、下記式（２）の関係により１対１に対応しているため、走査時間Ｔの代わりに短期往復時間ｔをモニターしながら、全偏向角Ａを調整することで走査時間Ｔを所望の走査時間Ｔと一致するように制御することが可能である。尚、下記式（２）において、Ｃは、導光ミラー１３にレーザビームが入射するときの、光偏向素子９の反射鏡４５で反射されたレーザビームの進行方向を示す直線と、光偏向素子９の反射鏡４５の振動の中心線とがなす角度である（図１参照、以下同じ）。
【００９３】
【数６】

【００９４】
この第１実施例の光走査装置における全偏向角調整処理は、実際の走査時間Ｔを直接測定する代わりに、書き込み信号のスタートタイミングを制御するためのビーム検出器１４の検出信号から実際の偏向周波数ｆを求めると共に短期往復時間ｔ（反射鏡４５が１周期分正弦揺動する際、ビーム検出器１４がレーザビームを受けた時から再びレーザビームを受ける時までの往復時間のうち短い方の往復時間）を測定し、この短期往復時間ｔに基づいて全偏向角Ａを調整し、実際の走査時間Ｔを所望の走査時間Ｔobj に一致させるものである。
【００９５】
第１実施例の全偏向角調整処理について、図６を参照しながら説明する。図６は第１実施例の全偏向角調整処理のフローチャートである。尚、第１実施例の光走査装置は、第２参考例と同様、この全偏向角調整処理を１頁分の画像を出力する前に行う。そして、この全偏向角調整処理が終了した後、１頁分の画像を出力する（画像出力については、第２参考例と同様にして行う）。
【００９６】
光走査装置１のスイッチがオンされると、制御ユニット５０は、光偏向素子９のコイルパターン４６に所定の電流を流し、また、レーザユニット２５に出射信号を出力する（Ｓ３０）。これにより、光偏向素子９の反射鏡４５は正弦揺動を開始し、レーザユニット２５はレーザビームを出射する。尚、制御ユニット５０のＲＯＭ５２には、予め設定された所望の走査時間Ｔobj が記憶されている。
【００９７】
制御ユニット５０は、光偏向素子９の反射鏡４５が安定して正弦揺動するまでの準備時間が経過したか否かを判断し（Ｓ３１）、この準備時間が経過していなければ（Ｓ３１でＮＯ）、この準備時間が経過するまで待機する。この準備時間が経過したならば（Ｓ３１でＹＥＳ）、実際の偏向周波数ｆを測定する（Ｓ３２）。この実際の偏向周波数ｆの測定は、制御ユニット５０がビーム検出器１４の検出信号を受けた時から次のビーム検出器１４の検出信号を受けるまでの往復時間ｔm1、及び、前記次のビーム検出器１４の検出信号を受けた時から更に次のビーム検出器１４の検出信号を受けるまでの往復時間ｔm2を測定し、それぞれＲＡＭ５３に記憶する。そして、往復時間ｔm1と往復時間ｔm2の和即ち偏向周期を求め、この偏向周期の逆数を算出して偏向周波数ｆを求める。
【００９８】
続いて、適正な短期往復時間ｔ１を上記式（２）により算出する（Ｓ３３）。即ち、上記式（２）のＴとして所望の走査時間Ｔobj 、ｆとしてＳ３２で求めた偏向周波数ｆを代入し、得られるｔを適正な短期往復時間ｔ１とする。その後、ＲＡＭ５３に記憶した往復時間ｔm1と往復時間ｔm2のうちいずれか短い方を実際の短期往復時間ｔとしてＲＡＭ５３に記憶し（Ｓ３４）、この実際の短期往復時間ｔと適正な短期往復時間ｔ１との比較を行い、両者の差の絶対値が許容範囲内か否かを判定する（Ｓ３５）。両者の差の絶対値が許容範囲内でなければ（Ｓ３５でＮＯ）、続いてＳ３６で両者の大小関係を判定する。
【００９９】
Ｓ３６で実際の短期往復時間ｔが適正な短期往復時間ｔ１より小さければ（Ｓ３６でＮＯ）、全偏向角Ａが大きくなるように全偏向角調整トリマ２２を回転させて光偏向素子９のコイルパターン４６に流れる電流量を調整する（Ｓ３７）。ここで、実際の短期往復時間ｔが適正な短期往復時間ｔ１よりも小さいということは、上記式（２）から実際の走査時間Ｔは所望の走査時間Ｔobj より大きいので、Ｓ３７のように調整することで、実際の走査時間Ｔを小さくして所望の走査時間Ｔobj に近づけるのである。
【０１００】
一方、Ｓ３６で実際の短期往復時間ｔが適正な短期往復時間ｔ１よりも大きければ（Ｓ３６でＹＥＳ）、全偏向角Ａが小さくなるように全偏向角調整トリマ２２を回転させて光偏向素子９のコイルパターン４６に流れる電流量を調整する（Ｓ３８）。ここで、実際の短期往復時間ｔが適正な短期往復時間ｔ１よりも大きいということは、上記式（２）から実際の走査時間Ｔは所望の走査時間Ｔobj より小さいので、Ｓ３８のように調整することで、実際の走査時間Ｔを大きくして所望の走査時間Ｔobj に近づけるのである。
【０１０１】
そして、Ｓ３７又はＳ３８で全偏向角調整トリマ２２を回転させてコイルパターン４６に流れる電流量を調整した後、再びＳ３２以下の処理を繰り返す。そして、Ｓ３５で実際の短期往復時間ｔと適正な短期往復時間ｔ１Ｔとの差の絶対値が許容範囲内となった時点で（Ｓ３５でＹＥＳ）、この処理を終える。
【０１０２】
このように、実際の短期往復時間ｔをフィードバック制御することで、実際の走査時間Ｔを所望の走査時間Ｔobj と一致するように制御することができる。このため、反射鏡４５の偏向周波数が設計値通りでない場合でも、出力画像の位置ズレを生じることがないという効果が得られる。また、第１実施例では、書き込み信号のスタートタイミングを制御するための前記ビーム検出器１４を用いて、走査時間を制御できるため、あらたに走査時間測定用の光電変換素子を備える必要がない。
【０１０３】
尚、制御ユニット５０が本発明の走査時間記憶手段、往復時間測定手段、偏向周波数測定手段、往復時間算出手段、往復時間比較手段、全偏向角調整手段に相当する。また、Ｓ３２が往復時間測定手段及び偏向周波数測定手段の処理に、Ｓ３３が往復時間算出手段の処理に、Ｓ３５及びＳ３６が往復時間比較手段の処理に、Ｓ３７及びＳ３８が全偏向角調整手段の処理に相当する。
［第２実施例］
第２実施例の光走査装置の構成は、第１実施例と同様の構成であるため、その説明を省略する。
【０１０４】
この第２実施例の光走査装置における全偏向角調整処理は、実際の走査時間Ｔを直接測定する代わりに、書き込み信号のスタートタイミングを制御するためのビーム検出器１４の検出信号から偏向周波数ｆを求めると共に長期往復時間ｔ’（反射鏡４５が１周期分正弦揺動する際、ビーム検出器１４がレーザビームを受けた時から再びレーザビームを受ける時までの往復時間のうち長い方の往復時間）を測定し、この長期往復時間ｔ’に基づいて全偏向角Ａを調整し、実際の走査時間Ｔを所望の走査時間Ｔobj に一致させるものである。
【０１０５】
偏向周期から偏向周波数ｆを求めれば、長期往復時間ｔ’と、所定の走査開始位置から所定の走査終了位置までに要する時間即ち走査時間Ｔとは、下記式（３）の関係により１対１に対応しているため、走査時間Ｔの代わりに長期往復時間ｔ’をモニターしながら、全偏向角Ａを調整することで走査時間Ｔを所望の走査時間Ｔobj と一致するように制御することが可能である。
【０１０６】
【数７】

【０１０７】
第２実施例の全偏向角調整処理について、図７を参照しながら説明する。図７は第２実施例の全偏向角調整処理のフローチャートである。尚、第２実施例の光走査装置は、第２、３実施例と同様、この全偏向角調整処理を１頁分の画像を出力する前に行う。そして、この全偏向角調整処理が終了した後、１頁分の画像を出力する。
【０１０８】
光走査装置１のスイッチがオンされると、制御ユニット５０は、上記Ｓ３０〜Ｓ３２と同様のＳ４０〜Ｓ４２の処理を行う。Ｓ４２で実際の偏向周波数ｆを測定した後、適正な長期往復時間ｔ２を上記式（３）により算出する（Ｓ４３）。即ち、上記式（３）のＴとして所望の走査時間Ｔobj 、ｆとしてＳ４２で求めた偏向周波数ｆを代入し、得られるｔを適正な長期往復時間ｔ２とする。
【０１０９】
その後、ＲＡＭ５３に記憶した往復時間ｔm1と往復時間ｔm2のうちいずれか長い方を実際の長期往復時間ｔ'としてＲＡＭ５３に記憶し（Ｓ４４）、この実際の長期往復時間ｔ'と適正な長期往復時間ｔ２との比較を行い、両者の差の絶対値が許容範囲内か否かを判定する（Ｓ４５）。両者の差の絶対値が許容範囲内でなければ（Ｓ４５でＮＯ）、続いてＳ４６で両者の大小関係を判定する。
【０１１０】
Ｓ４６で実際の長期往復時間ｔ’が適正な長期往復時間ｔ２より大きければ（Ｓ４６でＹＥＳ）、全偏向角Ａが大きくなるように全偏向角調整トリマ２２を回転させて光偏向素子９のコイルパターン４６に流れる電流量を調整する（Ｓ４７）。ここで、実際の長期往復時間ｔ’が適正な長期往復時間ｔ２よりも大きいということは、上記式（３）から実際の走査時間Ｔは所望の走査時間Ｔobj より大きいので、Ｓ４７のように調整することで、実際の走査時間Ｔを小さくして所望の走査時間Ｔobj に近づけるのである。
【０１１１】
一方、Ｓ４６で実際の長期往復時間ｔ’が適正な長期往復時間ｔ２より小さければ（Ｓ４６でＮＯ）、全偏向角Ａが小さくなるように全偏向角調整トリマ２２を回転させて光偏向素子９のコイルパターン４６に流れる電流量を調整する（Ｓ４８）。ここで、実際の長期往復時間ｔ’が適正な長期往復時間ｔ２より小さいということは、上記式（３）から実際の走査時間Ｔは所望の走査時間Ｔobj より小さいので、Ｓ４８のように調整することで、実際の走査時間Ｔを大きくして所望の走査時間Ｔobj に近づけるのである。
【０１１２】
そして、Ｓ４７又はＳ４８で全偏向角調整トリマ２２を回転させてコイルパターン４６に流れる電流量を調整した後、再びＳ４２以下の処理を繰り返し行う。そして、Ｓ４５で実際の長期往復時間ｔ’と適正な長期往復時間ｔ２との差の絶対値が許容範囲内となった時点で（Ｓ４５でＹＥＳ）、この処理を終える。
【０１１３】
このように、実際の長期往復時間ｔ’をフィードバック制御することで、実際の走査時間Ｔを所望の走査時間Ｔobj と一致するように制御することができる。このため、反射鏡４５の偏向周波数が設計値通りでない場合でも、出力画像の位置ズレを生じることがないという効果が得られる。また、第２実施例では、第１実施例と同様、書き込み信号のスタートタイミングを制御するための前記ビーム検出器１４を用いて、走査時間を制御できるため、あらたに走査時間測定用の光電変換素子を備える必要がない。
【０１１４】
尚、制御ユニット５０が本発明の走査時間記憶手段、往復時間測定手段、偏向周波数測定手段、往復時間算出手段、往復時間比較手段、全偏向角調整手段に相当する。また、Ｓ４２が往復時間測定手段及び偏向周波数測定手段の処理に、Ｓ４３が往復時間算出手段の処理に、Ｓ４５及びＳ４６が往復時間比較手段の処理に、Ｓ４７及びＳ４８が全偏向角調整手段の処理に相当する。
［第３実施例］
第３実施例の光走査装置の構成は、第１実施例と同様の構成であるため、その説明を省略する。
【０１１５】
この第３実施例の光走査装置における全偏向角調整処理は、実際の走査時間Ｔを直接測定する代わりに、所定の走査点における走査速度Ｖを測定し、この走査速度Ｖに基づいて全偏向角Ａを調整することにより、実際の走査時間Ｔを所望の走査時間Ｔobj に一致させるものである。
【０１１６】
第３実施例の光走査装置において、ビーム検出器１４は、小さな入射スリットと応答速度の速い光電変換素子基板から成る（例えば、図１１の一対のスリット板８２、８２により形成された入射スリットと応答速度の速い光電変換素子基板８３を参照）。この入射スリットのスリット幅は一定であるため、ビーム検出器１４の入射スリットにレーザビームが入射し始めてからスリット幅を通過するまでの時間ｔｓ（図５参照）を測定すれば、導光ミラー１３を設置した位置での走査速度Ｖが得られる。即ち、制御ユニット５０が、ビーム検出器１４の検出信号の出力が開始された時点からその出力が終了するまでの時間ｔｓを測定すれば、導光ミラー１３を設置した位置における走査速度Ｖが求められる。
【０１１７】
また、偏向周期から偏向周波数ｆを求めれば、走査速度Ｖと、所定の走査開始位置から所定の走査終了位置までに要する時間即ち走査時間Ｔとは、下記式（４）の関係により１対１に対応しているため、走査時間Ｔの代わりに走査速度Ｖをモニターしながら、全偏向角Ａを調整することで実際の走査時間Ｔを所望の走査時間Ｔobj と一致するように制御することが可能である。尚、下記式（４）中、Ｆは結像レンズ１２の焦点距離である。
【０１１８】
【数８】

【０１１９】
第３実施例の全偏向角調整処理について、図８を参照しながら説明する。図８は第３実施例の全偏向角調整処理のフローチャートである。尚、第３実施例の光走査装置は、第２〜４実施例と同様、この全偏向角調整処理を１頁分の画像を出力する前に行う。そして、この全偏向角調整処理が終了した後、１頁分の画像を出力する。
【０１２０】
光走査装置１のスイッチがオンされると、制御ユニット５０は、上記Ｓ３０〜Ｓ３１と同様のＳ５０〜Ｓ５１の処理を行う。Ｓ５１で準備時間が経過したならば（Ｓ５１でＹＥＳ）、実際の走査速度Ｖを測定し、ＲＡＭ５３に記憶する（Ｓ５２）。この実際の走査速度Ｖの測定は、制御ユニット５０がビーム検出器１４の検出信号の出力が開始された時点からその出力が終了するまでの時間ｔｓを測定することにより、ビーム検出器１４の所定のスリット幅を通過するのに要する時間がわかるため、導光ミラー１３を設置した位置での走査速度Ｖが求められる。
【０１２１】
続いて、実際の偏向周波数ｆを測定する（Ｓ５３）。この処理は、第１実施例のＳ３２と同様である。続いて、適正な走査速度Ｖ１を上記式（４）により算出する（Ｓ５４）。即ち、上記式（４）のＴとして所望の走査時間Ｔobj 、ｆとしてＳ５３で求めた偏向周波数ｆを代入し、得られるＶを適正な走査速度Ｖ１とする。
【０１２２】
そして、実際の走査速度Ｖと適正な走査速度Ｖ１との比較を行い、両者の差の絶対値が許容範囲内か否かを判定する（Ｓ５５）。両者の差の絶対値が許容範囲内でなければ（Ｓ５５でＮＯ）、続いてＳ５６で両者の大小関係を判定する。Ｓ５６で実際の走査速度Ｖが適正な走査速度Ｖ１より小さければ（Ｓ５６でＮＯ）、全偏向角Ａが大きくなるように全偏向角調整トリマ２２を回転させて光偏向素子９のコイルパターン４６に流れる電流量を調整する（Ｓ５７）。ここで、実際の走査速度Ｖが適正な走査速度Ｖ１より小さいということは、上記式（４）から実際の走査時間Ｔは所望の走査時間Ｔobj より大きいので、Ｓ５７のように調整することで、実際の走査時間Ｔを小さくして所望の走査時間Ｔobj に近づけるのである。
【０１２３】
一方、Ｓ５６で実際の走査速度Ｖが適正な走査速度Ｖ１より大きければ（Ｓ５６でＹＥＳ）、全偏向角Ａが小さくなるように全偏向角調整トリマ２２を回転させて光偏向素子９のコイルパターン４６に流れる電流量を調整する（Ｓ５８）。ここで、実際の走査速度Ｖが適正な走査速度Ｖ１より大きいということは、上記式（４）から実際の走査時間Ｔは所望の走査時間Ｔobj より小さいので、Ｓ５８のように調整することで、実際の走査時間Ｔを大きくして所望の走査時間Ｔobjに近づけるのである。
【０１２４】
そして、Ｓ５７またはＳ５８で全偏向角調整トリマ２２を回転させてコイルパターン４６に流れる電流量を調整した後、再びＳ５２以下の処理を行う。そして、Ｓ５５で実際の走査速度Ｖと適正な走査速度Ｖ１との差の絶対値が許容範囲内となった時点で（Ｓ５５でＹＥＳ）、この処理を終える。
【０１２５】
このように、実際の走査速度Ｖをフィードバック制御することで、実際の走査時間Ｔを所望の走査時間Ｔobj と一致するように制御することができる。このため、反射鏡４５の偏向周波数が設計値通りでない場合でも、出力画像の位置ズレを生じることがないという効果が得られる。また、この第３実施例では、第１実施例と同様、書き込み信号のスタートタイミングを制御するための前記ビーム検出器１４を用いて、走査時間を制御できるため、あらたに走査時間測定用の光電変換素子を備える必要がない。
【０１２６】
尚、制御ユニット５０が本発明の走査時間記憶手段、偏向周波数測定手段、全偏向角調整手段に相当する。また、Ｓ５３が偏向周波数測定手段の処理に、Ｓ５７及びＳ５８が全偏向角調整手段の処理に相当する。
［上記実施例の変形例］
上記各実施例にて示したような光偏向素子９とバイアス磁界を与えるための駆動部１１としての永久磁石とからなる正弦揺動共振型偏向器のみでなく、たとえば、永久磁石の代わりの駆動部として積層圧電素子と機械的変倍てこ機構を用いた正弦揺動共振型偏向器や、電磁駆動型のガルバノミラーのうち、レーザビームを偏向する偏向手段の機械共振点にて偏向に作用する素子が正弦的に揺動するような型のものであれば、いずれのものでもその偏向周波数が個体間でばらついたり、または、環境変動による偏向周波数の変化という共通の問題点を持ち得るため、上述した本実施例の主旨に添う構成をとることが可能となり、それにより得られる効果は本実施例と同様に大きいものである。
【図面の簡単な説明】
【図１】第１参考例の光走査装置の概略説明図である。
【図２】第１参考例の光偏向素子の斜視図である。
【図３】第１参考例の全偏向角調整処理のフローチャートである。
【図４】第２参考例の光走査装置の概略説明図である。
【図５】第１実施例のタイムチャートである。
【図６】第１実施例の全偏向角調整処理のフローチャートである。
【図７】第２実施例の全偏向角調整処理のフローチャートである。
【図８】第３実施例の全偏向角調整処理のフローチャートである。
【図９】全偏向角Ａと走査時間Ｔの関係を表すグラフである。
【図１０】出力画像の位置ズレを表す説明図である。
【図１１】従来の光走査装置の概略説明図である。
【図１２】従来の光偏向素子の斜視図である。
【符号の説明】
１・・・光走査装置、 ２・・・筐体、３・・・感光ドラム、 ４・・・半導体レーザ、５・・・コリメータレンズ、 ９・・・光偏向素子、１０・・・偏向器、 １１・・・駆動部、１２・・・結像レンズ、 １３・・・導光ミラー、１４・・・ビーム検出器、 １７・・・基板、１９・・・オリカエシミラー群、 ２５・・・レーザユニット、４１・・・フレーム、 ４２、４３・・・バネ部、４４・・・可動部、 ４５・・・反射鏡、４６・・・コイルパターン、 ５０・・・制御ユニット、[0001]
BACKGROUND OF THE INVENTION
The present invention is a recording apparatus of an electrophotographic system that prints out a coded signal sent from an electronic computer at a high speed, and deflects and modulates a beam such as a laser beam in accordance with a signal from the electronic computer or the like. The present invention relates to an optical scanning device.
[0002]
[Prior art]
Conventionally, an electrophotographic recording apparatus is used as a recording apparatus for recording image information from an electronic computer. Hereinafter, a conventional optical scanning device used in such a recording apparatus will be described with reference to FIG. FIG. 11 is a plan view showing a conventional optical scanning device 71.
[0003]
The optical scanning device 71 mainly includes a casing 72 and a photosensitive drum 73. The casing 72 is a member for forming a laser beam necessary for irradiating the photosensitive drum 73 as a recording medium, that is, a laser unit 76, a cylindrical lens 77, a polygon mirror 78, an imaging lens 79, and a beam detector unit 80. It has.
[0004]
The laser unit 76 includes a semiconductor laser 74 and a collimator lens 75. Among these, the semiconductor laser 74 oscillates a laser beam in the horizontal direction. The collimator lens 75 is installed so that a laser beam oscillated from the semiconductor laser 74 can enter. The laser beam that has passed through the collimator lens 75 becomes a parallel beam that coincides with the optical axis of the collimator lens 75.
[0005]
The cylindrical lens 77 causes the laser beam emitted from the collimator lens 75 to be incident on one reflecting surface of a regular hexagonal polygon mirror 78 having six reflecting surfaces. The polygon mirror 78 is mounted on a shaft supported by a high-precision bearing and is driven by a motor (not shown) that rotates at a constant speed. The polygon mirror 78 rotated by driving the motor sweeps the laser beam substantially horizontally and deflects it at an equal angular velocity. The polygon mirror 78 is mainly made of aluminum, and a cutting method is generally used for its production. Examples of the motor include known hysteresis synchronous motors and DC servo motors. Since the rotational force is obtained by the magnetic driving force, it is necessary to form a coil winding and a magnetic circuit including an iron plate in the motor, and the volume thereof is relatively large.
[0006]
The imaging lens 79 is a lens having fθ characteristics, and forms an image on the photosensitive drum 73 as spot light on the laser beam emitted after being swept almost horizontally by the polygon mirror 78. The beam detector unit 80 is provided in a range that does not obstruct the image area, and includes a single reflecting mirror 81, a slit plate 82 having a small incident slit, and a photoelectric conversion element substrate 83 having a high response speed. When the laser beam swept by the polygon mirror 78 enters the photoelectric conversion element substrate 83 via the slit plate 82, the photoelectric conversion element substrate 83 outputs a detection signal (not shown) indicating that the position of the laser beam has been detected. Output to the control unit.
[0007]
A laser beam emission control device (not shown) controls the start timing of the input signal to the semiconductor laser 74 for giving optical information corresponding to the image data on the photosensitive drum 73 by this detection signal. The laser beam modulated in accordance with the image signal as described above is irradiated onto the photosensitive drum 73, visualized by a known electrophotographic process, transferred onto a transfer material such as plain paper, and output as a hard copy. The
[0008]
However, since the conventional optical scanning device 71 uses an aluminum polygon mirror, a hysteresis synchronous motor, a DC servo motor, or the like for driving the same as described above, both the outer shape and weight are generally used. Therefore, there is a problem that it cannot contribute to the downsizing of a recording apparatus incorporating this optical scanning device.
[0009]
In view of this point, it is described in Japanese Patent Publication No. 60-57052, Japanese Patent Publication No. 60-57053, Japanese Utility Model Publication No. 2-19783, Japanese Utility Model Publication No. 2-19784, Japanese Utility Model Publication No. 2-19785. There has also been proposed an optical scanning device having an optical deflecting element in which a reflecting mirror for reflecting a laser beam is formed on the surface of a mechanical vibrator using a quartz substrate.
[0010]
For example, in Japanese Examined Patent Publication No. 60-57052, as shown in FIG. 12, a movable portion 94 supported by a frame 91 by spring portions 92 and 93, a reflecting mirror 95 and a coil pattern 96 provided on the movable portion 94 are disclosed. An optical deflecting element 90 including the above is disclosed. The light deflecting element 90 oscillates the deflecting surface, that is, the mirror surface of the reflecting mirror 95 in a sinusoidal manner by passing an electric current through the coil pattern 96 in a state where the coil pattern 96 is disposed in the magnetic field, and enters the reflecting mirror 95. The beam is deflected and scanned. The frequency of this reciprocating vibration is referred to as a deflection frequency.
[0011]
[Problems to be solved by the invention]
However, in the optical scanning device using the optical deflection element 90 disclosed in Japanese Patent Publication No. 60-57052, etc., when the optical deflection element 90 is mass-produced, the variation in deflection frequency of each optical deflection element becomes large. End up. Therefore, the deflection angular velocity of the light beam deflected by the light deflecting element 90 has a large individual difference depending on each light deflecting element 90, so that an optical scanning device using such a light deflecting element 90 records an image. When the image recording apparatus is used, the position of the image output according to the designed deflection angular velocity is different from the position of the image output according to the actual deflection angular velocity of the optical deflection element, so that the original image is accurate. There was a problem that it could not be reproduced.
[0012]
The above problem will be described based on a specific example. The optical deflection element 90 is formed by processing a single crystal quartz substrate by an etching process and a photolithography process as described in Japanese Patent Publication No. 60-57052 described above. Since the error of the deflection frequency is usually about ± 3% due to the imbalance of the etching or the error of the etching process, the variation of the deflection frequency by the individual optical deflection elements 90 is large at the time of mass production. The variation in the deflection frequency is the time from the laser beam deflected by the optical deflector 90 to the predetermined scan end position E from the predetermined scan start position S on the photosensitive drum, as shown in FIG. Since it appears as a variation in the scanning time of the laser beam, the following problem occurs.
[0013]
Now, if the semiconductor laser 4 as the light source is modulated according to a fixed clock according to the image information, the image information that should be written at the predetermined scanning end position E according to the above-described variation in the scanning time for each light deflection element. Is shifted in the range of ± 3% in the scanning direction, resulting in a positional deviation of the output image.
[0014]
This will be specifically described according to numerical examples. When the variation of the deflection frequency of the optical deflection element 90 is 800 Hz ± 3% and the distance from the predetermined scanning start position S to the predetermined scanning end position E is 210 mm (corresponding to the A4 size paper surface), the deflection frequency is 800 Hz. Assume that the semiconductor laser 4 is modulated according to a constant clock at a design value such that image information is written at a resolution of 300 dpi from a predetermined scanning start position S to a predetermined scanning end position E.
[0015]
At this time, if the deflection frequency inherent to the optical deflection element 90 is 3% lower than 800 Hz, the image information that should be written at the predetermined scanning end position E is shifted by 6.1 mm in the left direction in FIG. The image is written at the end position Ea, and the output image is reduced by 3% overall. On the other hand, if the deflection frequency inherent to the optical deflection element 90 is 3% higher than 800 Hz, the image information that should be written at the predetermined scanning end position E is shifted by 6.1 mm in the right direction of FIG. The image is written at the position Eb, and the output image is enlarged by 3% as a whole. In general, in a laser beam printer, the deviation of the scanning end position on the A4 paper surface is only allowed to be about ± 1.5 mm. Therefore, it is not practical that the above-described deviation of ± 6.1 mm is practical. .
[0016]
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an optical scanning device that does not cause positional deviation of an output image when scanning is performed with a sine swing of a deflection surface. To do.
[0017]
[Means for Solving the Problems and Effects of the Invention]
In order to solve the above-mentioned problems, a first aspect of the present invention provides a light beam emitting means for emitting a light beam, a light deflecting means for deflecting the light beam by deflecting a deflection surface, and the light deflecting means. And an emission control means for controlling the light beam emitting means so that the light beam deflected by the laser beam scans the scanned medium via the imaging lens. When the scanning time required for scanning from a predetermined scanning start position to a predetermined scanning end position on the medium is scanned, the scanning time storage means for storing the desired scanning time and the deflecting surface of the light deflecting means swing sine. Detects the light beam at a predetermined position within the maximum angle (ie total deflection angle) The detection signal indicating the detection result is output to the emission control unit as a signal for controlling the start timing of inputting image information to the light beam emission unit and controlling the scanning time. When the light beam detecting means 1 and the deflecting surface of the light deflecting means sine oscillate by one cycle, the round trip time from when the light beam detecting means detects the light beam to when the light beam is detected again is obtained. Round-trip time measuring means for measuring, deflection frequency measuring means for measuring a deflection frequency when the deflecting surface of the light deflecting means swings sinusoidally, deflection frequency measured by the deflection frequency measuring means and the scanning time storage means The round trip time calculating means for calculating an appropriate round trip time from the desired scanning time stored in the above, the actual round trip time measured by the round trip time measuring means, and the proper round trip time calculated by the round trip time calculating means And a total deflection angle that adjusts the total deflection angle based on the result of the round-trip time comparison unit so that the actual scanning time matches the desired scanning time. Characterized in that a settling unit.
[0018]
In the optical scanning device according to the first aspect, the light beam emitted by the light beam emitting means is incident on the deflecting surface of the light deflecting means. Since this deflection surface swings in a sinusoidal manner, the incident light beam is deflected toward the scanned medium. The emission control means controls the light beam emission means so that the light beam deflected by the light deflection means scans the scanned medium via the imaging lens. For example, when the deflection surface of the light deflecting means swings sine and reaches an angle at which a light beam can reach a predetermined scanning start position on the scanned medium, the emission control means uses the light beam emitting means at that timing. A light beam is emitted. Then, after the light beam is incident on the deflecting surface, the light beam is deflected and irradiated to a predetermined scanning start position of the scanned medium, and the light beam scans the scanned medium as the deflecting surface of the light deflecting means swings sine. Then, when the deflection surface of the light deflection unit reaches an angle at which the light beam can reach a predetermined scanning end position on the scanned medium, emission of the light beam from the light beam emission unit is stopped at that timing. This completes the scan. In this way, the emission control means controls the light beam emission means so that the light beam scans the scanned medium.
[0019]
Here, in the optical scanning device according to claim 1, the scanning time storage means scans the light beam from a predetermined scanning start position to a predetermined scanning end position (that is, a fixed length) on the scanned medium. For the time required (ie, scanning time), the desired scanning time is stored. The desired scanning time is, for example, a predetermined scanning start position when a sine rocking is performed at a predetermined deflection frequency (for example, 800 Hz) when the deflecting surface of the light deflecting unit is swung. The scanning time required until the scanning end position may be stored.
[0020]
The total deflection angle adjusting means adjusts the maximum angle (that is, the total deflection angle) when the deflecting surface of the light deflecting means swings sine so that the actual scanning time coincides with the desired scanning time. For example, when the desired scanning time is set as described above, if the actual deflection frequency of the deflecting surface of the light deflecting unit deviates from a predetermined deflection frequency, the actual scanning time deviates from the desired scanning time. Specifically, if the deflection frequency is lower than a predetermined deflection frequency, the deflection angular velocity is reduced, so the actual scanning time is longer than the desired scanning time. In order to make this actual scanning time coincide with the desired scanning time, the total deflection angle adjusting means adjusts the total deflection angle. This is because, in an optical scanning apparatus equipped with such an optical deflection means, the scanning time can be expressed as a function of the total deflection angle, so that the scanning time can be adjusted by adjusting the total deflection angle. is there.
In the optical scanning device according to the first aspect, the round trip time measuring means measures the round trip time from when the light beam detecting means detects the light beam to when the light beam is detected again. Further, the deflection frequency measuring means measures the deflection frequency when the deflection surface of the optical deflecting means swings sine, and the round trip time calculating means determines an appropriate value from the deflection frequency measured by the deflection frequency measuring means and the desired scanning time. Calculate the round trip time. Then, the round trip time comparing means compares the actual round trip time measured by the round trip time measuring means with the appropriate round trip time calculated by the round trip time calculating means. The total deflection angle adjusting means adjusts the total deflection angle based on the result of the round-trip time comparing means so that the actual scanning time matches the desired scanning time.
That is, the optical scanning device according to claim 1 does not control the deflection surface so that the total deflection angle becomes the target value, but the actual scanning time is set to the desired scanning time based on the result of the round-trip time comparison means. The total deflection angle is adjusted so as to match.
[0021]
Note that the total deflection angle adjusting means may determine that the actual scanning time coincides with the desired scanning time when the actual scanning time falls within the allowable range of the desired scanning time. As described above, according to the optical scanning device of the first aspect, when the scanning surface is swung with the deflection surface being sine oscillated, the deflection frequency of the deflection surface of the optical deflection means is different depending on individual differences. Even if it changes with time, it can always be adjusted to a stable scanning time. For this reason, the effect that the position shift of an output image does not arise is acquired.
The invention according to claim 2 is characterized in that the deflection frequency measuring means obtains the deflection frequency from a period in which the deflecting surface of the light deflecting means swings sine by one period (that is, a deflection period).
According to a third aspect of the present invention, the deflection frequency measuring means is measured by the round trip time measuring means as a round trip time from when the light beam detecting means detects the light beam to when the light beam is detected again. Obtain the sum of the time and the time measured by the round trip time measuring means as the round trip time from when the light beam detecting means detects the light beam again until it detects the next light beam, as the deflection period, The deflection frequency is obtained by calculating the reciprocal of the deflection cycle.
[0022]
[0023]
[0024]
[0025]
[0026]
[0027]
[0028]
[0029]
[0030]
[0031]
[0032]
[0033]
[0034]
[0035]
[0036]
[0037]
[0038]
A fourth aspect of the present invention is the optical scanning device according to any one of the first to third aspects, wherein the round trip time calculating means is based on the following equation (2), and the shorter of the round trip times: An appropriate time for the round trip time (that is, the short round trip time) is calculated.
[0039]
[Equation 3]

[0040]
However, t is a short round trip time, B is an effective deflection angle, C is a straight line indicating the traveling direction of the light beam reflected by the deflection surface when the light beam is incident on the light beam detecting means, and the deflection surface. An angle formed by the center line of vibration, f is a deflection frequency when the deflection surface swings sine, and T is a scanning time. According to the optical scanning device of the fourth aspect, the same effect as that of the first aspect can be obtained.
[0041]
According to a fifth aspect of the present invention, in the optical scanning device according to the fourth aspect of the invention, the total deflection angle adjusting means is a short-term round-trip time in which an actual short-term round-trip time is more appropriate as a result of the round-trip time comparing means. When it is smaller than this, it is adjusted so that the total deflection angle is increased, and when the actual short-term round-trip time is longer than the appropriate short-term round-trip time, the total deflection angle is adjusted to be small.
[0042]
In the optical scanning device according to claim 5, when the actual short-term reciprocation time is smaller than the appropriate short-term reciprocation time, the actual scanning time can be obtained by increasing the total deflection angle A from the above equation (2). Becomes smaller and approaches the desired scanning time. Further, when the actual short-term round trip time is larger than the appropriate short-term round-trip time, from the above equation (2), if the total deflection angle A is reduced, the actual scanning time becomes larger, and the desired scanning time is reached. Get closer. As described above, the actual scanning time is reduced by finely adjusting the sine fluctuation of the deflecting surface of the optical deflecting means in the direction in which the total deflection angle increases or decreases based on the comparison result of the short-term reciprocating time comparing means. Match the desired scan time. According to the optical scanning device of the fifth aspect, the same effect as that of the first aspect can be obtained.
[0043]
[0044]
[0045]
[0046]
A sixth aspect of the present invention is the optical scanning device according to any one of the first to third aspects, wherein the round trip time calculating means is based on the following formula (3), and the longer of the round trip times: An appropriate time for the round trip time (that is, the long-term round trip time) is calculated.
[0047]
[Expression 4]

[0048]
However, t2 is a long reciprocation time, B is an effective deflection angle, C is a straight line indicating the traveling direction of the light beam reflected by the deflection surface when the light beam is incident on the light beam detecting means, and the deflection surface. An angle formed by the center line of vibration, f is a deflection frequency when the deflection surface swings sine, and T is a scanning time. According to the optical scanning device of the sixth aspect, the same effect as that of the first aspect can be obtained.
[0049]
The invention according to claim 7 is the optical scanning device according to claim 6, wherein, as a result of the round-trip time comparison means, the total deflection angle adjusting means has an actual long-term round-trip time that is more appropriate than an appropriate long-term round-trip time. Is adjusted so as to increase the total deflection angle, and when the actual long-term reciprocation time is smaller than the appropriate long-term reciprocation time, the total deflection angle is adjusted to be small.
[0050]
In the optical scanning device according to claim 7, when the actual long-term reciprocation time is longer than the appropriate long-term reciprocation time, the actual scanning time can be obtained by increasing the total deflection angle A from the above equation (3). Becomes smaller and approaches the desired scanning time. Further, when the actual long-term reciprocation time is smaller than the appropriate long-term reciprocation time, the actual scanning time increases as the total deflection angle A is reduced from the above equation (3), and the desired scanning time is obtained. Get closer. As described above, the actual scanning time is reduced by finely adjusting the sine fluctuation of the deflecting surface of the optical deflecting means in the direction in which the total deflection angle increases or decreases based on the comparison result of the long-term reciprocating time comparing means. Match the desired scan time. According to the optical scanning device of the seventh aspect, the same effect as that of the first aspect can be obtained.
[0051]
An eighth aspect of the present invention is the optical scanning device according to any one of the first to seventh aspects, wherein the light beam detecting means takes a horizontal synchronization of the light beam scanned on the scanned medium. It is characterized by using a detector. In the optical scanning device according to claim 8, as the light beam detecting means, a detector provided in a general optical scanning device for aligning the scanning start position, that is, the light beam scanned on the scanned medium. A detector for horizontal synchronization is used. For this reason, it is not necessary to provide a separate light beam detecting means, and the number of parts can be reduced and the cost can be reduced.
[0052]
[0053]
[0054]
[0055]
[0056]
[0057]
[0058]
[0059]
[0060]
[0061]
A ninth aspect of the present invention is the optical scanning device according to any one of the first to eighth aspects, wherein the light deflecting means includes a light deflecting element manufactured by etching a single insulating substrate and the light. And a drive unit that swings the deflection element in a sinusoidal manner.
[0062]
Since the optical deflection element used in the optical scanning device according to claim 9 is manufactured by etching a single insulating substrate (for example, a single crystal quartz substrate), the thickness of the insulating substrate and the material Due to imbalance or an error in the etching process, the error of the deflection frequency is usually about ± 3%. For this reason, there is a large variation in deflection frequency due to individual optical deflection elements during mass production. Therefore, the conventional optical scanning device using such an optical deflection element has a high possibility of causing a positional deviation of an output image when scanning is performed with the deflection surface swinging in a sine. When the configuration of the invention described in claims 1 to 8 is adopted in such an optical scanning device, the effect is remarkably exhibited.
[0063]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The embodiments of the present invention are not limited to the following examples, and it goes without saying that various forms can be adopted as long as they belong to the technical scope of the present invention.
First, a reference example as a premise for explaining the present invention will be described.
[First Reference Example]
FIG. 1 is a schematic explanatory view of an optical scanning device of a first reference example, and FIG. 2 is a perspective view of an optical deflection element.
[0064]
The housing 2 of the optical scanning device 1 has all members for forming a laser beam necessary for irradiating the photosensitive drum 3 as a scanning medium, that is, a laser unit 25 (light beam emitting means of the present invention), a deflector. 10 (light deflecting means of the present invention), a beam detector 14, and a control unit 50 (exit control means of the present invention).
[0065]
The laser unit 25 is integrated and fixed to a cylindrical opening 6 that is a part of the housing 2, and is configured by a semiconductor laser 4, a collimator lens 5, and a lens barrel 7. Among these, the semiconductor laser 4 emits a laser beam that is modulated in accordance with an image signal input from the outside and makes it incident on the collimator lens 5. The collimator lens 5 is made of a cylindrical glass lens, and receives the laser beam emitted from the semiconductor laser 4 and emits it as parallel laser light from the opening of the lens barrel 7. As such a cylindrical lens, a GRIN lens having a refractive index distribution in a direction perpendicular to the cylindrical axis is known. The lens barrel 7 is made of a resin molded product, and holds the collimator lens 5 so that the central axis of the outer cylindrical surface of the lens barrel 7 and the optical axis of the collimator lens 5 substantially coincide. The semiconductor laser 4 and the collimator lens 5 are adjusted so that the emission point of the semiconductor laser 4 substantially coincides with the optical axis of the collimator lens 5 and the emission point of the semiconductor laser 4 coincides with the focal point of the collimator lens 5. By adjusting these, the laser beam emitted from the semiconductor laser 4 passes through the collimator lens 5 and then becomes a parallel beam substantially coincident with the optical axis of the collimator lens 5, and the cross-sectional shape of the parallel beam is predetermined by the opening of the lens barrel 7. The shape is regulated as much as possible and emitted.
[0066]
The deflector 10 includes an optical deflection element 9 and a drive unit 11 for causing the optical deflection element 9 to sine vibrate, and is disposed in the housing 2. The configuration of the light deflection element 9 will be described with reference to FIG. A movable portion 44 is supported on the frame 41 constituting the light deflection element 9 via spring portions 42 and 43 formed integrally on the upper and lower portions. The frame 41, the spring portions 42 and 43, and the movable portion 44 are configured by a single insulating substrate, and these shapes are formed by using photolithography and etching techniques. Here, as the insulating substrate, for example, a quartz substrate having a thickness of about 5 × 10 −5 m can be used. The frame 41 is not always necessary. Further, a reflecting mirror 45 and a coil pattern 46 are formed on the movable portion 44 by using photolithography and etching techniques. The surface accuracy of the reflecting mirror 45 is set to about ¼ of the wavelength of the laser beam emitted from the semiconductor laser 4 so as not to disturb the beam shape at the time of image formation. The upper and lower spring portions 42 and 43 are respectively provided with lead wires 47 and 48 for conduction to the coil pattern 46, and the upper lead wire 47 is connected to the coil pattern 46 so as to jump. A jumper wire 49 is provided. The method for forming the frame 41, the spring portions 42 and 43 and the movable portion 44 and the method for forming the reflecting mirror 45 and the coil pattern 46 are described in detail in Japanese Patent Publication No. 60-57052. The description in is omitted. Moreover, as the drive part 11 of the deflector 10, a permanent magnet is used, for example, and it arrange | positions so that a predetermined bias magnetic field may be formed.
[0067]
In the deflector 10 of this embodiment configured as described above, the coil pattern 46 of the optical deflection element 9 is arranged in the bias magnetic field given by the drive unit 11, and the coil is connected via the lead wires 47 and 48 and the jumper wire 49. By passing an electric current through the pattern 46, the movable portion 44 reciprocally swings around the upper and lower spring portions 42 and 43. As the movable portion 44 swings back and forth in this manner, the laser beam reflected by the reflecting mirror 45 is swept horizontally by receiving a deflection action.
[0068]
Here, the maximum angle at which the laser beam is deflected by the reciprocating swing of the movable portion 44 is referred to as a total deflection angle A (see FIG. 1). In addition, the effective deflection of the angle actually used for image writing, that is, the angle from the deflection angle at the time when the laser beam enters the scanning start position to the deflection angle at the time when the laser beam enters the scanning end position is set. Called the corner (see FIG. 1). The total deflection angle A is, for example, about 100 °, but the effective deflection angle is smaller than this and is about 80 °.
[0069]
The housing 2 is provided with a deflector driver 21 for controlling the driving of the deflector 10, and the deflector driver 21 includes a total deflection angle adjustment trimmer 22 capable of adjusting the total deflection angle A. The imaging lens 12 is composed of a single plastic lens, and forms an image on the photosensitive drum 3 with the laser beam deflected by the deflector 10, and the scanning line by the laser beam is substantially on the photosensitive drum 3. It has F · arcsin θ characteristics so as to move in the main scanning direction at a constant speed. By the way, in a general imaging lens, when the incident angle of the light beam to the lens is θ, the relation r = F · tan θ (F is the focal length of the imaging lens) is set at the imaging position r on the image plane. There is. However, as in this embodiment, the incident angle of the laser beam reflected by the sinusoidal deflector 10 with respect to the imaging lens 12 changes in a trigonometric manner with time. Therefore, when a general imaging lens is used and the semiconductor laser 4 is turned on at regular time intervals to intermittently emit a laser beam and form an image of the beam spot array on the photosensitive drum 3, these beam spots are obtained. The spacing between rows will not be equal. Therefore, in the optical scanning device 1 using the deflector 10 that swings in a sinusoidal manner as in this embodiment, the imaging lens 12 has a characteristic of r = F · arcsin θ in order to avoid the above-described phenomenon. Is used. Such an imaging lens 12 is referred to as an F arc sine θ lens.
[0070]
The laser beam emitted from the imaging lens 12 is folded back in the optical path by the light guide mirror 13 provided in the region where the irradiation onto the photosensitive drum 3 is not hindered and on the scanning start side of the forward path, It passes through a knife edge 20 formed as part of the body 2 and is guided to the beam detector 14.
[0071]
The beam detector 14 is composed of a photoelectric conversion element such as a pin photodiode, and detects a swept laser beam. The beam detector 14 outputs to the control unit 50 a detection signal for controlling the start timing for inputting image information in the forward path to the semiconductor laser 4. Thereby, it is possible to greatly reduce the horizontal signal synchronization deviation due to the deflection angular velocity unevenness when the movable portion 44 of the deflector 10 swings in a sine, so that a high-quality image can be obtained and the deflector 10 is required. The allowable range of the accuracy of the deflection angular velocity can be increased.
[0072]
The beam detector 14 is disposed on the same substrate 17 plane as that of the semiconductor laser 4. For this reason, since the path of the electric signal between the beam detector 14 and the driving circuit for driving the semiconductor laser 4 can be shortened, the possibility that the circuit system will malfunction due to ambient electric noise is reduced. Can do. Further, since the beam detector 14 and the semiconductor laser 4 are disposed on the same plane of the substrate 17 and both drive circuits coexist on the substrate 17, the number of substrates 17 can be reduced. Moreover, the effect that the number of the harnesses 18 connecting the substrates can be reduced at the same time is also obtained.
[0073]
The substrate 17 is fixed to the housing 2 with screws, and the semiconductor laser 4 is pulled out of the housing 2 due to the force transmitted through the harness 18 or by a direct external force, or the position thereof is shifted. It has the effect of preventing you.
[0074]
The knife edge 20 is provided as a part of the housing 2. Conventionally, a rectangular slit-shaped part obtained by punching a thin metal is positioned and fixed to the housing 2 with screws or the like. Therefore, the effect that the number of parts can be reduced can be obtained by forming the knife edge 20 as a part of the housing 2 as in the present embodiment.
[0075]
The housing | casing 2 is formed with the polycarbonate containing glass fiber generally used widely. For this reason, each component is supported with high positional accuracy and distortion due to vibration is small. The control unit 50 includes a known CPU 51, ROM 52, RAM 53, timer counter 54, and input / output port 56, which are connected by a bus 57. The control unit 50 is connected via an input / output port 56 so that a detection signal from the beam detector 14 can be input, and is connected to the laser unit 25 so that a control signal (exit signal, stop signal) can be output. The deflector 10 is connected to be able to output a signal for causing a current to flow.
[0076]
Next, the total deflection angle adjustment process in the process of assembling and adjusting the optical scanning device 1 will be described with reference to FIG. FIG. 3 is a flowchart of the total deflection angle adjustment process of the first reference example. First, the scan start timing detection sensor 26 is installed at a position corresponding to a predetermined scan start position, and the scan end timing detection sensor 27 is installed at a position corresponding to a predetermined scan end position. These sensors 26 and 27 are connected to output a detection signal to the control unit 50.
[0077]
When the switch of the optical scanning device 1 is turned on in this state, the control unit 50 causes a predetermined current to flow through the coil pattern 46 of the optical deflection element 9 and outputs an emission signal to the laser unit 25 (S10). As a result, the reflecting mirror 45 of the light deflection element 9 starts sine oscillation, and the laser unit 25 emits a laser beam. The ROM 52 of the control unit 50 stores a preset desired scanning time Tobj.
[0078]
The control unit 50 determines whether or not the preparation time until the reflecting mirror 45 of the light deflecting element 9 stably sine swings has elapsed (S11). If this preparation time has not elapsed (S11). NO), wait until this preparation time elapses. If this preparation time has elapsed (YES in S11), the actual scanning time T is measured (S12). The actual scanning time T is measured by measuring the time from the time when the detection signal of the scanning start time detection sensor 26 is input to the time when the detection signal of the scanning end time detection sensor 27 is input.
[0079]
After the measurement of the actual scanning time T is completed, it is determined whether or not the absolute value of the difference between the scanning time T and the desired scanning time Tobj is within an allowable range (S13). If the absolute value of the difference between the two is not within the allowable range (NO in S13), the magnitude relationship between the two is subsequently determined in S14.
[0080]
If the actual scanning time T is longer than the desired scanning time Tobj in S14 (YES in S14), the total deflection angle adjustment trimmer 22 is rotated so that the total deflection angle A becomes larger, and the coil pattern 46 of the optical deflection element 9 is rotated. The amount of current flowing through is adjusted (S15). That is, the relationship between the total deflection angle A and the scanning time T is
[0081]
[Equation 5]

[0082]
Therefore, when the actual scanning time T is larger than the desired scanning time Tobj, if the total deflection angle A is adjusted to be larger, the actual scanning time T becomes smaller and approaches the desired scanning time Tobj. That is, from the above equation (1), even if there is a variation in the deflection frequency f, the total deflection angle A is set so that the actual scanning time T matches the desired scanning time Tobj without measuring the deflection frequency f. It can be seen that if the fine adjustment is repeated, the actual scanning time T can be matched with the desired scanning time Tobj.
[0083]
If the actual scanning time T is shorter than the desired scanning time Tobj in S14 (NO in S14), the total deflection angle adjustment trimmer 22 is rotated so that the total deflection angle A becomes smaller, and the coil pattern 46 of the optical deflection element 9 is obtained. The amount of flowing current is adjusted (S16). By adjusting in this way, the actual scanning time T increases and approaches the desired scanning time Tobj.
[0084]
Then, in S15 or S16, the total deflection angle adjustment trimmer 22 is rotated to adjust the amount of current flowing through the coil pattern 46, and then the processing from S12 is repeated again. Then, when the absolute value of the difference between the scanning time T and the desired scanning time Tobj is within the allowable range in S13 (YES in S13), this process is finished.
[0085]
Thereafter, the scanning start timing detection sensor 26 and the scanning end timing detection sensor 27 are removed. Thus, in the optical scanning device 1 of the first reference example, the total deflection angle adjustment trimmer 22 is adjusted so that the actual scanning time T is within the specification range in the assembly and adjustment process. Even when the deflection frequency of 45 is not as designed, there is an effect that the output image is not misaligned. In particular, a single crystal quartz substrate processed by an etching process and a photolithography process, such as the optical deflection element 9, has a deflection frequency at the time of mass production due to a quartz substrate thickness or material imbalance or an etching process error. Since the variation is large, the above effect of the present embodiment is remarkably exhibited. Further, since the total deflection angle A is adjusted by changing the amount of current supplied to the coil pattern 46 of the optical deflection element 9 by rotating the total deflection angle adjusting trimmer 22, the adjustment can be performed quickly.
[0086]
The control unit 50 corresponds to the scanning time storage means and the total deflection angle adjusting means of the present invention. S15 and S16 correspond to the processing of the total deflection angle adjusting means.
[Second Reference Example]
The optical scanning device of the second reference example measures and controls the scanning time in real time. FIG. 4 is a schematic explanatory diagram of an optical scanning device of a second reference example.
[0087]
In the optical scanning device of the second reference example, the scanning start timing detection sensor 26 is provided at a position corresponding to a predetermined scanning start position of the photosensitive drum 3 in the casing 2, and the scanning end timing detection sensor 27 is positioned in the photosensitive drum 3 in the casing 2. Except for the fact that it is provided at a position corresponding to the predetermined scanning end position, since it is the same as the first reference example, the same components are denoted by the same reference numerals, and the description thereof is omitted. Both detection sensors 26 and 27 are connected so that detection signals can be output to the control unit 50.
[0088]
The optical scanning device of the second reference example performs the same process as the total deflection angle adjustment process of the first reference example before outputting an image for one page. Then, after the entire deflection angle adjustment process is completed, an image for one page is output. When outputting an image, the control unit 50 controls the laser unit 25 to emit a blinking laser beam based on the image information. The photosensitive drum 3 that has received this is visualized by a known electrophotographic process or the like, and then transferred and fixed on a transfer material made of plain paper or special paper by a known transfer mechanism and fixing mechanism, and output as a hard copy. The
[0089]
In the second reference example, since the total deflection angle adjustment process is performed before outputting an image for one page, not only individual differences of the optical deflection elements 9 can be corrected, but also fluctuations due to temperature, humidity, etc. of the deflection frequency and over time. Even when it fluctuates, it can be controlled so that the actual scanning time T always falls within the specification range. For this reason, the effect that the position shift of an output image does not arise is acquired.
[0090]
For the second reference example, the deflection cycle is measured using the detection signal of the scanning start timing detection sensor 26, the deflection frequency f is obtained from the deflection cycle, and the deflection frequency f and the desired scanning time are expressed by the above formula ( The value of the target total deflection angle A may be calculated by substituting in 1), and the rotation of the total deflection angle adjustment trimmer 22 may be adjusted while directly monitoring the total deflection angle A with, for example, an angle sensor. In this case, the same effect as described above can be obtained.
[First embodiment]
Since the configuration of the optical scanning device of the first embodiment is the same as that of the first reference example except that the scanning start timing detection sensor 26 and the scanning end timing detection sensor 27 are not provided, the description thereof is omitted. To do.
[0091]
Since the reflecting mirror 45 of the light deflecting element 9 swings in a sine, the laser beam deflected by the reflecting mirror 45 reciprocates. For this reason, the laser beam is incident on the beam detector 14 once in each reciprocation, that is, twice in one cycle. A time chart at this time is shown in FIG. As described above, the beam detector 14 is installed at a position where the laser beam reflected by the light guide mirror 13 installed in a region where the irradiation onto the photosensitive drum 3 is not hindered is incident. The long reciprocation time t ′ in which the laser beam reciprocates and the short reciprocation time t in which the laser beam reciprocates on the opposite side of the photosensitive drum 3 are alternately generated. The sum of the long round trip time t ′ and the short round trip time t is the deflection cycle.
[0092]
If the deflection frequency f is obtained from this deflection cycle, the short-term reciprocating time t and the time required from the predetermined scanning start position to the predetermined scanning end position, ie, the scanning time T, are 1: 1 on the basis of the relationship of the following formula (2). Therefore, it is possible to control the scanning time T to coincide with the desired scanning time T by adjusting the total deflection angle A while monitoring the short-term reciprocating time t instead of the scanning time T. It is. In the following formula (2), C is a straight line indicating the traveling direction of the laser beam reflected by the reflecting mirror 45 of the light deflection element 9 when the laser beam is incident on the light guide mirror 13, and the light deflection element. 9 is an angle formed by the center line of vibration of the reflecting mirror 45 (see FIG. 1, the same applies hereinafter).
[0093]
[Formula 6]

[0094]
The total deflection angle adjustment process in the optical scanning apparatus of the first embodiment is not based on directly measuring the actual scanning time T, but the actual deflection frequency from the detection signal of the beam detector 14 for controlling the start timing of the write signal. f is obtained and the short-time reciprocation time t (when the reflecting mirror 45 is sine-oscillated by one period, the shorter reciprocation time from the time when the beam detector 14 receives the laser beam to the time when it receives the laser beam again) Time) and the total deflection angle A is adjusted based on this short-term reciprocating time t, so that the actual scanning time T matches the desired scanning time Tobj.
[0095]
The total deflection angle adjustment process of the first embodiment will be described with reference to FIG. FIG. 6 is a flowchart of the total deflection angle adjustment process of the first embodiment. The optical scanning device of the first embodiment performs this total deflection angle adjustment process before outputting an image for one page, as in the second reference example. Then, after this all deflection angle adjustment processing is completed, an image for one page is output (image output is performed in the same manner as in the second reference example).
[0096]
When the switch of the optical scanning device 1 is turned on, the control unit 50 causes a predetermined current to flow through the coil pattern 46 of the optical deflection element 9 and outputs an emission signal to the laser unit 25 (S30). As a result, the reflecting mirror 45 of the light deflection element 9 starts sine oscillation, and the laser unit 25 emits a laser beam. The ROM 52 of the control unit 50 stores a preset desired scanning time Tobj.
[0097]
The control unit 50 determines whether or not the preparation time until the reflecting mirror 45 of the light deflecting element 9 stably sine swings has passed (S31), and if this preparation time has not passed (S31). NO), wait until this preparation time elapses. If this preparation time has elapsed (YES in S31), the actual deflection frequency f is measured (S32). The actual measurement of the deflection frequency f includes the round trip time tm1 from when the control unit 50 receives the detection signal of the beam detector 14 until the detection signal of the next beam detector 14 is received, and the next beam detection. The round trip time tm2 from when the detection signal of the detector 14 is received until the detection signal of the next beam detector 14 is received is measured and stored in the RAM 53. Then, the sum of the reciprocating time tm1 and the reciprocating time tm2, that is, the deflection cycle is obtained, and the reciprocal of this deflection cycle is calculated to obtain the deflection frequency f.
[0098]
Subsequently, an appropriate short-term round trip time t1 is calculated by the above equation (2) (S33). That is, the desired scanning time Tobj is substituted as T in the above equation (2), and the deflection frequency f obtained in S32 is substituted as f, and the obtained t is set as an appropriate short-term reciprocating time t1. Thereafter, the shorter one of the round trip time tm1 and the round trip time tm2 stored in the RAM 53 is stored in the RAM 53 as the actual short round trip time t (S34), and the actual short round trip time t and the appropriate short round trip time t1 Are compared to determine whether or not the absolute value of the difference between the two is within an allowable range (S35). If the absolute value of the difference between the two is not within the allowable range (NO in S35), the magnitude relationship between the two is subsequently determined in S36.
[0099]
If the actual short-term reciprocation time t is shorter than the appropriate short-term reciprocation time t1 in S36 (NO in S36), the total deflection angle adjustment trimmer 22 is rotated so that the total deflection angle A becomes large, and the coil pattern of the optical deflection element 9 is reached. The amount of current flowing through 46 is adjusted (S37). Here, the fact that the actual short-term round-trip time t is smaller than the appropriate short-term round-trip time t1 means that the actual scanning time T is larger than the desired scanning time Tobj from the above equation (2), so adjustment is made as in S37. As a result, the actual scanning time T is reduced to approach the desired scanning time Tobj.
[0100]
On the other hand, if the actual short-term reciprocation time t is longer than the appropriate short-term reciprocation time t1 in S36 (YES in S36), the total deflection angle adjustment trimmer 22 is rotated so that the total deflection angle A becomes small, and the optical deflection element 9 is rotated. The amount of current flowing through the coil pattern 46 is adjusted (S38). Here, the fact that the actual short-term round-trip time t is larger than the appropriate short-term round-trip time t1 means that the actual scanning time T is smaller than the desired scanning time Tobj from the above equation (2), so adjustment is made as in S38. Thus, the actual scanning time T is increased to approach the desired scanning time Tobj.
[0101]
Then, in S37 or S38, the total deflection angle adjustment trimmer 22 is rotated to adjust the amount of current flowing in the coil pattern 46, and then the processes in S32 and subsequent steps are repeated again. Then, when the absolute value of the difference between the actual short-term round-trip time t and the appropriate short-term round-trip time t1T is within the allowable range in S35 (YES in S35), this process is finished.
[0102]
As described above, the actual scanning time T can be controlled to coincide with the desired scanning time Tobj by performing feedback control of the actual short-term reciprocation time t. For this reason, even when the deflection frequency of the reflecting mirror 45 is not as designed, there is an effect that the output image is not misaligned. In the first embodiment, since the scanning time can be controlled using the beam detector 14 for controlling the start timing of the write signal, there is no need to newly provide a photoelectric conversion element for measuring the scanning time.
[0103]
The control unit 50 corresponds to the scanning time storage means, the round trip time measuring means, the deflection frequency measuring means, the round trip time calculating means, the round trip time comparing means, and the total deflection angle adjusting means of the present invention. S32 is processing of the round trip time measuring means and deflection frequency measuring means, S33 is processing of the round trip time calculating means, S35 and S36 are processing of the round trip time comparing means, and S37 and S38 are processing of the total deflection angle adjusting means. It corresponds to.
[Second Embodiment]
Since the configuration of the optical scanning device of the second embodiment is the same as that of the first embodiment, the description thereof is omitted.
[0104]
The total deflection angle adjustment process in the optical scanning device of the second embodiment is not the direct measurement of the actual scanning time T, but the deflection frequency f from the detection signal of the beam detector 14 for controlling the start timing of the write signal. Long-term reciprocation time t ′ (the longer reciprocation time of the reciprocation time from when the beam detector 14 receives the laser beam to when it receives the laser beam again when the reflecting mirror 45 is sine-oscillated by one period) ) And the total deflection angle A is adjusted based on the long-term reciprocating time t ′, and the actual scanning time T is made to coincide with the desired scanning time Tobj.
[0105]
If the deflection frequency f is obtained from the deflection cycle, the long-term reciprocating time t ′ and the time required from the predetermined scanning start position to the predetermined scanning end position, ie, the scanning time T, are 1: 1 on the basis of the relationship of the following formula (3). Therefore, it is possible to control the scanning time T to coincide with the desired scanning time Tobj by adjusting the total deflection angle A while monitoring the long-term reciprocating time t ′ instead of the scanning time T. Is possible.
[0106]
[Expression 7]

[0107]
The total deflection angle adjustment process of the second embodiment will be described with reference to FIG. FIG. 7 is a flowchart of the total deflection angle adjustment process of the second embodiment. In the optical scanning device of the second embodiment, as in the second and third embodiments, this total deflection angle adjustment processing is performed before outputting an image for one page. Then, after the entire deflection angle adjustment process is completed, an image for one page is output.
[0108]
When the switch of the optical scanning device 1 is turned on, the control unit 50 performs the processes of S40 to S42 similar to S30 to S32. After measuring the actual deflection frequency f in S42, an appropriate long-term reciprocating time t2 is calculated by the above equation (3) (S43). That is, the desired scanning time Tobj is substituted as T in the above equation (3), and the deflection frequency f obtained in S42 is substituted as f, and the obtained t is set as an appropriate long-term reciprocating time t2.
[0109]
Thereafter, the longer one of the round trip time tm1 and the round trip time tm2 stored in the RAM 53 is stored in the RAM 53 as the actual long round trip time t '(S44), and this actual long round trip time t' and the appropriate long round trip time are stored. Comparison with t2 is performed to determine whether or not the absolute value of the difference between the two is within an allowable range (S45). If the absolute value of the difference between the two is not within the allowable range (NO in S45), the magnitude relationship between the two is subsequently determined in S46.
[0110]
If the actual long-term reciprocation time t ′ is larger than the appropriate long-term reciprocation time t2 in S46 (YES in S46), the total deflection angle adjustment trimmer 22 is rotated so that the total deflection angle A becomes large, and the coil of the optical deflection element 9 is rotated. The amount of current flowing through the pattern 46 is adjusted (S47). Here, the fact that the actual long-term reciprocation time t ′ is larger than the appropriate long-term reciprocation time t2 means that the actual scanning time T is larger than the desired scanning time Tobj from the above equation (3). As a result, the actual scanning time T is shortened to approach the desired scanning time Tobj.
[0111]
On the other hand, if the actual long-term reciprocation time t ′ is smaller than the appropriate long-term reciprocation time t2 in S46 (NO in S46), the total deflection angle adjustment trimmer 22 is rotated so that the total deflection angle A becomes small, and the optical deflection element 9 is rotated. The amount of current flowing through the coil pattern 46 is adjusted (S48). Here, the fact that the actual long-term reciprocal time t ′ is smaller than the appropriate long-term reciprocal time t2 means that the actual scanning time T is smaller than the desired scanning time Tobj from the above equation (3). Thus, the actual scanning time T is increased to approach the desired scanning time Tobj.
[0112]
Then, in S47 or S48, the total deflection angle adjustment trimmer 22 is rotated to adjust the amount of current flowing through the coil pattern 46, and then the processes in and after S42 are repeated. Then, when the absolute value of the difference between the actual long-term round-trip time t ′ and the appropriate long-term round-trip time t2 is within the allowable range in S45 (YES in S45), the process is terminated.
[0113]
In this way, by performing feedback control of the actual long-term reciprocating time t ′, the actual scanning time T can be controlled to coincide with the desired scanning time Tobj. For this reason, even when the deflection frequency of the reflecting mirror 45 is not as designed, there is an effect that the output image is not misaligned. In the second embodiment, as in the first embodiment, the scanning time can be controlled by using the beam detector 14 for controlling the start timing of the write signal, so that a photoelectric conversion element for measuring the scanning time is newly provided. It is not necessary to have.
[0114]
The control unit 50 corresponds to the scanning time storage means, the round trip time measuring means, the deflection frequency measuring means, the round trip time calculating means, the round trip time comparing means, and the total deflection angle adjusting means of the present invention. S42 is processing of the round trip time measuring means and deflection frequency measuring means, S43 is processing of the round trip time calculating means, S45 and S46 are processing of the round trip time comparing means, and S47 and S48 are processing of the total deflection angle adjusting means. It corresponds to.
[Third embodiment]
Since the configuration of the optical scanning device of the third embodiment is the same as that of the first embodiment, the description thereof is omitted.
[0115]
In the total deflection angle adjustment process in the optical scanning apparatus of the third embodiment, instead of directly measuring the actual scanning time T, the scanning speed V at a predetermined scanning point is measured, and the total deflection is based on the scanning speed V. By adjusting the angle A, the actual scanning time T is matched with the desired scanning time Tobj.
[0116]
In the optical scanning device of the third embodiment, the beam detector 14 is composed of a small incident slit and a photoelectric conversion element substrate having a high response speed (for example, an incident slit formed by a pair of slit plates 82 and 82 in FIG. 11). (Refer to the photoelectric conversion element substrate 83 having a high response speed.) Since the slit width of this incident slit is constant, if the time ts (see FIG. 5) from when the laser beam begins to enter the incident slit of the beam detector 14 until it passes through the slit width is measured, the light guide mirror 13 is measured. A scanning speed V is obtained at the position where is installed. That is, if the control unit 50 measures the time ts from when the output of the detection signal of the beam detector 14 is started to when the output ends, the scanning speed V at the position where the light guide mirror 13 is installed is obtained. It is done.
[0117]
Further, when the deflection frequency f is obtained from the deflection cycle, the scanning speed V and the time required from the predetermined scanning start position to the predetermined scanning end position, that is, the scanning time T, are one-to-one according to the relationship of the following formula (4). Therefore, the actual scanning time T can be controlled to match the desired scanning time Tobj by adjusting the total deflection angle A while monitoring the scanning speed V instead of the scanning time T. Is possible. In the following formula (4), F is the focal length of the imaging lens 12.
[0118]
[Equation 8]

[0119]
The total deflection angle adjustment process of the third embodiment will be described with reference to FIG. FIG. 8 is a flowchart of the total deflection angle adjustment process of the third embodiment. Note that the optical scanning device of the third embodiment performs this total deflection angle adjustment process before outputting an image for one page, as in the second to fourth embodiments. Then, after the entire deflection angle adjustment process is completed, an image for one page is output.
[0120]
When the switch of the optical scanning device 1 is turned on, the control unit 50 performs the processes of S50 to S51 similar to S30 to S31. If the preparation time has elapsed in S51 (YES in S51), the actual scanning speed V is measured and stored in the RAM 53 (S52). The actual scanning speed V is measured by measuring a time ts from when the output of the detection signal of the beam detector 14 is started by the control unit 50 until the output is completed, so that the beam detector 14 has a predetermined value. Therefore, the scanning speed V at the position where the light guide mirror 13 is installed is obtained.
[0121]
Subsequently, the actual deflection frequency f is measured (S53). This process is the same as S32 in the first embodiment. Subsequently, an appropriate scanning speed V1 is calculated by the above equation (4) (S54). That is, the desired scanning time Tobj is substituted as T in the above equation (4), and the deflection frequency f obtained in S53 is substituted as f, and the obtained V is set as an appropriate scanning speed V1.
[0122]
Then, the actual scanning speed V is compared with the appropriate scanning speed V1, and it is determined whether or not the absolute value of the difference between the two is within an allowable range (S55). If the absolute value of the difference between the two is not within the allowable range (NO in S55), the magnitude relationship between the two is subsequently determined in S56. If the actual scanning speed V is smaller than the appropriate scanning speed V1 in S56 (NO in S56), the total deflection angle adjustment trimmer 22 is rotated so that the total deflection angle A becomes large, and the coil pattern 46 of the optical deflection element 9 is obtained. The amount of current flowing is adjusted (S57). Here, the fact that the actual scanning speed V is smaller than the appropriate scanning speed V1 means that the actual scanning time T is larger than the desired scanning time Tobj from the above equation (4). The actual scanning time T is reduced to approach the desired scanning time Tobj.
[0123]
On the other hand, if the actual scanning speed V is higher than the appropriate scanning speed V1 in S56 (YES in S56), the total deflection angle adjustment trimmer 22 is rotated so that the total deflection angle A becomes smaller, and the coil pattern of the optical deflection element 9 is thus achieved. The amount of current flowing through 46 is adjusted (S58). Here, the fact that the actual scanning speed V is larger than the appropriate scanning speed V1 means that the actual scanning time T is smaller than the desired scanning time Tobj from the above equation (4), and therefore, by adjusting as in S58, The actual scanning time T is increased to approach the desired scanning time Tobj.
[0124]
Then, in S57 or S58, the total deflection angle adjustment trimmer 22 is rotated to adjust the amount of current flowing through the coil pattern 46, and then the processing from S52 is performed again. Then, when the absolute value of the difference between the actual scanning speed V and the appropriate scanning speed V1 is within the allowable range in S55 (YES in S55), this process is finished.
[0125]
In this way, by performing feedback control of the actual scanning speed V, the actual scanning time T can be controlled to coincide with the desired scanning time Tobj. For this reason, even when the deflection frequency of the reflecting mirror 45 is not as designed, there is an effect that the output image is not misaligned. Further, in the third embodiment, similarly to the first embodiment, the scanning time can be controlled by using the beam detector 14 for controlling the start timing of the write signal, so that the photoelectric conversion for measuring the scanning time is newly performed. There is no need to provide an element.
[0126]
The control unit 50 corresponds to the scanning time storage means, the deflection frequency measuring means, and the total deflection angle adjusting means of the present invention. S53 corresponds to the processing of the deflection frequency measuring means, and S57 and S58 correspond to the processing of the total deflection angle adjusting means.
[Modification of the above embodiment]
In addition to the sinusoidal resonance type deflector comprising the optical deflection element 9 and the permanent magnet as the drive unit 11 for applying a bias magnetic field as shown in the above embodiments, for example, driving instead of the permanent magnet Among the sinusoidal oscillating resonance type deflector using a laminated piezoelectric element and a mechanical zoom lever mechanism as an element, and an electromagnetically driven galvanometer mirror, it acts on the deflection at the mechanical resonance point of the deflecting means for deflecting the laser beam. As long as the element is of a type that swings sinusoidally, the deflection frequency of each element may vary between individuals, or it may have a common problem of changes in the deflection frequency due to environmental fluctuations. It is possible to adopt a configuration that conforms to the gist of the present embodiment described above, and the effects obtained thereby are as great as those of the present embodiment.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory diagram of an optical scanning apparatus according to a first reference example.
FIG. 2 is a perspective view of a light deflection element of a first reference example.
FIG. 3 is a flowchart of a total deflection angle adjustment process of the first reference example.
FIG. 4 is a schematic explanatory diagram of an optical scanning device of a second reference example.
FIG. 5 is a time chart of the first embodiment.
FIG. 6 is a flowchart of a total deflection angle adjustment process of the first embodiment.
FIG. 7 is a flowchart of a total deflection angle adjustment process according to the second embodiment.
FIG. 8 is a flowchart of a total deflection angle adjustment process of the third embodiment.
9 is a graph showing the relationship between the total deflection angle A and the scanning time T. FIG.
FIG. 10 is an explanatory diagram illustrating a positional shift of an output image.
FIG. 11 is a schematic explanatory diagram of a conventional optical scanning device.
FIG. 12 is a perspective view of a conventional optical deflection element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Optical scanning device, 2 ... Housing | casing, 3 ... Photosensitive drum, 4 ... Semiconductor laser, 5 ... Collimator lens, 9 ... Optical deflection element, 10 ... Deflector 11... Drive unit, 12... Imaging lens, 13... Light guide mirror, 14... Beam detector, 17 .. Substrate, 19. -Laser unit, 41 ... frame, 42, 43 ... spring part, 44 ... movable part, 45 ... reflecting mirror, 46 ... coil pattern, 50 ... control unit,

Claims (9)

A light beam emitting means for emitting a light beam;
A light deflecting means for deflecting the light beam by a sinusoidal deflection surface;
An emission control unit that controls the light beam emission unit so that the light beam deflected by the light deflection unit scans the scanned medium via an imaging lens;
A scanning time storage means for storing a desired scanning time for a scanning time required for the light beam to scan from a predetermined scanning start position to a predetermined scanning end position on the scanned medium;
A light beam at a predetermined position within a maximum angle (that is, a total deflection angle) when the deflecting surface of the light deflecting means swings sine is detected , and a detection signal indicating the detection result is sent to the light beam emitting means as image information A light beam detecting means for controlling the start timing for inputting the light and outputting to the emission control means as a signal for controlling the scanning time ;
A round trip time measuring means for measuring a round trip time from the time when the light beam detecting means detects the light beam to the time when the light beam is detected again when the deflecting surface of the light deflecting means swings sine by one cycle;
Deflection frequency measuring means for measuring a deflection frequency when the deflecting surface of the light deflecting means swings sinusoidally;
A round trip time calculating means for calculating an appropriate round trip time from the deflection frequency measured by the deflection frequency measuring means and the desired scanning time stored by the scanning time storage means;
Round-trip time comparison means for comparing the actual round-trip time measured by the round-trip time measurement means with the appropriate round-trip time calculated by the round-trip time calculation means;
An optical scanning apparatus comprising: a total deflection angle adjusting unit that adjusts a total deflection angle so that an actual scanning time matches a desired scanning time based on a result of the round-trip time comparison unit. 2. The optical scanning device according to claim 1, wherein the deflection frequency measuring unit obtains the deflection frequency from a cycle (that is, a deflection cycle) in which the deflection surface of the optical deflecting unit sine swings by one cycle. The deflection frequency measuring means includes a time measured by the round trip time measuring means as a round trip time from when the light beam detecting means detects the light beam to when the light beam is detected again, and the light beam detecting means Obtaining the sum of the round trip time from the time when the light beam is detected again until the next light beam is further detected as the deflection cycle, and calculating the reciprocal of the deflection cycle. The optical scanning device according to claim 2, wherein the deflection frequency is obtained. The round trip time calculating means calculates an appropriate time of the shorter round trip time (that is, the short round trip time) of the round trip times based on the following formula (2). An optical scanning device according to claim 1.

However, t is a short round trip time, B is an effective deflection angle, C is a straight line indicating the traveling direction of the light beam reflected by the deflection surface when the light beam is incident on the light beam detecting means, and the deflection surface. An angle formed by the center line of vibration, f is a deflection frequency when the deflection surface swings sine, and T is a scanning time. The total deflection angle adjusting means adjusts the total deflection angle so that when the actual short-term round-trip time is smaller than the appropriate short-term round-trip time as a result of the round-trip time comparison means, The optical scanning device according to claim 4, wherein the total deflection angle is adjusted to be smaller when the time is longer than an appropriate short-term reciprocation time. The round trip time calculation means calculates an appropriate time of the longer round trip time (that is, the long round trip time) of the round trip times based on the following formula (3). An optical scanning device according to claim 1.

However, t2 is a long reciprocation time, B is an effective deflection angle, C is a straight line indicating the traveling direction of the light beam reflected by the deflection surface when the light beam is incident on the light beam detecting means, and the deflection surface. An angle formed by the center line of vibration, f is a deflection frequency when the deflection surface swings sine, and T is a scanning time. The total deflection angle adjusting means adjusts the total deflection angle so that when the actual long-term round-trip time is larger than the appropriate long-term round-trip time as a result of the round-trip time comparison means, The optical scanning device according to claim 6, wherein the total deflection angle is adjusted to be smaller when the time is shorter than an appropriate long-term reciprocation time. 8. The optical scanning device according to claim 1, wherein the light beam detection unit uses a detector for horizontally synchronizing a light beam scanned on the scanned medium. 9. 9. The optical deflecting unit includes an optical deflecting element manufactured by etching a single insulating substrate and a drive unit that swings the optical deflecting element in a sinusoidal manner. An optical scanning device according to claim 1.

Images