JP4636736B2 - Scanning optical device and image forming apparatus using the same - Google Patents

Description

【００５６】
但し、Ｒは曲率半径、ｋ、Ｂ₄、Ｂ₆、Ｂ₈、Ｂ₁₀は非球面係数
（係数に添字ｕが付く場合、走査開始側
係数に添字１が付く場合、走査終了側）
副走査方向‥‥曲率半径がＹ軸方向に連続的に変化する球面形状
ｒ'＝ｒ(１＋Ｄ₂Ｙ²＋Ｄ₄Ｙ⁴＋Ｄ₆Ｙ⁶＋Ｄ₈Ｙ⁸＋Ｄ₁₀Ｙ¹⁰)
但し、ｒは曲率半径、Ｄ₂、Ｄ₄、Ｄ₆、Ｄ₈、Ｄ₁₀は非球面係数
（係数に添字ｕが付く場合、走査開始側
係数に添字１が付く場合、走査終了側）
表−１に本実施形態における光学配置を示し、表−２に本実施形態における入射光学手段の形状を示し、表−３（Ａ），（Ｂ）に本実施形態における走査光学手段の非球面係数を示し、表−４に本実施形態における各条件式（１）〜（５）に対する値を示す。
【００５７】
【表１】

【００５８】
【表２】

【００５９】
【表３】

【００６０】
【表４】

【００６１】
【表５】

【００６２】
本実施形態では表−４に示すように各条件式（１）〜（５）をすべて満足している。
【００６３】
図２は本実施形態における主走査方向の像面湾曲を示した図、図３は本実施形態における副走査方向の像面湾曲を示した図、図４は本実施形態におけるｆθ特性を示した図、図５は本実施形態における主走査方向のコマ収差を示した図、図６は本実施形態の走査開始位置合わせ後の主走査方向における相対的な走査位置ずれを示した図である。各図に示すように本実施形態では実用上問題の無いレベルまで補正されていることが分かる。図１３は偏向手段の偏向角に対する偏向面と入射光学手段の光軸との交点の移動量を示した図である。
【００６４】
このように本実施形態においては上記の条件式（１）〜（４）及び条件式（５）を満足させることにより、発光部１ａ，１ｂの主走査方向に対する走査位置ずれを軽減することができ、これによりコンパクトで高精細な印字を可能にしている。また本実施形態では入射光学手段１１から回転多面鏡５に導光される光束を収束光束とすることにより、装置全体の小型化を図っている。
【００６５】
尚、本実施形態では上記の条件式（１）〜（４）及び条件式（５）を全て満足させたが、条件式（１）、（５）のいずれか一方のみを満足させれば本発明の目的は達せられる。
【００６６】
［実施形態２］
図７は本発明の実施形態２の主走査方向の要部断面図（主走査断面図）である。同図において図１に示した要素と同一要素には同符番を付している。
【００６７】
本実施形態において前述の実施形態１と異なる点は入射光学手段１１の一要素を構成するシリンドリカルレンズ部を第１、第２のシリンドリカルレンズの２枚より構成したことと、走査光学手段の光学配置及び各レンズの形状を異ならせて形成したことである。その他の構成及び光学的作用は実施形態１と略同様である。
【００６８】
即ち、同図において７４はシリンドリカルレンズ部であり、凸の第１のシリンドリカルレンズ７４ａと凹の第２のシリンドリカルレンズ７４ｂとを有している。７６はｆθ特性を有する走査光学手段（ｆθレンズ系）であり、主走査方向と副走査方向とで互いに異なるパワーを有する第１の光学素子７６ａ及び第２の光学素子７６ｂとを有している。
【００６９】
表−５（Ａ），（Ｂ）に本実施形態における光学配置を示し、表−６に本実施形態における入射光学手段の非球面係数を示し、表−７（Ａ），（Ｂ）に本実施形態における走査光学手段の非球面係数を示し、前記表−４に本実施形態における各条件式（１）〜（５）に対する値を示す。
【００７０】
【表６】

【００７１】
【表７】

【００７２】
【表８】

【００７３】
【表９】

【００７４】
【表１０】

【００７５】
本実施形態では前記表−４に示すように各条件式（１）〜（５）をすべて満足している。
【００７６】
図８は本実施形態における主走査方向の像面湾曲を示した図、図９は本実施形態における副走査方向の像面湾曲を示した図、図１０は本実施形態におけるｆθ特性を示した図、図１１は本実施形態における主走査方向のコマ収差を示した図、図１２は本実施形態の走査開始位置合わせ後の主走査方向における相対的な走査位置ずれを示した図である。各図に示すように本実施形態では実用上問題の無いレベルまで補正されていることが分かる。
【００７７】
このように本実施形態においては上記の条件式（１）〜（４）及び条件式（５）を全て満足させることにより、発光部１ａ，１ｂの主走査方向に対する走査位置ずれを軽減することができ、これによりコンパクトで高精細な印字を可能にしている。更に前述の実施形態１と同様に入射光学手段１１から回転多面鏡５に導光される光束を収束光束とすることにより、装置全体の小型化を図っている。
【００７８】
尚、本実施形態においても前述の実施形態１と同様に条件式（１）〜（４）及び条件式（５）を全て満足させたが、条件式（１）、（５）のいずれか一方のみを満足させれば本発明の目的は達せられる。
【００７９】
また本発明においては条件式（１）〜（５）のうちの少なくとも１つを満足させても所定の効果が得られる。
【００８０】
［画像形成装置］
図１７は、前述した実施形態１又は２の走査光学装置を用いた画像形成装置（電子写真プリンタ）の実施形態を示す副走査方向の要部断面図である。図１７において、符号１０４は画像形成装置を示す。この画像形成装置１０４には、パーソナルコンピュータ等の外部機器１１７からコードデータＤｃが入力する。このコードデータＤｃは、装置内のプリンタコントローラ１１１によって、画像データ（ドットデータ）Ｄｉに変換される。この画像データＤｉは、各実施形態１、２で示した構成を有する光走査ユニット１００に入力される。そして、この光走査ユニット（走査光学装置）１００からは、画像データＤｉに応じて変調された光ビーム（光束）１０３が射出され、この光ビーム１０３によって感光ドラム１０１の感光面が主走査方向に走査される。
【００８１】
静電潜像担持体（感光体）たる感光ドラム１０１は、モータ１１５によって時計廻りに回転させられる。そして、この回転に伴って、感光ドラム１０１の感光面が光ビーム１０３に対して、主走査方向と直交する副走査方向に移動する。感光ドラム１０１の上方には、感光ドラム１０１の表面を一様に帯電せしめる帯電ローラ１０２が表面に当接するように設けられている。そして、帯電ローラ１０２によって帯電された感光ドラム１０１の表面に、前記光走査ユニット１００によって走査される光ビーム１０３が照射されるようになっている。
【００８２】
先に説明したように、光ビーム１０３は、画像データＤｉに基づいて変調されており、この光ビーム１０３を照射することによって感光ドラム１０１の表面に静電潜像を形成せしめる。この静電潜像は、上記光ビーム１０３の照射位置よりもさらに感光ドラム１０１の回転方向の下流側で感光ドラム１０１に当接するように配設された現像器１０７によってトナー像として現像される。
【００８３】
現像器１０７によって現像されたトナー像は、感光ドラム１０１の下方で、感光ドラム１０１に対向するように配設された転写ローラ（転写器）１０８によって被転写材たる用紙１１２上に転写される。用紙１１２は感光ドラム１０１の前方（図１７において右側）の用紙カセット１０９内に収納されているが、手差しでも給紙が可能である。用紙カセット１０９端部には、給紙ローラ１１０が配設されており、用紙カセット１０９内の用紙１１２を搬送路へ送り込む。
【００８４】
以上のようにして、未定着トナー像を転写された用紙１１２はさらに感光ドラム１０１後方（図１７において左側）の定着器へと搬送される。定着器は内部に定着ヒータ（図示せず）を有する定着ローラ１１３とこの定着ローラ１１３に圧接するように配設された加圧ローラ１１４とで構成されており、転写部から撒送されてきた用紙１１２を定着ローラ１１３と加圧ローラ１１４の圧接部にて加圧しながら加熱することにより用紙１１２上の未定着トナー像を定着せしめる。更に定着ローラ１１３の後方には排紙ローラ１１６が配設されており、定着された用紙１１２を画像形成装置の外に排出せしめる。
【００８５】
図１７においては図示していないが、プリントコントローラ１１１は、先に説明したデータの変換だけでなく、モータ１１５を始め画像形成装置内の各部や、光走査ユニット１００内のポリゴンモータなどの制御を行う。
【００８６】
【発明の効果】
本発明によれば前述の如く光源手段として複数の発光部を有するマルチ半導体レーザーと、偏向手段として回転多面鏡とが用いられる走査光学装置において、該走査光学装置を構成する各要素を適切に設定すると共に、条件式（１）、（５）のいずれか一方を満足させることにより、被走査面上における複数の光束の結像点の主走査方向の位置ずれを軽減し、コンパクトで高精細な印字が可能な走査光学装置及びそれを用いた画像形成装置を達成することができる。
【図面の簡単な説明】
【図１】 本発明の実施形態１の主走査方向の要部断面図（主走査断面図）
【図２】 本発明の実施形態１の主走査方向の像面湾曲を示す図
【図３】 本発明の実施形態１の副走査方向の像面湾曲を示す図
【図４】 本発明の実施形態１の歪曲収差（ｆθ特性）、像高ずれを示す図
【図５】 本発明の実施形態１の主走査方向のコマ収差を示す図
【図６】 本実施形態の走査開始位置合わせ後の主走査方向における相対的な走査位置ずれを示した図
【図７】 本発明の実施形態２の主走査方向の要部断面図（主走査断面図）
【図８】 本発明の実施形態２の主走査方向の像面湾曲を示す図
【図９】 本発明の実施形態２の副走査方向の像面湾曲を示す図
【図１０】 本発明の実施形態２の歪曲収差（ｆθ特性）、像高ずれを示す図
【図１１】 本発明の実施形態２の主走査方向のコマ収差を示す図
【図１２】 本実施形態の走査開始位置合わせ後の主走査方向における相対的な走査位置ずれを示した図
【図１３】 偏向手段の偏向角に対する偏向面と入射光学手段の光軸との交点の移動量
【図１４】 偏向手段を回転したときの像点の移動の仕方を示す説明図
【図１５】 偏向手段を回転したときの像点の移動の仕方を示す説明図
【図１６】 偏向手段を回転したときの像点の移動の仕方を示す説明図
【図１７】 本発明の走査光学装置を用いた画像形成装置（電子写真プリンタ）の構成例を示す副走査方向の要部断面図
【符号の説明】
１ 光源手段（マルチ半導体レーザ）
１ａ，１ｂ 発光部
２ 集光レンズ（コリメーターレンズ）
３ 開口絞り
４，７４ シリンドリカルレンズ部
５ 偏向手段（回転多面鏡）
５ａ 偏向面
６ 走査光学手段
６ａ 第１光学素子
６ｂ 第２光学素子
７ 被走査面（感光ドラム面）
１１ 入射光学手段
７４ａ 第１のシリンドリカルレンズ
７４ｂ 第２のシリンドリカルレンズ
１００ 走査光学装置
１０１ 感光ドラム
１０２ 帯電ローラ
１０３ 光ビーム
１０４ 画像形成装置
１０７ 現像装置
１０８ 転写ローラ
１０９ 用紙カセット
１１０ 給紙ローラ
１１１ プリンタコントローラ
１１２ 転写材（用紙）
１１３ 定着ローラ
１１４ 加圧ローラ
１１５ モータ
１１６ 排紙ローラ
１１７ 外部機器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a scanning optical apparatus and an image forming apparatus using the same, and in particular, by appropriately setting each element constituting the scanning optical apparatus, a main scanning direction of an imaging point of a plurality of light beams on a scanned surface This is suitable for an apparatus such as a laser beam printer or a digital copying machine capable of reducing the positional deviation and enabling compact and high-definition printing.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in a scanning optical device used in an image forming apparatus such as a laser beam printer (LBP) or a digital copying machine, a light beam that is light-modulated and emitted from a light source unit according to an image signal is transmitted through an incident optical unit, for example, a rotating multi-plane. The light is deflected periodically by an optical deflector composed of a mirror (polygon mirror), converged in a spot shape on a photosensitive recording medium (photosensitive drum) surface by scanning optical means having fθ characteristics, and the surface is optically scanned. Image recording.
[0003]
2. Description of the Related Art In recent years, with the improvement in performance and functionality of image forming apparatuses, there has been an increasing demand for speeding up. To meet this demand, a scanning optical apparatus using light source means having a plurality of light emitting units (light sources) has been developed. Various proposals have been made.
[0004]
For example, in Japanese Patent Application Laid-Open No. 9-54263, a multi-beam laser chip that emits a plurality of laser beams (light beams) arranged in a straight line from one chip is used as a light source.
[0005]
At the same time, there is an increasing demand for miniaturization of the entire apparatus. For example, various scanning optical apparatuses have been proposed which are miniaturized by converging the light beam directed toward the deflecting means in the main scanning direction.
[0006]
For example, in Japanese Patent Application Laid-Open No. 5-0455580, the entire apparatus is used by using a first condensing optical system that converts a light beam from a light source device into a convergent light beam that converges toward a natural convergence point set behind the surface to be scanned. The size is reduced.
[0007]
[Problems to be solved by the invention]
However, in a scanning optical device using a light source unit having a plurality of light emitting portions (light sources) and a rotating polygon mirror as a deflecting unit, when the incident optical unit is a converging system or a diverging system, Even if the scanning start timing is appropriately determined for each light emitting unit so that the scanning start positions on the surface to be scanned are aligned, the relative positional relationship of the image points of the respective light emitting units with respect to the main scanning direction is in the middle of scanning. There is a problem of shifting to.
[0008]
Since the deflecting means is a rotating polygon mirror, the reflection point moves back and forth with respect to the optical axis as the rotating polygon mirror rotates. As a result, the positional relationship of the image points in the incident optical means of each light emitting unit changes. Because it ends up.
[0009]
Hereinafter, the above phenomenon will be described with reference to FIGS. FIG. 14 to FIG. 16 are explanatory views showing how the image point moves when the rotary polygon mirror as the deflecting means is rotated. In order to simplify the explanation, the configuration is made up of only incident optical means including three light emitting sections (light source means) and an aperture stop, and a rotating polygon mirror, and the rotating polygon mirror from the three light emitting section sides on the optical axis. , The left light-emitting part is the light-emitting part a, the right light-emitting part is the light-emitting part b, and the light-emitting part on the optical axis is the light-emitting part c. Further, the scanning start side is set to a positive (+) image height, the scanning end side is set to a negative (−) image height, and the rotary polygon mirror has an image height where the image point of the light emitting part a is always higher than the image point of the light emitting part b. Rotate in the direction of
[0010]
Now, since the rotary polygon mirror used as the deflecting means is not a cylinder, the distance from the rotation center to the peripheral portion differs depending on the angle. For this reason, the position of the reflection point of the principal ray of the light beam emitted from the light emitting section c reciprocates on the optical axis for each deflection surface as the rotary polygon mirror rotates.
[0011]
The movement of the reflection point on a certain deflection surface does not change linearly with respect to the rotation angle of the rotary polygon mirror, but changes parabolically, and when reflected at both ends on the deflection surface, the reflection point emits light. On the contrary, the reflection point moves away from the light emitting portion at the central portion of the deflecting surface. For this reason, for example, if the angle of the rotary polygon mirror is to be corrected so that the position of the image point of the light emitting unit a is aligned with the position of the image point of the light emitting unit a, when the image height is high, Since the light is reflected at a position closer to the light emitting part, the correction angle is relatively small. Conversely, when the image height is low, the light is reflected at a position away from the light emitting part, so it is necessary to increase the correction angle. There is.
[0012]
This is because when the rotation angle of the rotating polygon mirror is the same, the movement of the object point due to the pure rotation of the deflecting surface is almost the same regardless of the height of the image height, whereas the amount of translation varies depending on the image height, When the reflection point moves further due to parallel movement, the image point moves away from the original emission direction by the distance that the reflection point has moved to the light source side, and in addition to this, the reflection point moves in this direction. This is because it moves in the same direction.
[0013]
For this reason, the corrected image point of the light emitting portion b has a higher image height when the image height is positive, and conversely, when the image height is negative, the image height decreases accordingly. Therefore, the final correction angle is small when the image height is high and increases as the image height decreases. Therefore, if the correction angle during scanning is made constant, the relative positional relationship of the image points by the incident optical means of each light emitting unit with respect to the main scanning direction changes.
[0014]
Naturally, since the correction angle of the image point of the incident optical means changes as described above, the correction angle for matching the image points of the light emitting sections a and b also changes in the optical system including the scanning optical means. Go. In addition, if the partial magnification of the scanning optical means differs depending on the image height, this amount is further added. As a result, when the correction angle during scanning is made constant, the relative positional relationship of the image points of the light emitting units with respect to the scanning direction changes.
[0015]
The present invention relates to a scanning optical device using a multi-semiconductor laser having a plurality of light emitting portions as a light source means and a rotating polygon mirror as a deflecting means, and by appropriately setting each element constituting the scanning optical device, a surface to be scanned An object of the present invention is to provide a scanning optical device capable of reducing the positional deviation in the main scanning direction of the imaging points of a plurality of light beams on the upper side and capable of compact and high-definition printing, and an image forming apparatus using the scanning optical device.
[0016]
[Means for Solving the Problems]
  A scanning optical device according to a first aspect of the present invention comprises:A multi-semiconductor laser having a plurality of light emitting parts;Incident optical means for guiding a plurality of light beams emitted from the plurality of light emitting sections to a rotating polygon mirror, and a scanning optical means for forming an image on the surface to be scanned with the plurality of light beams deflected by the deflection surfaces of the rotating polygon mirror In a scanning optical device having
  In the main scanning section, the light beam guided from the incident optical means to the rotary polygon mirror is a convergent light beam,
W / | d1 · β | ≦ 1.16 × 10 ^-3
(Ha−Hb) /L·f≦15.2 [μm]
Ha = −0.5 · rp · β · W / L · {tan (θa) / cos (θa)} · sin (ψa)
Hb = −0.5 · rp · β · W / L · {tan (θb) / cos (θb)} · sin (Ψb)
Ψa:At the start of IndiaThe angle in the main scanning direction formed by the light beam before being deflected by the deflection surface and the light beam after being deflected by the deflection surface
Ψb:End of stampingThe angle in the main scanning direction formed by the light beam before being deflected by the deflection surface and the light beam after being deflected by the deflection surface
L:Reflection point of light beam on the deflection surface of the rotary polygon mirrorTo the natural convergence point of the incident optical means
f: fθ coefficient of the scanning optical means
θa: when the optical axis of the incident optical means intersects at the center of the deflection surface of the rotary polygon mirrorAt the start of IndiaDeflection angle
θb: when the optical axis of the incident optical means intersects at the center of the deflection surface of the rotary polygon mirrorEnd of stampingDeflection angle
W: Overall width of the plurality of light emitting portions in the main scanning direction
β: lateral magnification of the incident optical means in the main scanning direction
rp: Inscribed circle radius of the rotating polygon mirror
d1: Distance from the multi-semiconductor laser to the front main plane of the incident optical means in the main scanning direction
It is characterized by satisfying the following conditions.
[0017]
  According to a second aspect of the present invention, in the first aspect of the invention, the scanning optical device includes:
0.92 ≦ L / (f ·| Θa-θb |)
It is characterized by satisfying the following conditions.
[0018]
  The invention of claim 3 is the invention of claim 1 or 2, wherein the scanning optical device is
rp / L ≦ 0.134
It is characterized by satisfying the following conditions.
[0019]
  The image forming apparatus of the invention of claim 4Any one of claims 1 to 3And developing the electrostatic latent image formed on the photosensitive member by a light beam scanned by the scanning optical device as a toner image. And a transfer device that transfers the developed toner image onto the transfer material, and a fixing device that fixes the transferred toner image onto the transfer material.
[0020]
  An image forming apparatus according to a fifth aspect of the invention converts the code data input from the scanning optical device according to any one of the first to third aspects and an external device into an image signal and inputs the image signal to the scanning optical device. And a printer controller.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
FIG. 1 is a sectional view (main scanning sectional view) of the main part in the main scanning direction of Embodiment 1 of the present invention.
[0027]
In this specification, the direction in which the light beam is reflected and deflected by the deflecting means is defined as the main scanning direction, and the optical axis of the scanning optical means and the direction orthogonal to the main scanning direction are defined as the sub-scanning direction.
[0028]
In the figure, reference numeral 1 denotes light source means, which is composed of, for example, a multi-semiconductor laser having a plurality of light emitting portions (two in this embodiment, but may be three or more) 1a, 1b. The plurality of light emitting units 1a and 1b exist on a plane perpendicular to the optical axis, and the interval between the scanning lines formed on the multiple scanning planes in the sub-scanning direction (child line direction) is the plurality of light emitting units 1a and 1b. Since the light source means 1 is rotated around the optical axis, the light emitting units 1a and 1b are set at a desired interval.
[0029]
  Reference numeral 3 denotes an aperture stop, which forms a plurality of divergent light beams emitted from the light source means 1 into a desired optimum beam shape. A condenser lens (collimator lens) 2 converts a plurality of light beams restricted by the aperture stop 3 into convergent light beams. A cylindrical lens unit 4 has a single cylindrical lens having a predetermined power in the sub-scanning direction, and a plurality of light beams emitted from the condensing lens 2 are placed near the deflection surface of an optical deflector described later.Light guideEach image is formed in the sub-scan section (long line image in the main scan section). Each element such as the collimator lens 2, the aperture stop 3, and the cylindrical lens unit 4 constitutes one element of the incident optical means 11.
[0030]
  Reference numeral 5 denotes an optical deflector as a deflecting means, which is composed of, for example, a rotating polygon mirror (polygon mirror), and is rotated at a constant speed in the direction of arrow A in the figure by a driving means (not shown) such as a motor. Reference numeral 6 denotes a scanning optical means (fθ lens system) having an fθ characteristic, a first optical element 6a having a positive power, and a second optical element 6b having different powers in the main scanning direction and the sub-scanning direction. And have. The scanning optical means 6 has a deflection surface 5a in the sub-scan section.CoveredBy making a conjugate relationship with the scanning surface 7, the tilt of the deflection surface is corrected. Reference numeral 7 denotes a photosensitive drum surface (recording medium surface) as a surface to be scanned.
[0031]
In the present embodiment, a plurality of divergent light beams that are light-modulated and emitted from the light source means 1 in accordance with image information are limited in size by the aperture stop 3, converted into convergent light beams by the condenser lens 2, and cylindrical. The light enters the lens unit 4. Among the light beams incident on the cylindrical lens unit 4, the light beams are emitted as they are in the main scanning section. In the sub-scan section, the light beam converges and forms a substantially linear image (long-line image in the main scanning direction) on the deflecting surface 5a of the optical deflector 5. The plurality of light beams reflected and deflected by the deflecting surface 5a of the optical deflector 5 are imaged in a spot shape on the photosensitive drum surface 7 by the scanning optical means 6, and the optical deflector 5 is rotated in the direction of arrow A by rotating it. The photosensitive drum surface 7 is optically scanned at a constant speed in the direction of arrow B (main scanning direction) with the plurality of light beams. As a result, an image is recorded on the photosensitive drum surface 7 as a recording medium.
[0032]
In this embodiment, when the light emission timings of the plurality of light emitting units are shifted so that the scanning start positions in the main scanning direction of the plurality of light beams on the photosensitive drum surface are aligned,
J_max≦ 15.2 [μm] (1)
(However,
J_max: Relative maximum displacement amount of image points of light emitting portions in the main scanning direction at the end of scanning)
Each element is set to satisfy the following conditions.
[0033]
As a result, in this embodiment, the positional deviation in the main scanning direction of the image forming points of a plurality of light beams on the surface of the photosensitive drum can be reduced, and a scanning optical device capable of compact and high-definition printing is obtained.
[0034]
Conditional expression (1) indicates that main scanning at the end of scanning is performed when the scanning start timing is shifted for each of the plurality of light emitting sections so that the scanning start positions of the plurality of light beams on the photosensitive drum surface are aligned in the main scanning direction. This defines the relative maximum positional deviation amount of the image points of the light emitting portions in the direction.
[0035]
If the conditional expression (1) is deviated, the printing position by each light emitting unit will be shifted so much that it cannot be ignored, and high definition printing cannot be realized. In particular, when scanning lines are drawn in the sub-scanning direction for each light emitting unit, the intervals between the scanning lines are extremely biased, which is not good.
[0036]
The amount of deviation at the end of scanning defines the amount of deviation during scanning when the ideal scanning optical means without partial magnification is used and the position at the start of scanning is adjusted. It is because it becomes the maximum in.
[0037]
In the scanning optical apparatus of the present invention, it is more preferable that at least one of the following conditions (2) to (4) is satisfied.
[0038]
(A-1)
    0.92 ≦ L / (f · |θs−θe｜) …… (2)
(Where L: distance from the deflection surface of the rotating polygon mirror to the natural convergence point of the incident optical means f: fθ coefficient of the scanning optical means)
θs: Light of incident optical meansaxisIs the deflection angle [rad] of the deflection surface at the start of scanning with reference to the time at which they intersect at the center of the deflection surface of the rotary polygon mirror
θe: Deflection angle [rad] of the deflection surface at the end of scanning when the optical axis of the incident optical means intersects at the center of the deflection surface of the rotary polygon mirror
Satisfy the following conditions.
[0039]
(A-2)
W / | d1 · β | ≦ 1.16 × 10^-3        (3)
(However,
W: width of the entire plurality of light emitting portions in the main scanning direction
d1: Distance from the light source means to the front main plane of the incident optical means in the main scanning direction
β: lateral magnification of the incident optical means in the main scanning direction)
Satisfy the following conditions.
[0040]
(A-3)
rp / L ≦ 0.134 (4)
(However,
rp: Inscribed circle radius of rotating polygon mirror
L: distance from the deflection surface of the rotating polygon mirror to the natural convergence point of the incident optical means)
To satisfy the following conditions.
[0041]
The natural convergence point is a condensing point where a light beam emitted from the collimator lens is collected without an optical element after the collimator lens.
[0042]
Conditional expression (2) defines the distance from the deflection surface of the rotary polygon mirror to the natural convergence point of the incident optical means with respect to the scanning width on the photosensitive drum surface.
[0043]
If the distance from the deflecting surface to the natural convergence point of the incident optical means is shortened by deviating from the conditional expression (2), the angle shift amount of the deflecting surface at the time of aligning each light emitting unit becomes large. This is not good because the amount of movement to the optical means side becomes large and the scanning position between the light emitting portions tends to shift.
[0044]
Conditional expression (3) indicates that, among the light rays passing from the respective light emitting portions through the principal point in the main scanning direction of the incident optical means, the angle formed by each light emitting portion and the principal point having the largest angle in the main scanning direction, and the incident optical means This defines the relationship between the horizontal magnifications.
[0045]
If the conditional expression (3) is deviated, the angle shift amount of the deflecting surface at the time of aligning each light emitting portion increases, and therefore the amount of movement of the deflecting surface toward the incident optical means increases, and between the light emitting portions. This is not good because the scanning position is likely to shift. Since the angle shift amount is further inversely proportional to the lateral magnification within the normal use range of the incident optical means, it is defined by conditional expression (3).
[0046]
Conditional expression (4) defines the relationship between the size of the rotating polygon mirror used as the deflecting means, in particular, the radius of the inscribed circle and the distance from the deflecting surface to the natural convergence point of the incident optical means. If the size of the rotary polygon mirror becomes too large, the amount of movement of the deflecting surface in the direction of the incident optical means increases in proportion to this, and the scanning position between the light emitting sections tends to be displaced. However, by increasing the distance from the deflection surface to the natural convergence point of the incident optical means, the influence of the amount of movement of the deflection surface in the direction of the incident optical means can be suppressed.
[0047]
If the conditional expression (4) is deviated, the influence of the deflecting surface on the incident means side direction with respect to the scanning position shift between the light emitting sections becomes large, and the scanning position shift between the light emitting sections tends to occur, which is not good.
[0048]
In the present embodiment, not only the conditional expressions (1) to (4), but also satisfying the following conditional expression (5), the same effect as in the first embodiment can be obtained. That is,
(Ha−Hb) /L·f≦15.2 [μm] (5)
(However,
Ha = −0.5 · rp · β · W / L · {tan (θa) / cos (θa)} · sin (ψa) (5a)
Hb = −0.5 · rp · β · W / L · {tan (θb) / cos (θb)} · sin (ψb) (5b)
Ψa: angle formed between the light beam before being deflected and the light beam after being deflected at the start of scanning
Ψb: angle formed between the light beam before being deflected and the light beam after being deflected at the end of scanning
L: Distance from the deflection surface of the rotating polygon mirror to the natural convergence point of the incident optical means
f: fθ coefficient of scanning optical means
θa: deflection angle of the deflection surface at the start of scanning when the optical axis of the incident optical means intersects the center of the deflection surface of the rotary polygon mirror
θb: deflection angle of the deflection surface at the end of scanning when the optical axis of the incident optical means intersects at the center of the deflection surface of the rotary polygon mirror
W: width of the entire plurality of light emitting portions in the main scanning direction
β: lateral magnification of the incident optical means in the main scanning direction
rp: Inscribed circle radius of rotating polygon mirror
To satisfy the following conditions.
[0049]
The parameter Ha [Expression (5a)] in the conditional expression (5) is a value at the start of scanning. That is, it is assumed that there is no movement of the deflection surface in the direction of the incident optical means when the light emitting units are aligned. When the angle of the deflection surface is shifted so that the light beam reflected at the center of the deflecting surface of the rotary polygon mirror matches the light beam deflected at the center of the deflecting surface at the start of scanning of the light emitting unit that starts scanning most recently Since there is a movement of the deflecting surface in the direction of the incident optical means, they exist in parallel to each other, but the distance of the parallel light flux at this time is expressed by equation (5a).
[0050]
The parameter Hb [Expression (5b)] in the conditional expression (5) is a value at the end of scanning of the parameter Ha [Expression (5a)].
[0051]
Conditional expression (5) is obtained by multiplying the difference in the angle shift amount of the deflecting surface for correcting the positional deviation of the image due to the existence of the discrete distance of the parallel light beam by the fθ coefficient of the scanning optical device. The relative maximum positional shift amount of the image point of each light emitting unit is obtained and defined.
[0052]
If the conditional expression (5) is not satisfied, the printing position by each light-emitting portion gradually shifts and it becomes impossible to realize high-definition printing. In particular, when scanning lines are drawn in the sub-scanning direction for each light emitting unit, the intervals between the scanning lines are extremely biased, which is not good.
[0053]
The aspherical shapes of the first optical element 6a and the second optical element 6b constituting the scanning optical means 6 in this embodiment are based on the intersection of each optical element surface and the optical axis, and the optical axis direction is the X axis. If the direction perpendicular to the optical axis in the main scanning section is the Y-axis, and the direction perpendicular to the optical axis in the sub-scanning section is the Z-axis, each can be expressed as follows.
[0054]
Main scanning direction ... Aspherical shape expressed by function up to 10th order
[0055]
[Expression 1]

[0056]
Where R is the radius of curvature, k, B_Four, B₆, B₈, B_TenIs the aspheric coefficient
(When subscript u is added to the coefficient, the scanning start side
(If the coefficient has a subscript 1)
Sub-scanning direction ... Spherical shape whose radius of curvature continuously changes in the Y-axis direction
r ′ = r (1 + D₂Y²+ D_FourY^Four+ D₆Y⁶+ D₈Y⁸+ D_TenY^Ten)
Where r is the radius of curvature and D₂, D_Four, D₆, D₈, D_TenIs the aspheric coefficient
(When subscript u is added to the coefficient, the scanning start side
(If the coefficient has a subscript 1)
Table 1 shows the optical arrangement in the present embodiment, Table 2 shows the shape of the incident optical means in the present embodiment, and Tables 3A and 3B show the aspherical surfaces of the scanning optical means in the present embodiment. The coefficients are shown, and Table 4 shows values for the conditional expressions (1) to (5) in the present embodiment.
[0057]
[Table 1]

[0058]
[Table 2]

[0059]
[Table 3]

[0060]
[Table 4]

[0061]
[Table 5]

[0062]
In this embodiment, as shown in Table 4, all conditional expressions (1) to (5) are satisfied.
[0063]
FIG. 2 is a diagram showing field curvature in the main scanning direction in the present embodiment, FIG. 3 is a diagram showing field curvature in the sub-scanning direction in the present embodiment, and FIG. 4 shows fθ characteristics in the present embodiment. 5 is a diagram showing coma aberration in the main scanning direction in the present embodiment, and FIG. 6 is a diagram showing relative scanning position deviation in the main scanning direction after the alignment of the scan start position in the present embodiment. As shown in each figure, it can be seen that the present embodiment is corrected to a level causing no practical problem. FIG. 13 is a diagram showing the amount of movement of the intersection of the deflecting surface and the optical axis of the incident optical means with respect to the deflection angle of the deflecting means.
[0064]
As described above, in this embodiment, by satisfying the conditional expressions (1) to (4) and the conditional expression (5), it is possible to reduce the scanning position deviation of the light emitting units 1a and 1b with respect to the main scanning direction. This enables compact and high-definition printing. In the present embodiment, the light beam guided from the incident optical means 11 to the rotary polygon mirror 5 is used as a convergent light beam, thereby reducing the size of the entire apparatus.
[0065]
In this embodiment, all the conditional expressions (1) to (4) and the conditional expression (5) are satisfied. However, if only one of the conditional expressions (1) and (5) is satisfied, the present condition is satisfied. The object of the invention is achieved.
[0066]
[Embodiment 2]
FIG. 7 is a sectional view (main scanning sectional view) of the main part in the main scanning direction of Embodiment 2 of the present invention. In the figure, the same elements as those shown in FIG.
[0067]
This embodiment differs from the first embodiment described above in that the cylindrical lens portion constituting one element of the incident optical means 11 is composed of two lenses, the first and second cylindrical lenses, and the optical arrangement of the scanning optical means. In addition, the shape of each lens is made different. Other configurations and optical actions are substantially the same as those of the first embodiment.
[0068]
That is, in the figure, reference numeral 74 denotes a cylindrical lens portion, which has a convex first cylindrical lens 74a and a concave second cylindrical lens 74b. Reference numeral 76 denotes scanning optical means (fθ lens system) having fθ characteristics, and includes a first optical element 76a and a second optical element 76b having different powers in the main scanning direction and the sub-scanning direction. .
[0069]
Tables 5 (A) and (B) show the optical arrangement in this embodiment, Table 6 shows the aspheric coefficient of the incident optical means in this embodiment, and Tables 7 (A) and (B) The aspherical coefficients of the scanning optical means in the embodiment are shown, and the values for the conditional expressions (1) to (5) in this embodiment are shown in Table-4.
[0070]
[Table 6]

[0071]
[Table 7]

[0072]
[Table 8]

[0073]
[Table 9]

[0074]
[Table 10]

[0075]
In the present embodiment, all the conditional expressions (1) to (5) are satisfied as shown in Table-4.
[0076]
FIG. 8 is a diagram showing field curvature in the main scanning direction in the present embodiment, FIG. 9 is a diagram showing field curvature in the sub-scanning direction in the present embodiment, and FIG. 10 shows fθ characteristics in the present embodiment. FIG. 11 is a diagram showing coma aberration in the main scanning direction in the present embodiment, and FIG. 12 is a diagram showing relative scanning position deviation in the main scanning direction after the scan start position alignment in the present embodiment. As shown in each figure, it can be seen that the present embodiment is corrected to a level causing no practical problem.
[0077]
As described above, in this embodiment, by satisfying all the conditional expressions (1) to (4) and the conditional expression (5), it is possible to reduce the scanning position deviation of the light emitting units 1a and 1b with respect to the main scanning direction. This enables compact and high-definition printing. Further, as in the first embodiment described above, the light beam guided from the incident optical means 11 to the rotary polygon mirror 5 is used as a convergent light beam, thereby reducing the size of the entire apparatus.
[0078]
In the present embodiment, the conditional expressions (1) to (4) and the conditional expression (5) are all satisfied as in the first embodiment, but either one of the conditional expressions (1) or (5) is satisfied. If only the above is satisfied, the object of the present invention can be achieved.
[0079]
In the present invention, a predetermined effect can be obtained even if at least one of conditional expressions (1) to (5) is satisfied.
[0080]
[Image forming apparatus]
FIG. 17 is a cross-sectional view of a main part in the sub-scanning direction showing an embodiment of an image forming apparatus (electrophotographic printer) using the scanning optical apparatus of Embodiment 1 or 2 described above. In FIG. 17, reference numeral 104 denotes an image forming apparatus. Code data Dc is input to the image forming apparatus 104 from an external device 117 such as a personal computer. The code data Dc is converted into image data (dot data) Di by a printer controller 111 in the apparatus. The image data Di is input to the optical scanning unit 100 having the configuration shown in the first and second embodiments. The light scanning unit (scanning optical device) 100 emits a light beam (light beam) 103 modulated in accordance with the image data Di, and the light beam 103 causes the photosensitive surface of the photosensitive drum 101 to move in the main scanning direction. Scanned.
[0081]
The photosensitive drum 101 serving as an electrostatic latent image carrier (photoconductor) is rotated clockwise by a motor 115. With this rotation, the photosensitive surface of the photosensitive drum 101 moves in the sub-scanning direction perpendicular to the main scanning direction with respect to the light beam 103. Above the photosensitive drum 101, a charging roller 102 for uniformly charging the surface of the photosensitive drum 101 is provided so as to contact the surface. The surface of the photosensitive drum 101 charged by the charging roller 102 is irradiated with the light beam 103 scanned by the optical scanning unit 100.
[0082]
As described above, the light beam 103 is modulated based on the image data Di, and by irradiating the light beam 103, an electrostatic latent image is formed on the surface of the photosensitive drum 101. The electrostatic latent image is developed as a toner image by a developing unit 107 disposed so as to contact the photosensitive drum 101 further downstream in the rotation direction of the photosensitive drum 101 than the irradiation position of the light beam 103.
[0083]
The toner image developed by the developing unit 107 is transferred onto a sheet 112 as a transfer material by a transfer roller (transfer unit) 108 disposed below the photosensitive drum 101 so as to face the photosensitive drum 101. The paper 112 is stored in a paper cassette 109 in front of the photosensitive drum 101 (on the right side in FIG. 17), but can be fed manually. A paper feed roller 110 is provided at the end of the paper cassette 109, and feeds the paper 112 in the paper cassette 109 into the transport path.
[0084]
As described above, the sheet 112 on which the unfixed toner image has been transferred is further conveyed to a fixing device behind the photosensitive drum 101 (left side in FIG. 17). The fixing device includes a fixing roller 113 having a fixing heater (not shown) therein and a pressure roller 114 disposed so as to be in pressure contact with the fixing roller 113, and has been fed from the transfer unit. The unfixed toner image on the sheet 112 is fixed by heating the sheet 112 while being pressed by the pressure contact portion between the fixing roller 113 and the pressure roller 114. Further, a paper discharge roller 116 is disposed behind the fixing roller 113, and the fixed paper 112 is discharged out of the image forming apparatus.
[0085]
Although not shown in FIG. 17, the print controller 111 controls not only the data conversion described above but also each part in the image forming apparatus including the motor 115 and the polygon motor in the optical scanning unit 100. Do.
[0086]
【The invention's effect】
According to the present invention, as described above, in a scanning optical device using a multi-semiconductor laser having a plurality of light emitting portions as a light source means and a rotating polygon mirror as a deflecting means, each element constituting the scanning optical device is appropriately set. In addition, by satisfying either one of the conditional expressions (1) and (5), the positional deviation in the main scanning direction of the image forming points of a plurality of light beams on the surface to be scanned is reduced, and the compact and high definition is achieved. A scanning optical device capable of printing and an image forming apparatus using the same can be achieved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of main parts in a main scanning direction according to Embodiment 1 of the present invention (main scanning cross-sectional view).
FIG. 2 is a diagram showing field curvature in the main scanning direction according to the first embodiment of the present invention.
FIG. 3 is a diagram illustrating field curvature in the sub-scanning direction according to the first embodiment of the present invention.
FIG. 4 is a diagram showing distortion (fθ characteristics) and image height deviation according to the first embodiment of the present invention.
FIG. 5 is a diagram illustrating coma aberration in the main scanning direction according to the first embodiment of the present invention.
FIG. 6 is a diagram showing a relative scanning position shift in the main scanning direction after the scan start position alignment of the present embodiment.
FIG. 7 is a cross-sectional view of main parts in the main scanning direction according to Embodiment 2 of the present invention (main scanning cross-sectional view).
FIG. 8 is a diagram illustrating curvature of field in the main scanning direction according to the second embodiment of the present invention.
FIG. 9 is a diagram showing field curvature in the sub-scanning direction according to the second embodiment of the present invention.
FIG. 10 is a diagram showing distortion aberration (fθ characteristics) and image height deviation according to the second embodiment of the present invention.
FIG. 11 is a diagram illustrating coma aberration in the main scanning direction according to the second embodiment of the present invention.
FIG. 12 is a diagram showing a relative scanning position shift in the main scanning direction after the scan start position alignment of the present embodiment.
FIG. 13 shows the amount of movement of the intersection of the deflecting surface and the optical axis of the incident optical means with respect to the deflection angle of the deflecting means.
FIG. 14 is an explanatory diagram showing how the image point moves when the deflecting means is rotated.
FIG. 15 is an explanatory diagram showing how the image point moves when the deflecting means is rotated.
FIG. 16 is an explanatory diagram showing how the image point moves when the deflecting means is rotated.
FIG. 17 is a cross-sectional view of an essential part in the sub-scanning direction showing a configuration example of an image forming apparatus (electrophotographic printer) using the scanning optical apparatus of the present invention.
[Explanation of symbols]
1 Light source means (multi-semiconductor laser)
1a, 1b Light emitting part
2 Condenser lens (collimator lens)
3 Aperture stop
4,74 Cylindrical lens part
5 Deflection means (rotating polygon mirror)
5a Deflection surface
6 Scanning optical means
6a First optical element
6b Second optical element
7 Scanned surface (photosensitive drum surface)
11 Incident optical means
74a First cylindrical lens
74b Second cylindrical lens
100 Scanning optical device
101 Photosensitive drum
102 Charging roller
103 Light beam
104 Image forming apparatus
107 Developing device
108 Transfer roller
109 Paper cassette
110 Paper feed roller
111 Printer controller
112 Transfer material (paper)
113 Fixing roller
114 Pressure roller
115 motor
116 Paper discharge roller
117 External equipment

Claims (5)

A multi-semiconductor laser having a plurality of light emitting portions; incident optical means for guiding a plurality of light beams emitted from the plurality of light emitting portions to a rotating polygon mirror; and a plurality of light beams deflected by a deflection surface of the rotating polygon mirror Scanning optical means for forming an image on a surface to be scanned,
In the main scanning section, the light beam guided from the incident optical means to the rotary polygon mirror is a convergent light beam,
W / | d1 · β | ≦ 1.16 × 10 ⁻³
(Ha−Hb) /L·f≦15.2 [μm]
Ha = −0.5 · rp · β · W / L · {tan (θa) / cos (θa)} · sin (ψa)
Hb = −0.5 · rp · β · W / L · {tan (θb) / cos (θb)} · sin (Ψb)
Ψa: angle in the main scanning direction formed by the light beam before being deflected by the deflection surface at the start of printing and the light beam after being deflected by the deflection surface ψb: at the deflection surface at the end of printing time Angle L in the main scanning direction between the light beam before being deflected and the light beam after being deflected by the deflection surface: from the reflection point of the light beam on the deflection surface of the rotary polygon mirror, the natural convergence point of the incident optical means Distance f: fθ coefficient θa of the scanning optical means θa: deflection angle of the deflection surface at the start of printing when the optical axis of the incident optical means intersects at the center of the deflection surface of the rotary polygon mirror θb: deflection angle of the deflecting surface at the end of printing when the optical axis of the incident optical means intersects at the center of the deflecting surface of the rotary polygon mirror
W: overall width of the plurality of light emitting portions in the main scanning direction β: lateral magnification rp of the incident optical means in the main scanning direction rp: inscribed circle radius of the rotary polygon mirror
d1: A scanning optical apparatus satisfying the condition of the distance from the multi-semiconductor laser to the front main plane of the incident optical means in the main scanning direction . The scanning optical device includes:
0.92 ≦ L / (f · | θa−θb | )
The scanning optical apparatus according to claim 1 , wherein the following condition is satisfied. The scanning optical device includes:
rp / L ≦ 0.134
The scanning optical apparatus according to claim 1 , wherein the following condition is satisfied. A scanning optical device according to any one of claims 1 to 3, a photosensitive member disposed on the surface to be scanned, and a static light formed on the photosensitive member by a light beam scanned by the scanning optical device. A developing device that develops an electrostatic latent image as a toner image, a transfer device that transfers the developed toner image onto a transfer material, and a fixing device that fixes the transferred toner image onto the transfer material. Image forming apparatus. Wherein the scanning optical apparatus according to any one of claims 1 to 3, that converts code data inputted from an external device into an image signal and a printer controller for inputting the imagewise signal into said optical scanning device An image forming apparatus.

Images