JP3822280B2 - Image reading device - Google Patents

Description

上式において、偏心方向をＹ方向とするとき、Ｘの奇数次項は全て０である。
【００２６】
この定義式により、以下に説明する各収差の補正を良好に補正することが可能となり、本発明のように傾いて配置された反射鏡により結像光学系（読み取り光学系）として使用できる程の屈折力（パワー）を付加することが可能となった。
【００２７】
まず、基準となる面は２乗の項の放物面を元にしているので、球面収差が発生し難い。次に、Ｙの奇数次項とＸの奇数次項が存在するので、Ｘ軸の任意の位置でＹ軸方向の傾きを与えることができる。
【００２８】
ＹとＸのそれぞれに対して、奇数次と偶数次が掛け合わさっているので、各軸の正負に対して自由な曲率を与えることができる。
【００２９】
以上のように様々な自由度があり、偏心して配置された反射面として使用した場合に、パワーを持たせても、収差を十分に補正することがこの定義式を使うことによって初めて可能となった。
【００３０】
この自由度が収差補正にいかに重要であるかを説明する。傾いてなおかつパワーを持った反射鏡の場合には、回転非対称な像面湾曲が発生する。この像面湾曲は、瞳を通過しＸ軸方向に広がりを持った光線は、偏心して配置された反射鏡に当たって反射されるが、光線が当たって以降の像面までの距離は、裏面鏡の焦点距離の式
ｆ＝−ｒ／２ｎ
に従い、光線が当たった部分の曲率ｒと屈折率ｎからｒ／２ｎである。つまり、偏心して配置された凹面鏡の反射後の光線の進む方向に対して、傾いた反射鏡と平行に光軸に対して傾いて、なおかつ、反射鏡の曲率ｒのｒ／２ｎの湾曲した像面を形成する。
【００３１】
自由曲面は、上述のように、Ｙ軸の正負によって曲率を任意に変えることが可能なＹの奇数次項を持っているため、偏心して配置された凹面鏡で発生する回転非対称な像面湾曲、特に像面の傾きを補正することに対して有効に作用する。
【００３２】
次に、回転対称な像面湾曲について説明する。反射鏡により一般的に反射面に沿った像面湾曲が発生する。本発明の場合は、上に述べたように、凹面鏡と対をなした凸面鏡により像面湾曲を補正できる構成も可能であるし、凹面を２面使用してそれぞれで発生する像面湾曲を少なくする工夫をしている。しかし、従来の面形状では面数も少ないために、完全には補正されない。この補正し切れない像面湾曲を補正するためには、任意の場所で任意の曲率を与えることができる自由曲面は収差補正上好ましい。これは、Ｙ軸の正負によって曲率をＹの奇数次項とＸの２乗以上の組み合わせにより可能となる。
【００３３】
さらに、任意の場所の非点収差の発生を少なくするためには、Ｘ軸方向の曲率とＹ軸方向の曲率の差を任意に変えることにより補正することが可能となる。これは、Ｘの２乗項とＹの２乗項が独立に存在していることにより可能となる。
【００３４】
さらに好ましくは、光学部品製作性を考慮すると、自由曲面は必要最低限にすることが望ましい。そこで、少なくとも３つの面の中、１つの面を上記自由曲面とし、他の面を平面もしくは球面又は偏心した回転対称面にすることによって、製作性を上げることが可能となる。
【００３５】
さらに好ましくは、以下の条件を満足することによって、広画角で瞳径が大きく、かつ、収差補正の良好に行われた読み取り光学系を提供することができる。
【００３６】
上述の定義に従って、Ｘ軸、Ｙ軸、Ｚ軸とするとき、瞳位置中心を射出し、像を形成する読み取り光学系に入射する光線の最大画角の光線が各面と交差する領域を有効領域と定義し、次の表−１に示すような光線▲１▼〜▲６▼を追跡する。
【００３７】

【００３８】
すなわち、画面中心の光軸方向の軸上主光線を▲２▼とし、上側中心画角の光線を▲１▼、右上画角の光線を▲４▼、右中心画角の光線を▲５▼、右下画角の光線を▲６▼、下側中心画角の光線を▲３▼とする。これら光線▲１▼〜▲６▼が光学系の各面に当たる部分の面形状を記述する式（Ｚ軸を面の軸として表した式、あるいは、その面を偏心がないとして、Ｚ＝ｆ（Ｘ，Ｙ）の形式で表した式）の１次微分と曲率の値を求める。つまり、１次微分は面の定義座標に対する光線が当たる部分の傾きを表し、曲率は光線の当たる部分の部分的曲率を表す。これは、光学系の各面が偏心して配置された場合には、面形状を定義する座標は任意の位置に定義でき、前記座標中心での曲率等を記述しても、その部分を光線が通過していないことがあり、面形状を限定したことにならないためである。
【００３９】
ところで、まず、ＴＦＣ面の軸上主光線▲２▼が当たる位置のＸ方向の部分的曲率について説明する。本発明において、面の部分的曲率を規定する意味は、いくら収差が良好に補正されるＴＦＣ面であっても、余りに面のパワーが大きすぎると、収差発生が大きくなりすぎ、他の面で補正することが不可能になるからである。Ｘ方向の主光線▲２▼が当たる部分の曲率をＲＸとすると、
｜ＲＸ｜＜０．５ （１／ｍｍ） ・・・（Ａ−１）
なる条件を満足することが重要である。この偏心して配置された反射面の曲率が上限の０．５を越えない場合には、対称面を１面しか持たない面で反射面を構成することによって、収差発生の少ない光学系を構成することが可能となる。この上限０．５を越えている反射面では、偏心による各種収差の発生が極めて大きくなり、他の面で補正することが難しくなる。
【００４０】
さらに好ましくは、
｜ＲＸ｜＜０．１ （１／ｍｍ） ・・・（Ａ−２）
なる条件を満足するときに、対称面を１面しか持たない面で反射面を構成することが、偏心による収差を発生させないために重要となる。
【００４１】
さらに好ましくは、
｜ＲＸ｜＜０．０５（１／ｍｍ） ・・・（Ａ−３）
なる条件を満足するときに、対称面を１面しか持たない面で反射面を構成することが、偏心による収差を発生させないために重要となる。
【００４２】
次に、ＴＦＣ面の軸上主光線▲２▼が当たる位置のＹ方向の部分的曲率について説明する。本発明において、面の部分的曲率を規定する意味は、いくら収差が良好に補正されるＴＦＣ面であっても、余りに面のパワーが大きすぎると、収差発生が大きくなりすぎ、他の面で補正することが不可能になるからである。Ｙ方向の主光線▲２▼が当たる部分の曲率をＲＹとすると、
｜ＲＹ｜＜０．５ （１／ｍｍ） ・・・（Ｂ−１）
なる条件を満足することが重要である。この偏心して配置された反射面の曲率が、上限の０．５を越えない場合には、対称面を１面しか持たない面で反射面を構成することによって、収差発生の少ない光学系を構成することが可能となる。この上限０．５を越えている反射面では、偏心による各種収差の発生が極めて大きくなり、他の面で補正することが難しくなる。
【００４３】
さらに好ましくは、
｜ＲＹ｜＜０．１ （１／ｍｍ） ・・・（Ｂ−２）
なる条件を満足するときに、対称面を１面しか持たない面で反射面を構成することが、偏心による収差を発生させないために重要となる。
【００４４】
さらに好ましくは、
｜ＲＹ｜＜０．０５（１／ｍｍ） ・・・（Ｂ−３）
なる条件を満足するときに、対称面を１面しか持たない面で反射面を構成することが、偏心による収差を発生させないために重要となる。
【００４５】
次に、反射面において、Ｘ軸方向の１回微分の値ＤＸが、瞳中心を通り、像面中心に達する主光線▲２▼が当たる位置の傾きＤＸ_axisと曲率ＲＸに対して、ＤＸ_max1＝ＭＡＸ（（ＤＸ−ＤＸ_axis）／ＲＸ）とするとき、以下の条件を満足することが重要となる。
【００４６】
｜ＤＸ_max1｜＜１００．０ （ｍｍ） ・・・（１−１）
この条件は、反射面のＸ方向の傾きを表し、上記条件式の上限の１００．０を越えると、各像高の主光線に対し反射面の傾きが大きくなりすぎ、偏心による収差発生が大きくなりすぎ、他の面で補正することが不可能になる。
【００４７】
さらに好ましくは、
｜ＤＸ_max1｜＜１０．０ （ｍｍ） ・・・（１−２）
なる条件式を満足することが重要である。
【００４８】
さらに好ましくは、
｜ＤＸ_max1｜＜６．０ （ｍｍ） ・・・（１−３）
なる条件式を満足することが重要である。
【００４９】
上記条件式（１−１）〜（１−３）は共に、広い画角において良好な観察像を得るために必要なものである。特に条件式（１−２）は１０度以上の半画角において重要となり、条件式（１−３）は１５度以上の半画角において満足することが好ましい。
【００５０】
次に、反射面において、面の偏心方向の傾き、つまり、Ｙ軸方向の１回微分の値ＤＹが、瞳中心を通り、像面中心に達する主光線▲２▼が当たる位置の傾きＤＹ_axisと曲率ＲＹに対して、ＤＹ_max2＝ＭＡＸ（（ＤＹ−ＤＹ_axis）／ＲＹ）とするとき、以下の条件を満足することが重要となる。
【００５１】
｜ＤＹ_max2｜＜１００．０ （ｍｍ） ・・・（２−１）
この条件は、反射面のＹ方向の傾きを表し、上記条件式の上限の１００．０を越えると、各像高の主光線に対し反射面の傾きが大きくなりすぎ、偏心による収差発生が大きくなりすぎ、他の面で補正することが不可能になる。
【００５２】
さらに好ましくは、
｜ＤＹ_max2｜＜１０．０ （ｍｍ） ・・・（２−２）
なる条件式を満足することが重要である。
【００５３】
さらに好ましくは、
｜ＤＹ_max2｜＜６．０ （ｍｍ） ・・・（２−３）
なる条件式を満足することが重要である。
【００５４】
上記条件式（２−１）〜（２−３）は共に、広い画角において良好な観察像を得るために必要なものである。特に条件式（２−２）は１０度以上の半画角において重要となり、条件式（２−３）は１５度以上の半画角において満足することが好ましい。
【００５５】
次に、Ｘ方向の最大画角の主光線▲４▼と▲６▼が偏心して配置された反射面に当たる位置でのＸ方向の傾きと、Ｘ方向画角ゼロの主光線▲１▼と▲３▼がその反射面に当たる位置でのＸ方向の傾きとの差それぞれを（ＤＸ４−ＤＸ１）、（ＤＸ６−ＤＸ３）とし、その差をＤＸ₃ ＝（ＤＸ４−ＤＸ１）−（ＤＸ６−ＤＸ３）とするとき、
｜ＤＸ₃ ｜＜０．４ ・・・（３−１）
なる条件を満足することが好ましい。
【００５６】
上記条件式（３−１）は、Ｘ方向の周辺画像のＸ方向の歪みを表している。この条件式の上限の０．４を越えると、観察像の左右端がＸ軸方向に変化し、台形の像歪みが大きくなり、他の面で補正することが不可能となり、歪んだ観察像になってしまう。
【００５７】
さらに好ましくは、
｜ＤＸ₃ ｜＜０．２ ・・・（３−２）
なる条件式を満足することが好ましい。これは、特に１０度以上の半画角を確保しようとした場合に、像歪みの少ない観察像を観察する場合に重要となる。
【００５８】
さらに好ましくは、
｜ＤＸ₃ ｜＜０．１ ・・・（３−３）
なる条件式を満足することが好ましい。これは、特に１５度以上の半画角を確保しようとした場合に、像歪みの少ない観察像を観察する場合に重要となる。
【００５９】
さらに好ましくは、
｜ＤＸ₃ ｜＜０．０５ ・・・（３−４）
これは、特に２０度以上の半画角を確保しようとした場合に、像歪みのほとんどない観察像を観察する場合に重要となる。
【００６０】
次に、Ｘ方向の最大画角の主光線▲４▼と▲６▼が偏心して配置された反射面に当たる位置でのＹ方向の傾きと、Ｘ方向画角ゼロの主光線▲１▼と▲３▼がその反射面に当たる位置でのＹ方向の傾きとの差それぞれを（ＤＹ４−ＤＹ１）、（ＤＹ６−ＤＹ３）とし、その差をＤＹ₄ ＝（ＤＹ４−ＤＹ１）−（ＤＹ６−ＤＹ３）とするとき、
｜ＤＹ₄ ｜＜０．４ ・・・（４−１）
なる条件を満足することが好ましい。
【００６１】
上記条件式（４−１）は、Ｘ方向の周辺画像のＹ方向の歪みを表している。この条件式の上限の０．４を越えると、観察像の左右端がＹ軸方向に変化し、周辺画像が弓なりになる像歪みが大きくなり、他の面で補正することが不可能になり、歪んだ観察像になってしまう。
【００６２】
さらに好ましくは、
｜ＤＹ₄ ｜＜０．２ ・・・（４−２）
なる条件式を満足することが好ましい。これは、特に１０度以上の半画角を確保しようとした場合に、像歪みの少ない観察像を観察する場合に重要となる。
【００６３】
さらに好ましくは、
｜ＤＹ₄ ｜＜０．１ ・・・（４−３）
なる条件式を満足することが好ましい。これは、特に１５度以上の半画角を確保しようとした場合に、像歪みの少ない観察像を観察する場合に重要となる。
【００６４】
さらに好ましくは、
｜ＤＹ₄ ｜＜０．０５ ・・・（４−４）
これは、特に２０度以上の半画角を確保しようとした場合に、像歪みのほとんどない観察像を観察する場合に重要となる。
【００６５】
次に、画面中心のＸ方向の１回微分値ＤＸ_axisとＸ軸上のＸ方向最大画角の右端におけるＸ方向の１回微分値ＤＸ５の差（ＤＸ５−ＤＸ_axis）をＤＸ_max5とするとき、反射面のＤＸ_max5の値が、
｜ＤＸ_max5｜＜０．５ ・・・（５−１）
なる条件式を満足することが重要である。
【００６６】
これは、画面中心を通る左右方向の直線、例えば水平線等が弓なりに湾曲して観察される像歪みとなる。この数値が上限の０．５を越えると、弓なりの像歪みが下に凸に大きく発生し、他の面で補正することが不可能となってしまう。
【００６７】
さらに好ましくは、
｜ＤＸ_max5｜＜０．１ ・・・（５−２）
なる条件式を満足することが重要であり、特に１０度を越える半画角の場合には、この条件を満足することが重要である。なお、上限については、上記条件式（５−１）と同じである。
【００６８】
さらに好ましくは、
｜ＤＸ_max5｜＜０．０５ ・・・（５−３）
なる条件式を満足することが重要であり、特に１５度を越える半画角の場合には、この条件を満足することが重要である。なお、上限については、上記条件式（５−１）と同じである。
【００６９】
さらに好ましくは、
｜ＤＸ_max5｜＜０．０２ ・・・（５−４）
なる条件式を満足することが重要であり、特に２０度を越える半画角の場合にはこの条件を満足することが重要である。なお、上限については上記条件式（５−１）と同じである。
【００７０】
次に、画面中心のＹ方向の１回微分値ＤＹ_axisとＸ軸上のＸ方向最大画角の右端におけるＹ方向の１回微分値ＤＹ５の差（ＤＹ５−ＤＹ_axis）をＤＹ_max6とするとき、反射面のＤＹ_max6の値が、
｜ＤＹ_max6｜＜０．５ ・・・（６−１）
なる条件式を満足することが重要である。これは、画面中心を通る左右方向の直線、例えば水平線等が弓なり湾曲して観察される像歪みとなる。この数値が上限の０．５を越えると、弓なりの像歪みが下に凸に大きく発生し、他の面で補正することが不可能となってしまう。
【００７１】
さらに好ましくは、
｜ＤＹ_max6｜＜０．１ ・・・（６−２）
なる条件式を満足することが重要であり、特に１０度を越える半画角の場合には、この条件を満足することが重要である。なお、上限については、上記条件式（６−１）と同じである。
【００７２】
さらに好ましくは、
｜ＤＹ_max6｜＜０．０５ ・・・（６−３）
なる条件式を満足することが重要であり、特に１５度を越える半画角の場合には、この条件を満足することが重要である。なお、上限については、上記条件式（６−１）と同じである。
【００７３】
さらに好ましくは、
｜ＤＹ_max6｜＜０．０２ ・・・（６−４）
なる条件式を満足することが重要であり、特に２０度を越える半画角の場合にはこの条件を満足することが重要である。なお、上限については上記条件式（６−１）と同じである。
【００７４】
次に、ＴＦＣ面のＸ方向の部分的曲率の有効域内での最大値と最小値の差をＤＤＸ_max7とするとき、以下の条件式を満たすことが重要である。
【００７５】
ＤＤＸ_max7＜０．５ （１／ｍｍ） ・・・（７−１）
この条件は、Ｘ軸方向に曲率が変化し難いことが像面湾曲、特にＸ軸方向の像面湾曲を少なくするために重要であることを示す。偏心して配置された反射面のＸ方向の曲率の差が上限の０．５を越えると、像面湾曲が大きくなり、平坦な像面を得ることが難しくなる。
【００７６】
さらに好ましくは、
ＤＤＸ_max7＜０．１ （１／ｍｍ） ・・・（７−２）
なる条件を満足すると、周辺まで良好に補正された像を得ることが可能となる。
【００７７】
さらに好ましくは、
ＤＤＸ_max7＜０．０５（１／ｍｍ） ・・・（７−３）
なる条件を満足すると、周辺までさらに良好に補正された像を得ることが可能となる。
【００７８】
次に、ＴＦＣ面のＹ方向の部分的曲率の有効域内での最大値と最小値の差をＤＤＹ_max8とするとき、以下の条件式を満たすことが重要である。
【００７９】
ＤＤＹ_max8＜０．５ （１／ｍｍ） ・・・（８−１）
この条件は、Ｙ軸方向に曲率が変化し難いことが像面湾曲、特にＹ軸方向の像面湾曲を少なくするために重要であることを示す。偏心して配置された反射面のＹ方向の曲率の差が上限の０．５を越えると、像面湾曲が大きくなり、平坦な像面を得ることが難しくなる。
【００８０】
さらに好ましくは、
ＤＤＹ_max8＜０．１ （１／ｍｍ） ・・・（８−２）
なる条件を満足すると、周辺まで良好に補正された像を得ることが可能となる。
【００８１】
さらに好ましくは、
ＤＤＹ_max8＜０．０５（１／ｍｍ） ・・・（８−３）
なる条件をともに満足すると、周辺までさらに良好に補正された像を得ることが可能となる。
【００８２】
次に、有効面内の各光線が面に当たる位置での｜Ｘ方向の曲率／Ｙ方向の曲率｜＝｜ＤＤＸｎ｜／｜ＤＤＹｎ｜（ｎは主光線の番号▲１▼〜▲６▼に対応して１〜６）をＤＤ_xy9 とするとき、反射面の有効領域全てでＤＤ_xy9 が、
０．０１＜ＤＤ_xy9 ＜４０ ・・・（９−１）
なる条件式を満足することが重要である。
【００８３】
これは、有効領域のＸ方向の結像位置とＹ方向の結像位置の比に相当し、非点収差が良好に補正されているための条件である。下限の０．０１を越えると、Ｘ方向の光線がＹ方向の光線に対して光学系側により近く結像してしまい、非点収差の発生が大きくなる。逆に、上限の４０を越えると、Ｘ方向の光線がＹ方向の光線に対して光学系より遠くに結像してしまい、非点収差が逆に大きく発生してしまい、共に他の面で補正することが不可能となってしまう。ただし、トーリック面等のＹ軸とＸ軸の両方に対して対称性を持つ面の場合は本条件内に入るが、コマ収差と像歪みの発生が大きくなってしまう。
【００８４】
さらに好ましくは、
０．１＜ＤＤ_xy9 ＜２０ ・・・（９−２）
なる条件式を満足することが重要であり、特に２０度を越える半画角の場合には、この条件を満足することが重要である。
【００８５】
さらに好ましくは、
０．３＜ＤＤ_xy9 ＜１０ ・・・（９−３）
なる条件式を満足することが重要であり、特に２５度を越える半画角の場合には、この条件を満足することが重要である。
【００８６】
さらに好ましくは、
０．５＜ＤＤ_xy9 ＜６ ・・・（９−４）
なる条件式を満足することが重要であり、特に３０度を越える半画角の場合には、この条件を満足することが重要である。
【００８７】
【発明の実施の形態】
次に、本発明の像読み取り装置及びそれを用いた情報再生システムの実施例について説明する。まず、本発明において用いる読み取り光学系の実施例として、実施例１〜６について説明する。実施例１〜６の断面図をそれぞれ図１〜図６に示す。後記する数値データにおいて、面番号は、実施例１、２については、結像面から物体面に至る逆光線追跡の順で、実施例３〜６については、物体面から結像面に至る順追跡の順での光学系を構成する面の番号で示してある。したがって、実施例１、２については、実際には、物体面Ｏが像面に、像面Ｉが物体面になる。また、面間隔は前の面と次の面の間の軸上主光線に沿って測った長さを（ただし、反射後には符号が反転する。）、偏心は入射軸上主光線に対する面の定義軸のティルト角（°）（反時計周りを正にとる。）を示す。屈折率は実施例１〜３は波長６６０ｎｍに対する値を、実施例４〜６はｄ線に対する値を示す。なお、長さの単位はｍｍである。
【００８８】
また、後記する数値データにおいて、自由曲面の面の形状は、前記の式（ａ）により定義され、そのＹ軸とＺ軸は図の紙面内にあり、このＹ−Ｚ面が対称面を１面しか持たない自由曲面の対称面となる。なお、データの記載されていない次数に関する項は０である。
【００８９】
さて、実施例１〜６は何れも、五角プリズム状の屈折率が１より大きい媒質からなるプリズム体を形成する４つの光学面の中の、２つの反射面を含む２ないし３つの光学面を対称面を１面しか持たない自由曲面で構成し、残りの２面ないし１面を球面で構成することによって、このプリズム体に結像性能を持たせたものである。
【００９０】
すなわち、実施例１、２は、それぞれ図１、図２に断面を示すように、第１面１、第２面２、第３面３、第４面４からなる五角プリズム状のプリズム体５であり、第１面１と第４面４が屈折面、第２面２と第３面３が反射面であり、第１面１は球面、第２面２、第３面３、第４面４は自由曲面からなる。カバーガラス６の裏面に設けられた物体面Ｏからの光線は、カバーガラス６を経てプリズム体５の第１面１から入射し、第２面２と第３面３で順に反射され、反射光は第１面１から第２面２に到る光線と交差して第４面４からプリズム体５の外へ射出し、像面Ｉに到る（実際には、これとは逆の光路を辿り、像面Ｉが物体面に、物体面Ｏが像面になる。）。これらの実施例は、水平画角（紙面に垂直方向の画角）５０度、垂直画角（紙面内の画角）３７度、共軸系に換算しての焦点距離６ｍｍ、瞳径１．７８５７ｍｍの結像光学系である。
【００９１】
実施例３は、図３に断面を示すように、第１面１、第２面２、第３面３、第４面４からなる五角プリズム状のプリズム体５であり、第１面１と第４面４が屈折面、第２面２と第３面３が反射面であり、第１面１、第４面は球面、第２面２、第３面３は自由曲面からなる。物体面Ｏからの光線は、プリズム体５の第１面１から入射し、第２面２と第３面３で順に反射され、反射光は第１面１から第２面２に到る光線と交差して第４面４からプリズム体５の外へ射出し、カバーガラス６を経てその裏面に設けられた像面Ｉに到る。この実施例は、水平画角（紙面に垂直方向の画角）５０度、垂直画角（紙面内の画角）３７度、共軸系に換算しての焦点距離６ｍｍ、瞳径１．７８５７ｍｍの結像光学系である。
【００９２】
実施例４は、図４に断面を示すように、第１面１、第２面２、第３面３、第４面４からなる五角プリズム状のプリズム体５であり、第１面１と第４面４が屈折面、第２面２と第３面３が反射面であり、第１面１は球面、第２面２、第３面３、第４面４は自由曲面からなる。この光学系は投影光学系であり、無限遠からの物体光は、プリズム体５の第１面１から入射し、第２面２と第３面３で順に反射され、反射光は第１面１から第２面２に到る光線と交差して第４面４からプリズム体５の外へ射出し、カバーガラス６を経てその裏面に設けられた像面Ｉに到る。この実施例は、物体高Ｘ軸方向（紙面に垂直方向）１．４４７ｍｍ、Ｙ軸方向（紙面内の方向）１．０９１５ｍｍ、物体側ＮＡ（開口数）０．０３５７の投影光学である。
【００９３】
実施例５は、図５に断面を示すように、第１面１、第２面２、第３面３、第４面４からなる五角プリズム状のプリズム体５であり、第１面１と第４面４が屈折面、第２面２と第３面３が反射面であり、第１面１、第２面２、第３面３は自由曲面、第４面４は球面からなる。この光学系は投影光学系であり、無限遠からの物体光は、プリズム体５の第１面１から入射し、第２面２と第３面３で順に反射され、反射光は第１面１から第２面２に到る光線と交差して第４面４からプリズム体５の外へ射出し、カバーガラス６を経てその裏面に設けられた像面Ｉに到る。この実施例は、物体高Ｘ軸方向（紙面に垂直方向）１．４４７ｍｍ、Ｙ軸方向（紙面内の方向）１．０９１５ｍｍ、物体側ＮＡ（開口数）０．０３５７の投影光学である。
【００９４】
実施例６は、図６に断面を示すように、第１面１、第２面２、第３面３、第４面４からなる五角プリズム状のプリズム体５であり、第１面１と第４面４が屈折面、第２面２と第３面３が反射面であり、第１面１は球面、第２面２、第３面３、第４面４は自由曲面球面からなる。この光学系は投影光学系であり、無限遠からの物体光は、別体の絞りを経て、プリズム体５の第１面１から入射し、第２面２と第３面３で順に反射され、反射光は第１面１から第２面２に到る光線と交差して第４面４からプリズム体５の外へ射出し、カバーガラス６を経てその裏面に設けられた像面Ｉに到る。この実施例は、物体高Ｘ軸方向（紙面に垂直方向）４．０２ｍｍ、Ｙ軸方向（紙面内の方向）３．０３ｍｍ、物体側ＮＡ（開口数）０．０１２９の投影光学である。
【００９５】
以下に、上記実施例１〜６の構成パラメータを示す。

【００９６】

【００９７】

【００９８】

【００９９】

【０１００】

【０１０１】
次に、上記実施例２の横収差図を図７、図８に示す。これらの横収差図において、括弧内に示された数字は（水平画角（紙面に垂直方向の画角），垂直画角（紙面内の画角））を表し、その画角における横収差を示す。実施例６の同様の横収差図を図９、図１０に示す。
【０１０２】
以下に、上記の各実施例における前記条件式（Ａ−１）、（Ｂ−１）、（１−１）〜（９−１）に関するパラメータの値を示す（条件式（９−１）以外につては、上段が第１の反射面２、下段が第２の反射面３に関する値を示し、条件式（９−１）については、上段がそれぞれの反射面の最小値、下段が最大値を示す。）。
【０１０３】

。
【０１０４】
以上の実施例では、前記定義式（ａ）の自由曲面で構成したが、あらゆる定義の曲面が使えることはいうまでもない。しかし、どのような定義式を用いようとも、本発明に示されている条件式を単独で、あるいは、組み合わせて満足しても、また、いくつかを満足することでも、収差の非常に良く補正された結像光学系を得られることはいうまでもない。なお、偏心を無視して面を定義する座標系の中心で規定される面の曲率、面の焦点距離等の従来の無偏心系で使われる条件式は、本発明のように各面が大きく偏心して配置されている場合には、なんら意味を持たない。
【０１０５】
以上、本発明の特徴となる光学系の詳細を説明した。以下に、これらの光学系を像読み取り装置及びそれを用いた情報再生システムに組み込んだ例について説明する。
【０１０６】
図１１は、実施例１の光学系５を本発明に基づく像読み取り装置４０に適用したものの断面図である。図中、５は実施例１によるプリズム体、１０は撮像素子、１１が外装、１２は基板、２０は情報記録媒体（被写体）、４０はペン型情報再生装置であり、図１１に示すように、１つの光学部材（プリズム体）５に結像作用及び光路を曲げる作用を同時に持たせ、撮像素子１０をその他の電気部品と共に同一の基板１２に実装することができる。
【０１０７】
このように、本発明に基づく読み取り光学系を用いることにより、実装効率が向上する。また、必要な基板の数を減らせるので（図１１の場合は、１個）、コスト低減を図ることができる。また、その他の作用として、図示のように、情報記録媒体２０に対してペン型情報再生装置４０を所定の角度傾けた構成にすることもできる。ペン型情報再生装置４０を操作するときは、図１２に示すように、情報記録媒体２０の法線に対してペン型情報再生装置４０を所定の角度θ傾けて使用する構成の方が操作性が良い。
【０１０８】
このように、本発明の光学系５の場合、光路を折り曲げる角度に対する自由度が高く、実装上の効果に加え、操作上の効果も得られる。なお、実際の情報再生装置４０には、図１１に示した部材以外のものも配置されるが、説明を簡略化するために、主要部分のみを図示した。このような像読み取り装置を用いた情報再生システムの詳細は後に説明する。
【０１０９】
図１１とは別の実施の形態として、情報記録媒体２０を照明する照明光学系の光路と撮影光学系の光路とを撮影光学部材５の中に重複して配置した本発明の具体例を図１３〜図１５に示す。これらの図に示すように、撮影光学系を構成する光学部材５の撮影光路の有効範囲内又は有効範囲外の部分に光源４４Ａからの照明光を導く入射面を設け、撮影光路と重複した照明光路を形成する。
【０１１０】
図１３の場合は、情報記録媒体２０側から順に第２番目の面（図１の第３面３）の中の撮影光路の有効範囲内の反射面をハーフミラー１４とし、光源４４Ａからの照明光を導く補助レンズ、プリズム等の光学部材１３を配置し、その近傍に光源４４Ａを配置する。この補助レンズ、プリズム等の光学部材１３の光源４４Ａ側の面から入射した光線は、ハーフミラー１４から撮影光学系を構成する光学部材５に入射した後、撮影光路と重複した光路を通り情報記録媒体２０を照明する。なお、補助レンズ、プリズム等の光学部材１３の光源４４Ａ側の面は凸面等でレンズ作用を持たせてあり、均一な照明のために有利となっている。このように光路を重複することで、装置の小型化が可能となる。また、情報記録媒体２０を略正面から照明できるので、照明むらが発生し難い。
【０１１１】
また、図１４の場合は、情報記録媒体２０側から順に第３番目の面（図１の第２面２）の中の撮影光路の有効範囲内の反射面をハーフミラー１４としたこと以外は、図１３と同様である。
【０１１２】
また、図１５の場合は、情報記録媒体２０側から順に第２番目の面（図１の第３面３）の中の撮影光路の有効範囲以外の部分３’を用いて照明光路を構成する。有効範囲以外の部分３’を用いるため、ハーフミラーを設ける必要はなく、照明光路の入射面を撮影光学系を構成する光学部材５と一体で構成することができ、コストの点で有利である。
【０１１３】
以上のように、各実施例で示した光学系を像読み取り装置や情報再生システムに備えることで、情報再生システム特有の問題点を解決することができる。無論、適用する情報再生装置の形態はペン型に限らず他の形態のものにも適用可能である。
【０１１４】
以下に、上記のような像読み取り装置を用いた情報再生システムについての詳細な説明を行う。より詳細な説明は、特開平６−２３１４６６号公報にあるので、ここでは具体的な構成と作用の概略のみ示すこととする。
【０１１５】
以下、情報再生システムにかかる本発明の実施例を説明するが、ここでは、マルチメディア情報の中、音声、音楽等のオーディオ情報に関連する実施例について説明する。
音声や音楽等のオーディオ情報を光学的に読み取り可能なディジタル信号として紙に記録するためのオーディオ情報記録装置については、特開平６−２３１４６６号の図に示されているので、説明は省略する。
【０１１６】
この装置により、例えば図１６（Ａ）に示すような書式で紙３０に記録される。すなわち、画像３２や文字３４と一緒にディジタル信号化された音のデータが記録データ３６として印刷される。ここで、記録データ３６は複数のブロック３８から構成されており、各ブロック３８は、マーカ３８Ａ、誤り訂正用符号３８Ｂ、オーディオデータ３８Ｃ、ｘアドレスデータ３８Ｄ、ｙアドレスデータ３８Ｅ及び誤り判定符号３８Ｆから構成されている。
【０１１７】
なお、マーカ３８Ａは同期信号としても機能するもので、ＤＡＴのように通常は記録変調で出てこないようなパターンを用いている。また、誤り訂正用符号３８Ｂは、オーディオデータ３８Ｃの誤り訂正に用いられているものである。オーディオデータ３８Ｃは、マイクロフォン又はオーディオ信号に対応するものである。ｘアドレスデータ３８Ｄ及びｙアドレスデータ３８Ｅは当該ブロック３８の位置を表すデータであり、誤り判定符号３８Ｆは、これらｘアドレス、ｙアドレスの誤り判定に用いられる。
【０１１８】
このようなフォーマットの記録データ３６は、「１」、「０」のデータを、例えばバーコードと同様に、「１」を黒ドット有り、「０」を黒ドットなしというようにしてプリンタシステム又は印刷用製版システムによって印刷記録される。以下、このような記録データをドットコードと称する。
【０１１９】
図１６（Ｂ）は、図１６（Ａ）に示したような紙３０に記録された音のデータをペン型の情報再生装置（情報再生システム）４０で読み出している場面を示している。図１１、図１３〜図１５のようなペン型情報再生装置４０でドットコード３６の上をなぞることにより、ドットコード３６を検出し、音に変換してイヤホン等の音声出力器４２で聞くことができる。
【０１２０】
図１７は本発明の１つの実施例における情報再生装置４０のブロック構成図である。本実施例の情報再生装置４０は、ヘッドホンやイヤホン等の音声出力器４２以外の部分を携帯可能なペン型の１つの筐体（図示せず）内に収納するものとする。もちろん、筐体内にスピーカを内蔵するものとしてもよい。
【０１２１】
検出部４４は、光源４４Ａにて被写体である紙面上のドットコード３６を照明し、反射光を読み取り光学系４４Ｂ（プリズム体５）及び空間フィルタ４４Ｃを介して、半導体エリアセンサ等である撮像部４４Ｄ（撮像素子１０）で画像として検出し、プリアンプ４４Ｅにて増幅して出力する。
【０１２２】
ここで、エリアセンサ４４Ｄの画素ピッチは、標本化定理により撮像面上のドットコード３６のドットピッチ以下に設定されている。さらに、撮像面上に設置された空間フィルタ４４Ｃもこの定理に基づいて撮像面上のモアレ現像（エリアジング）を防ぐために挿入されている。
【０１２３】
上記のようにして検出部４４により検出された画像信号は、まず、Ａ／Ｄ変換器４６Ａでディジタル信号に変換され、フレームメモリ４６Ｂ内に蓄えられる。このフレームメモリ４６Ｂは８ビットの階調を持っている。
【０１２４】
また、マーカ検出回路４６Ｃは、フレームメモリ４６Ｂに記憶された画像信号を特定の方向にスキャンしてマーカ３８Ａを検出する。θ検出回路４６Ｄはマーカ検出回路４６Ｃで検出した各マーカ３８Ａが撮像面上のどのアドレス値に対応しているのかを検出して、そのアドレス値からドットコードの配列方向に対する撮像面の傾きθを演算する。
【０１２５】
一方、レンズ収差情報メモリ４６Ｅには、読み取り光学系の歪み補正を行うための上記検出部４４の結像系４４Ｂに用いられている読み取り光学系の予め測定された収差情報を記録してある。むろん、本発明の光学系では収差が補正されているので、この処理も簡易にすることができる。アドレス制御回路４６Ｆは、次にフレームメモリ４６Ｂ内に蓄えられたデータを読み出す際には、上記θ検出回路４６Ｄで演算された傾きθの値とレンズ収差情報メモリ４６Ｅに記憶されているレンズ収差情報とに従って読み出しアドレスをフレームメモリ４６Ｂに与え、補間回路４６Ｇにてデータ補間を行いながらデータの配列方向への走査変換を行う。
【０１２６】
走査変換を受けてフレームメモリ４６Ｂから読み出されたドットコード３６は、次にラッチ４８Ａ及びコンパレータ４８Ｂで構成された２値化回路４８にて２値化される。この２値化を行う際の閾値は、閾値判定回路５０にて画面毎若しくは画面内のブロック毎のヒストグラムの値等を利用して決定される。すなわち、ドットコード３６上の染みや紙３０の歪み、内蔵クロックの精度等に応じて閾値を決定する。この閾値判定回路５０としては、例えば本出願人による特願平４−１３１０５１号に開示されたニューラルネットワークを利用した回路を使用するのが好ましい。
【０１２７】
また、これと平行してフレームメモリ４６Ｂから読み出されたドットコード３６は、ＰＬＬ回路５２に入力され、再生データと同期したクロックパルスＣＫを発生する。このクロックパルスＣＫは、走査変換後の２値化や復調、及び、後述するデータ列調整部５６内の誤り判定回路５６Ａ、ｘ，ｙアドレス検出回路５６Ｂやメモリ部５６Ｃ等の基準クロックとして使用される。
【０１２８】
２値化されたデータは、復調回路５４にて復調され、データ列調整部５６内の誤り判定回路５６Ａと、ｘ，ｙアドレス検出回路５６Ｂに入力される。誤り判定回路５６Ａは、ブロック３８内の誤り判定符号３８Ｆを用いて、ｘ、ｙアドレスデータ３８Ｄ、３８Ｅに誤りがないかどうかの判定を行う。誤りがない場合は、ｘ，ｙアドレス検出回路５６Ａで検出したアドレスに従って、オーディオデータ３８Ｃはオーディオデータ列調整用のメモリ部５６Ｃには記録されない。
【０１２９】
このデータ列調整部５６の目的は、上記走査変換及びレンズ歪み補正部４６における走査変換の精度（基準クロックの精度及び撮像素子のＳ／Ｎに左右される。）や紙の歪み等により、データ配列方向と走査変換後の走査方向に生じた僅かなずれを補正することにある。
そして、それぞれのブロック３８内のｘ、ｙアドレス３８Ｄ、３８Ｅに従ってデータ列調整用のメモリ部５６Ｃに格納される。
【０１３０】
次に、検出部４４を手動で走査することにより、紙３０の上の音声ドットコード３６をもれなくデータ列調整用のメモリ部５６Ｃに格納することができる。
【０１３１】
このようなデータ列調整部５６にてデータ列が調整された音声ドットコードは、次に、上記ＰＬＬ回路５２とは別の基準クロック発生回路５３により発生した基準クロックＣＫ’に従い、データ列調整用にメモリ部５６Ｃから読み出される。そして、このときに、デ・インタリーブ回路５８によりデ・インタリーブがかけられ、正式なデータ列に変換される。次に、ブロック３８内の誤り訂正用符号３８Ｂを用いた誤り訂正が誤り訂正回路６０にて行われる。そして、復号回路６２で圧縮されたデータの復号が行われ、さらに、データ補間回路６４にて誤り訂正不能なオーディオデータの補間が行われる。その後、Ｄ／Ａ変換回路６６にてアナログのオーディオ信号に変換され、増幅器６８にて増幅され、音声出力器（イヤホン、ヘッドホン、スピーカ等）４２にて音に変換される。
【０１３２】
以上のようにして、音声や音楽等のオーディオ情報を紙に記録できるようにし、また、再生装置を小型の携帯型の装置としたことにより、プリントアウトしたものやそれをファクシミリ伝送したもの、あるいは、印刷製版により本の形式で印刷されたものを何処でも、また、何回でも聞くことができるようになる。
【０１３３】
なお、上記のデータ列調整部５６内のデータ列調整用メモリ部５６Ｃは、半導体メモリに限らず、フロッピーディスク、光ディスク等の他の記録媒体を利用することが可能である。
【０１３４】
上記のようにオーディオ情報を記録したものの応用例としては、種々のものが考えられる。例えば、一般用として、語学教材、楽譜、通信教育等の各種のテキスト、商品仕様、修理等のマニュアル、外国語等の辞書、百科事典、絵本等の書籍、商品カタログ、旅行案内、ダイレクトメールや案内状、新聞、雑誌、チラシ、アルバム、祝電、葉書等が考えられる。また、業務用としては、ＦＡＸ（ボイス及びファックス）業務指示書、議事録、電子黒板、ＯＨＰ、身分証明書（声紋）、名刺、電話用メモ、付箋紙、上質紙をロール状にしたサプライ商品（消耗品）等といったものが考えられる。
【０１３５】
ここでは、記録された情報を、音声、音楽等のオーディオ情報を例にあげて説明したが、本発明はオーディオ情報に限らず、特開平６−２３１４６６号に示されるように、カメラ、ビデオ等から得られる映像情報及びパーソナルコンピュータ、ワードプロセッサ等から得られるディジタルコードデータ等を含めたいわゆるマルチメディア情報を取り扱う装置であってもかまわない。
【０１３６】
以上の本発明の像読み取り装置及びそれを用いた情報再生システムは例えば次のように構成することができる。
〔１〕 オーディオ情報、映像情報、ディジタルコードデータの少なくとも１つを含むマルチメディア情報が光学的に読み取り可能なドットコードで記録されている部分を備えた記録媒体から、前記ドットコードを光学的に読み取る像読み取り装置において、
少なくとも１面の反射作用を有する反射面を備え、前記反射面の面形状がその面内及び面外共に回転対称軸を有さない回転非対称な曲面からなる読み取り光学系と、
前記読み取り光学系により形成される物体面の結像面上に位置した撮像素子とを有することを特徴とする像読み取り装置。
【０１３７】
〔２〕 前記反射面の面形状が、対称面を１つのみ有する面対称自由曲面であることを特徴とする上記〔１〕記載の像読み取り装置。
【０１３８】
〔３〕 前記反射面が、前記撮像素子の結像位置中心に到達する前記読み取り光学系の軸上主光線が前記読み取り光学系に入射する線分の延長方向をＺ軸、前記軸上主光線が前記反射面で反射される際の折り返し線分を含む平面内で前記Ｚ軸に垂直な方向をＹ軸、前記Ｚ軸と前記Ｙ軸とに垂直な方向をＸ軸と定義したときに、以下の条件（Ａ−１）を満足することを特徴とする上記〔１〕又は〔２〕記載の像読み取り装置。
｜ＲＸ｜＜０．５ （１／ｍｍ） ・・・（Ａ−１）
ただし、ＲＸは前記反射面に前記軸上主光線が当たる部分のＸ方向の曲率である。
【０１３９】
〔４〕 前記反射面が、前記撮像素子の結像位置中心に到達する前記読み取り光学系の軸上主光線が前記読み取り光学系に入射する線分の延長方向をＺ軸、前記軸上主光線が前記反射面で反射される際の折り返し線分を含む平面内で前記Ｚ軸に垂直な方向をＹ軸、前記Ｚ軸と前記Ｙ軸とに垂直な方向をＸ軸と定義したときに、以下の条件（Ｂ−１）を満足することを特徴とする上記〔１〕又は〔２〕記載の像読み取り装置。
｜ＲＹ｜＜０．５ （１／ｍｍ） ・・・（Ｂ−１）
ただし、ＲＹは前記反射面に前記軸上主光線が当たる部分のＹ方向の曲率である。
【０１４０】
〔５〕 前記反射面が、前記撮像素子の結像位置中心に到達する前記読み取り光学系の軸上主光線が前記読み取り光学系に入射する線分の延長方向をＺ軸、前記軸上主光線が前記反射面で反射される際の折り返し線分を含む平面内で前記Ｚ軸に垂直な方向をＹ軸、前記Ｚ軸と前記Ｙ軸とに垂直な方向をＸ軸と定義したときに、以下の条件（Ａ−１）及び（Ｂ−１）を満足することを特徴とする上記〔１〕又は〔２〕記載の像読み取り装置。
｜ＲＸ｜＜０．５ （１／ｍｍ） ・・・（Ａ−１）
｜ＲＹ｜＜０．５ （１／ｍｍ） ・・・（Ｂ−１）
ただし、ＲＸ、ＲＹはそれぞれ前記反射面に前記軸上主光線が当たる部分のＸ方向、Ｙ方向の曲率である。
【０１４１】
〔６〕 前記反射面が以下の条件（Ａ−２）を満足することを特徴とする上記〔３〕又は〔５〕記載の像読み取り装置。
｜ＲＸ｜＜０．１ （１／ｍｍ） ・・・（Ａ−２）。
【０１４２】
〔７〕 前記反射面が以下の条件（Ａ−３）を満足することを特徴とする上記〔３〕又は〔５〕記載の像読み取り装置。
｜ＲＸ｜＜０．０５（１／ｍｍ） ・・・（Ａ−３）。
【０１４３】
〔８〕 前記反射面が以下の条件（Ｂ−２）を満足することを特徴とする上記〔４〕又は〔５〕記載の像読み取り装置。
｜ＲＹ｜＜０．１ （１／ｍｍ） ・・・（Ｂ−２）。
【０１４４】
〔９〕 前記反射面が以下の条件（Ｂ−３）を満足することを特徴とする上記〔４〕又は〔５〕記載の像読み取り装置。
｜ＲＹ｜＜０．０５（１／ｍｍ） ・・・（Ｂ−３）。
【０１４５】
〔１０〕 前記面対称自由曲面の対称面が、前記撮像素子の結像位置中心に到達する前記読み取り光学系の軸上主光線が前記読み取り光学系に入射する線分の延長方向をＺ軸、前記軸上主光線が前記反射面で反射される際の折り返し線分を含む平面内で前記Ｚ軸に垂直な方向をＹ軸、前記Ｚ軸と前記Ｙ軸とに垂直な方向をＸ軸と定義したときに、Ｙ−Ｚ面若しくはそれと平行な面上に存在することを特徴とする上記〔２〕から〔９〕の何れか１項記載の像読み取り装置。
【０１４６】
〔１１〕 前記反射面中で前記軸上主光線が反射される領域のＹ−Ｚ面内の反射屈折力、及び、Ｙ−Ｚ面に垂直な面内の反射屈折力の少なくとも一方が正であることを特徴とする上記〔３〕から〔１０〕の何れか１項記載の像読み取り装置。
【０１４７】
〔１２〕 前記反射面中で前記軸上主光線が反射される領域のＹ−Ｚ面内の反射屈折力、及び、Ｙ−Ｚ面に垂直な面内の反射屈折力が共に正であることを特徴とする上記〔３〕から〔１０〕の何れか１項記載の像読み取り装置。
【０１４８】
〔１３〕 前記撮像素子の結像位置中心に到達する前記読み取り光学系の軸上主光線が前記読み取り光学系に入射する線分の延長方向をＺ軸、前記軸上主光線が前記反射面で反射される際の折り返し線分を含む平面内で前記Ｚ軸に垂直な方向をＹ軸、前記Ｚ軸と前記Ｙ軸とに垂直な方向をＸ軸と定義したときに、前記反射面が次の条件を満足することを特徴とする上記〔１〕から〔１２〕の何れか１項記載の像読み取り装置。
｜ＤＸ_max1｜＜１００．０ （ｍｍ） ・・・（１−１）
ただし、ＤＸ_max1＝ＭＡＸ（（ＤＸ−ＤＸ_axis）／ＲＸ）であり、Ｙ軸方向を上下方向として、結像画面中心の軸上主光線、上側中心画角の主光線、右上画角の主光線、右中心画角の主光線、右下画角の主光線、下側中心画角の主光線が対象面と交差する領域を有効領域と定義し、これら６つの主光線が対象面と当たる部分の面の偏心方向と直交する方向に当たるＸ軸について面の形状を定義する式を１回微分した値をそれぞれＤＸ_axis、ＤＸ１、ＤＸ４、ＤＸ５、ＤＸ６、ＤＸ３とするとき、ＤＸはＤＸ１、ＤＸ４、ＤＸ５、ＤＸ６、ＤＸ３の値、ＲＸは前記反射面に前記軸上主光線が当たる部分のＸ方向の曲率とする。
【０１４９】
〔１４〕 前記撮像素子の結像位置中心に到達する前記読み取り光学系の軸上主光線が前記読み取り光学系に入射する線分の延長方向をＺ軸、前記軸上主光線が前記反射面で反射される際の折り返し線分を含む平面内で前記Ｚ軸に垂直な方向をＹ軸、前記Ｚ軸と前記Ｙ軸とに垂直な方向をＸ軸と定義したときに、前記反射面が次の条件を満足することを特徴とする上記〔１〕から〔１３〕の何れか１項記載の像読み取り装置。
｜ＤＹ_max2｜＜１００．０ （ｍｍ） ・・・（２−１）
ただし、ＤＹ_max2＝ＭＡＸ（（ＤＹ−ＤＹ_axis）／ＲＹ）であり、Ｙ軸方向を上下方向として、結像画面中心の軸上主光線、上側中心画角の主光線、右上画角の主光線、右中心画角の主光線、右下画角の主光線、下側中心画角の主光線が対象面と交差する領域を有効領域と定義し、これら６つの主光線が対象面と当たる部分の面の偏心方向に当たるＹ軸について面の形状を定義する式を１回微分した値をそれぞれＤＹ_axis、ＤＹ１、ＤＹ４、ＤＹ５、ＤＹ６、ＤＹ３とするとき、ＤＹはＤＹ１、ＤＹ４、ＤＹ５、ＤＹ６、ＤＹ３の値、ＲＹは前記反射面に前記軸上主光線が当たる部分のＹ方向の曲率とする。
【０１５０】
〔１５〕 前記撮像素子の結像位置中心に到達する前記読み取り光学系の軸上主光線が前記読み取り光学系に入射する線分の延長方向をＺ軸、前記軸上主光線が前記反射面で反射される際の折り返し線分を含む平面内で前記Ｚ軸に垂直な方向をＹ軸、前記Ｚ軸と前記Ｙ軸とに垂直な方向をＸ軸と定義したときに、前記反射面が次の条件を満足することを特徴とする上記〔１〕から〔１４〕の何れか１項記載の像読み取り装置。
｜ＤＸ₃ ｜＜０．４ ・・・（３−１）
ただし、ＤＸ₃ ＝（ＤＸ４−ＤＸ１）−（ＤＸ６−ＤＸ３）であり、Ｙ軸方向を上下方向として、結像画面中心の軸上主光線、上側中心画角の主光線、右上画角の主光線、右中心画角の主光線、右下画角の主光線、下側中心画角の主光線が対象面と交差する領域を有効領域と定義し、これら６つの主光線が対象面と当たる部分の面の偏心方向と直交する方向に当たるＸ軸について面の形状を定義する式を１回微分した値をそれぞれＤＸ_axis、ＤＸ１、ＤＸ４、ＤＸ５、ＤＸ６、ＤＸ３とする。
【０１５１】
〔１６〕 前記撮像素子の結像位置中心に到達する前記読み取り光学系の軸上主光線が前記読み取り光学系に入射する線分の延長方向をＺ軸、前記軸上主光線が前記反射面で反射される際の折り返し線分を含む平面内で前記Ｚ軸に垂直な方向をＹ軸、前記Ｚ軸と前記Ｙ軸とに垂直な方向をＸ軸と定義したときに、前記反射面が次の条件を満足することを特徴とする上記〔１〕から〔１５〕の何れか１項記載の像読み取り装置。
｜ＤＹ₄ ｜＜０．４ ・・・（４−１）
ただし、ＤＹ₄ ＝（ＤＹ４−ＤＹ１）−（ＤＹ６−ＤＹ３）であり、Ｙ軸方向を上下方向として、結像画面中心の軸上主光線、上側中心画角の主光線、右上画角の主光線、右中心画角の主光線、右下画角の主光線、下側中心画角の主光線が対象面と交差する領域を有効領域と定義し、これら６つの主光線が対象面と当たる部分の面の偏心方向に当たるＹ軸について面の形状を定義する式を１回微分した値をそれぞれＤＹ_axis、ＤＹ１、ＤＹ４、ＤＹ５、ＤＹ６、ＤＹ３とする。
【０１５２】
〔１７〕 前記撮像素子の結像位置中心に到達する前記読み取り光学系の軸上主光線が前記読み取り光学系に入射する線分の延長方向をＺ軸、前記軸上主光線が前記反射面で反射される際の折り返し線分を含む平面内で前記Ｚ軸に垂直な方向をＹ軸、前記Ｚ軸と前記Ｙ軸とに垂直な方向をＸ軸と定義したときに、前記反射面が次の条件を満足することを特徴とする上記〔１〕から〔１６〕の何れか１項記載の像読み取り装置。
｜ＤＸ_max5｜＜０．５ ・・・（５−１）
ただし、ＤＸ_max5＝（ＤＸ５−ＤＸ_axis）であり、Ｙ軸方向を上下方向として、結像画面中心の軸上主光線、上側中心画角の主光線、右上画角の主光線、右中心画角の主光線、右下画角の主光線、下側中心画角の主光線が対象面と交差する領域を有効領域と定義し、これら６つの主光線が対象面と当たる部分の面の偏心方向と直交する方向に当たるＸ軸について面の形状を定義する式を１回微分した値をそれぞれＤＸ_axis、ＤＸ１、ＤＸ４、ＤＸ５、ＤＸ６、ＤＸ３とする。
【０１５３】
〔１８〕 前記撮像素子の結像位置中心に到達する前記読み取り光学系の軸上主光線が前記読み取り光学系に入射する線分の延長方向をＺ軸、前記軸上主光線が前記反射面で反射される際の折り返し線分を含む平面内で前記Ｚ軸に垂直な方向をＹ軸、前記Ｚ軸と前記Ｙ軸とに垂直な方向をＸ軸と定義したときに、前記反射面が次の条件を満足することを特徴とする上記〔１〕から〔１７〕の何れか１項記載の像読み取り装置。
｜ＤＹ_max6｜＜０．５ ・・・（６−１）
ただし、ＤＹ_max6＝（ＤＹ５−ＤＹ_axis）であり、Ｙ軸方向を上下方向として、結像画面中心の軸上主光線、上側中心画角の主光線、右上画角の主光線、右中心画角の主光線、右下画角の主光線、下側中心画角の主光線が対象面と交差する領域を有効領域と定義し、これら６つの主光線が対象面と当たる部分の面の偏心方向に当たるＹ軸について面の形状を定義する式を１回微分した値をそれぞれＤＹ_axis、ＤＹ１、ＤＹ４、ＤＹ５、ＤＹ６、ＤＹ３とする。
【０１５４】
〔１９〕 前記撮像素子の結像位置中心に到達する前記読み取り光学系の軸上主光線が前記読み取り光学系に入射する線分の延長方向をＺ軸、前記軸上主光線が前記反射面で反射される際の折り返し線分を含む平面内で前記Ｚ軸に垂直な方向をＹ軸、前記Ｚ軸と前記Ｙ軸とに垂直な方向をＸ軸と定義したときに、前記反射面が次の条件を満足することを特徴とする上記〔１〕から〔１８〕の何れか１項記載の像読み取り装置。
ＤＤＸ_max7＜０．５ （１／ｍｍ） ・・・（７−１）
ただし、Ｙ軸方向を上下方向として、結像画面中心の軸上主光線、上側中心画角の主光線、右上画角の主光線、右中心画角の主光線、右下画角の主光線、下側中心画角の主光線が対象面と交差する領域を有効領域と定義し、この有効領域内でのＸ方向の曲率の最大値と最小値の差をＤＤＸ_max7とする。
【０１５５】
〔２０〕 前記撮像素子の結像位置中心に到達する前記読み取り光学系の軸上主光線が前記読み取り光学系に入射する線分の延長方向をＺ軸、前記軸上主光線が前記反射面で反射される際の折り返し線分を含む平面内で前記Ｚ軸に垂直な方向をＹ軸、前記Ｚ軸と前記Ｙ軸とに垂直な方向をＸ軸と定義したときに、前記反射面が次の条件を満足することを特徴とする上記〔１〕から〔１９〕の何れか１項記載の像読み取り装置。
ＤＤＹ_max8＜０．５ （１／ｍｍ） ・・・（８−１）
ただし、Ｙ軸方向を上下方向として、結像画面中心の軸上主光線、上側中心画角の主光線、右上画角の主光線、右中心画角の主光線、右下画角の主光線、下側中心画角の主光線が対象面と交差する領域を有効領域と定義し、この有効領域内でのＹ方向の曲率の最大値と最小値の差をＤＤＹ_max8とする。
【０１５６】
〔２１〕 前記撮像素子の結像位置中心に到達する前記読み取り光学系の軸上主光線が前記読み取り光学系に入射する線分の延長方向をＺ軸、前記軸上主光線が前記反射面で反射される際の折り返し線分を含む平面内で前記Ｚ軸に垂直な方向をＹ軸、前記Ｚ軸と前記Ｙ軸とに垂直な方向をＸ軸と定義したときに、前記反射面が次の条件を満足することを特徴とする上記〔１〕から〔２０〕の何れか１項記載の像読み取り装置。
０．０１＜ＤＤ_xy9 ＜４０ ・・・（９−１）
ただし、Ｙ軸方向を上下方向として、結像画面中心の軸上主光線、上側中心画角の主光線、右上画角の主光線、右中心画角の主光線、右下画角の主光線、下側中心画角の主光線が対象面と交差する領域を有効領域と定義し、これら６つの主光線が対象面と当たる部分の面の偏心方向に直交するＸ軸についての面の形状を定義する式の曲率をそれぞれＤＤＸ２、ＤＤＸ１、ＤＤＸ４、ＤＤＸ５、ＤＤＸ６、ＤＤＸ３とし、同じく面の偏心方向に当たるＹ軸についての面の形状を定義する式の曲率をＤＤＹ２、ＤＤＹ１、ＤＤＹ４、ＤＤＹ５、ＤＤＹ６、ＤＤＹ３とし、ＤＤ_xy9 ＝｜ＤＤＸｎ｜／｜ＤＤＹｎ｜（ｎは１〜６）とする。
【０１５７】
〔２２〕 前記反射面が屈折率（ｎ）が１よりも大きい（ｎ＞１）媒質を有する裏面反射鏡から構成されていることを特徴とする上記〔１〕から〔２１〕の何れか１項記載の像読み取り装置。
【０１５８】
〔２３〕 前記読み取り光学系は少なくとも第１、第２、第３の３つの面を有し、前記３つの面の中の少なくとも１つの面が前記裏面反射鏡から構成されていることを特徴とする上記〔２２〕記載の像読み取り装置。
【０１５９】
〔２４〕 前記読み取り光学系が、前記撮像素子に対向配置された第１の面と、物体側に対向配置された第２の面と、少なくとも前記第１の面及び第２の面と、屈折率ｎが１よりも大きい（ｎ＞１）媒質を挟んだ第３の面とを有するプリズム部材を備え、前記第３の面が前記反射面にて形成されていることを特徴とする上記〔１〕から〔２３〕の何れか１項記載の像読み取り装置。
【０１６０】
〔２５〕 前記読み取り光学系が、前記撮像素子に対向配置された第１の面と、物体側に対向配置された第２の面と、少なくとも前記第１の面及び第２の面と、屈折率ｎが１よりも大きい（ｎ＞１）媒質を挟んだ第１の反射面及び第２の反射面とを有するプリズム部材を備え、前記第１の反射面及び第２の反射面が前記反射面にて形成されていることを特徴とする上記〔１〕から〔２３〕の何れか１項記載の像読み取り装置。
【０１６１】
〔２６〕 前記第１の反射面が前記第１の面に対して前記撮像素子とは反対側に配され、前記第２の反射面が前記第２面に対して前記物体面とは反対側に配され、かつ、前記第１の反射面と前記撮像素子とを結ぶ主光線が前記物体面と前記第２の反射面とを結ぶ主光線と交差するように配置されたことを特徴とする上記〔２５記載の像読み取り装置。
【０１６２】
〔２７〕 前記反射面が前記読み取り光学系に入射する軸上主光線に対して傾いて配されたことを特徴とする上記〔１〕記載の像読み取り装置。
【０１６３】
〔２８〕 前記撮像素子の撮像面側の法線が前記読み取り光学系へ入射する軸上主光線と交差することを特徴とする上記〔１〕又は〔２７〕記載の像読み取り装置。
【０１６４】
〔２９〕 前記読み取り光学系による前記撮像素子の撮像面の共役面が、前記撮像面に対して斜めに傾いていることを特徴とする上記〔１〕、〔２７〕、〔２８〕の何れか１項記載の像読み取り装置。
【０１６５】
〔３０〕 前記共役面と前記撮像面とのなす角が鈍角となることを特徴とする上記〔２９〕記載の像読み取り装置。
【０１６６】
〔３１〕 前記共役面の法線と前記像読み取り装置の長手方向とのなす角が鋭角となることを特徴とする上記〔２９〕又は３０〕記載の像読み取り装置。
【０１６７】
〔３２〕 前記撮像面が前記像読み取り装置の長手方向に略平行に配されていることを特徴とする上記〔２９〕、〔３０〕、〔３１〕の何れか１項記載の像読み取り装置。
【０１６８】
〔３３〕 前記読み取り光学系による前記撮像素子の撮像面の共役面位置に配された情報記録媒体を照明する照明手段を有し、前記照明手段が発光素子と前記発光素子からの光束を前記情報記録媒体へ導く照明光学系とを有し、前記照明光学系の少なくとも一部が前記読み取り光学系の少なくとも一部と共有することを特徴とする上記〔１〕から〔３２〕の何れか１項記載の像読み取り装置。
【０１６９】
〔３４〕 前記読み取り光学系の撮像光路の反射面の有効範囲の外側から前記発光素子の光束を前記読み取り光学系内に入射させることを特徴とする上記〔３３〕記載の像読み取り装置。
【０１７０】
〔３５〕 前記読み取り光学系の前記発光素子の光束が入射する面が前記発光素子側に凸面を向けて形成されていることを特徴とする上記〔３４〕記載の像読み取り装置。
【０１７１】
〔３６〕 前記発光素子が前記読み取り光学系の反射面の裏側に配され、前記反射面の裏側から前記発光素子の光束を入射させることを特徴とする上記〔３３〕記載の像読み取り装置。
【０１７２】
〔３７〕 前記発光素子の光束が入射する前記読み取り光学系の面に補助レンズを設けたことを特徴とする上記〔３３〕又は〔３６〕記載の像読み取り装置。
【０１７３】
〔３８〕 前記補助レンズが前記発光素子側に凸面を向けていることを特徴とする上記〔３７〕記載の像読み取り装置。
【０１７４】
〔３９〕 前記読み取り光学系による前記撮像素子の撮像面の共役面から前記読み取り光学系の入射面までの距離が１０センチメートル以下であることを特徴とする上記〔１〕から〔３８〕の何れか１項記載の像読み取り装置。
【０１７５】
〔４０〕 上記〔１〕から〔３９〕の何れか１項記載の像読み取り装置と、前記像読み取り装置で読み取ったドットコードを元のマルチメディア情報に変換する復元手段と、前記復元手段により復元されたマルチメディア情報を出力する出力手段とを具備することを特徴とする情報再生システム。
【０１７６】
【発明の効果】
以上の説明から明らかなように、本発明によれば、簡易な構成であって小型化された像読み取り装置及びそれを用いた情報再生システムを提供することができる。
【図面の簡単な説明】
【図１】本発明において用いる読み取り光学系の実施例１の断面図である。
【図２】本発明において用いる読み取り光学系の実施例２の断面図である。
【図３】本発明において用いる読み取り光学系の実施例３の断面図である。
【図４】本発明において用いる読み取り光学系の実施例４の断面図である。
【図５】本発明において用いる読み取り光学系の実施例５の断面図である。
【図６】本発明において用いる読み取り光学系の実施例６の断面図である。
【図７】実施例２の読み取り光学系の横収差図の一部を示す図である。
【図８】実施例２の読み取り光学系の横収差図の残りを示す図である。
【図９】実施例６の読み取り光学系の横収差図の一部を示す図である。
【図１０】実施例６の読み取り光学系の横収差図の残りを示す図である。
【図１１】本発明に基づく像読み取り装置の１つの具体例の断面図である。
【図１２】情報記録媒体に対して傾けて使用するペン型情報再生装置の操作性を説明するための図である。
【図１３】像読み取り装置の照明光学系の具体的配置の１例を示す要部断面図である。
【図１４】照明光学系の具体的配置の別の例を示す要部断面図である。
【図１５】照明光学系の具体的配置のさらに別の例を示す要部断面図である。
【図１６】ドットコード化したマルチメディア情報の１例と情報再生装置の使用状況を示す図である。
【図１７】本発明に基づく１つの実施例の情報再生装置のブロック構成図である。
【図１８】先の提案による像読み取り装置の断面図である。
【符号の説明】
１…第１面
２…第２面
３…第３面
４…第４面
５…プリズム体（読み取り光学系）
６…カバーガラス
３’…読み取り光学系の有効範囲以外の部分
１０…撮像素子
１１…外装
１２…基板
１３…補助レンズ、プリズム等の光学部材
１４…ハーフミラー
２０…情報記録媒体（被写体）
３０…紙
３２…画像
３４…文字
３６…記録データ（ドットコード）
３８…ブロック
３８Ａ…マーカ
３８Ｂ…誤り訂正用符号
３８Ｃ…オーディオデータ
３８Ｄ…ｘアドレスデータ
３８Ｅ…ｙアドレスデータ
３８Ｆ…誤り判定符号
４０…像読み取り装置（ペン型情報再生装置（情報再生システム））
４２…音声出力器
４４…検出部
４４Ａ…光源
４４Ｂ…読み取り光学系
４４Ｃ…空間フィルタ
４４Ｄ…撮像部
４４Ｅ…プリアンプ
４６…走査変換及びレンズ歪み補正部
４６Ａ…Ａ／Ｄ変換器
４６Ｂ…フレームメモリ
４６Ｃ…マーカ検出回路
４６Ｄ…θ検出回路
４６Ｅ…レンズ収差情報メモリ
４６Ｆ…アドレス制御回路
４６Ｇ…補間回路
４８…２値化回路
４８Ａ…ラッチ
４８Ｂ…コンパレータ
５０…閾値判定回路
５２…ＰＬＬ回路
５４…復調回路
５６…データ列調整部
５６Ａ…誤り判定回路
５６Ｂ…ｘ，ｙアドレス検出回路
５６Ｃ…メモリ部
５３…基準クロック発生回路
５８…デ・インタリーブ回路
６０…誤り訂正回路
６２…復号回路
６４…データ補間回路
６６…Ｄ／Ａ変換回路
６８…増幅器
Ｏ…物体面
Ｉ…像面
ＣＫ…クロックパルス
ＣＫ’…基準クロック[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image reading apparatus, and more particularly to image reading for imaging an information recording medium recorded by encoding multimedia information so as to be optically readable on paper, a resin film, a metal sheet, or the like. The present invention relates to an apparatus and an information reproduction system using the apparatus.
[0002]
[Prior art]
Various media other than magnetic tapes and optical disks are known as media for recording audio information such as voice and music. However, even if all of these media are made in large quantities, the unit price is somewhat expensive, and a certain amount of space is required for storage. In addition, when handing a medium with such audio recording to another person at a remote location, someone will either bring it directly or mail it, and it will take time to reach the remote person's hand. . The same applies to information other than audio information, for example, video information obtained from a camera, video equipment, etc., and digital code data obtained from a personal computer, a word processor, or the like.
[0003]
In view of such circumstances, the present applicant has disclosed in Japanese Patent Application Laid-Open No. 6-231466, audio information such as voice and music, video information obtained from a camera or video equipment, digital code data obtained from a personal computer, a word processor, etc. The so-called multimedia information is recorded as code information (image) optically readable on paper, resin film, metal sheet, etc., for example, as an encoded dot pattern, and when reading this recorded information recording medium, An information processing system has been proposed to reproduce recorded multimedia information by irradiating illumination light to the dot pattern and reading the reflected light using an optical means.
[0004]
In this information processing system, multimedia information is recorded on paper, which is considered to be the most economical medium, or a sheet-like medium equivalent thereto. This is very useful for cost reduction and space saving of the medium. Information recorded as a dot pattern can be easily transmitted by fax. Thereby, information transmission to a remote person can be performed easily. In particular, this is very meaningful for voice information, and the voice information exchange that has been performed by the delivery of the medium itself can be easily and instantly performed by a remote person by fax in this information system.
[0005]
[Problems to be solved by the invention]
As a form of the information reproducing apparatus, Japanese Patent Application Laid-Open No. 6-231466 shows a pen type information reproducing apparatus (for example, FIG. 41B).
However, as the first problem, there is a problem in mounting the electric substrate. With respect to the layout (mounting) inside the information reproducing apparatus, as shown in FIG. 18, the electric boards 91 and 91 ′ on which the electric circuits such as the image processing unit, the data processing unit, and the image sensor are mounted It is preferable to dispose the substrate in the direction and substantially parallel to the exterior 90 because the number of substrates can be reduced. However, in that case, since the image pickup element 92 needs to be arranged facing the information recording medium 100 and is arranged substantially orthogonal to the electric board 91, it is difficult to make the boards 91 and 91 ′ common. Yes, it is problematic in terms of mounting efficiency and cost. It is possible to add a new optical member such as a mirror to the optical system 93 shown in FIG. 18 to bend the optical path, but in this case, the number of constituent members of the optical system increases and the cost increases, and the lens frame The configuration becomes complicated, which is not preferable.
[0006]
In addition, in an optical system for an image reading apparatus, in order to construct an optical system free from image distortion in which a wide angle of view and aberration are well corrected, in a rotationally symmetric optical system, the number of lenses increases and the size is large. It must be expensive.
[0007]
Another problem is mounting of the illumination system. When an illumination system is configured using a light source such as an LED to illuminate the information recording medium, illumination unevenness is likely to occur because it is necessary to avoid the mechanical interference with the imaging optical system.
The cause of this problem is that the configuration of the optical system has a low degree of freedom for mounting. Therefore, the same problem can occur not only in the pen-type information reproducing apparatus but also in other forms of information reproducing systems.
[0008]
The present invention has been made in view of such problems, and an object of the present invention is to provide a small optical system that can take a wide image area and is small in size by reducing the image distortion by bending the optical path. It is to provide an image reading apparatus used.
[0009]
Another object of the present invention is to provide an image reading apparatus and an information reproduction system using the image reading apparatus that have a simple configuration but have a high degree of freedom in mounting and are advantageous for downsizing the apparatus.
[0010]
[Means for Solving the Problems]
An image reading apparatus of the present invention that achieves the above object is a recording comprising a portion in which multimedia information including at least one of audio information, video information, and digital code data is recorded in an optically readable dot code. In an image reading device that optically reads the dot code from a medium,
A reading optical system comprising at least one reflecting surface having a reflecting action, and the surface shape of the reflecting surface is a rotationally asymmetric curved surface having no rotational symmetry axis both inside and outside the surface;
An imaging element positioned on the image plane of the object plane formed by the reading optical system,
The reflecting surface has an axial principal ray of the reading optical system that reaches the center of the image forming position of the image sensor, and the extending direction of the line segment incident on the reading optical system is the Z axis, and the axial principal ray is reflected. When a direction perpendicular to the Z-axis is defined as a Y-axis and a direction perpendicular to the Z-axis and the Y-axis is defined as an X-axis in a plane including a folded line segment when reflected by a surface, the following conditions are satisfied. (A-1) is satisfied.
| RX | <0.5 (1 / mm) (A-1)
However, RX is a curvature in the X direction of a portion where the axial principal ray hits the reflecting surface.
[0011]
In this case, it is desirable that the surface shape of the reflecting surface is a plane-symmetric free-form surface having only one symmetry surface.
Another image reading apparatus of the present invention is a recording medium including a portion in which multimedia information including at least one of audio information, video information, and digital code data is recorded in an optically readable dot code. In the image reading device for optically reading the dot code,
A light source for illuminating the recording medium;
A rotationally asymmetric curved surface having at least one reflecting surface having a reflecting action and an incident surface on which illumination light from the light source is incident, and the surface shape of the reflecting surface does not have a rotationally symmetric axis both inside and outside the surface. An optical member,
An imaging element located on the image plane of the object plane formed by the optical member,
An imaging optical path of an imaging optical system from the image sensor through the optical member to the recording medium and an illumination optical path of an illumination optical system from the light source through the optical member to the recording medium are included in the optical member. It is characterized by being arranged redundantly.
[0012]
Hereinafter, the reason and effect | action which take such a structure in this invention are demonstrated.
As in the present invention, the reading optical system is provided with a reflecting surface having at least one reflecting surface, and the surface shape of the reflecting surface is a rotationally asymmetric curved surface that does not have an axis of rotational symmetry both inside and outside the surface. With this configuration, the optical path can be bent to reduce the size, and the aberration caused by the bending of the optical path can be a rotationally asymmetric surface, so that the aberration can be corrected by the surface itself and the optical performance can be improved. Therefore, it is possible to provide a small-sized image reading apparatus and an information reproduction system using the same with a simple configuration.
[0013]
The information reproduction system according to the present invention is a dot code which can optically read multimedia information including at least one of audio information, video information and digital code data by such an image reading device (image reading means). The dot code is optically read from the recording medium having the portion recorded in the above, the read dot code is converted into the original multimedia information by the restoring means, and the restored multimedia information is output by the output means. Is output.
[0014]
In the present invention, the fact that the reading optical system has a plane having only one plane of symmetry (hereinafter referred to as a TFC plane) will be described in detail below.
[0015]
First, in the following description, a coordinate system to be used will be described.
The optical axis defined by the straight line from the object side through the pupil center to the image forming position center until the principal ray at the image center intersects the first surface of the decentered optical system is defined as the Z axis, and is orthogonal to the Z axis. An axis in the decentered surface of each surface constituting the decentered optical system is defined as a Y axis, and an axis perpendicular to the optical axis and perpendicular to the Y axis is defined as an X axis.
Further, the tracking direction of the light beam will be described by forward tracking from the pupil position to the imaging position.
[0016]
An overview of conventional aberration correction
(1) Generally, in order to correct aberrations satisfactorily with a small number of surfaces, an aspherical surface is generally used in a rotationally symmetric optical system. Similarly, in the reflection optical system, the spherical aberration generated by the spherical reflecting mirror is not generated by using a rotationally symmetric aspherical surface such as a paraboloid. That is, it is a well-known fact that a rotationally symmetric aspheric surface is used in a rotationally symmetric optical system.
[0017]
(2) It is also a well-known fact that the occurrence of spherical aberration can be reduced by using a back reflecting mirror such as a Mangin mirror (A. Mangin, 1876).
[0018]
This is because the focal length f of the back mirror is based on the curvature radius r of the back mirror and the refractive index n of the medium.
f = −r / 2n
In the case where the same focal length f is obtained, for example, if the rear surface mirror is made of glass having a refractive index of 1.5, the radius of curvature r is 1.5 times larger than that of the front surface mirror. This is because it is possible to reduce the occurrence of this.
[0019]
(3) On the other hand, the concave mirror arranged eccentrically shifts the focal position of the light beam in the Y-axis direction and the light beam in the X-axis direction at the portion where the light beam hits the reflecting mirror due to the eccentricity, and astigmatism on the axis as well. Will occur.
[0020]
In order to eliminate the occurrence of this astigmatism on the axis, as described in Japanese Patent Application No. 6-211067 or Japanese Patent Application No. 6-256676 of the present applicant, anamorphic having different curvatures depending on directions. A surface or a toric surface is used.
[0021]
(4) Next, image plane distortion will be described. The fact that the arrangement of the concave mirror and the convex mirror exerts a good effect on the field curvature aberration is described in detail in Japanese Patent Application No. 5-264828 of the present applicant. 6-127453 and the like. Japanese Patent Application No. 6-256676 also successfully corrects the curvature of field by constructing two concave mirrors.
[0022]
(5) As for image distortion, as described in JP-A-5-303056, it is possible to obtain a good result by configuring the surfaces with different curvatures depending on whether the X axis direction or the Y axis direction is positive or negative. Although the application is different, a rear projection television uses a Fresnel reflection surface similar to the TFC surface used in the present invention in Japanese Patent Laid-Open No. 1-257834, the purpose of which is to correct trapezoidal image distortion. Therefore, when a real image is projected onto a screen by a projection optical system, it is reflected by the reflecting surface, and at this time, only a trapezoidal image distortion is corrected. Japanese Patent Laid-Open No. 5-303056 describes trapezoidal and bow-shaped image distortion generated by an inclined concave mirror.
[0023]
The element lacking in each of the above inventions has been made an attempt to correct aberrations by using an optical system with a folded optical path and a combination of each of the above-described structures, with sufficient aberration performance as an imaging optical system or imaging optical system. It is a matter.
[0024]
As for the aberration due to the rotationally symmetric optical system, the behavior of the light beam incident on the lens changes depending on only the height from the optical axis, which is the rotation axis, and thereby aberration is generated. How to correct this. However, in the decentered optical system, the height and position at which the light ray strikes the surface greatly differ between the upper and lower surfaces of the decentered direction. In other words, although there is no rotational symmetry, cylindrical surfaces, toric surfaces, and anamorphic surfaces based on rotationally symmetric spheres will not be able to correct aberrations in response to this complex behavior of rays. .
[0025]
Here, the free-form surface used in the present invention is defined by the following equation.

In the above equation, when the eccentric direction is the Y direction, all odd-order terms of X are zero.
[0026]
This definition makes it possible to satisfactorily correct each aberration described below, and can be used as an imaging optical system (reading optical system) by a reflecting mirror arranged in a tilted manner as in the present invention. It became possible to add refractive power.
[0027]
First, since the reference surface is based on the paraboloid of the square term, it is difficult for spherical aberration to occur. Next, since there are an odd-order term of Y and an odd-order term of X, an inclination in the Y-axis direction can be given at an arbitrary position on the X-axis.
[0028]
Since odd order and even order are multiplied for each of Y and X, a free curvature can be given to the positive and negative of each axis.
[0029]
As described above, there are various degrees of freedom, and when this lens is used as a reflecting surface that is decentered, it is possible to correct aberrations for the first time by using this definition even if power is given. It was.
[0030]
The importance of this degree of freedom for aberration correction will be described. In the case of a reflecting mirror that is tilted and has power, rotationally asymmetric field curvature occurs. In this curvature of field, a light beam that passes through the pupil and has a spread in the X-axis direction is reflected by a reflecting mirror that is decentered, and the distance to the image surface after the light beam strikes is reflected by the back mirror. Focal length formula
f = −r / 2n
Accordingly, the curvature r and the refractive index n of the portion hit by the light beam are r / 2n. That is, an image that is inclined with respect to the optical axis in parallel with the inclined reflecting mirror with respect to the direction of travel of the light beam after being reflected by the decentered concave mirror and is curved with an r / 2n curvature r of the reflecting mirror. Form a surface.
[0031]
As described above, the free-form surface has an odd-order term of Y whose curvature can be arbitrarily changed by positive / negative of the Y-axis, and therefore, a rotationally asymmetric field curvature generated by a decentered concave mirror, particularly It works effectively for correcting the tilt of the image plane.
[0032]
Next, rotationally symmetric field curvature will be described. In general, the reflecting mirror causes curvature of field along the reflecting surface. In the case of the present invention, as described above, a configuration in which the field curvature can be corrected by the convex mirror paired with the concave mirror is possible, and two concave surfaces are used to reduce the field curvature generated in each of the two. I am trying to devise. However, the conventional surface shape is not completely corrected because the number of surfaces is small. In order to correct this uncorrectable curvature of field, a free-form surface capable of giving an arbitrary curvature at an arbitrary place is preferable in terms of aberration correction. This is made possible by a combination of the odd-order terms of Y and the squares of X or more depending on whether the Y axis is positive or negative.
[0033]
Furthermore, in order to reduce the occurrence of astigmatism at an arbitrary location, it is possible to correct by arbitrarily changing the difference between the curvature in the X-axis direction and the curvature in the Y-axis direction. This is possible because the X squared term and the Y squared term exist independently.
[0034]
More preferably, it is desirable to minimize the free-form surface in consideration of optical component manufacturability. Therefore, it is possible to improve manufacturability by setting one of the at least three surfaces as the above-described free-form surface and the other surface as a flat surface, a spherical surface, or an eccentric rotationally symmetric surface.
[0035]
More preferably, by satisfying the following conditions, it is possible to provide a reading optical system having a wide angle of view, a large pupil diameter, and good aberration correction.
[0036]
In accordance with the above definition, when the X, Y, and Z axes are used, the area where the light beam with the maximum field angle that exits the pupil center and enters the reading optical system that forms the image intersects each surface is effective. A region is defined, and rays (1) to (6) as shown in Table 1 below are traced.
[0037]

[0038]
That is, the axial principal ray in the optical axis direction at the center of the screen is set to {circle around (2)}, the ray at the upper center field angle is set to (1), the beam at the upper right field angle is set to (4), and the beam at the right center field angle is set to (5). The light beam at the lower right field angle is set to {circle around (6)} and the light beam at the lower center field angle is set to {circle around (3)}. An expression describing the surface shape of the portion where these rays (1) to (6) impinge on each surface of the optical system (an expression expressing the Z axis as the surface axis, or assuming that the surface is not decentered, Z = f ( The value of the first derivative and the curvature of the equation (X, Y) is obtained. That is, the first derivative represents the inclination of the portion hit by the light ray with respect to the surface definition coordinates, and the curvature represents the partial curvature of the portion hit by the light ray. This is because, when each surface of the optical system is arranged eccentrically, the coordinates defining the surface shape can be defined at an arbitrary position. It is because it may not pass and it does not limit the surface shape.
[0039]
First, the partial curvature in the X direction at the position where the axial principal ray {circle around (2)} of the TFC plane will be described. In the present invention, the meaning of defining the partial curvature of a surface is that even if it is a TFC surface where aberrations are favorably corrected, if the power of the surface is too large, the generation of aberration becomes too large, This is because it becomes impossible to correct. If the curvature of the portion where the principal ray (2) in the X direction hits is RX,
| RX | <0.5 (1 / mm) (A-1)
It is important to satisfy the following conditions. If the curvature of the decentered reflecting surface does not exceed the upper limit of 0.5, an optical system with less aberration is formed by configuring the reflecting surface with a surface having only one symmetrical surface. It becomes possible. On the reflecting surface exceeding the upper limit of 0.5, various aberrations due to decentering become extremely large, and correction on other surfaces becomes difficult.
[0040]
More preferably,
| RX | <0.1 (1 / mm) (A-2)
When satisfying the above condition, it is important to form the reflecting surface with a surface having only one plane of symmetry in order to prevent aberration due to decentration.
[0041]
More preferably,
| RX | <0.05 (1 / mm) (A-3)
When satisfying the above condition, it is important to form the reflecting surface with a surface having only one plane of symmetry in order to prevent aberration due to decentration.
[0042]
Next, the partial curvature in the Y direction at the position where the axial principal ray {circle around (2)} of the TFC plane will be described. In the present invention, the meaning of defining the partial curvature of a surface is that even if it is a TFC surface where aberrations are favorably corrected, if the power of the surface is too large, the generation of aberration becomes too large, This is because it becomes impossible to correct. If the curvature of the portion where the principal ray (2) in the Y direction hits is RY,
| RY | <0.5 (1 / mm) (B-1)
It is important to satisfy the following conditions. If the curvature of the decentered reflecting surface does not exceed the upper limit of 0.5, an optical system with less aberration is formed by configuring the reflecting surface with a surface having only one symmetric surface. It becomes possible to do. On the reflecting surface exceeding the upper limit of 0.5, various aberrations due to decentering become extremely large, and correction on other surfaces becomes difficult.
[0043]
More preferably,
| RY | <0.1 (1 / mm) (B-2)
When satisfying the above condition, it is important to form the reflecting surface with a surface having only one plane of symmetry in order to prevent aberration due to decentration.
[0044]
More preferably,
| RY | <0.05 (1 / mm) (B-3)
When satisfying the above condition, it is important to configure the reflecting surface with a surface having only one plane of symmetry in order to prevent aberration due to decentration.
[0045]
Next, on the reflecting surface, the slope DX of the position at which the principal ray (2) that reaches the center of the image plane through the pupil center through the single-difference value DX in the X-axis direction hits. _axis And curvature RX, DX _max1 = MAX ((DX-DX _axis ) / RX), it is important to satisfy the following conditions.
[0046]
｜ DX _max1 | <100.0 (mm) (1-1)
This condition represents the tilt of the reflecting surface in the X direction. If the upper limit of 100.0 in the above conditional expression is exceeded, the tilt of the reflecting surface becomes too large with respect to the principal ray at each image height, and aberrations due to decentration are large. It becomes too much and it becomes impossible to correct in other aspects.
[0047]
More preferably,
｜ DX _max1 | <10.0 (mm) (1-2)
It is important to satisfy the following conditional expression.
[0048]
More preferably,
｜ DX _max1 | <6.0 (mm) (1-3)
It is important to satisfy the following conditional expression.
[0049]
The above conditional expressions (1-1) to (1-3) are all necessary for obtaining a good observation image at a wide angle of view. In particular, conditional expression (1-2) is important at a half angle of view of 10 degrees or more, and conditional expression (1-3) is preferably satisfied at a half angle of view of 15 degrees or more.
[0050]
Next, on the reflecting surface, the tilt in the eccentric direction of the surface, that is, the tilt DY at the position where the principal ray {circle around (2)} passing through the center of the pupil and the value DY of the first derivative in the Y-axis direction hits. _axis And DY for curvature RY _max2 = MAX ((DY-DY _axis ) / RY), it is important to satisfy the following conditions.
[0051]
｜ DY _max2 | <100.0 (mm) (2-1)
This condition represents the Y-direction tilt of the reflecting surface. If the upper limit of 100.0 in the above conditional expression is exceeded, the tilting of the reflecting surface becomes too large with respect to the principal ray at each image height, and the occurrence of aberration due to decentration is large. It becomes too much and it becomes impossible to correct in other aspects.
[0052]
More preferably,
｜ DY _max2 | <10.0 (mm) (2-2)
It is important to satisfy the following conditional expression.
[0053]
More preferably,
｜ DY _max2 | <6.0 (mm) (2-3)
It is important to satisfy the following conditional expression.
[0054]
The conditional expressions (2-1) to (2-3) are all necessary for obtaining a good observation image at a wide angle of view. In particular, conditional expression (2-2) is important at a half angle of view of 10 degrees or more, and conditional expression (2-3) is preferably satisfied at a half angle of view of 15 degrees or more.
[0055]
Next, the X-direction tilt at the position where the principal rays (4) and (6) with the maximum angle of view in the X direction hit the eccentrically disposed reflecting surface, and chief rays (1) and (▲) with zero X-direction angle of view. Differences from the X direction inclination at the position where 3 ▼ hits the reflecting surface are (DX4-DX1) and (DX6-DX3), respectively, and the difference is DX. _Three = (DX4-DX1)-(DX6-DX3)
｜ DX _Three | <0.4 (3-1)
It is preferable to satisfy the following conditions.
[0056]
The conditional expression (3-1) represents the distortion in the X direction of the peripheral image in the X direction. If the upper limit of 0.4 of this conditional expression is exceeded, the left and right edges of the observed image change in the X-axis direction, the trapezoidal image distortion becomes large, and correction on other surfaces becomes impossible, and the distorted observation image Become.
[0057]
More preferably,
｜ DX _Three | <0.2 (3-2)
It is preferable to satisfy the following conditional expression: This is important when observing an observation image with little image distortion, particularly when trying to secure a half angle of view of 10 degrees or more.
[0058]
More preferably,
｜ DX _Three | <0.1 (3-3)
It is preferable to satisfy the following conditional expression: This is important when observing an observation image with little image distortion, particularly when a half field angle of 15 degrees or more is to be secured.
[0059]
More preferably,
｜ DX _Three | <0.05 (3-4)
This is particularly important when observing an observation image with almost no image distortion when trying to secure a half angle of view of 20 degrees or more.
[0060]
Next, the principal rays (4) and (6) having the maximum field angle in the X direction are inclined in the Y direction at positions where they strike the reflecting surfaces arranged eccentrically, and the principal rays (1) and (▲) with zero field angle in the X direction. Differences from the inclination in the Y direction at the position where 3 ▼ hits the reflecting surface are (DY4-DY1) and (DY6-DY3), respectively, and the difference is DY. _Four = (DY4-DY1)-(DY6-DY3)
｜ DY _Four | <0.4 (4-1)
It is preferable to satisfy the following conditions.
[0061]
The conditional expression (4-1) represents the distortion in the Y direction of the peripheral image in the X direction. If the upper limit of 0.4 of this conditional expression is exceeded, the left and right edges of the observed image will change in the Y-axis direction, and the image distortion that causes the surrounding image to become bowed will increase, making correction impossible on other surfaces. It becomes a distorted observation image.
[0062]
More preferably,
｜ DY _Four | <0.2 (4-2)
It is preferable to satisfy the following conditional expression: This is important when observing an observation image with little image distortion, particularly when trying to secure a half angle of view of 10 degrees or more.
[0063]
More preferably,
｜ DY _Four | <0.1 (4-3)
It is preferable to satisfy the following conditional expression: This is important when observing an observation image with little image distortion, particularly when a half field angle of 15 degrees or more is to be secured.
[0064]
More preferably,
｜ DY _Four | <0.05 (4-4)
This is particularly important when observing an observation image with almost no image distortion when trying to secure a half angle of view of 20 degrees or more.
[0065]
Next, the first derivative DX in the X direction at the center of the screen _axis Difference between the first derivative DX5 in the X direction at the right end of the maximum field angle in the X direction on the X axis (DX5-DX _axis ) DX _max5 The DX on the reflective surface _max5 Value of
｜ DX _max5 | <0.5 (5-1)
It is important to satisfy the following conditional expression.
[0066]
This is an image distortion observed when a straight line in the horizontal direction passing through the center of the screen, for example, a horizontal line is curved like a bow. If this numerical value exceeds the upper limit of 0.5, bow-shaped image distortion will occur greatly convexly downward, making it impossible to correct on other surfaces.
[0067]
More preferably,
｜ DX _max5 | <0.1 (5-2)
It is important to satisfy the following conditional expression. In particular, in the case of a half angle of view exceeding 10 degrees, it is important to satisfy this condition. The upper limit is the same as the conditional expression (5-1).
[0068]
More preferably,
｜ DX _max5 | <0.05 (5-3)
It is important to satisfy the following conditional expression. In particular, in the case of a half angle of view exceeding 15 degrees, it is important to satisfy this condition. The upper limit is the same as the conditional expression (5-1).
[0069]
More preferably,
｜ DX _max5 | <0.02 (5-4)
It is important to satisfy the following conditional expression, and it is important to satisfy this condition particularly in the case of a half angle of view exceeding 20 degrees. The upper limit is the same as the conditional expression (5-1).
[0070]
Next, Y-direction differential value DY at the center of the screen _axis Difference between the first derivative DY5 in the Y direction at the right end of the maximum field angle in the X direction on the X axis (DY5-DY _axis ) DY _max6 DY of the reflective surface _max6 Value of
｜ DY _max6 | <0.5 (6-1)
It is important to satisfy the following conditional expression. This is an image distortion observed when a straight line in the left-right direction passing through the center of the screen, for example, a horizontal line or the like is bowed and curved. If this numerical value exceeds the upper limit of 0.5, bow-shaped image distortion will occur greatly convexly downward, making it impossible to correct on other surfaces.
[0071]
More preferably,
｜ DY _max6 | <0.1 (6-2)
It is important to satisfy the following conditional expression. In particular, in the case of a half angle of view exceeding 10 degrees, it is important to satisfy this condition. The upper limit is the same as the conditional expression (6-1).
[0072]
More preferably,
｜ DY _max6 | <0.05 (6-3)
It is important to satisfy the following conditional expression. In particular, in the case of a half angle of view exceeding 15 degrees, it is important to satisfy this condition. The upper limit is the same as the conditional expression (6-1).
[0073]
More preferably,
｜ DY _max6 | <0.02 (6-4)
It is important to satisfy the following conditional expression, and it is important to satisfy this condition particularly in the case of a half angle of view exceeding 20 degrees. The upper limit is the same as the conditional expression (6-1).
[0074]
Next, the difference between the maximum value and the minimum value in the effective range of the partial curvature in the X direction of the TFC surface is expressed as DDX. _max7 It is important to satisfy the following conditional expression.
[0075]
DDX _max7 <0.5 (1 / mm) (7-1)
This condition indicates that it is important to reduce the curvature of field, in particular, the curvature of field in the X-axis direction, that the curvature is difficult to change in the X-axis direction. When the difference in curvature in the X direction between the reflecting surfaces arranged eccentrically exceeds the upper limit of 0.5, the field curvature becomes large, and it becomes difficult to obtain a flat image surface.
[0076]
More preferably,
DDX _max7 <0.1 (1 / mm) (7-2)
If this condition is satisfied, it is possible to obtain an image that is well corrected to the periphery.
[0077]
More preferably,
DDX _max7 <0.05 (1 / mm) (7-3)
When the above condition is satisfied, it is possible to obtain an image that has been further corrected to the periphery.
[0078]
Next, the difference between the maximum value and the minimum value within the effective range of the partial curvature in the Y direction of the TFC surface is expressed as DDY. _max8 It is important to satisfy the following conditional expression.
[0079]
DDY _max8 <0.5 (1 / mm) (8-1)
This condition indicates that it is important for the curvature of field to be difficult to change in the Y-axis direction in order to reduce the curvature of field, particularly the curvature of field in the Y-axis direction. When the difference in curvature in the Y direction between the reflecting surfaces arranged eccentrically exceeds the upper limit of 0.5, the field curvature becomes large, and it becomes difficult to obtain a flat image surface.
[0080]
More preferably,
DDY _max8 <0.1 (1 / mm) (8-2)
If this condition is satisfied, it is possible to obtain an image that is well corrected to the periphery.
[0081]
More preferably,
DDY _max8 <0.05 (1 / mm) (8-3)
If both of these conditions are satisfied, it is possible to obtain an image that has been further corrected to the periphery.
[0082]
Next, | X direction curvature / Y direction curvature | = | DDXn | / | DDYn | (where n is the principal ray number (1) to (6)) at the position where each ray in the effective surface hits the surface. 1-6) to DD _xy9 , DD in all the effective area of the reflective surface _xy9 But,
0.01 <DD _xy9 <40 (9-1)
It is important to satisfy the following conditional expression.
[0083]
This corresponds to the ratio of the image forming position in the X direction and the image forming position in the Y direction of the effective region, and is a condition for correcting astigmatism satisfactorily. When the lower limit of 0.01 is exceeded, the X-direction light beam forms an image closer to the optical system side than the Y-direction light beam, and astigmatism increases. On the other hand, if the upper limit of 40 is exceeded, the X-direction light beam forms an image farther than the optical system with respect to the Y-direction light beam, resulting in large astigmatism. It becomes impossible to correct. However, in the case of a surface having symmetry with respect to both the Y axis and the X axis, such as a toric surface, this condition is satisfied, but coma aberration and image distortion are increased.
[0084]
More preferably,
0.1 <DD _xy9 <20 (9-2)
It is important to satisfy the following conditional expression. In particular, in the case of a half angle of view exceeding 20 degrees, it is important to satisfy this condition.
[0085]
More preferably,
0.3 <DD _xy9 <10 (9-3)
It is important to satisfy the following conditional expression. In particular, in the case of a half angle of view exceeding 25 degrees, it is important to satisfy this condition.
[0086]
More preferably,
0.5 <DD _xy9 <6 (9-4)
It is important to satisfy the following conditional expression. In particular, in the case of a half angle of view exceeding 30 degrees, it is important to satisfy this condition.
[0087]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of an image reading apparatus and an information reproduction system using the same according to the present invention will be described. First, Examples 1 to 6 will be described as examples of the reading optical system used in the present invention. Cross-sectional views of Examples 1 to 6 are shown in FIGS. In numerical data to be described later, the surface numbers are in the order of backward ray tracing from the imaging surface to the object surface in the first and second embodiments, and in order from the object surface to the imaging surface in the third to sixth embodiments. The numbers of the surfaces constituting the optical system in this order are shown. Therefore, in the first and second embodiments, the object plane O is actually the image plane and the image plane I is the object plane. The distance between the surfaces is the length measured along the axial principal ray between the previous surface and the next surface (however, the sign is reversed after reflection). Indicates the tilt angle (°) of the definition axis (counterclockwise is positive). In Examples 1 to 3, the refractive index is a value for a wavelength of 660 nm, and Examples 4 to 6 are values for a d-line. The unit of length is mm.
[0088]
In the numerical data described later, the shape of the surface of the free-form surface is defined by the above formula (a), the Y axis and the Z axis are in the drawing sheet, and this YZ plane has a symmetry plane of 1 It becomes a symmetrical surface of a free-form surface that has only a surface. Note that the term relating to the order for which no data is described is zero.
[0089]
In each of Examples 1 to 6, two to three optical surfaces including two reflecting surfaces among four optical surfaces forming a prism body made of a medium having a pentagonal prism-like refractive index larger than 1 are provided. The prism body is provided with imaging performance by forming a free-form surface having only one plane of symmetry and the remaining two or one planes by a spherical surface.
[0090]
That is, in the first and second embodiments, a pentagonal prism-shaped prism body 5 including a first surface 1, a second surface 2, a third surface 3, and a fourth surface 4, as shown in cross sections in FIGS. The first surface 1 and the fourth surface 4 are refractive surfaces, the second surface 2 and the third surface 3 are reflection surfaces, the first surface 1 is a spherical surface, the second surface 2, the third surface 3, and the fourth surface. The surface 4 is a free-form surface. Light rays from the object surface O provided on the back surface of the cover glass 6 enter the first surface 1 of the prism body 5 through the cover glass 6, are sequentially reflected on the second surface 2 and the third surface 3, and are reflected light. Intersects with the light beam from the first surface 1 to the second surface 2 and exits from the fourth surface 4 to the outside of the prism body 5 and reaches the image surface I (in practice, the opposite optical path is used). The image plane I becomes the object plane, and the object plane O becomes the image plane. In these examples, the horizontal angle of view (the angle of view perpendicular to the paper surface) is 50 degrees, the vertical angle of view (the angle of view within the paper surface) is 37 degrees, the focal length is 6 mm in terms of a coaxial system, 7857 mm imaging optical system.
[0091]
Example 3 is a pentagonal prism-shaped prism body 5 composed of a first surface 1, a second surface 2, a third surface 3, and a fourth surface 4, as shown in cross section in FIG. The fourth surface 4 is a refracting surface, the second surface 2 and the third surface 3 are reflecting surfaces, the first surface 1 and the fourth surface are spherical surfaces, and the second surface 2 and the third surface 3 are free curved surfaces. A light ray from the object plane O is incident from the first surface 1 of the prism body 5 and is sequentially reflected by the second surface 2 and the third surface 3, and the reflected light reaches the second surface 2 from the first surface 1. Intersects with the second surface 4 and exits from the prism body 5 through the cover glass 6 to the image surface I provided on the back surface thereof. In this embodiment, the horizontal angle of view (the angle of view in the direction perpendicular to the paper surface) is 50 degrees, the vertical angle of view (the angle of view within the paper surface) is 37 degrees, the focal length is 6 mm in terms of a coaxial system, and the pupil diameter is 1.7857 mm. This is an imaging optical system.
[0092]
Example 4 is a pentagonal prism-shaped prism body 5 composed of a first surface 1, a second surface 2, a third surface 3, and a fourth surface 4, as shown in cross section in FIG. The fourth surface 4 is a refractive surface, the second surface 2 and the third surface 3 are reflective surfaces, the first surface 1 is a spherical surface, and the second surface 2, the third surface 3, and the fourth surface 4 are free-form surfaces. This optical system is a projection optical system, and object light from infinity is incident on the first surface 1 of the prism body 5 and is sequentially reflected by the second surface 2 and the third surface 3, and the reflected light is reflected on the first surface 1. From the fourth surface 4 to the outside of the prism body 5 through the cover glass 6 and to the image surface I provided on the back surface thereof. This embodiment is a projection optical system having an object height X-axis direction (direction perpendicular to the paper surface) of 1.447 mm, a Y-axis direction (direction in the paper surface) of 1.0915 mm, and an object-side NA (numerical aperture) of 0.0357.
[0093]
Example 5 is a pentagonal prism-shaped prism body 5 composed of a first surface 1, a second surface 2, a third surface 3, and a fourth surface 4, as shown in cross section in FIG. The fourth surface 4 is a refracting surface, the second surface 2 and the third surface 3 are reflecting surfaces, the first surface 1, the second surface 2, and the third surface 3 are free-form surfaces, and the fourth surface 4 is a spherical surface. This optical system is a projection optical system, and object light from infinity is incident on the first surface 1 of the prism body 5 and is sequentially reflected by the second surface 2 and the third surface 3, and the reflected light is reflected on the first surface 1. From the fourth surface 4 to the outside of the prism body 5 through the cover glass 6 and to the image surface I provided on the back surface thereof. This embodiment is a projection optical system having an object height X-axis direction (direction perpendicular to the paper surface) of 1.447 mm, a Y-axis direction (direction in the paper surface) of 1.0915 mm, and an object-side NA (numerical aperture) of 0.0357.
[0094]
Example 6 is a pentagonal prism-shaped prism body 5 composed of a first surface 1, a second surface 2, a third surface 3, and a fourth surface 4, as shown in cross section in FIG. The fourth surface 4 is a refractive surface, the second surface 2 and the third surface 3 are reflective surfaces, the first surface 1 is a spherical surface, and the second surface 2, the third surface 3 and the fourth surface 4 are free-form spherical surfaces. . This optical system is a projection optical system, and object light from infinity is incident on the first surface 1 of the prism body 5 through a separate diaphragm, and is sequentially reflected by the second surface 2 and the third surface 3. The reflected light intersects with the light beam from the first surface 1 to the second surface 2 and exits from the fourth surface 4 to the outside of the prism body 5, passes through the cover glass 6 and reaches the image surface I provided on the back surface thereof. The This embodiment is a projection optical system having an object height in the X-axis direction (perpendicular to the paper surface) of 4.02 mm, a Y-axis direction (direction in the paper surface) of 3.03 mm, and an object-side NA (numerical aperture) of 0.0129.
[0095]
The configuration parameters of Examples 1 to 6 are shown below.

[0096]

[0097]

[0098]

[0099]

[0100]

[0101]
Next, lateral aberration diagrams of Example 2 are shown in FIGS. In these lateral aberration diagrams, the numbers in parentheses indicate (horizontal angle of view (angle of view perpendicular to the paper surface), vertical angle of view (angle of view within the paper surface)), and the lateral aberration at that angle of view. Show. Similar lateral aberration diagrams of Example 6 are shown in FIGS.
[0102]
The parameter values relating to the conditional expressions (A-1), (B-1), (1-1) to (9-1) in the above-described embodiments are shown below (other than the conditional expression (9-1)). For the conditional expression (9-1), the upper part shows the values of the first reflecting surface 2 and the lower part shows the values of the second reflecting surface 3, and the upper part shows the minimum value of each reflecting surface and the lower part shows the maximum value. Is shown.)
[0103]

.
[0104]
In the above embodiments, the free-form surface of the definition formula (a) is used, but it goes without saying that any definition of the curved surface can be used. However, no matter what definition formula is used, aberrations can be corrected very well, whether the conditional formulas shown in the present invention are satisfied singly or in combination, or even a few are satisfied. Needless to say, an image forming optical system can be obtained. In addition, the conditional expressions used in the conventional non-eccentric system such as the curvature of the surface and the focal length of the surface defined by the center of the coordinate system that defines the surface ignoring the eccentricity are large for each surface as in the present invention. If it is arranged eccentrically, it has no meaning.
[0105]
The details of the optical system that characterizes the present invention have been described above. Hereinafter, an example in which these optical systems are incorporated in an image reading apparatus and an information reproduction system using the image reading apparatus will be described.
[0106]
FIG. 11 is a cross-sectional view of the optical system 5 of the first embodiment applied to the image reading device 40 according to the present invention. In the figure, 5 is a prism body according to the first embodiment, 10 is an image sensor, 11 is an exterior, 12 is a substrate, 20 is an information recording medium (subject), 40 is a pen-type information reproducing device, as shown in FIG. The imaging element 10 can be mounted on the same substrate 12 together with other electrical components by simultaneously providing an optical member (prism body) 5 with an imaging action and an action of bending an optical path.
[0107]
Thus, the mounting efficiency is improved by using the reading optical system according to the present invention. In addition, since the number of necessary substrates can be reduced (in the case of FIG. 11, one), the cost can be reduced. As another function, as shown in the figure, the pen-type information reproducing device 40 may be inclined at a predetermined angle with respect to the information recording medium 20. When the pen-type information reproducing apparatus 40 is operated, as shown in FIG. 12, the operability is better when the pen-type information reproducing apparatus 40 is used at a predetermined angle θ with respect to the normal line of the information recording medium 20. Is good.
[0108]
Thus, in the case of the optical system 5 of the present invention, the degree of freedom with respect to the angle at which the optical path is bent is high, and in addition to the mounting effect, an operational effect is also obtained. In addition, although members other than the members shown in FIG. 11 are also arranged in the actual information reproducing apparatus 40, only the main part is shown in order to simplify the description. Details of the information reproducing system using such an image reading apparatus will be described later.
[0109]
FIG. 11 shows a specific example of the present invention in which the optical path of the illumination optical system that illuminates the information recording medium 20 and the optical path of the imaging optical system are arranged in the imaging optical member 5 as an embodiment different from FIG. It is shown in FIGS. As shown in these drawings, an incident surface for guiding illumination light from the light source 44A is provided in a portion within or outside the effective range of the imaging optical path of the optical member 5 constituting the imaging optical system, and the illumination overlaps with the imaging optical path. Form an optical path.
[0110]
In the case of FIG. 13, the reflective surface within the effective range of the imaging optical path in the second surface (third surface 3 in FIG. 1) in order from the information recording medium 20 side is the half mirror 14, and illumination from the light source 44A. An optical member 13 such as an auxiliary lens that guides light or a prism is disposed, and a light source 44A is disposed in the vicinity thereof. A light beam incident from the surface of the optical member 13 such as the auxiliary lens and prism on the light source 44A side enters the optical member 5 constituting the photographing optical system from the half mirror 14, and then passes through an optical path overlapping the photographing optical path to record information. The medium 20 is illuminated. The surface on the light source 44A side of the optical member 13 such as an auxiliary lens or a prism is a convex surface or the like, which is advantageous for uniform illumination. By overlapping the optical paths in this way, the device can be miniaturized. In addition, since the information recording medium 20 can be illuminated from substantially the front, uneven illumination hardly occurs.
[0111]
In the case of FIG. 14, except that the reflecting surface within the effective range of the photographing optical path in the third surface (second surface 2 in FIG. 1) in order from the information recording medium 20 side is the half mirror 14. This is the same as FIG.
[0112]
In the case of FIG. 15, the illumination optical path is configured using a portion 3 ′ outside the effective range of the imaging optical path in the second surface (the third surface 3 in FIG. 1) in order from the information recording medium 20 side. . Since the portion 3 ′ outside the effective range is used, it is not necessary to provide a half mirror, and the incident surface of the illumination optical path can be formed integrally with the optical member 5 constituting the photographing optical system, which is advantageous in terms of cost. .
[0113]
As described above, the problems inherent to the information reproduction system can be solved by providing the image reading apparatus and the information reproduction system with the optical system shown in each embodiment. Of course, the form of the information reproducing apparatus to be applied is not limited to the pen type, but can be applied to other forms.
[0114]
Hereinafter, an information reproduction system using the image reading apparatus as described above will be described in detail. A more detailed description can be found in Japanese Patent Application Laid-Open No. 6-231466, and only a specific configuration and an outline of the operation are shown here.
[0115]
Hereinafter, embodiments of the present invention relating to an information reproduction system will be described. Here, embodiments related to audio information such as voice and music in multimedia information will be described.
An audio information recording apparatus for recording audio information such as voice and music on paper as an optically readable digital signal is shown in FIG. 6 and is not described here.
[0116]
By this apparatus, for example, the data is recorded on the paper 30 in a format as shown in FIG. That is, sound data converted into a digital signal together with the image 32 and the characters 34 is printed as the recording data 36. Here, the recording data 36 includes a plurality of blocks 38, and each block 38 includes a marker 38A, an error correction code 38B, audio data 38C, x address data 38D, y address data 38E, and an error determination code 38F. It is configured.
[0117]
The marker 38A also functions as a synchronization signal, and uses a pattern that does not normally come out by recording modulation like DAT. The error correction code 38B is used for error correction of the audio data 38C. The audio data 38C corresponds to a microphone or an audio signal. The x address data 38D and the y address data 38E are data representing the position of the block 38, and the error determination code 38F is used for error determination of these x address and y address.
[0118]
The recording data 36 in such a format includes data “1” and “0” in the printer system or “1” with black dots and “0” with no black dots, for example, as in the case of barcodes. Printed and recorded by a printing plate making system. Hereinafter, such recording data is referred to as a dot code.
[0119]
FIG. 16B shows a scene in which sound data recorded on the paper 30 as shown in FIG. 16A is read out by a pen-type information reproducing apparatus (information reproducing system) 40. The dot code 36 is detected by tracing the dot code 36 with a pen-type information reproducing device 40 as shown in FIGS. 11 and 13 to 15, converted into sound, and listened to by an audio output device 42 such as an earphone. Can do.
[0120]
FIG. 17 is a block diagram of the information reproducing apparatus 40 in one embodiment of the present invention. In the information reproducing apparatus 40 of this embodiment, parts other than the audio output device 42 such as headphones and earphones are housed in a portable pen-type housing (not shown). Of course, it is good also as what incorporates a speaker in a housing | casing.
[0121]
The detection unit 44 illuminates the dot code 36 on the paper surface, which is the subject, with the light source 44A, reads the reflected light, and passes through the optical system 44B (prism body 5) and the spatial filter 44C, and is an imaging unit such as a semiconductor area sensor. It is detected as an image by 44D (imaging device 10), amplified by a preamplifier 44E, and output.
[0122]
Here, the pixel pitch of the area sensor 44D is set to be equal to or less than the dot pitch of the dot code 36 on the imaging surface by the sampling theorem. Furthermore, a spatial filter 44C installed on the imaging surface is also inserted to prevent moire development (aliasing) on the imaging surface based on this theorem.
[0123]
The image signal detected by the detection unit 44 as described above is first converted into a digital signal by the A / D converter 46A and stored in the frame memory 46B. The frame memory 46B has an 8-bit gradation.
[0124]
The marker detection circuit 46C detects the marker 38A by scanning the image signal stored in the frame memory 46B in a specific direction. The θ detection circuit 46D detects which address value on the imaging surface each marker 38A detected by the marker detection circuit 46C corresponds to, and calculates the inclination θ of the imaging surface with respect to the dot code arrangement direction from the address value. Calculate.
[0125]
On the other hand, in the lens aberration information memory 46E, previously measured aberration information of the reading optical system used in the imaging system 44B of the detection unit 44 for correcting the distortion of the reading optical system is recorded. Of course, since the aberration is corrected in the optical system of the present invention, this processing can be simplified. When the address control circuit 46F next reads the data stored in the frame memory 46B, the value of the inclination θ calculated by the θ detection circuit 46D and the lens aberration information stored in the lens aberration information memory 46E. According to the above, a read address is given to the frame memory 46B, and scanning conversion in the data array direction is performed while data interpolation is performed by the interpolation circuit 46G.
[0126]
The dot code 36 read from the frame memory 46B in response to the scan conversion is then binarized by a binarization circuit 48 constituted by a latch 48A and a comparator 48B. The threshold for binarization is determined by the threshold determination circuit 50 using the value of the histogram for each screen or each block in the screen. That is, the threshold is determined according to the stain on the dot code 36, the distortion of the paper 30, the accuracy of the built-in clock, and the like. As the threshold determination circuit 50, for example, a circuit using a neural network disclosed in Japanese Patent Application No. 4-131051 by the present applicant is preferably used.
[0127]
In parallel with this, the dot code 36 read from the frame memory 46B is input to the PLL circuit 52 and generates a clock pulse CK synchronized with the reproduction data. This clock pulse CK is used as a reference clock for binarization and demodulation after scan conversion, and an error determination circuit 56A, x, y address detection circuit 56B, memory unit 56C, etc. in the data string adjustment unit 56 described later. The
[0128]
The binarized data is demodulated by the demodulation circuit 54 and input to the error determination circuit 56A and the x, y address detection circuit 56B in the data string adjustment unit 56. The error determination circuit 56A uses the error determination code 38F in the block 38 to determine whether or not there is an error in the x and y address data 38D and 38E. If there is no error, the audio data 38C is not recorded in the audio data string adjustment memory unit 56C according to the address detected by the x, y address detection circuit 56A.
[0129]
The purpose of the data string adjustment unit 56 is to perform data conversion according to the accuracy of scan conversion in the scan conversion and lens distortion correction unit 46 (which depends on the accuracy of the reference clock and the S / N of the image sensor), paper distortion, and the like. The purpose is to correct a slight deviation occurring in the array direction and the scan direction after scan conversion.
Then, it is stored in the data string adjusting memory unit 56C according to the x and y addresses 38D and 38E in the respective blocks 38.
[0130]
Next, by manually scanning the detection unit 44, the audio dot code 36 on the paper 30 can be stored in the memory unit 56C for data string adjustment without exception.
[0131]
The voice dot code whose data string is adjusted by the data string adjusting unit 56 is then used for data string adjustment in accordance with a reference clock CK ′ generated by a reference clock generating circuit 53 different from the PLL circuit 52. Are read from the memory unit 56C. At this time, de-interleaving is performed by the de-interleaving circuit 58 and converted into a formal data string. Next, error correction using the error correction code 38 </ b> B in the block 38 is performed by the error correction circuit 60. Then, the compressed data is decoded by the decoding circuit 62, and further, the data interpolation circuit 64 performs interpolation of audio data that cannot be error-corrected. Thereafter, it is converted into an analog audio signal by the D / A conversion circuit 66, amplified by the amplifier 68, and converted into sound by the sound output device (earphone, headphone, speaker, etc.) 42.
[0132]
As described above, audio information such as voice and music can be recorded on paper, and the playback device is a small portable device so that it can be printed out, facsimile-transmitted, or You will be able to listen to the books printed in book format by printing plate making anywhere and any number of times.
[0133]
The data string adjustment memory unit 56C in the data string adjustment unit 56 is not limited to a semiconductor memory, and other recording media such as a floppy disk and an optical disk can be used.
[0134]
There are various possible application examples of the audio information recorded as described above. For example, for general use, various textbooks such as language teaching materials, sheet music, correspondence courses, product specifications, manuals for repair, foreign language dictionaries, encyclopedias, books such as picture books, product catalogs, travel guides, direct mail, Guidance letters, newspapers, magazines, flyers, albums, telegraphs, postcards, etc. can be considered. In addition, for business use, FAX (voice and fax) business instructions, minutes, electronic blackboard, OHP, identification card (voice print), business cards, telephone memos, sticky notes, and high-quality paper supply products (Consumables) etc. can be considered.
[0135]
Here, the recorded information has been described taking audio information such as voice and music as an example. However, the present invention is not limited to audio information, and as disclosed in JP-A-6-231466, a camera, video, etc. It may be a device that handles so-called multimedia information including video information obtained from the above and digital code data obtained from a personal computer, a word processor or the like.
[0136]
The image reading apparatus of the present invention and the information reproduction system using the same can be configured as follows, for example.
[1] Optically reading the dot code from a recording medium having a portion in which multimedia information including at least one of audio information, video information, and digital code data is recorded in an optically readable dot code In the image reading device to read,
A reading optical system comprising at least one reflecting surface having a reflecting action, and the surface shape of the reflecting surface is a rotationally asymmetric curved surface having no rotational symmetry axis both inside and outside the surface;
An image reading apparatus comprising: an image pickup element positioned on an image plane of an object plane formed by the reading optical system.
[0137]
[2] The image reading apparatus according to [1], wherein the surface shape of the reflection surface is a plane-symmetry free-form surface having only one symmetry surface.
[0138]
[3] The axial principal ray of the reading optical system in which the reflecting surface reaches the center of the imaging position of the image sensor is the Z axis, and the axial principal ray is the extension direction of the line segment on the reading optical system. When a direction perpendicular to the Z-axis is defined as a Y-axis and a direction perpendicular to the Z-axis and the Y-axis is defined as an X-axis in a plane including a folded line segment when the light is reflected by the reflecting surface, The image reading apparatus according to [1] or [2], wherein the following condition (A-1) is satisfied.
| RX | <0.5 (1 / mm) (A-1)
However, RX is a curvature in the X direction of a portion where the axial principal ray hits the reflecting surface.
[0139]
[4] The axial principal ray of the reading optical system in which the reflecting surface reaches the center of the imaging position of the image sensor is the Z axis, and the axial principal ray is the extension direction of the line segment on the reading optical system. When a direction perpendicular to the Z-axis is defined as a Y-axis and a direction perpendicular to the Z-axis and the Y-axis is defined as an X-axis in a plane including a folded line segment when the light is reflected by the reflecting surface, The image reading apparatus according to the above [1] or [2], wherein the following condition (B-1) is satisfied.
| RY | <0.5 (1 / mm) (B-1)
However, RY is the curvature in the Y direction of the portion where the axial principal ray hits the reflecting surface.
[0140]
[5] The axial principal ray of the reading optical system in which the reflecting surface reaches the center of the imaging position of the image sensor is the Z axis, and the axial principal ray is the extension direction of the line segment incident on the reading optical system. When a direction perpendicular to the Z-axis is defined as a Y-axis and a direction perpendicular to the Z-axis and the Y-axis is defined as an X-axis in a plane including a folded line segment when the light is reflected by the reflecting surface, The image reading apparatus according to the above [1] or [2], wherein the following conditions (A-1) and (B-1) are satisfied.
| RX | <0.5 (1 / mm) (A-1)
| RY | <0.5 (1 / mm) (B-1)
However, RX and RY are the curvatures in the X direction and Y direction of the portion where the axial principal ray hits the reflecting surface, respectively.
[0141]
[6] The image reading apparatus according to [3] or [5], wherein the reflecting surface satisfies the following condition (A-2).
| RX | <0.1 (1 / mm) (A-2).
[0142]
[7] The image reading apparatus according to [3] or [5], wherein the reflecting surface satisfies the following condition (A-3).
| RX | <0.05 (1 / mm) (A-3).
[0143]
[8] The image reading apparatus according to [4] or [5] above, wherein the reflecting surface satisfies the following condition (B-2).
| RY | <0.1 (1 / mm) (B-2).
[0144]
[9] The image reading apparatus according to [4] or [5], wherein the reflecting surface satisfies the following condition (B-3).
| RY | <0.05 (1 / mm) (B-3).
[0145]
[10] The symmetric plane of the plane-symmetry free-form surface reaches the center of the imaging position of the image sensor, and the extension direction of the line segment on which the axial principal ray of the reading optical system enters the reading optical system is Z-axis, A direction perpendicular to the Z axis in a plane including a folded line segment when the axial principal ray is reflected by the reflecting surface is a Y axis, and a direction perpendicular to the Z axis and the Y axis is an X axis. The image reading apparatus according to any one of [2] to [9] above, wherein when defined, the image reading apparatus exists on a YZ plane or a plane parallel to the YZ plane.
[0146]
[11] At least one of the reflective refractive power in the YZ plane of the region where the axial principal ray is reflected in the reflective surface and the reflective refractive power in the plane perpendicular to the YZ plane is positive. The image reading apparatus according to any one of [3] to [10], wherein the image reading apparatus is provided.
[0147]
[12] The catadioptric power in the YZ plane of the region where the axial principal ray is reflected in the reflecting surface and the catadioptric power in the plane perpendicular to the YZ plane are both positive. The image reading apparatus according to any one of [3] to [10], wherein:
[0148]
[13] The axial principal ray of the reading optical system that reaches the center of the imaging position of the image sensor is the Z axis, and the axial principal ray is the reflecting surface. When a direction perpendicular to the Z-axis is defined as a Y-axis and a direction perpendicular to the Z-axis and the Y-axis is defined as an X-axis in a plane including a folded line segment when reflected, the reflection surface is The image reading apparatus according to any one of [1] to [12], wherein the condition (1) is satisfied.
｜ DX _max1 | <100.0 (mm) (1-1)
However, DX _max1 = MAX ((DX-DX _axis ) / RX), with the Y-axis direction being the vertical direction, the axial principal ray at the center of the imaging screen, the principal ray at the upper central field angle, the principal ray at the upper right field angle, the principal ray at the right central field angle, and the lower right corner An area where the chief ray of the field angle and the chief ray of the lower central field angle intersect with the target surface is defined as an effective region, and these six chief rays hit the direction orthogonal to the eccentric direction of the surface that hits the target surface. Each value obtained by differentiating the expression defining the shape of the surface about the axis once is DX _axis , DX1, DX4, DX5, DX6, DX3, DX is the value of DX1, DX4, DX5, DX6, DX3, and RX is the curvature in the X direction of the portion where the axial principal ray hits the reflecting surface.
[0149]
[14] The axial principal ray of the reading optical system that reaches the center of the imaging position of the image sensor is the Z axis, and the axial principal ray is the reflecting surface. When a direction perpendicular to the Z-axis is defined as a Y-axis and a direction perpendicular to the Z-axis and the Y-axis is defined as an X-axis in a plane including a folded line segment when reflected, the reflection surface is The image reading apparatus according to any one of [1] to [13], wherein the condition (1) is satisfied.
｜ DY _max2 | <100.0 (mm) (2-1)
However, DY _max2 = MAX ((DY-DY _axis ) / RY) where the Y-axis direction is the vertical direction, the axial principal ray at the center of the imaging screen, the principal ray at the upper central field angle, the principal ray at the upper right field angle, the principal ray at the right central field angle, the lower right corner The area where the chief ray of the angle of view and the chief ray of the lower central field angle intersect with the target surface is defined as an effective region, and the surface of the surface about the Y axis where these six chief rays hit the eccentric direction of the surface where it hits the target surface Each value obtained by differentiating the expression defining the shape once is DY. _axis , DY1, DY4, DY5, DY6, DY3, DY is the value of DY1, DY4, DY5, DY6, DY3, and RY is the curvature in the Y direction of the portion where the axial principal ray hits the reflecting surface.
[0150]
[15] The axial principal ray of the reading optical system that reaches the center of the imaging position of the image sensor is the Z axis, and the axial principal ray is the reflecting surface. When a direction perpendicular to the Z-axis is defined as a Y-axis and a direction perpendicular to the Z-axis and the Y-axis is defined as an X-axis in a plane including a folded line segment when reflected, the reflection surface is The image reading apparatus according to any one of [1] to [14], wherein the condition (1) is satisfied.
｜ DX _Three | <0.4 (3-1)
However, DX _Three = (DX4-DX1)-(DX6-DX3), where the Y-axis direction is the vertical direction, the axial principal ray at the center of the imaging screen, the principal ray at the upper central field angle, the principal ray at the upper right field angle, and the right center The area where the principal ray of the angle of view, the principal ray of the lower right field angle, and the principal ray of the lower center field angle intersects the target surface is defined as an effective region, and the surface of the portion where these six principal rays hit the target surface Each value obtained by differentiating once the expression defining the shape of the surface about the X axis corresponding to the direction orthogonal to the eccentric direction is DX _axis , DX1, DX4, DX5, DX6, DX3.
[0151]
[16] The axial principal ray of the reading optical system that reaches the center of the imaging position of the image sensor is the Z axis, and the axial principal ray is the reflecting surface. When a direction perpendicular to the Z-axis is defined as a Y-axis and a direction perpendicular to the Z-axis and the Y-axis is defined as an X-axis in a plane including a folded line segment when reflected, the reflection surface is The image reading apparatus according to any one of [1] to [15], wherein the condition (1) is satisfied.
｜ DY _Four | <0.4 (4-1)
However, DY _Four = (DY4-DY1)-(DY6-DY3), where the Y-axis direction is the vertical direction, the axial principal ray at the center of the imaging screen, the principal ray at the upper central field angle, the principal ray at the upper right field angle, and the right center The area where the principal ray of the angle of view, the principal ray of the lower right field angle, and the principal ray of the lower center field angle intersects the target surface is defined as an effective region, and the surface of the portion where these six principal rays hit the target surface The values obtained by differentiating the expression defining the shape of the surface about the Y axis in the eccentric direction once are expressed as DY. _axis , DY1, DY4, DY5, DY6, DY3.
[0152]
[17] The axial principal ray of the reading optical system that reaches the center of the imaging position of the image sensor is an extension direction of a line segment incident on the reading optical system, and the axial principal ray is the reflection surface. When a direction perpendicular to the Z-axis is defined as a Y-axis and a direction perpendicular to the Z-axis and the Y-axis is defined as an X-axis in a plane including a folded line segment when reflected, the reflection surface is The image reading apparatus according to any one of [1] to [16], wherein the condition (1) is satisfied.
｜ DX _max5 | <0.5 (5-1)
However, DX _max5 = (DX5-DX _axis ), With the Y-axis direction as the vertical direction, the axial principal ray at the center of the imaging screen, the principal ray at the upper central field angle, the principal ray at the upper right field angle, the principal ray at the right central field angle, and the lower right field angle The area where the chief ray and the chief ray of the lower central angle of view intersect the target surface is defined as the effective area, and the surface about the X axis where these six chief rays hit the direction perpendicular to the eccentric direction of the surface of the target surface Each value obtained by differentiating the expression that defines the shape of _axis , DX1, DX4, DX5, DX6, DX3.
[0153]
[18] The axial principal ray of the reading optical system that reaches the center of the imaging position of the image sensor is the Z axis, and the axial principal ray is the reflecting surface. When a direction perpendicular to the Z-axis is defined as a Y-axis and a direction perpendicular to the Z-axis and the Y-axis is defined as an X-axis in a plane including a folded line segment when reflected, the reflection surface is The image reading apparatus according to any one of [1] to [17], wherein the following condition is satisfied.
｜ DY _max6 | <0.5 (6-1)
However, DY _max6 = (DY5-DY _axis ), With the Y-axis direction as the vertical direction, the axial principal ray at the center of the imaging screen, the principal ray at the upper central field angle, the principal ray at the upper right field angle, the principal ray at the right central field angle, and the lower right field angle The area where the chief ray and the chief ray at the lower central angle of view intersect the target surface is defined as the effective area, and the shape of the surface is defined with respect to the Y axis where these six chief rays hit the target surface in the eccentric direction. The value obtained by differentiating the expression to be DY _axis , DY1, DY4, DY5, DY6, DY3.
[0154]
[19] The axial principal ray of the reading optical system that reaches the center of the image forming position of the image pickup device has a Z-axis as the extension direction of the line segment incident on the reading optical system, and the axial principal ray is the reflecting surface. When a direction perpendicular to the Z-axis is defined as a Y-axis and a direction perpendicular to the Z-axis and the Y-axis is defined as an X-axis in a plane including a folded line segment when reflected, the reflection surface is The image reading apparatus according to any one of [1] to [18], wherein the following condition is satisfied.
DDX _max7 <0.5 (1 / mm) (7-1)
However, with the Y-axis direction as the vertical direction, the axial principal ray at the center of the imaging screen, the principal ray at the upper central field angle, the principal ray at the upper right field angle, the principal ray at the right central field angle, and the principal ray at the lower right field angle The area where the principal ray of the lower central field angle intersects the target surface is defined as the effective area, and the difference between the maximum value and the minimum value of the curvature in the X direction within this effective area is defined as DDX. _max7 And
[0155]
[20] The axial principal ray of the reading optical system that reaches the center of the imaging position of the image sensor is the Z axis, and the axial principal ray is the reflecting surface. When a direction perpendicular to the Z-axis is defined as a Y-axis and a direction perpendicular to the Z-axis and the Y-axis is defined as an X-axis in a plane including a folded line segment when reflected, the reflection surface is The image reading apparatus according to any one of [1] to [19], wherein the condition (1) is satisfied.
DDY _max8 <0.5 (1 / mm) (8-1)
However, with the Y-axis direction as the vertical direction, the axial principal ray at the center of the imaging screen, the principal ray at the upper central field angle, the principal ray at the upper right field angle, the principal ray at the right central field angle, and the principal ray at the lower right field angle , The region where the principal ray of the lower central field angle intersects the target surface is defined as an effective region, and the difference between the maximum value and the minimum value of the curvature in the Y direction within this effective region is defined as DDY. _max8 And
[0156]
[21] The axial principal ray of the reading optical system that reaches the center of the imaging position of the image sensor is the Z axis, and the axial principal ray is the reflecting surface. When a direction perpendicular to the Z-axis is defined as a Y-axis and a direction perpendicular to the Z-axis and the Y-axis is defined as an X-axis in a plane including a folded line segment when reflected, the reflection surface is The image reading apparatus according to any one of [1] to [20], wherein the condition (1) is satisfied.
0.01 <DD _xy9 <40 (9-1)
However, with the Y-axis direction as the vertical direction, the axial principal ray at the center of the imaging screen, the principal ray at the upper central field angle, the principal ray at the upper right field angle, the principal ray at the right central field angle, and the principal ray at the lower right field angle The region where the principal ray of the lower central field angle intersects the target surface is defined as the effective region, and the shape of the surface about the X axis perpendicular to the eccentric direction of the surface where these six principal rays hit the target surface is defined as The curvatures of the formulas to be defined are DDX2, DDX1, DDX4, DDX5, DDX6, and DDX3, respectively, and the curvatures of the formulas that define the shape of the surface with respect to the Y-axis corresponding to the eccentric direction of the surface are DDY2, DDY1, DDY4, DDY5, DDY6, DDY3 and DD _xy9 = | DDXn | / | DDYn | (n is 1 to 6).
[0157]
[22] Any one of the above [1] to [21], wherein the reflecting surface is constituted by a back reflecting mirror having a medium having a refractive index (n) larger than 1 (n> 1). The image reading apparatus according to item.
[0158]
[23] The reading optical system has at least first, second, and third surfaces, and at least one of the three surfaces is constituted by the back reflector. The image reading apparatus according to [22] above.
[0159]
[24] The reading optical system includes a first surface disposed to face the imaging element, a second surface disposed to face the object side, at least the first surface and the second surface, and refraction. A prism member having a third surface sandwiching a medium having a ratio n larger than 1 (n> 1), and the third surface is formed by the reflective surface. The image reading apparatus according to any one of [1] to [23].
[0160]
[25] The reading optical system includes a first surface disposed to face the imaging element, a second surface disposed to face the object side, at least the first surface and the second surface, and refraction. A prism member having a first reflection surface and a second reflection surface sandwiching a medium having a ratio n larger than 1 (n> 1), wherein the first reflection surface and the second reflection surface are the reflection members; The image reading apparatus according to any one of [1] to [23], wherein the image reading apparatus is formed on a surface.
[0161]
[26] The first reflecting surface is disposed on the opposite side to the imaging element with respect to the first surface, and the second reflecting surface is opposite to the object surface with respect to the second surface. And a principal ray connecting the first reflecting surface and the image sensor is arranged so as to intersect with a principal ray connecting the object surface and the second reflecting surface. The image reading apparatus according to [25].
[0162]
[27] The image reading apparatus according to [1], wherein the reflecting surface is inclined with respect to an axial principal ray incident on the reading optical system.
[0163]
[28] The image reading apparatus according to [1] or [27], wherein the normal on the imaging surface side of the imaging element intersects with an axial principal ray incident on the reading optical system.
[0164]
[29] Any one of the above [1], [27], and [28], wherein a conjugate plane of the imaging surface of the imaging device by the reading optical system is inclined with respect to the imaging surface The image reading apparatus according to claim 1.
[0165]
[30] The image reading apparatus according to [29], wherein an angle formed by the conjugate plane and the imaging surface is an obtuse angle.
[0166]
[31] The image reading apparatus according to [29] or [30], wherein an angle formed between a normal line of the conjugate plane and a longitudinal direction of the image reading apparatus is an acute angle.
[0167]
[32] The image reading apparatus according to any one of [29], [30], and [31], wherein the imaging surface is disposed substantially parallel to a longitudinal direction of the image reading apparatus.
[0168]
[33] Illuminating means for illuminating an information recording medium arranged at a conjugate plane position of the imaging surface of the imaging element by the reading optical system, and the illuminating means emits light from the light emitting element and the light flux from the light emitting element. Any one of [1] to [32] above, wherein the illumination optical system guides to a recording medium, and at least a part of the illumination optical system is shared with at least a part of the reading optical system. The image reading apparatus described.
[0169]
[34] The image reading apparatus according to [33], wherein the light beam of the light emitting element is incident on the reading optical system from outside the effective range of the reflecting surface of the imaging optical path of the reading optical system.
[0170]
[35] The image reading apparatus according to [34], wherein a surface on which the light beam of the light emitting element of the reading optical system is incident is formed with a convex surface facing the light emitting element.
[0171]
[36] The image reading apparatus according to [33], wherein the light emitting element is disposed on the back side of the reflecting surface of the reading optical system, and the light beam of the light emitting element is incident from the back side of the reflecting surface.
[0172]
[37] The image reading apparatus according to [33] or [36], wherein an auxiliary lens is provided on a surface of the reading optical system on which a light beam of the light emitting element is incident.
[0173]
[38] The image reading apparatus according to [37], wherein the auxiliary lens has a convex surface facing the light emitting element.
[0174]
[39] Any one of [1] to [38], wherein a distance from a conjugate plane of the imaging surface of the imaging element to the incident surface of the reading optical system by the reading optical system is 10 centimeters or less. The image reading apparatus according to claim 1.
[0175]
[40] The image reading device according to any one of [1] to [39], a restoration unit that converts the dot code read by the image reading device into original multimedia information, and restoration by the restoration unit And an output means for outputting the multimedia information.
[0176]
【The invention's effect】
As is clear from the above description, according to the present invention, it is possible to provide an image reading apparatus having a simple configuration and reduced in size, and an information reproduction system using the image reading apparatus.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of Embodiment 1 of a reading optical system used in the present invention.
FIG. 2 is a cross-sectional view of Embodiment 2 of a reading optical system used in the present invention.
FIG. 3 is a sectional view of Embodiment 3 of a reading optical system used in the present invention.
FIG. 4 is a cross-sectional view of Embodiment 4 of the reading optical system used in the present invention.
FIG. 5 is a sectional view of Embodiment 5 of a reading optical system used in the present invention.
FIG. 6 is a cross-sectional view of Embodiment 6 of a reading optical system used in the present invention.
7 is a diagram illustrating a part of a lateral aberration diagram of the reading optical system according to Example 2. FIG.
8 is a diagram illustrating the remainder of the lateral aberration diagram of the reading optical system according to Example 2. FIG.
9 is a diagram illustrating a part of a lateral aberration diagram of the reading optical system according to Example 6. FIG.
10 is a diagram illustrating the remainder of the lateral aberration diagram of the reading optical system according to Example 6. FIG.
FIG. 11 is a cross-sectional view of one specific example of an image reading apparatus according to the present invention.
FIG. 12 is a diagram for explaining the operability of a pen-type information reproducing apparatus that is used while being tilted with respect to an information recording medium.
FIG. 13 is a cross-sectional view of a principal part showing an example of a specific arrangement of an illumination optical system of the image reading apparatus.
FIG. 14 is a cross-sectional view of the principal part showing another example of the specific arrangement of the illumination optical system.
FIG. 15 is a cross-sectional view of the principal part showing still another example of the specific arrangement of the illumination optical system.
FIG. 16 is a diagram illustrating an example of dot-coded multimedia information and a usage status of the information reproducing apparatus.
FIG. 17 is a block diagram of an information reproducing apparatus according to one embodiment based on the present invention.
FIG. 18 is a cross-sectional view of an image reading apparatus according to the previous proposal.
[Explanation of symbols]
1 ... first side
2 ... Second side
3 ... Third surface
4 ... Fourth side
5. Prism body (reading optical system)
6 ... Cover glass
3 '... part outside the effective range of the reading optical
10: Image sensor
11 ... Exterior
12 ... Board
13. Optical members such as auxiliary lenses and prisms
14 ... Half mirror
20. Information recording medium (subject)
30 ... paper
32 ... Image
34 ... characters
36 ... Recording data (dot code)
38 ... Block
38A ... Marker
38B ... Error correction code
38C ... Audio data
38D ... x address data
38E ... y address data
38F: Error determination code
40. Image reading device (pen-type information reproducing device (information reproducing system))
42 ... Audio output device
44... Detection unit
44A ... Light source
44B: Reading optical system
44C ... Spatial filter
44D ... Imaging unit
44E ... Preamplifier
46: Scan conversion and lens distortion correction unit
46A ... A / D converter
46B ... Frame memory
46C ... Marker detection circuit
46D ... θ detection circuit
46E ... Lens aberration information memory
46F ... Address control circuit
46G ... Interpolation circuit
48 ... binarization circuit
48A ... Latch
48B ... Comparator
50. Threshold determination circuit
52. PLL circuit
54. Demodulator circuit
56: Data string adjustment unit
56A ... Error determination circuit
56B ... x, y address detection circuit
56C ... Memory section
53. Reference clock generation circuit
58 ... De-interleave circuit
60. Error correction circuit
62 ... Decoding circuit
64: Data interpolation circuit
66 ... D / A conversion circuit
68 ... Amplifier
O ... Object surface
I ... Image plane
CK ... Clock pulse
CK '... Reference clock

Claims (3)

Image reading that optically reads the dot code from a recording medium having a portion in which multimedia information including at least one of audio information, video information, and digital code data is recorded as an optically readable dot code In the device
A reading optical system comprising at least one reflecting surface having a reflecting action, and the surface shape of the reflecting surface is a rotationally asymmetric curved surface having no rotational symmetry axis both inside and outside the surface;
Possess an imaging device located on the image plane of the object plane formed by the reading optical system,
The reflecting surface has an axial principal ray of the reading optical system that reaches the center of the image forming position of the image sensor, and the extending direction of the line segment incident on the reading optical system is the Z axis, and the axial principal ray is reflected. When a direction perpendicular to the Z-axis is defined as a Y-axis and a direction perpendicular to the Z-axis and the Y-axis is defined as an X-axis in a plane including a folded line segment when reflected by a surface, the following conditions are satisfied. An image reading apparatus satisfying (A-1) .
| RX | <0.5 (1 / mm) (A-1)
However, RX is a curvature in the X direction of a portion where the axial principal ray hits the reflecting surface.   2. The image reading apparatus according to claim 1, wherein the surface shape of the reflecting surface is a plane-symmetry free-form surface having only one symmetry surface. Image reading that optically reads the dot code from a recording medium having a portion in which multimedia information including at least one of audio information, video information, and digital code data is recorded as an optically readable dot code In the device
A light source for illuminating the recording medium;
A rotationally asymmetric curved surface having at least one reflecting surface having a reflecting action and an incident surface on which illumination light from the light source is incident, and the surface shape of the reflecting surface does not have a rotationally symmetric axis both inside and outside the surface. An optical member,
An imaging element located on the image plane of the object plane formed by the optical member,
An imaging optical path of an imaging optical system from the image sensor through the optical member to the recording medium and an illumination optical path of an illumination optical system from the light source through the optical member to the recording medium are included in the optical member. An image reading apparatus characterized by being arranged in an overlapping manner .

Images