JP5027446B2 - Scanning lens and diffraction lens - Google Patents
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- JP5027446B2 JP5027446B2 JP2006148011A JP2006148011A JP5027446B2 JP 5027446 B2 JP5027446 B2 JP 5027446B2 JP 2006148011 A JP2006148011 A JP 2006148011A JP 2006148011 A JP2006148011 A JP 2006148011A JP 5027446 B2 JP5027446 B2 JP 5027446B2
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Description
本発明は、レンズ面上に複数の輪帯を持つ回折レンズ構造を形成した走査レンズ、及び回折レンズに関する。 The present invention relates to a scanning lens having a diffractive lens structure having a plurality of annular zones on a lens surface, and a diffractive lens.
レンズ面上に回折レンズ構造を形成した回折レンズは、種々の用途に使用されている。例えば、特許文献１，２には、走査レンズとして回折レンズを含む走査光学系が開示されている。走査光学系は、レーザー光源からの光束をポリゴンミラーやガルバノミラー等の偏向器により偏向、走査させ、ｆθレンズのような走査レンズを介して感光体ドラム等の走査対象面上にスポットとして結像させる。感光体ドラム上のスポットは、偏向器の回転に伴って主走査方向に走査し、この際レーザー光をオンオフ変調することにより走査対象面上に静電潜像を形成する。 A diffractive lens in which a diffractive lens structure is formed on a lens surface is used in various applications. For example, Patent Documents 1 and 2 disclose a scanning optical system including a diffractive lens as a scanning lens. A scanning optical system deflects and scans a light beam from a laser light source by a deflector such as a polygon mirror or a galvanometer mirror, and forms an image as a spot on a scanning target surface such as a photosensitive drum via a scanning lens such as an fθ lens. Let The spot on the photosensitive drum is scanned in the main scanning direction as the deflector rotates, and an electrostatic latent image is formed on the surface to be scanned by performing on-off modulation of the laser light.
近年、レーザープリンタの高速化やカラー化の要求を受けて、複数光源からの光束を単一の偏向器で走査させるマルチビーム走査光学系やタンデム走査光学系が実用化されている。ただし、複数の光源を有する走査光学系では、複数の光源の発光波長が互いに異なる場合、光学系の持つ倍率色収差により複数の走査線の長さが変化する現象(走査幅誤差)が起こる。特許文献１，２に開示される走査光学系は、このような走査幅誤差を低減するため、走査レンズ面に色収差補正用の回折レンズ構造を形成している。
なお、レーザープリンタに用いられる一般的な走査レンズはプラスチックの射出成型で製造されるが、上記公報に開示される回折レンズ構造が形成された走査レンズを射出成型で製造すると、離型する際のレンズの収縮により、回折レンズ構造を形成する各輪帯間の段差面及びその近傍が崩れ、設計形状、すなわち金型通りの形状にならず、回折効率の低下を招くという問題がある。特に、輪帯の幅が狭く密度が大きいレンズ周辺部では、上記の形状の崩れによる影響が大きく、周辺光量が低下して印字品質の悪化を招く。 A general scanning lens used in a laser printer is manufactured by plastic injection molding. However, when a scanning lens having a diffractive lens structure disclosed in the above publication is manufactured by injection molding, it is necessary to release the mold. Due to the contraction of the lens, the step surface between the annular zones forming the diffractive lens structure and the vicinity thereof collapse, and there is a problem that the design shape, that is, the shape as the mold does not become, and the diffraction efficiency is lowered. In particular, at the lens periphery where the width of the annular zone is narrow and the density is high, the influence of the above-described shape collapse is large, and the amount of peripheral light is reduced, leading to deterioration in print quality.
本発明は、上述した従来技術の問題点に鑑みてなされたものであり、回折レンズ構造が形成されたレンズを射出成型により製造する場合にも、段差面及びその近傍での形状の崩れを防ぎ、回折効率を高く保つことができる走査レンズ、及び回折レンズを提供することを目的とする。 The present invention has been made in view of the above-mentioned problems of the prior art, and prevents the collapse of the shape on the step surface and its vicinity even when a lens having a diffractive lens structure is manufactured by injection molding. Another object of the present invention is to provide a scanning lens and a diffractive lens capable of maintaining high diffraction efficiency.
本発明にかかる走査レンズは、光源部から発して偏向器により反射、偏向された光束を収束させて被走査面上で主走査方向に走査するスポットを形成する結像光学系に含まれ、少なくとも一面に同心円状の複数の輪帯を有する回折レンズ構造が形成され、射出成型により製造される樹脂製レンズであり、回折レンズ構造は、透過する光を回折させる回折作用面と、隣接する回折作用面の間をつなぐ段差面とを有し、回折レンズ構造の設計形状は、段差面を、輪帯の回転軸を含み主走査方向に平行な一断面において、離型時の樹脂収縮に伴うレンズの変形方向にほぼ平行な面とすることにより、離型時に段差面と金型との間に作用する応力を軽減した形状であることを特徴とする。 A scanning lens according to the present invention is included in an imaging optical system that converges a light beam emitted from a light source unit and reflected and deflected by a deflector to form a spot that scans in a main scanning direction on a scanned surface. A diffractive lens structure having a plurality of concentric annular zones formed on one surface is a resin lens manufactured by injection molding, and the diffractive lens structure has a diffractive action surface that diffracts transmitted light and an adjacent diffractive action. and a step surface that connects between the surfaces, the design shape of the diffractive lens structure, a stepped surface, in a section parallel to comprise the main scanning direction the rotation axis of the ring-shaped zone, the lens associated with the resin shrinkage during release By making the surface substantially parallel to the deformation direction, it is characterized in that the stress acting between the step surface and the mold during release is reduced.
また、本発明の他の態様の走査レンズは、光源部から発して偏向器により反射、偏向された光束を収束させて被走査面上で主走査方向に走査するスポットを形成する結像光学系に含まれ、少なくとも一面に同心円状の複数の輪帯を有する回折レンズ構造が形成され、前記輪帯の回転軸を含み前記主走査方向に平行な一断面に略平行な面上に配置されたゲートから樹脂が射出される射出成型により製造される樹脂製レンズであり、前記回折レンズ構造は、透過する光を回折させる回折作用面と、隣接する回折作用面の間をつなぐ段差面とを有し、前記回折レンズ構造の設計形状は、前記段差面を、前記一断面内において、該段差面とそれに接続する回折作用面との境界点と、前記ゲートの略中心を前記一断面上に投影した点とを結ぶ直線に対してほぼ平行な面とすることにより、離型時に前記段差面と金型との間に作用する応力を軽減した形状であることを特徴とする。 According to another aspect of the present invention, there is provided an imaging optical system that forms a spot that scans in a main scanning direction on a surface to be scanned by converging a light beam emitted from a light source unit and reflected and deflected by a deflector. And a diffractive lens structure having a plurality of concentric annular zones on at least one surface is formed, and is disposed on a plane that is substantially parallel to a section that includes the rotation axis of the annular zone and is parallel to the main scanning direction. A resin lens manufactured by injection molding in which resin is injected from a gate, and the diffractive lens structure has a diffractive action surface that diffracts transmitted light and a step surface that connects between adjacent diffractive action surfaces. The design shape of the diffractive lens structure is such that, in the one cross section, the step surface is projected on the one cross section at the boundary point between the step surface and the diffraction action surface connected to the step surface. For a straight line connecting the points By substantially parallel surfaces, characterized in that it is a shape that reduces the stress acting between the stepped surface and the die at the time of release.
一方、本発明にかかる回折レンズは、少なくとも一面に同心円状の複数の輪帯を有する回折レンズ構造が形成され、射出成型により製造される樹脂製レンズであり、回折レンズ構造は、透過する光を回折させる回折作用面と、隣接する回折作用面の間をつなぐ段差面とを有し、回折レンズ構造の設計形状は、段差面を、輪帯の回転軸を含む少なくとも一断面において、離型時の樹脂収縮に伴うレンズの変形方向にほぼ平行な面とすることにより
、離型時に段差面と金型との間に作用する応力を軽減した形状であることを特徴とする。
On the other hand, the diffractive lens according to the present invention is a resin lens in which a diffractive lens structure having a plurality of concentric annular zones is formed on at least one surface, and is manufactured by injection molding. a diffraction action surface to diffract, and a step surface running between the diffraction action surface adjacent, designing the shape of the diffractive lens structure, a stepped surface, at least one cross section including the rotation axis of the ring-shaped zone, the time of demolding By making the surface substantially parallel to the deformation direction of the lens due to the resin shrinkage, it is characterized by reducing the stress acting between the step surface and the mold during mold release.
また、本発明の他の態様の回折レンズは、少なくとも一面に同心円状の複数の輪帯を有する回折レンズ構造が形成され、前記輪帯の回転軸を含む一断面に略平行な面上に配置されたゲートから樹脂が射出される射出成型により製造される樹脂製レンズであり、前記回折レンズ構造は、透過する光を回折させる回折作用面と、隣接する回折作用面の間をつなぐ段差面とを有し、前記回折レンズの設計形状は、前記段差面を、前記一断面内において、該段差面とそれに接続する回折作用面との境界点と、前記ゲートの略中心を前記一断面上に投影した点とを結ぶ直線に対してほぼ平行な面とすることにより、離型時に前記段差面と金型との間に作用する応力を軽減した形状であることを特徴とする。 The diffractive lens according to another aspect of the present invention has a diffractive lens structure having a plurality of concentric annular zones formed on at least one surface, and is disposed on a plane substantially parallel to one cross section including the rotation axis of the annular zone. A resin lens manufactured by injection molding in which resin is injected from a gate formed, and the diffractive lens structure includes a diffractive action surface that diffracts transmitted light, and a step surface that connects between adjacent diffractive action surfaces. The design shape of the diffractive lens is such that the step surface is located within the one cross section, the boundary point between the step surface and the diffraction action surface connected thereto, and the approximate center of the gate on the one cross section. By forming a plane substantially parallel to a straight line connecting the projected points, it is characterized in that the stress acting between the stepped surface and the mold during release is reduced .
本発明によれば、走査レンズに形成される回折レンズ構造の輪帯間の段差面を、隣接する輪帯の法線に対して傾けることにより、離型時に段差面と金型との間に作用する応力を軽減することができ、走査レンズを射出成型により製造する場合にも、段差面及びその近傍での形状の崩れを防ぎ、回折効率を高く保つことができる。 According to the present invention, the step surface between the annular zones of the diffractive lens structure formed in the scanning lens is inclined with respect to the normal line of the adjacent annular zone, so that the step surface and the mold are separated at the time of mold release. The acting stress can be reduced, and even when the scanning lens is manufactured by injection molding, it is possible to prevent the shape of the step surface and the vicinity thereof from collapsing and to keep the diffraction efficiency high.
以下、本発明にかかる走査レンズの実施形態を図面を参照しつつ説明する。図１(Ａ)は、第１の実施形態に係る走査レンズの主走査方向の断面図、図１(Ｂ)はその正面図である。なお、図１(Ａ)は、図１(Ｂ)のＰ−Ｐ線に沿う断面図である。この走査レンズ１０は、走査光学系のポリゴンミラーと感光体ドラムとの間に配置される。図中左側となる第１面１１がポリゴンミラー側、右側となる第２面１２が感光体ドラム側となるように配置される。光束が透過するレンズ面の周囲には、レンズを装置に組み付ける際の固定部となる外枠部(リブ)１３が形成されている。図中の符号Ｇはゲート、ＧＣはその中心である。 Hereinafter, embodiments of a scanning lens according to the present invention will be described with reference to the drawings. FIG. 1A is a sectional view of the scanning lens according to the first embodiment in the main scanning direction, and FIG. 1B is a front view thereof. Note that FIG. 1A is a cross-sectional view taken along the line P-P in FIG. The scanning lens 10 is disposed between the polygon mirror of the scanning optical system and the photosensitive drum. In the drawing, the first surface 11 on the left side is arranged on the polygon mirror side, and the second surface 12 on the right side is arranged on the photosensitive drum side. An outer frame portion (rib) 13 is formed around the lens surface through which the light beam is transmitted. The outer frame portion (rib) 13 serves as a fixing portion when the lens is assembled to the apparatus. In the figure, symbol G is a gate and GC is the center thereof.
レーザープリンタ等に使用される走査レンズは、一方向(主走査方向)に走査する光束を透過させるため、主走査方向には所定の幅が必要であるが、副走査方向(光軸に対して垂直な面内で主走査方向と直交する方向)の幅は小さくとも足りる。このため、図１(Ｂ)に示すように、主、副走査方向の長さが異なる。 A scanning lens used in a laser printer or the like transmits a light beam scanned in one direction (main scanning direction), and thus requires a predetermined width in the main scanning direction. A small width in a direction perpendicular to the main scanning direction in the vertical plane is sufficient. For this reason, as shown in FIG. 1B, the lengths in the main and sub-scanning directions are different.
図１(Ａ)に示すように、走査レンズ１０は、第１面１１が凹面、第２面１２の巨視的形状が凸面のメニスカス形状の正レンズであり、第２面１２には、回折レンズ構造が形成されている。回折レンズ構造は、光軸Ａｘ1を中心として同心円状に形成された回転対称な複数の輪帯を有する。回折レンズ構造は、透過する光を回折させる回折作用面１２ｂと、隣接する回折作用面の間をつなぐ段差面１２ａとを有する。なお、図１では、形状の理解を容易にするため、輪帯数を実際より少なく示している。実際には、より細かいピッチで輪帯が形成される。 As shown in FIG. 1A, the scanning lens 10 is a meniscus positive lens in which the first surface 11 is concave and the second surface 12 is convex, and the second surface 12 has a diffractive lens. A structure is formed. The diffractive lens structure has a plurality of rotationally symmetric annular zones formed concentrically around the optical axis Ax1. The diffractive lens structure has a diffractive action surface 12b that diffracts transmitted light and a step surface 12a that connects between adjacent diffractive action surfaces. In FIG. 1, in order to facilitate understanding of the shape, the number of annular zones is shown to be smaller than the actual number. In practice, the annular zone is formed at a finer pitch.
回折レンズ構造の段差面１２ａの設計形状は、輪帯の回転軸を含み主走査方向に平行な一断面において、回転軸(この例では光軸Ａｘ1に一致する)に対して傾くよう定められている。第１の実施形態の走査レンズ１０は、金型を用いてプラスチックの射出成型により製造される。段差面１２ａの設計上の傾きは、金型からの離型時に段差面１２ａと金型との間に作用する応力を軽減できるように定められている。離型時には、金型が光軸方向にスライドしてレンズから離れる。なお、段差面１２ａの光軸方向から見た幅は微小であるため、図１(Ｂ)では図示されていない。 The design shape of the step surface 12a of the diffractive lens structure is determined to be inclined with respect to the rotation axis (in this example, coincident with the optical axis Ax1) in one cross section including the rotation axis of the annular zone and parallel to the main scanning direction. Yes. The scanning lens 10 of the first embodiment is manufactured by plastic injection molding using a mold. The design inclination of the step surface 12a is determined so that the stress acting between the step surface 12a and the mold can be reduced when released from the mold. At the time of mold release, the mold slides in the optical axis direction and moves away from the lens. In addition, since the width | variety seen from the optical axis direction of the level | step difference surface 12a is very small, it is not illustrated in FIG.1 (B).
以下、離型時の段差面近傍の形状の変化について、金型の段差面が隣接する輪帯の法線に対してほぼ平行な比較例と、第１の実施形態とを比較し、図２〜図４に基づいて説明する。 Hereinafter, with respect to the change in shape near the step surface at the time of mold release, a comparison example in which the step surface of the mold is substantially parallel to the normal line of the adjacent annular zone is compared with the first embodiment, and FIG. Description will be made with reference to FIG.
比較例の金型は、図２に拡大して示すように、隣り合う回折作用面Ｄどうしをつなぐ段差面Ｓが隣接する回折作用面Ｄの法線に対してほぼ平行になるように形成されている。一方、プラスチックレンズの凸面は、冷却・固化時に図３に示すように破線で示した金型形状に対して、実線で示したように弓なりにカーブがきつくなる方向に収縮する。したがって、収縮による応力Ｆは図３に矢印で示すように回折レンズ構造が形成されたレンズ面の曲率中心側に向かい、かつ、光軸からの距離に応じて異なる方向となる。それぞれの段差面に着目すると、この応力Ｆは段差面に垂直な成分Ｆ1と平行な成分Ｆ2とに分解することができる。平行な成分Ｆ2は、離型の際にレンズを金型に沿って滑らせる方向に作用するため、レンズに対してストレスとならないが、垂直な成分Ｆ1は、段差面を金型に押し付ける方向に作用するため、離型時にレンズに対してストレスとなる。比較例のように段差面が輪帯に対して垂直であると、段差面に垂直な成分Ｆ1が比較的大きく、離型時に段差面及びその近傍の形状を崩す原因となる。 As shown in an enlarged view in FIG. 2, the comparative mold is formed so that the stepped surface S connecting adjacent diffraction action surfaces D is substantially parallel to the normal line of the adjacent diffraction action surfaces D. ing. On the other hand, the convex surface of the plastic lens contracts in a direction in which the curve becomes tight like a bow as shown by the solid line, as shown by the solid line, with respect to the mold shape shown by the broken line as shown in FIG. 3 during cooling and solidification. Therefore, the stress F due to the shrinkage is directed toward the center of curvature of the lens surface on which the diffractive lens structure is formed as indicated by an arrow in FIG. 3, and is in a different direction depending on the distance from the optical axis. Focusing on each step surface, this stress F can be decomposed into a component F1 perpendicular to the step surface and a component F2 parallel to the step surface. The parallel component F2 acts in the direction in which the lens slides along the mold at the time of mold release, so it does not cause stress on the lens, but the vertical component F1 in the direction to press the step surface against the mold. Since it acts, it becomes a stress with respect to a lens at the time of mold release. When the step surface is perpendicular to the annular zone as in the comparative example, the component F1 perpendicular to the step surface is relatively large, which causes the step surface and the shape in the vicinity thereof to be destroyed during mold release.
図４は、比較例の金型を用いて成型した場合の離型後の段差面近傍の形状の一例を示す。実線が実際の形状、破線が設計形状(収縮がないと仮定した金型通りの形状)を示している。レンズは全体としては収縮するが、段差面が金型に引っかかるようにして局部的に膨張し、実際の形状が設計形状から大きく崩れる。このため、回折効率が低下し、光量の損失が大きくなる。 FIG. 4 shows an example of the shape in the vicinity of the step surface after mold release when molding is performed using the mold of the comparative example. A solid line indicates an actual shape, and a broken line indicates a design shape (a shape according to a mold assuming no contraction). Although the lens shrinks as a whole, the stepped surface is locally expanded as if it is caught by the mold, and the actual shape is greatly collapsed from the design shape. For this reason, the diffraction efficiency is lowered, and the loss of light quantity is increased.
一方、第１の実施形態の走査レンズ１０は、図５に拡大して示すような金型により成型される。この金型は、回折作用面Ｄ間の段差面Ｓを隣接する回折作用面Ｄの法線に対して傾け、かつ、段差面Ｓを回転軸に対して傾けることにより、収縮による応力Fのうち段差面に対して垂直な成分Ｆ1を比較例より小さくし、これにより離型時の段差面近傍の変形を抑えることができる。 On the other hand, the scanning lens 10 of the first embodiment is molded by a mold as shown in an enlarged view in FIG. In this mold, the step surface S between the diffractive action surfaces D is inclined with respect to the normal line of the adjacent diffractive action surface D, and the step surface S is inclined with respect to the rotation axis. The component F1 perpendicular to the step surface is made smaller than that of the comparative example, thereby suppressing deformation near the step surface at the time of mold release.
図６は、第１の実施形態の走査レンズを形成するための他の金型の拡大図である。図６の例では、段差面Ｓの傾きを図５の例より大きくし、収縮による応力Ｆの方向にほぼ一致するように設定している。レンズの収縮による変形は、レンズの各部分に作用した応力によって生じたものであるから、レンズの各部分が変形した方向と応力が作用した方向は概ね一致すると予測される。したがって，段差面の傾きを図６のように応力Ｆの方向と一致させることにより、離型時にレンズに作用するストレスを図５の例より低減し、段差面近傍の変形をより小さく抑えることができる。 FIG. 6 is an enlarged view of another mold for forming the scanning lens of the first embodiment. In the example of FIG. 6, the slope of the step surface S is made larger than that of the example of FIG. 5 and is set so as to substantially match the direction of the stress F due to shrinkage. Since deformation due to lens contraction is caused by stress applied to each part of the lens, it is predicted that the direction in which each part of the lens is deformed and the direction in which the stress is applied substantially coincide. Therefore, by making the inclination of the step surface coincide with the direction of the stress F as shown in FIG. 6, the stress acting on the lens at the time of releasing can be reduced as compared with the example of FIG. it can.
図７は、第１の実施形態の金型を用いて成型した場合の離型後の段差面近傍の形状を示す。実線が実際の形状、破線が設計形状を示している。段差面の設計形状を隣接する回折作用面の法線に対して傾け、かつ、段差面Ｓを回転軸に対して傾けることにより、成型後の実際のレンズ形状と設計形状との差を小さくすることができ、これにより、使用時の回折効率の低下と、これに伴う光量の損失を抑えることができる。 FIG. 7 shows the shape in the vicinity of the step surface after mold release in the case of molding using the mold according to the first embodiment. The solid line indicates the actual shape, and the broken line indicates the design shape. By tilting the design shape of the step surface with respect to the normal line of the adjacent diffraction action surface and tilting the step surface S with respect to the rotation axis, the difference between the actual lens shape after molding and the design shape is reduced. As a result, it is possible to suppress a decrease in diffraction efficiency during use and a loss of light amount associated therewith.
なお、上記の段差面に関する説明は、光軸(輪帯の回転軸)を含み、主走査方向に平行な一断面(主走査断面)内の形状に関する。輪帯構造は回転対称であるため、主走査断面を光軸回りに回転させた平面内では、同一の段差面は主走査断面内と同一の傾きを持つ。 The above description regarding the step surface relates to a shape in one section (main scanning section) that includes the optical axis (rotary axis of the annular zone) and is parallel to the main scanning direction. Since the annular structure is rotationally symmetric, the same step surface has the same inclination as the main scanning section in the plane obtained by rotating the main scanning section about the optical axis.
各輪帯間の段差面の法線が光軸に対してなす角度(鋭角)は、比較例では図８のグラフに破線で示したように変化する。回折レンズ構造は凸面のベースカーブ上に形成されているため、各回折作用面の法線が光軸に対してなす角度は、レンズ周辺に向かうにしたがって大きくなる。このため、比較例のように段差面を隣接する回折作用面の法線とほぼ平行になるよう設計した場合、設計上は段差面の法線が光軸に対してなす角度は、図８に破線で示したように光軸からの距離が大きくなるにしたがって小さくなる。 In the comparative example, the angle (acute angle) formed by the normal line of the step surface between the annular zones with respect to the optical axis changes as indicated by the broken line in the graph of FIG. Since the diffractive lens structure is formed on the convex base curve, the angle formed by the normal line of each diffractive surface with respect to the optical axis increases toward the periphery of the lens. For this reason, when the step surface is designed to be substantially parallel to the normal line of the adjacent diffraction action surface as in the comparative example, the angle formed by the normal line of the step surface with respect to the optical axis is as shown in FIG. As shown by the broken line, the distance decreases as the distance from the optical axis increases.
一方、第１の実施形態の図６の構成では、段差面は応力Ｆとほぼ平行になるよう形成されている。応力Ｆが光軸に対してなす角度は、図３に示したように光軸からの距離が大きくなるにしたがって大きくなるため、設計上は段差面の法線が光軸に対してなす角度は、図８に破線で示したように光軸からの距離が大きくなるにしたがって小さくなる。比較例と第１の実施形態とで光軸からの距離に対する角度変化の傾向は同一であるが、同一の距離における角度は第１の実施形態の方が比較例より１５度から３４度小さく、光軸からの距離が大きくなるにしたがって角度の差が大きくなる傾向がある。 On the other hand, in the configuration of FIG. 6 of the first embodiment, the step surface is formed to be substantially parallel to the stress F. Since the angle formed by the stress F with respect to the optical axis increases as the distance from the optical axis increases as shown in FIG. 3, the angle formed by the normal of the step surface with respect to the optical axis is designed. As shown by the broken line in FIG. 8, the distance from the optical axis increases as the distance increases. Although the tendency of the angle change with respect to the distance from the optical axis is the same in the comparative example and the first embodiment, the angle at the same distance is 15 to 34 degrees smaller in the first embodiment than in the comparative example, The difference in angle tends to increase as the distance from the optical axis increases.
なお、回折レンズ構造の回折作用は、隣接する段差面の光路長差により生じるため、回折作用面間の段差面は回折作用には寄与しない無効部分となる。したがって、段差面が設計値通りに形成されるのであれば、光軸に垂直な面内に投影した段差面の幅は小さい方が望ましい。しかしながら、実際には段差面の幅を小さくしようとすると、図４に示すような形状の崩れが生じる。このような形状の崩れがあるよりは、第１の実施形態のように無効部分が増加したとしても、形状の崩れが小さい方が総合的な光の利用効率は高くなる。 Note that the diffractive action of the diffractive lens structure is caused by a difference in optical path length between adjacent stepped surfaces, so that the stepped surfaces between the diffractive acting surfaces become ineffective portions that do not contribute to the diffractive action. Therefore, if the step surface is formed as designed, it is desirable that the width of the step surface projected on the surface perpendicular to the optical axis is small. However, in reality, when the width of the stepped surface is reduced, the shape collapses as shown in FIG. Rather than such shape collapse, even if the ineffective portion increases as in the first embodiment, the overall light utilization efficiency is higher when the shape collapse is smaller.
次に、第１の実施形態の走査レンズ１０の製造方法について説明する。段差面の離型時の変形を避けるためには、レンズに対してどのような力が作用するか把握する必要がある。上述のように、凸面の場合には、弓なりにカーブがきつくなる方向に収縮するため、応力は概ね曲率中心に向かう方向となる。しかしながら、段差面の角度を決める際には、レンズの各部位について変形の方向をより正確に把握することが望ましい。なお、前記のように走査レンズ１０は主走査方向に長いため、収縮についても主走査方向についてのみ考慮すればよい。 Next, a method for manufacturing the scanning lens 10 of the first embodiment will be described. In order to avoid deformation at the time of mold release of the step surface, it is necessary to grasp what force acts on the lens. As described above, in the case of a convex surface, the curve is contracted in a direction in which the curve becomes tight like a bow, so the stress is generally in the direction toward the center of curvature. However, when determining the angle of the step surface, it is desirable to more accurately grasp the direction of deformation for each part of the lens. Since the scanning lens 10 is long in the main scanning direction as described above, it is only necessary to consider shrinkage only in the main scanning direction.
そこで、試作した走査レンズの回折レンズ構造の段差面を計測し、レンズ各部の変形状況に基づいて各段差面での変形方向を求め、この変形方向に合わせて段差面の傾きを決定する。そして、各段差面がそれぞれ決定された傾きを持つように製造用の金型を製作し、その製造用の金型を用いてレンズを製造する。これにより、回折レンズ構造の段差面においてレンズを金型に押し付ける方向の応力F1を小さくすることができ、結果として段差面近傍での形状の崩れを小さくすることができる。 Therefore, the step surface of the diffractive lens structure of the prototyped scanning lens is measured, the deformation direction at each step surface is obtained based on the deformation state of each part of the lens, and the inclination of the step surface is determined according to this deformation direction. Then, a manufacturing mold is manufactured so that each step surface has a determined inclination, and a lens is manufactured using the manufacturing mold. Thereby, the stress F1 in the direction in which the lens is pressed against the mold on the step surface of the diffractive lens structure can be reduced, and as a result, the shape collapse in the vicinity of the step surface can be reduced.
図９は、本発明の第２の実施形態にかかる走査レンズ１００を示す。第２の実施形態の走査レンズは、射出成型時のゲートを外枠部１０３のうち主走査断面に平行な面の光軸上に設定する場合に有効である。図９の走査レンズ１００は、第１面１０１が凹面、第２面１０２の巨視的形状が凸面のメニスカス形状の正レンズであり、第２面１０２には、回折レンズ構造が形成されている。回折レンズ構造は、光軸Ａｘ1を中心として同心円状に形成された回転対称な複数の輪帯を有する。回折レンズ構造は、透過する光を回折させる回折作用面１０２ｂと、隣接する回折作用面の間をつなぐ段差面１０２ａとを有する。光束が透過するレンズ面の周囲には、レンズを装置に組み付ける際の固定部となる外枠部(リブ)１０３が形成されている。図中の符号Ｇはゲート、ＧＣはその中心である。 FIG. 9 shows a scanning lens 100 according to the second embodiment of the present invention. The scanning lens of the second embodiment is effective when the gate at the time of injection molding is set on the optical axis of the surface parallel to the main scanning section in the outer frame portion 103. The scanning lens 100 of FIG. 9 is a meniscus positive lens in which the first surface 101 is concave and the second surface 102 is convex, and the second surface 102 has a diffractive lens structure. The diffractive lens structure has a plurality of rotationally symmetric annular zones formed concentrically around the optical axis Ax1. The diffractive lens structure has a diffractive surface 102b that diffracts transmitted light and a step surface 102a that connects between adjacent diffractive surfaces. An outer frame portion (rib) 103 is formed around the lens surface through which the light beam is transmitted. The outer frame portion (rib) 103 is a fixed portion when the lens is assembled to the apparatus. In the figure, symbol G is a gate and GC is the center thereof.
図１０は、図９の走査レンズ１００を設計する際の手順を示す。図１０(Ａ)は離型時の変形を考慮しない設計例、(Ｂ)は(Ａ)に基づいて図９の走査レンズ１００を設計する際の基準となる直線を加えた図、(Ｃ)は、(Ｂ)の拡大図である。図１０(Ａ)の設計形状では、離型時に金型との間に作用する応力により、回折レンズ構造の形状が崩れ、回折効率が低下する。そこで、第２の実施形態では、図１０(Ｂ)及び(Ｃ)に示すように、回折レンズ構造の段差面１０２ａを、主走査断面内において、段差面１０２ａとそれに接続する回折作用面１０２ｂとの境界点と、ゲートのほぼ中心ＧＣを主走査断面に投影した点とを結ぶ直線Ｌ1、Ｌ2、Ｌ3、Ｌ4…に対して設計上ほぼ平行となる(この例では各直線に一致する)よう決定している。一般的に、射出成型により成型されるレンズは、ゲート方向に向かって収縮する傾向がある。したがって、各段差面の傾きを上記の直線とほぼ平行にすることにより、回折レンズ構造の段差面においてレンズを金型に押し付ける方向の応力F1を小さくすることができる。なお、図９及び図１０においては、説明のため段差面を強調して表現している。また、本発明の実施例においては、走査レンズの光軸上にゲートが存在する場合を用いて説明を行なったが、ゲートが光軸から外れた位置にある場合においても本発明の内容は有効である。つまり、隣接する回折面の間をつなぐ段差面の光軸に対する傾きが、光軸を軸として回転対称でない場合も含まれる。 FIG. 10 shows a procedure for designing the scanning lens 100 of FIG. 10A is a design example that does not take into account deformation at the time of mold release, FIG. 10B is a diagram in which a straight line serving as a reference in designing the scanning lens 100 of FIG. 9 is added based on FIG. FIG. 4 is an enlarged view of (B). In the design shape of FIG. 10A, the shape of the diffractive lens structure collapses due to the stress acting between the mold and the mold, and the diffraction efficiency is lowered. Therefore, in the second embodiment, as shown in FIGS. 10B and 10C, the step surface 102a of the diffractive lens structure is divided into a step surface 102a and a diffraction action surface 102b connected to the step surface 102a in the main scanning section. Are substantially parallel in design with respect to the straight lines L1, L2, L3, L4... Connecting the boundary point of the gate and a point obtained by projecting the approximate center GC of the gate onto the main scanning section (in this example, it corresponds to each straight line). Has been decided. Generally, a lens molded by injection molding tends to shrink toward the gate direction. Therefore, the stress F1 in the direction in which the lens is pressed against the mold on the step surface of the diffractive lens structure can be reduced by making the inclination of each step surface substantially parallel to the straight line. In FIG. 9 and FIG. 10, the step surface is expressed with emphasis for explanation. In the embodiments of the present invention, the case where the gate is present on the optical axis of the scanning lens has been described. However, the present invention is effective even when the gate is located away from the optical axis. It is. That is, the case where the inclination with respect to the optical axis of the step surface connecting between adjacent diffractive surfaces is not rotationally symmetric about the optical axis is also included.
次に、実施形態の走査レンズを適用した走査光学系について説明する。図１１は、第１の実施形態の走査レンズ１０を適用したマルチビーム走査光学系の斜視図である。図１１に示すマルチビーム走査光学系は、光源部２０から発した２本のレーザー光束をポリゴンミラー３０により反射・偏向させ、ポリゴンミラー３０により反射された光束を結像光学系Ｌによって被走査面である感光体ドラム４０上に収束させ、主走査方向に走査する２つのスポットを形成する。 Next, a scanning optical system to which the scanning lens of the embodiment is applied will be described. FIG. 11 is a perspective view of a multi-beam scanning optical system to which the scanning lens 10 of the first embodiment is applied. The multi-beam scanning optical system shown in FIG. 11 reflects and deflects two laser light beams emitted from the light source unit 20 by the polygon mirror 30, and the light beam reflected by the polygon mirror 30 is scanned by the imaging optical system L. The two spots are converged on the photosensitive drum 40 and scanned in the main scanning direction.
光源部２０は、それぞれ発散光を発する第１，第２の半導体レーザー２１，２２と、各半導体レーザーから発した発散光を平行光にする第１，第２のコリメートレンズ２３，２４と、平行光とされたレーザー光を副走査方向に収束させるアナモフィック光学素子(シリンドリカルレンズ)２５とを備えている。また、結像光学系Ｌは、図１に示した第１の実施形態の走査レンズ(第１レンズ)１０と、この第１レンズ１０と感光体ドラム４０との間に配置された第２レンズ５０とから構成されている。 The light source unit 20 includes first and second semiconductor lasers 21 and 22 that emit divergent light, first and second collimator lenses 23 and 24 that convert the divergent light emitted from each semiconductor laser into parallel light, and parallel. And an anamorphic optical element (cylindrical lens) 25 for converging the laser light, which is made light, in the sub-scanning direction. The imaging optical system L includes a scanning lens (first lens) 10 according to the first embodiment shown in FIG. 1 and a second lens disposed between the first lens 10 and the photosensitive drum 40. 50.
図１１に示すマルチビーム走査光学系では、第１，第２の半導体レーザー２１，２２の発光波長が互いに異なる場合にも走査幅誤差を発生させないように、第１レンズ１０の第２面に形成した回折レンズ構造に、倍率色収差を補正する機能を持たせている。なお、第１の実施形態の走査レンズ１０に代えて、第２の実施形態の走査レンズ１００を用いることもできる。 In the multi-beam scanning optical system shown in FIG. 11, the first and second semiconductor lasers 21 and 22 are formed on the second surface of the first lens 10 so as not to generate a scanning width error even when the emission wavelengths of the first and second semiconductor lasers 21 and 22 are different from each other. The diffractive lens structure has a function of correcting the lateral chromatic aberration. Note that the scanning lens 100 of the second embodiment can be used instead of the scanning lens 10 of the first embodiment.
次に、第１の実施形態の走査レンズ１０の具体的な設計例について説明する。走査レンズ１０の第１面１１は、回転対称な凹の非球面である。また、第２面１２は、回転対称な凸の非球面であるベースカーブ上に倍率色収差を補正する作用を持つ回折レンズ構造が形成されている。 Next, a specific design example of the scanning lens 10 of the first embodiment will be described. The first surface 11 of the scanning lens 10 is a concave aspherical surface that is rotationally symmetric. The second surface 12 has a diffractive lens structure having an effect of correcting lateral chromatic aberration on a base curve which is a rotationally symmetric convex aspherical surface.
回転対称な非球面の形状は、走査レンズの光軸Ａｘ1からの距離ｈにおける光軸Ａｘ1と回折レンズ構造との交点での接平面からのサグ量Ｘ(ｈ)で表すことができ、そのサグ量は、以下の式(１)で表される。
X(h)＝h2／［r{1＋√(1−(κ＋1)h2／r2)}］＋A4h4＋A6h6＋A8h8＋A10h10…(１)
上式中、ｒは光軸上の曲率半径、κは円錐係数、A4,A6,A8,A10はそれぞれ４次、６次、８次、１０次の非球面係数である。
The rotationally symmetric aspherical shape can be represented by a sag amount X (h) from the tangential plane at the intersection of the optical axis Ax1 and the diffractive lens structure at a distance h from the optical axis Ax1 of the scanning lens. The amount is represented by the following formula (1).
X (h) = h 2 / [r {1 + √ (1− (κ + 1) h 2 / r 2 )}] + A 4 h 4 + A 6 h 6 + A 8 h 8 + A 10 h 10 (1)
In the above equation, r is a radius of curvature on the optical axis, κ is a conical coefficient, and A 4 , A 6 , A 8 , and A 10 are fourth-order, sixth-order, eighth-order, and tenth-order aspherical coefficients, respectively.
回折レンズ構造の形状は、走査レンズの光軸Ａｘ1からの距離ｈにおける光軸Ａｘ1と回折レンズ構造輪帯構造との交点での接平面からのサグ量SAG(h)で表すことができ、かつ、そのサグ量SAG(h)は以下の式(２)で表される。
ＳＡＧ(ｈ)＝Ｘ(ｈ)＋Ｓ(ｈ) …(２)
ここで、X(h)は回折レンズ構造の巨視的形状(ベースカーブ)で、球面の場合には曲率半径をｒとして以下の(３)式で表される。
X(h)＝h2／［r{1＋√(1−h2／r2)}］…(３)
The shape of the diffractive lens structure can be represented by a sag amount SAG (h) from the tangential plane at the intersection of the optical axis Ax1 and the diffractive lens structure annular zone structure at a distance h from the optical axis Ax1 of the scanning lens, and The sag amount SAG (h) is expressed by the following equation (2).
SAG (h) = X (h) + S (h) (2)
Here, X (h) is a macroscopic shape (base curve) of the diffractive lens structure. In the case of a spherical surface, X (h) is expressed by the following equation (3), where the radius of curvature is r.
X (h) = h 2 / [r {1 + √ (1−h 2 / r 2 )}] (3)
一方、回折レンズ構造が持つべき光路長付加量Δφ(h)は、光軸Ａｘ1からの高さをｈ、ｎ次(偶数次)の光路差関数係数をＰnとして、以下の式(４)により求められる。
Δφ(ｈ)＝Ｐ2ｈ2＋Ｐ4ｈ4＋Ｐ6ｈ6＋Ｐ8ｈ8＋Ｐ10ｈ10 …(４)
式(２)中のＳ(ｈ)は、この光路長付加量Δφ(ｈ)に基づいて以下の式(５)により求められる値であり、主走査方向に変化する階段状のサグ量を表す。
S(h)={|MOD(Δφ(h)＋C，−1)|−C}λ／{n−1+Dh2} …(５)
ここで、MOD（X、Y）はXをYで割った剰余を与える関数、Ｃは輪帯の境界位置の位相を設定する定数であり、0から1の任意の値をとる。また、Ｄは、光束が回折レンズ構造に対して斜めに入射するために生じる位相付加量の変化を補正する係数である。
On the other hand, the optical path length addition amount Δφ (h) that the diffractive lens structure should have is expressed by the following equation (4), where h is the height from the optical axis Ax1 and Pn is the optical path difference function coefficient of the nth order (even order). Desired.
Δφ (h) = P 2 h 2 + P 4 h 4 + P 6 h 6 + P 8 h 8 + P 10 h 10 (4)
S (h) in equation (2) is a value obtained by the following equation (5) based on this optical path length addition amount Δφ (h), and represents a stepped sag amount that changes in the main scanning direction. .
S (h) = {| MOD (Δφ (h) + C, −1) | −C} λ / {n−1 + Dh 2 } (5)
Here, MOD (X, Y) is a function that gives a remainder obtained by dividing X by Y, C is a constant that sets the phase of the boundary position of the annular zone, and takes an arbitrary value from 0 to 1. D is a coefficient for correcting a change in the amount of phase addition caused by the incident light beam obliquely with respect to the diffractive lens structure.
回折レンズ構造の各輪帯の番号Ｎは、光軸上の領域を０として、以下の式(６)により表される。INT(X)は、Ｘの整数部分を与える関数である。
Ｎ＝INT(｜Δφ(h)＋C｜) …(６)
The number N of each annular zone of the diffractive lens structure is expressed by the following formula (6), where 0 is the area on the optical axis. INT (X) is a function that gives the integer part of X.
N = INT (| Δφ (h) + C |) (6)
表１は、第１の実施形態の走査レンズの基本形状の数値構成を示す。表中の記号ｒは光軸上での各レンズ面の曲率半径(単位：mm)、他は上記の通りである。 Table 1 shows the numerical configuration of the basic shape of the scanning lens of the first embodiment. The symbol r in the table is the radius of curvature (unit: mm) of each lens surface on the optical axis, and the others are as described above.
上記の数値例により、走査レンズ１０の第１面１１の形状、第２面１２のベースカーブ、そして、第２面１２に形成された回折レンズ構造の各輪帯の形状が特定される。そして、各輪帯間の段差面の角度を上述した第１の実施形態のいずれかで決定することにより、走査レンズ１０の具体的な形状が決定される。決定された形状に基づいて金型を製作し、製作した金型を用いて射出成型により実施形態の走査レンズ１０が成型される。 The numerical example above specifies the shape of the first surface 11 of the scanning lens 10, the base curve of the second surface 12, and the shape of each annular zone of the diffractive lens structure formed on the second surface 12. And the specific shape of the scanning lens 10 is determined by determining the angle of the level | step difference surface between each annular zone in any of 1st Embodiment mentioned above. A mold is manufactured based on the determined shape, and the scanning lens 10 of the embodiment is molded by injection molding using the manufactured mold.
１０、１００ 走査レンズ
１１、１０１ 第１面
１２、１０２ 第２面
１２ａ、１０２ａ 段差面
１２ｂ、１０２ｂ 回折作用面
１３ 外枠部
10, 100 Scanning lens 11, 101 First surface 12, 102 Second surface 12a, 102a Step surface 12b, 102b Diffraction action surface 13 Outer frame
Claims (4)
少なくとも一面に同心円状の複数の輪帯を有する回折レンズ構造が形成され、射出成型により製造される樹脂製レンズであり、前記回折レンズ構造は、透過する光を回折させる回折作用面と、隣接する回折作用面の間をつなぐ段差面とを有し、前記回折レンズ構造の設計形状は、前記段差面を、前記輪帯の回転軸を含み前記主走査方向に平行な一断面において、離型時の樹脂収縮に伴うレンズの変形方向にほぼ平行な面とすることにより、離型時に前記段差面と金型との間に作用する応力を軽減した形状であることを特徴とする走査レンズ。 In a scanning lens included in an imaging optical system that forms a spot that scans in a main scanning direction on a scanned surface by converging a light beam emitted from a light source unit and reflected and deflected by a deflector,
A diffractive lens structure having a plurality of concentric annular zones formed on at least one surface is a resin lens manufactured by injection molding, and the diffractive lens structure is adjacent to a diffractive surface that diffracts transmitted light. and a step surface running between the diffraction action surface, the design shape of the diffractive lens structure, the stepped surface, in a section parallel to the main scanning direction includes a rotation axis of the ring-shaped zone, the time of demolding A scanning lens having a shape in which stress acting between the step surface and the mold during release is reduced by forming a surface substantially parallel to the deformation direction of the lens accompanying the resin shrinkage .
少なくとも一面に同心円状の複数の輪帯を有する回折レンズ構造が形成され、前記輪帯の回転軸を含み前記主走査方向に平行な一断面に略平行な面上に配置されたゲートから樹脂が射出される射出成型により製造される樹脂製レンズであり、前記回折レンズ構造は、透過する光を回折させる回折作用面と、隣接する回折作用面の間をつなぐ段差面とを有し、前記回折レンズ構造の設計形状は、前記段差面を、前記一断面内において、該段差面とそれに接続する回折作用面との境界点と、前記ゲートの略中心を前記一断面上に投影した点とを結ぶ直線に対してほぼ平行な面とすることにより、離型時に前記段差面と金型との間に作用する応力を軽減した形状であることを特徴とする走査レンズ。 In a scanning lens included in an imaging optical system that forms a spot that scans in a main scanning direction on a scanned surface by converging a light beam emitted from a light source unit and reflected and deflected by a deflector,
A diffractive lens structure having a plurality of concentric annular zones on at least one surface is formed, and a resin is supplied from a gate disposed on a plane substantially parallel to one section including the rotation axis of the annular zones and parallel to the main scanning direction. a resin lens produced by injection molding emitted, the diffractive lens structure has a diffraction action surface for diffracting the transmitted light, and a step surface running between the diffraction action surface adjacent said diffraction The design shape of the lens structure is such that the step surface has a boundary point between the step surface and a diffraction action surface connected to the step surface, and a point obtained by projecting the approximate center of the gate onto the one cross section. A scanning lens having a shape in which stress acting between the step surface and the mold during mold release is reduced by forming a surface substantially parallel to a straight line to be connected .
により製造される樹脂製レンズであり、前記回折レンズ構造は、透過する光を回折させる回折作用面と、隣接する回折作用面の間をつなぐ段差面とを有し、前記回折レンズの設計形状は、前記段差面を、前記一断面内において、該段差面とそれに接続する回折作用面との境界点と、前記ゲートの略中心を前記一断面上に投影した点とを結ぶ直線に対してほぼ平行な面とすることにより、離型時に前記段差面と金型との間に作用する応力を軽減した形状であることを特徴とする回折レンズ。 Injection molding in which a diffractive lens structure having a plurality of concentric annular zones is formed on at least one surface, and resin is injected from a gate disposed on a plane substantially parallel to one section including the rotation axis of the annular zone
The diffractive lens structure has a diffractive action surface that diffracts transmitted light and a step surface that connects between adjacent diffractive action surfaces, and the design shape of the diffractive lens is The step surface is approximately within a straight line connecting a boundary point between the step surface and a diffraction action surface connected to the step surface and a point obtained by projecting the approximate center of the gate onto the cross section. A diffractive lens characterized by having a shape in which stress acting between the step surface and the mold is reduced during mold release by forming parallel surfaces .
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| JPH07290462A (en) * | 1994-04-22 | 1995-11-07 | Asahi Optical Co Ltd | Mold of bracelet lens made of synthetic resin |
| JP3559710B2 (en) * | 1998-05-25 | 2004-09-02 | キヤノン株式会社 | Diffractive optical element and scanning optical device using the same |
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