JP4526413B2 - Image forming apparatus - Google Patents

Description

本発明は，電子写真方式の画像形成装置に関し，特に，感光体表面の露光感度のムラや帯電のムラによって生じる露光後の電位の過不足を適正に調節する画像形成装置に関するものである。   The present invention relates to an electrophotographic image forming apparatus, and more particularly to an image forming apparatus that appropriately adjusts the excess or deficiency of a post-exposure potential caused by uneven exposure sensitivity or uneven charging on the surface of a photoreceptor.

電子写真方式の画像形成装置（複写機，プリンタ，ファクシミリ装置等）では，帯電装置（帯電手段）により感光体の表面を所定の初期電位まで一様に帯電させ，その帯電済みの感光体表面にビーム光を走査させて，或いはドラム状の感光体の回転軸方向に配列されたＬＥＤアレイ光源により露光することによって静電潜像が書き込まれる。
感光体表面にビーム光を走査させる手段としては，高速回転する多面鏡を有するポリゴンミラー（ポリゴンスキャナ）が一般的であるが，ビーム光を反射する鏡面を所定の回動範囲において高速で往復回動させることにより，ビーム光を感光体表面に対して走査させるレゾナントスキャナ（ミラーを一定周波数で共振させる共振型光学スキャナ）やバルガノスキャナ（ミラーを外部磁界で制御するもの）等の往復走査型スキャナもある。
ここで，ポリゴンミラーは，一方向に高速回転する複数の鏡面によりビーム光を一方向に複連続的に走査させるので，時間的な無駄がなく効率的であるというメリットを有する反面，設置スペースが大きく，定常回転速度に至るまでの立ち上がりに時間を要し，また，耳障りな風切り音が発生するというデメリットがある。
また，ＬＥＤアレイ光源は，光を走査するための光学機器を省略できるので比較的構成がシンプルになるというメリットを有する反面，その発光強度が弱いため，感光体に近接して設けなければならず，感光体の周辺装置についてレイアウト設計上の制約が大きいというデメリットがある。特に，各々現像色が異なる複数の感光体を設けてカラー画像形成を行うタンデム式のカラー画像形成装置では，感光体ごとにＬＥＤアレイ光源を設ける必要が生じ，そのデメリットが顕著となる。 In electrophotographic image forming apparatuses (copiers, printers, facsimile machines, etc.), the surface of the photoconductor is uniformly charged to a predetermined initial potential by a charging device (charging means), and the charged photoconductor surface is applied. The electrostatic latent image is written by scanning the light beam or by exposing with an LED array light source arranged in the direction of the rotation axis of the drum-shaped photoconductor.
A polygon mirror (polygon scanner) having a polygon mirror that rotates at high speed is generally used as a means for scanning the surface of the photosensitive member with beam light, but the mirror surface that reflects the beam light is reciprocated at high speed within a predetermined rotation range. Reciprocating scanning type such as a resonant scanner (resonance type optical scanner that resonates the mirror at a constant frequency) and a balgano scanner (one that controls the mirror with an external magnetic field) There is also a scanner.
Here, the polygon mirror scans the beam light continuously in one direction with a plurality of mirror surfaces that rotate at high speed in one direction. Therefore, the polygon mirror has the merit that it is efficient with no waste of time. It has a demerit that it takes a long time to reach a steady rotational speed and generates an annoying wind noise.
In addition, the LED array light source has an advantage that the configuration is relatively simple because an optical device for scanning light can be omitted. However, since the light emission intensity is weak, the LED array light source must be provided close to the photoconductor. However, there is a demerit that the layout design of the peripheral device of the photosensitive member is largely limited. In particular, in a tandem type color image forming apparatus that forms a color image by providing a plurality of photoconductors each having a different development color, it is necessary to provide an LED array light source for each photoconductor, and the demerits are remarkable.

これに対し，往復走査型のスキャナは，小型で立ち上がり時間が短く，動作音も静かであり，電力消費が少なく，感光体周辺装置のレイアウト設計上の制約も少ないというメリットを有する反面，回転するドラム状の感光体に対し，その回転軸に平行にビーム光を走査させることができるのは，往復走査における一方の走査方向（往路方向又は復路方向）のみであるので，他方の走査方向に走査中は静電潜像書き込みのための露光を行うことができず効率が悪いというデメリットがある。
図３は，ドラム状の感光体の表面を平面として表したときの前記往復走査型のスキャナによるビーム光の走査経路を模式的に表した図であり，Ｒ１及びＲ２は，各々往路方向及び復路方向を表す。即ち，往路方向Ｒ１と平行な横方向Ｒ１１が感光体の回転軸に平行ないわゆる主走査方向であり，それに直交する縦方向Ｒ２２がいわゆる副走査方向である。
図３に示すように，往路の走査経路を感光体の回転軸に平行となるように前記往復走査型のスキャナの走査方向（走査角度）を設定すると，復路の走査経路Ｒは感光体回転軸に対して斜め方向となる。この斜め方向に走査されるビーム光は画像形成（静電潜像書き込み）に適さないため，一般には，ビーム光の出射が停止されることになる。 In contrast, a reciprocating scanner is advantageous in that it is compact and has a short rise time, quiet operation noise, low power consumption, and less restrictions on layout design of peripheral devices. The drum-shaped photosensitive member can be scanned with the light beam parallel to the rotation axis only in one scanning direction (forward direction or backward direction) in the reciprocating scanning, so that scanning is performed in the other scanning direction. There is a demerit that the exposure for writing the electrostatic latent image cannot be performed and the efficiency is low.
FIG. 3 is a diagram schematically showing the scanning path of the beam light by the reciprocating scanner when the surface of the drum-shaped photoconductor is represented as a plane. R1 and R2 are the forward direction and the backward path, respectively. Represents the direction. That is, a lateral direction R11 parallel to the forward direction R1 is a so-called main scanning direction parallel to the rotation axis of the photosensitive member, and a longitudinal direction R22 orthogonal thereto is a so-called sub-scanning direction.
As shown in FIG. 3, when the scanning direction (scanning angle) of the reciprocating scanner is set so that the forward scanning path is parallel to the rotational axis of the photoreceptor, the backward scanning path R is the photosensitive body rotational axis. It becomes a diagonal direction. Since the light beam scanned in the oblique direction is not suitable for image formation (electrostatic latent image writing), the emission of the light beam is generally stopped.

一方，画像形成が行われる際には，まず，所定の画像処理手段により画像形成対象となる画像データに基づいて画素ごとの濃淡レベルを表す画素階調が決定され，予め帯電装置により帯電済みの感光体の表面を前記画像処理手段により決定された前記画素階調を所定の変換情報に基づいて露光量に変換され（通常は線形変換），これにより得られる露光量に従って露光手段により露光される。
ところで，感光体にはその表層部の膜厚や材料特性のばらつき等に起因する個体差があり，その表面を帯電装置により一定条件で一様に帯電させても，感光体ごとに固有の電位の分布が生じる。これがいわゆる帯電ムラである。また，初期電位が等しい領域各々を同一の露光量で露光しても，必ずしも同じ電位にまで下がるわけではなくばらつきが生じる。即ち，露光量の差異に対する電位低下量の差異の比（傾き）に分布（ムラ）がある状況であり，これがいわゆる感度ムラである。
このような各々固有の帯電ムラや感度ムラを有する感光体の表面の各領域について，前記画素階調から前記露光量への変換を同一の（共通の）変換情報に基づいて行うと，同じ露光量で露光しても領域ごとに露光後の電位が異なってしまい，トナーによって現像される濃度（現像濃度）が本来あるべき濃度に対して過不足が生じ，現像ムラ（濃度ムラ）となって表れる。
一般に，画像の濃淡を複数画素の前記画素階調の配列で表現する面積階調方式で階調表現を行う装置（いわゆるデジタル機）の場合，画像の濃淡を画素単位の濃淡のみで表現する装置（いわゆるアナログ機）に比べ，微小な感度ムラや帯電ムラが画像の濃度ムラとして表れにくいものの，空間周期が比較的大きな帯電ムラが存在する場合，面積階調方式で階調表現を行うデジタル機においても濃度ムラを防ぎきれない。
特に，ＣＭＹＫ（シアン，マゼンタ，イエロー，ブラック）の４色のトナー像を重ねるカラー画像形成装置では，ＣＭＹの３色のトナー像を重ねて混色グレーの画像を形成するが，露光後の感光体表面に帯電ムラがあると，ＣＭＹのバランスが崩れて均一な混色グレー像が形成されない（濃度ムラが生じる）。 On the other hand, when image formation is performed, first, a pixel gradation representing a light and shade level for each pixel is determined by a predetermined image processing unit based on image data to be image formed, and is charged in advance by a charging device. The pixel gradation determined by the image processing means is converted into an exposure amount based on predetermined conversion information (usually linear conversion), and the surface of the photoreceptor is exposed by the exposure means according to the exposure amount obtained thereby. .
By the way, there are individual differences due to variations in film thickness and material characteristics of the surface layer of the photoconductor. Even if the surface is uniformly charged by a charging device under a certain condition, a unique potential is generated for each photoconductor. Distribution occurs. This is so-called charging unevenness. Further, even if each region having the same initial potential is exposed with the same exposure amount, it does not necessarily decrease to the same potential, but causes variations. That is, there is a distribution (unevenness) in the ratio (slope) of the difference in potential drop amount to the difference in exposure amount, which is so-called sensitivity unevenness.
When the conversion from the pixel gradation to the exposure amount is performed based on the same (common) conversion information for each region of the surface of the photoconductor having such inherent charging unevenness and sensitivity unevenness, the same exposure is performed. Even if the exposure is performed in an amount, the potential after exposure varies from region to region, and the density developed by the toner (development density) becomes excessive or insufficient with respect to the original density, resulting in development unevenness (density unevenness). appear.
In general, in the case of an apparatus (so-called digital machine) that performs gradation expression by an area gradation method that expresses the lightness and darkness of an image by the array of pixel gradations of a plurality of pixels, an apparatus that expresses the lightness and darkness of an image only by the lightness and darkness of a pixel unit. Compared to (so-called analog machines), even though minute sensitivity unevenness and charging unevenness are less likely to appear as image density unevenness, if there is charging unevenness with a relatively large spatial period, a digital machine that expresses gradation using the area gradation method In this case, uneven density cannot be prevented.
In particular, in a color image forming apparatus that superimposes four color toner images of CMYK (cyan, magenta, yellow, and black), a mixed color gray image is formed by superimposing the three color toner images of CMY. If there is uneven charging on the surface, the CMY balance is lost and a uniform mixed color gray image is not formed (density unevenness occurs).

例えば，特許文献１によれば，露光後の電位に５Ｖ以上の電位ムラがあると，濃度ムラが顕著に表れるとされている。このような現象は，特に，いわゆるタンデム式のカラー画像形成装置において顕著である。また，ａ−Ｓｉ感光体（感光層がアモルファスシリコンからなる感光体）では，一般にＯＰＣ感光体よりも帯電ムラが大きいため，画像の濃度ムラがより顕著となる。かといって，ａ−Ｓｉ感光体において，帯電ムラが５Ｖ以下であることを品質規格（合格レベル）とすると，歩留まりが著しく悪化して現実的でない。
これに対し，特許文献１には，静電潜像書き込み用の露光前に，初期電位の分布を補正するための補助露光手段を設ける技術が示されている。
また，特許文献２には，感光体の感度情報に基づいて露光量を補正する技術が，特許文献３には，感光体の回転位置ごとに感度ムラを補正する技術が，特許文献４には，感光体の露光位置ごとに感度ムラを補正する技術が，特許文献５には，感光体の感度分布データに従って感度ムラを補正する技術が各々示されている。
なお，特許文献１〜５に示される装置では，露光手段として，ポリゴンミラーによりビーム光を感光体上に走査させて露光するもの，或いはＬＥＤアレイにより露光するものが採用されている。
特開２００３−１５４７０６号公報 特開平１０−３１３３２号公報 特開２０００−１６２８３４号公報 特開２００４−６１８６０号公報 特開２００４−２３３６９４号公報 For example, according to Patent Document 1, if there is a potential unevenness of 5 V or more in the potential after exposure, the density unevenness appears remarkably. Such a phenomenon is particularly remarkable in a so-called tandem color image forming apparatus. In addition, since an a-Si photosensitive member (photosensitive member whose photosensitive layer is made of amorphous silicon) generally has larger charging unevenness than an OPC photosensitive member, unevenness in image density becomes more remarkable. However, in the a-Si photosensitive member, if the charging irregularity is 5 V or less as the quality standard (acceptable level), the yield is remarkably deteriorated, which is not realistic.
On the other hand, Patent Document 1 discloses a technique of providing auxiliary exposure means for correcting the distribution of the initial potential before exposure for writing an electrostatic latent image.
Patent Document 2 discloses a technique for correcting the exposure amount based on the sensitivity information of the photoconductor. Patent Document 3 discloses a technique for correcting sensitivity unevenness for each rotational position of the photoconductor. A technique for correcting the sensitivity unevenness for each exposure position of the photosensitive member is disclosed in Patent Document 5, and a technique for correcting the sensitivity unevenness according to the sensitivity distribution data of the photosensitive member is disclosed.
In the apparatuses shown in Patent Documents 1 to 5, as the exposure means, an exposure unit that uses a polygon mirror to scan the light beam on the photosensitive member and an exposure unit that uses an LED array are employed.
JP 2003-154706 A JP 10-31332 A JP 2000-162834 A JP 2004-61860 A JP 2004-233694 A

しかしながら，特許文献１に示されるように，静電潜像書き込み用の露光手段とは別個に独立した露光手段を設けることは，装置の大型化や高コスト化につながるため，適用が困難な場合が多いという問題点があった。特に，タンデム式のカラー画像形成装置の場合，複数（通常は４つ）の感光体ごとに新たな露光手段を設ける必要が生じ，スペース上及びコスト上の問題がより顕著となる。
また，特許文献２〜５に示される技術は，いずれも感光体の感度ムラを補正するもの，即ち，基準となる感光体の露光特性（露光量と電位低下量との関係）と制御対象となる感光体の露光特性とにおける傾き（露光量の差異に対する電位低下量の差異の比）の相違分を補正するものであるため，帯電済み感光体の露光前の初期電位に分布がある（帯電ムラがある）場合には，その電位分布がそのままオフセットとして残り，画像の濃度ムラが解消されないという問題点があった。 However, as disclosed in Patent Document 1, providing an exposure unit that is independent from the exposure unit for writing an electrostatic latent image leads to an increase in the size and cost of the apparatus, and is difficult to apply. There was a problem that there were many. In particular, in the case of a tandem type color image forming apparatus, it is necessary to provide a new exposure unit for each of a plurality of (usually four) photoconductors, and space and cost problems become more prominent.
The techniques disclosed in Patent Documents 2 to 5 all correct the sensitivity unevenness of the photoconductor, that is, the exposure characteristics (relationship between the exposure amount and the potential decrease amount) of the photoconductor as a reference, and the control target. This is to correct the difference in slope (ratio of the difference in potential drop to the difference in exposure amount) from the exposure characteristics of the photosensitive member, so that there is a distribution in the initial potential of the charged photoreceptor before exposure (charging) In the case of unevenness), the potential distribution remains as an offset as it is, and there is a problem that the density unevenness of the image cannot be resolved.

図９は，帯電ムラと感度ムラとが併存するａ−Ｓｉ感光体における前記画素階調とその画素階調に対応する露光量で露光した後の感光体の電位との関係を表すもの（図中，破線で表す）であり，図９（ａ）は露光量補正を行わない場合（太い破線ｇ０１で表す），同（ｂ）は露光量の感度ムラ補正を行った場合（太い実線ｇ０２で表す）の各特性を表す。なお，図中，太い実線（ｇ０）で表す特性は，基準となる（標準的な）感光体の特性（以下，基準特性という）を表す。
ここで，図９（ａ）に示すグラフは前記画素階調を横軸としているが，前記画素階調から前記露光量への変換を，ある一の変換式（係数は固定）或いは変換テーブルに基づいて行う限り，横軸を露光量と見ても等価である。即ち，図９（ａ）においては，基準となる感光体の特性を表すグラフ線ｇ０と，制御対象となる測定対象である感光体の特性を表すグラフ線ｇ０１とは，いずれも同じ変換式（即ち，補正なし）に従って前記画素階調から前記露光量への変換が行われた例であるので，横軸を露光量に置き換えて露光特性（露光量に対する電位の特性（露光電位特性））であるとして見ても等価である。 FIG. 9 shows a relationship between the pixel gradation in the a-Si photosensitive member in which charging unevenness and sensitivity unevenness coexist and the potential of the photosensitive member after exposure with an exposure amount corresponding to the pixel gradation (FIG. 9). 9A shows a case where exposure amount correction is not performed (shown by a thick broken line g01), and FIG. 9B shows a case where exposure amount sensitivity unevenness correction is performed (shown by a thick solid line g02). Represent each characteristic. In the drawing, the characteristic represented by the thick solid line (g0) represents the characteristic of the standard (standard) photoconductor (hereinafter referred to as the standard characteristic).
Here, the graph shown in FIG. 9A has the pixel gradation as the horizontal axis, but the conversion from the pixel gradation to the exposure amount is converted into a certain conversion formula (coefficient is fixed) or a conversion table. As long as it is performed based on this, it is equivalent even if the horizontal axis is regarded as the exposure amount. That is, in FIG. 9A, the graph line g0 representing the characteristics of the photoconductor as the reference and the graph line g01 representing the characteristics of the photoconductor as the measurement target to be controlled are both the same conversion formula ( In other words, since the conversion from the pixel gradation to the exposure amount is performed in accordance with no correction), the horizontal axis is replaced with the exposure amount, and exposure characteristics (characteristic of potential with respect to exposure amount (exposure potential characteristics)) are used. Even if it is seen, it is equivalent.

図９（ａ）に示すように，一般に，感光体（特に，ａ−Ｓｉ感光体）における露光量と電位との対応を表す露光電位特性においては，露光量が増大するにつれてほぼ線形的に露光後の電位が下がり，残留電位（最大露光量で露光後に残る電位）への収束領域（露光量の増加に対して電位が低下する傾きがごく緩やとなる範囲）を除く部分ではほぼ線形の露光特性を示す。例えば，図９（ａ）における測定対象の感光体の露光特性ｇ０１においては，前記画素階調をＩ２としたときの帯電量Ｅ２以下の範囲でほぼ線形の露光特性を示し，基準となる感光体の露光特性ｇ０においては，前記画素階調をＩｓ２としたときの帯電量Ｅｓ２以下の範囲でほぼ線形の露光特性を示している。
また，測定対象の感光体に帯電ムラと感度ムラとが併存する場合，図９（ａ）に示すように，前記基準露光特性ｇ０との間で，初期電位（露光前の帯電電位，即ち，ｙ切片）の差異（帯電ムラ相当分）と，露光特性の傾きの差異（感度ムラ相当分）とが生じる。このような感光体に対し，露光量の感度ムラ補正（傾きを一致させる補正）を行うと，図９（ｂ）に示すように，帯電ムラに対応する電位差（初期電位の差分）がオフセットとして残り，これが画像の濃度ムラの原因となる。
一方，ビーム光の走査手段として前記往復走査型のスキャナを採用し，感光体の回転軸に平行とならない走査方向におけるビーム光を有効活用できれば，小型化，省電力化，静音化及び起動時間の短縮というメリットを活かした画像形成装置を構成することができる。
従って，本発明は上記事情に鑑みてなされたものであり，その目的とするところは，往復走査型のスキャナにより往路・復路の双方向に走査されるビーム光を有効活用しつつ，帯電ムラや感度ムラが併存する感光体についても画像の濃度ムラの発生を極力防止できる画像形成装置を提供することにある。 As shown in FIG. 9A, in general, in the exposure potential characteristic representing the correspondence between the exposure amount and the potential on the photosensitive member (particularly, the a-Si photosensitive member), the exposure is almost linear as the exposure amount increases. The potential later decreases and is almost linear in the area excluding the convergence area (the range in which the slope at which the potential decreases with increasing exposure) becomes a residual potential (the potential remaining after exposure at the maximum exposure). The exposure characteristics are shown. For example, the exposure characteristic g01 of the photoconductor to be measured in FIG. 9A shows a substantially linear exposure characteristic in the range of the charge amount E2 or less when the pixel gradation is I2, and serves as a reference photoconductor. The exposure characteristic g0 shows a substantially linear exposure characteristic in a range equal to or less than the charge amount Es2 when the pixel gradation is Is2.
Further, in the case where charging unevenness and sensitivity unevenness coexist on the photoconductor to be measured, as shown in FIG. 9A, an initial potential (charging potential before exposure, that is, a charging potential before exposure, that is, the reference exposure characteristic g0). A difference in y intercept (corresponding to charging unevenness) and a difference in inclination of exposure characteristics (corresponding to sensitivity unevenness) occur. When exposure sensitivity unevenness correction (correction for matching inclinations) is performed on such a photoconductor, as shown in FIG. 9B, a potential difference (initial potential difference) corresponding to charging unevenness is used as an offset. This will cause uneven density in the image.
On the other hand, if the above-mentioned reciprocating scanner is used as the beam scanning means and the beam light in the scanning direction that is not parallel to the rotation axis of the photosensitive member can be used effectively, miniaturization, power saving, noise reduction, and start-up time An image forming apparatus utilizing the advantage of shortening can be configured.
Therefore, the present invention has been made in view of the above circumstances, and the object of the present invention is to make effective use of light beams scanned in both forward and backward directions by a reciprocating scanning scanner, An object of the present invention is to provide an image forming apparatus capable of preventing the occurrence of density unevenness of an image as much as possible even with respect to a photoreceptor having uneven sensitivity.

上記目的を達成するために本発明は，予め帯電手段により帯電済みの感光体の表面にビーム光を走査させることにより，前記画像処理手段により決定された前記画素階調に基づく前記感光体の露光を行う画像形成装置に適用されるものであり，前記ビーム光を前記感光体表面に対し往復走査させる光往復走査手段を備え，これにより往復走査される前記ビーム光のうち往路若しくは復路のいずれか一方の方向に走査される第１ビーム光（ドラム状の前記感光体の回転軸に平行に走査されるビーム光）による露光量を前記画像処理手段により決定される前記画素階調に基づいて制御する一方（以下，第１露光量制御という），前記感光体の表面を複数に分割した分割領域ごとに前記第１ビーム光の走査方向と反対方向に走査される第２ビーム光による露光量を制御する（以下，第２露光量制御という）ことを特徴とするものである。ここで，前記第２ビーム光による露光量制御は，前記分割領域ごとに，その分割領域における電位特性と全ての前記分割領域に共通の所定の基準電位特性との差分に応じて露光量制御を行う。
このように，前記光往復走査手段（往復走査型のスキャナ）により往路・復路の双方向に走査されるビーム光の一方（往路又は復路のビーム光）を前記画素階調に基づく静電潜像書き込みに用いるとともに，他方を前記感光体の領域ごとの電位特性の分布（基準特性との差分）の補正に用いて有効活用すれば，前記往復走査型のスキャナのメリット（小型化，省電力化，静音化及び起動時間の短縮）を活かした画像形成装置を構成することができるとともに，帯電ムラや感度ムラが併存する感光体についても画像の濃度ムラの発生を極力防止できる。
しかも，新たな露光手段等を追加する必要がないので，装置の大型化や高コスト化を招くことがない。 In order to achieve the above object, the present invention provides an exposure of the photoconductor based on the pixel gradation determined by the image processing means by scanning the surface of the photoconductor previously charged by the charging means with a beam of light. And an optical reciprocating scanning means for reciprocatingly scanning the light beam with respect to the surface of the photosensitive member, so that either the forward path or the backward path of the beam light that is reciprocally scanned is provided. The exposure amount by the first beam light scanned in one direction (beam light scanned parallel to the rotation axis of the drum-shaped photoconductor) is controlled based on the pixel gradation determined by the image processing means. On the other hand (hereinafter referred to as first exposure amount control), the second beam light scanned in the direction opposite to the scanning direction of the first beam light for each of the divided areas obtained by dividing the surface of the photosensitive member into a plurality of areas. The exposure quantity is controlled by and is characterized in (hereinafter, second of exposure control) that. Here, the exposure amount control by the second beam light is performed for each divided region according to the difference between the potential characteristic in the divided region and a predetermined reference potential characteristic common to all the divided regions. Do.
Thus, one of the light beams scanned in the forward and backward directions by the optical reciprocating scanning means (reciprocating scanner) (outward or backward beam light) is converted into an electrostatic latent image based on the pixel gradation. If it is used for writing and the other is effectively used to correct the distribution of potential characteristics (difference from the reference characteristics) for each area of the photoconductor, the advantage of the reciprocating scanner (miniaturization and power saving) In addition, it is possible to configure an image forming apparatus that takes advantage of noise reduction and start-up time reduction, and it is possible to prevent image density unevenness as much as possible even with respect to a photoconductor in which charging unevenness and sensitivity unevenness coexist.
In addition, since it is not necessary to add new exposure means or the like, the apparatus is not increased in size and cost.

より具体的には，従来から行われているように，前記第１露光量制御においては，画素ごとの濃淡レベルを表す画素階調を，全ての前記分割領域に共通の係数を用いて比例換算した露光量を前記第１ビーム光による露光量として設定することが考えられる（以下，共通第１露光量制御という）。前記画素階調は，所定の画像データ，例えば，複写機における原稿からの読み取り画像データやプリンタにおける印刷ジョブ等の画像データに基づいて，所定の画像処理手段により決定されるものである。
また，前記分割領域ごとに前記画素階調を露光量に略比例換算する際の傾き情報を記憶手段に予め記憶しておき，前記第１露光量制御において，画素ごとに前記画像処理手段により決定される前記画素階調を前記分割領域ごとの前記傾き情報に従って略比例換算した露光量を前記第１ビーム光による露光量として設定すれば，前記分割領域各々における感度ムラ分について露光量の補正を行うことができる（以下，個別第１露光量制御という）。
この個別第１露光量制御においては，前記画素階調に応じて前記第１ビーム光の画素ごとの露光時間を調節するとともに，前記傾き情報に応じて前記第１ビーム光の前記分割領域ごとの露光強度を調節して露光量を制御することが考えられる。 More specifically, as has been conventionally performed, in the first exposure amount control, the pixel gradation representing the gray level for each pixel is proportionally converted using a coefficient common to all the divided regions. It is conceivable to set the exposure amount obtained as the exposure amount by the first beam light (hereinafter referred to as common first exposure amount control). The pixel gradation is determined by predetermined image processing means based on predetermined image data, for example, image data read from an original in a copying machine or image data such as a print job in a printer.
In addition, inclination information when the pixel gradation is substantially proportionally converted to the exposure amount for each divided region is stored in advance in a storage unit, and is determined by the image processing unit for each pixel in the first exposure amount control. If the exposure amount obtained by approximately proportionally converting the pixel gradation according to the inclination information for each divided region is set as the exposure amount by the first beam light, the exposure amount correction for the sensitivity unevenness in each of the divided regions is performed. (Hereinafter referred to as individual first exposure amount control).
In the individual first exposure amount control, the exposure time for each pixel of the first beam light is adjusted according to the pixel gradation, and the first beam light for each divided area according to the tilt information. It is conceivable to control the exposure amount by adjusting the exposure intensity.

一方，前記第２露光量制御においては，全ての前記分割領域に共通の所定の基準露光量と，前記分割領域各々における露光電位特性に対し全ての前記分割領域に共通の所定の基準電位を適用して得られる露光量と，の差分露光量を特定するかさ上げ露光量情報を記憶手段に予め記憶しておき，そのかさ上げ露光量情報に基づいて前記第２ビーム光による露光量を設定（制御）することが考えられる（以下，かさ上げ露光量設定という）。
ここで，前記分割領域各々における露光電位特性とは，前記分割領域各々における露光量（露光量＝０を含む）と電位（初期電位及び露光後電位）との対応関係を表す特性を意味し，通常は，前記基準露光量及び前記基準電位は，前記露光電位特性のうちの略線形特性を示す範囲，即ち，前記露光電位特性における残留電位への収束領域を除く部分である略線形な露光電位特性の範囲において定められる。
例えば，前記基準電位及び前記基準露光量としては，例えば，全ての前記分割領域に共通の基準となる前記露光電位特性における初期電位と残留電位との略中点の電位及びその略中点の電位に対応する露光量（いわゆる半減露光量）とすることが好適である。
これにより，後述するように，前記分割領域各々における露光後電位を，露光量全範囲に渡って全体的に，或いは設定頻度の高い特定の露光量の範囲において前記基準となる露光電位特性に対して近づくように露光することができ，帯電ムラや感度ムラが併存する感光体についても画像の濃度ムラの発生を極力防止できる。特に，前記傾き情報に基づく前記第１露光量制御と併せて行えば，前記分割領域各々における露光後電位をほぼ同一レベルに均一化することが可能となる。
また，前記第１露光量制御として前記共通露光量制御が採用される場合，前記分割領域各々についての前記露光電位特性のうちの残留電位への収束領域を除く部分である略線形の露光電位特性における傾きと，全ての前記分割領域に共通の基準となる傾きと，の差分に関する差分傾き情報を記憶手段に予め記憶しておき，前記第２露光量制御において，前記かさ上げ露光量設定により設定される前記第２ビーム光の露光量に対し，前記画像処理手段により決定される前記画素階調を前記差分傾き情報に基づいて比例換算した露光量分の補正を行う（露光感度補正）ことも考えられる。
これによっても，前記分割領域各々における感度ムラ分について露光量の補正を行うことができる。
これら第２露光量制御においては，例えば，前記第２ビーム光の露光時間を調節することにより露光量を制御することが考えられる。 On the other hand, in the second exposure amount control, a predetermined reference exposure amount common to all the divided regions and a predetermined reference potential common to all the divided regions are applied to the exposure potential characteristics in each of the divided regions. The exposure amount information for specifying the difference exposure amount from the exposure amount obtained in this manner is stored in advance in the storage means, and the exposure amount by the second beam light is set based on the increase exposure amount information ( Control) (hereinafter referred to as raising exposure amount setting).
Here, the exposure potential characteristic in each of the divided areas means a characteristic representing a correspondence relationship between an exposure amount (including exposure amount = 0) and a potential (initial potential and post-exposure potential) in each of the divided areas. Usually, the reference exposure amount and the reference potential are a range showing a substantially linear characteristic of the exposure potential characteristics, that is, a substantially linear exposure potential that is a portion excluding a convergence area to a residual potential in the exposure potential characteristics. It is defined in the range of characteristics.
For example, as the reference potential and the reference exposure amount, for example, a potential at a substantially middle point between the initial potential and the residual potential in the exposure potential characteristic that is a reference common to all the divided regions, and a potential at the substantially middle point It is preferable to set the exposure amount corresponding to (so-called half exposure amount).
As a result, as described later, the post-exposure potential in each of the divided regions is compared with the reference exposure potential characteristic as a whole over the entire exposure amount range or in a specific exposure amount range with a high setting frequency. It is possible to perform exposure so as to approach each other, and it is possible to prevent image density unevenness as much as possible even with respect to a photoconductor in which uneven charging and uneven sensitivity exist. In particular, when performed together with the first exposure amount control based on the tilt information, the post-exposure potential in each of the divided regions can be made uniform at substantially the same level.
When the common exposure amount control is employed as the first exposure amount control, a substantially linear exposure potential characteristic that is a portion excluding a convergence region to a residual potential in the exposure potential characteristics for each of the divided regions. Difference inclination information regarding the difference between the inclination at, and the reference inclination common to all the divided areas is stored in advance in the storage means, and is set by the raised exposure amount setting in the second exposure amount control. The exposure amount of the second beam light to be corrected may be corrected by the exposure amount obtained by proportionally converting the pixel gradation determined by the image processing unit based on the difference inclination information (exposure sensitivity correction). Conceivable.
This also makes it possible to correct the exposure amount for the sensitivity unevenness in each of the divided areas.
In the second exposure amount control, for example, it is conceivable to control the exposure amount by adjusting the exposure time of the second beam light.

また，前記分割領域としては，ドラム状の前記感光体の表面をその軸方向若しくは周方向に複数分割した領域（一次元の分割），或いはその両方向に複数分割した領域（２次元の分割）が考えられる。例えば，１画素の幅或いは高さの単位で分割することや，複数画素分の幅や高さの単位で分割することが考えられる。
ここで，前記露光手段による露光は，前記分割領域の各位置を認識して行う必要があることはいうまでもない。一般に，前記感光体表面の軸方向（即ち，主走査方向）の露光位置については，前記露光手段（或いはその制御手段）において少なくとも画素単位で書き込み位置は認識（検出）されている。一方，前記感光体表面の周方向（副走査方向）の絶対位置については，画像形成に直接的に必要な情報ではないため，前記感光体の回転位置を検出する手段を設ける必要がある。
また，前記感光体がａ−Ｓｉ感光体である場合に，特に帯電ムラが顕著に表れることが多いため，本発明の適用に好適である。
また，本発明は，前記画像データに基づく画像処理が，複数画素の前記画素階調の配列を決定する面積階調方式で階調表現を行う処理である場合に，空間周期が比較的大きい帯電ムラが存在しても，それが画像の濃度ムラとなって表れることを防止できる点で好適である。
また，複数色のトナーによりカラー画像形成を行う画像形成装置，特に複数の感光体により複数色のトナー像を重ねて画像形成を行うタンデム式の画像形成装置は，帯電ムラや感度ムラにより生じる画像の濃度ムラが形成画像においてより顕著に視認されるので，本発明の適用対象として好適である。 The divided area includes an area obtained by dividing the surface of the drum-shaped photosensitive member into a plurality of parts in the axial direction or the circumferential direction (one-dimensional division), or a plurality of areas divided in both directions (two-dimensional division). Conceivable. For example, it is conceivable to divide in units of width or height of one pixel, or to divide in units of width or height for a plurality of pixels.
Here, it is needless to say that the exposure by the exposure means needs to be performed by recognizing each position of the divided area. In general, with respect to the exposure position in the axial direction (that is, the main scanning direction) of the surface of the photoreceptor, the writing position is recognized (detected) at least in pixel units in the exposure means (or its control means). On the other hand, since the absolute position in the circumferential direction (sub-scanning direction) of the surface of the photoconductor is not information directly necessary for image formation, it is necessary to provide means for detecting the rotational position of the photoconductor.
In addition, when the photoconductor is an a-Si photoconductor, charging unevenness is particularly noticeable in many cases, which is suitable for application of the present invention.
In addition, the present invention provides a charging method having a relatively large spatial period when the image processing based on the image data is a processing that performs gradation expression by an area gradation method that determines an array of pixel gradations of a plurality of pixels. Even if unevenness exists, it is preferable in that it can be prevented from appearing as uneven density in the image.
In addition, an image forming apparatus that forms a color image with a plurality of color toners, particularly a tandem type image forming apparatus that forms an image by superimposing a plurality of color toner images with a plurality of photoconductors, has an image caused by uneven charging or uneven sensitivity. This is preferable as an application target of the present invention.

本発明によれば，共振型光学スキャナ等の往復走査型のスキャナにより往路と復路との双方向に走査されるビーム光の一方（往路又は復路のビーム光）を，画像処理手段により決定される画素階調に基づく静電潜像書き込みに用いるとともに，他方を前記感光体の領域ごとの電位特性の分布（基準特性との差分）の補正に用いて有効活用されるので，往復走査型のスキャナのメリット（小型化，省電力化，静音化及び起動時間の短縮）を活かした画像形成装置を構成することができるとともに，帯電ムラや感度ムラが併存する感光体についても画像の濃度ムラの発生を極力防止できる。
しかも，新たな露光手段等を追加する必要がないので，装置の大型化や高コスト化を招くことがない。
特に，帯電ムラが顕著に表れることが多いａ−Ｓｉ感光体が用いられる画像形成装置や，帯電ムラや感度ムラにより生じる画像の濃度ムラが形成画像においてより顕著に視認されるカラー画像形成装置への適用に好適である。 According to the present invention, one of the light beams scanned in both directions of the forward path and the backward path by the reciprocating scanner such as a resonance type optical scanner (outward path or backward path beam light) is determined by the image processing means. A reciprocating scanner is used for writing an electrostatic latent image based on pixel gradation and effectively using the other for correcting the distribution of potential characteristics (difference from the reference characteristics) for each area of the photoconductor. Image forming devices that take advantage of the advantages (miniaturization, power saving, noise reduction and shortening of start-up time), as well as image density unevenness on photoconductors with uneven charging and sensitivity unevenness. Can be prevented as much as possible.
In addition, since it is not necessary to add new exposure means or the like, the apparatus is not increased in size and cost.
In particular, to an image forming apparatus using an a-Si photosensitive member in which charging unevenness often appears remarkably, and a color image forming apparatus in which density unevenness of an image caused by charging unevenness or sensitivity unevenness is more noticeable in a formed image. It is suitable for application.

以下添付図面を参照しながら，本発明の実施の形態について説明し，本発明の理解に供する。尚，以下の実施の形態は，本発明を具体化した一例であって，本発明の技術的範囲を限定する性格のものではない。
ここに，図１は本発明の実施形態に係る画像形成装置Ｘの概略断面図，図２は画像形成装置Ｘにおける往復スキャナによるビーム光の走査状態を表す斜視図，図３はドラム状の感光体の表面を平面として表したときの往復走査型のスキャナによるビームの走査経路を表す模式図，図４は画像形成装置Ｘの主要部の概略構成を表すブロック図，図５は第１実施例に係る画素階調とビーム光の光量との関係を表すグラフ及びそのときの画素階調と電位との関係を表すグラフ，図６は第２実施例に係る画素階調とビーム光の光量との関係を表すグラフ及びそのときの画素階調と電位との関係を表すグラフ，図７は第３実施例に係る画素階調とビーム光の光量との関係を表すグラフ及びそのときの画素階調と電位との関係を表すグラフ，図８は第４実施例に係る画素階調とビーム光の光量との関係を表すグラフ及びそのときの画素階調と電位との関係を表すグラフ，図９は帯電ムラと感度ムラとが並存する感光体表面における従来の画素階調と露光後の電位との関係の一例を表すグラフである。 Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
FIG. 1 is a schematic sectional view of an image forming apparatus X according to an embodiment of the present invention, FIG. 2 is a perspective view showing a scanning state of beam light by a reciprocating scanner in the image forming apparatus X, and FIG. FIG. 4 is a block diagram showing a schematic configuration of a main part of the image forming apparatus X, and FIG. 5 is a first embodiment. FIG. 6 is a graph showing the relationship between the pixel gradation and the light amount of the light beam and the graph showing the relationship between the pixel gradation and the potential at that time. FIG. FIG. 7 is a graph showing the relationship between the pixel gradation and the potential of the beam light according to the third embodiment. FIG. 8 is a graph showing the relationship between tone and potential. FIG. 9 is a graph showing the relationship between the pixel gradation and the light amount of the beam light according to the example, and the graph showing the relationship between the pixel gradation and the potential at that time. FIG. It is a graph showing an example of the relationship between the pixel gradation of this and the electric potential after exposure.

まず，図１に示す断面図を用いて，本発明の実施形態に係る画像形成装置Ｘの全体構成について説明する。
画像形成装置Ｘは，ブラック（ＢＫ），マゼンダ（Ｍ），イエロー（Ｙ），シアン（Ｃ），の４色のトナーを用いて画像形成を行うタンデム方式のカラー画像形成装置の一例であるプリンタである。
画像形成装置Ｘは，トナー像を形成して記録紙に画像形成を行う画像形成部α１，その記録紙を前記画像形成部α１に供給する給紙部α２，及び画像形成の行われた記録紙の排出がなされる排紙部α３を有する。
パーソナルコンピュータ等の外部装置から不図示の通信部により受信された画像情報（印刷ジョブ）は，後述する画像処理部５２によりブラック（ＢＫ），マゼンダ（Ｍ），イエロー（Ｙ），シアン（Ｃ），の４色各々に対する画素ごとの濃淡値情報である画素階調に変換される。 First, the overall configuration of the image forming apparatus X according to the embodiment of the present invention will be described using the cross-sectional view shown in FIG.
The image forming apparatus X is a printer that is an example of a tandem color image forming apparatus that forms an image using toners of four colors of black (BK), magenta (M), yellow (Y), and cyan (C). It is.
The image forming apparatus X includes an image forming unit α1, which forms a toner image and forms an image on a recording sheet, a paper feeding unit α2, which supplies the recording sheet to the image forming unit α1, and a recording sheet on which image formation has been performed. Is discharged.
Image information (print job) received from a communication unit (not shown) from an external device such as a personal computer is black (BK), magenta (M), yellow (Y), cyan (C) by an image processing unit 52 described later. Are converted into pixel gradations which are grayscale information for each pixel for each of the four colors.

前記画像形成部α１は，上記４色各々の像を担持する４つの感光体ドラム１（ブラック用１ＢＫ，マゼンダ用１Ｍ，イエロー用１Ｙ，シアン用１Ｃ），その感光体ドラム１各々の表面を一様に帯電させる帯電装置３（３ＢＫ，３Ｍ，３Ｙ，３Ｃ），前記感光体ドラム１各々に対応する複数のビーム光を出力する露光源Ｚ（図１には不図示），この露光源Ｚから出力されるビーム光を前記感光体ドラム１の回転軸方向に往復走査させる共振型光学スキャナ等の往復スキャナ９，この往復スキャナ９により走査されるビーム光を反射して前記感光体ドラム１各々の表面に導く反射ミラー８を備えている。
この反射ミラー８を通じて前記感光体ドラム１各々の表面に走査されるビーム光により，前記帯電装置３により予め帯電済みの前記感光体ドラム１各々の表面に対し，後述する画像処理部１２により決定される前記画素階調に基づく露光が行われ，静電潜像が書き込まれる。
さらに，前記画像形成部αは，前記感光体ドラム１各々に書き込まれた静電潜像にトナーを供給することによりトナー像として現像する現像装置２（２ＢＫ，２Ｍ，２Ｙ，２Ｃ），前記感光体ドラム１各々の表面に形成されたトナー像が順次転写され，そのトナー像を転写部４０において記録紙に転写する中間転写ベルト７，記録紙を搬送する搬送ローラ４，記録紙上に転写されたトナー像を加熱定着させる定着装置１３，トナー像を記録紙に転写後の前記感光体ドラム１表面の除電を行う除電装置５（５ＢＫ，５Ｍ，５Ｙ，５Ｃ）等を備えて概略構成される。 The image forming unit α1 has four photosensitive drums 1 (1BK for black, 1M for magenta, 1Y for yellow, 1C for cyan) carrying the images of the above four colors, and the surface of each of the photosensitive drums 1 is integrated. Charging device 3 (3BK, 3M, 3Y, 3C) for charging in such a manner, an exposure source Z (not shown in FIG. 1) for outputting a plurality of light beams corresponding to each of the photosensitive drums 1, from the exposure source Z A reciprocating scanner 9 such as a resonance type optical scanner that reciprocally scans the output light beam in the direction of the rotation axis of the photosensitive drum 1, and the light beam scanned by the reciprocating scanner 9 is reflected to reflect each of the photosensitive drums 1. A reflection mirror 8 that leads to the surface is provided.
The surface of each of the photosensitive drums 1 that has been charged in advance by the charging device 3 is determined by an image processing unit 12 to be described later by the beam light scanned on the surface of each of the photosensitive drums 1 through the reflection mirror 8. Exposure based on the pixel gradation is performed, and an electrostatic latent image is written.
Further, the image forming unit α supplies a developing device 2 (2BK, 2M, 2Y, 2C) that develops a toner image by supplying toner to the electrostatic latent image written on each of the photosensitive drums 1, and the photosensitive drum. The toner image formed on the surface of each of the body drums 1 is sequentially transferred, and the toner image is transferred onto the recording paper in the transfer unit 40, the intermediate transfer belt 7 that transfers the recording paper, the transport roller 4 that transports the recording paper, and the transfer onto the recording paper. A fixing device 13 for heating and fixing the toner image, a neutralizing device 5 (5BK, 5M, 5Y, 5C) for neutralizing the surface of the photosensitive drum 1 after the toner image is transferred to the recording paper are schematically configured.

前記感光体ドラム１は，例えば，高硬度で性状が安定しているため耐久性に優れる一方，感度ムラに加えて帯電ムラが比較的顕著に表れやすいａ−Ｓｉ感光体等である。
前記帯電装置３は，前記感光体ドラム１の表面をその軸方向に沿って一様に帯電させるものであるが，前記感光体ドラム１に帯電ムラがある場合，前記帯電装置３による帯電後（露光前）の電位（初期電位）には分布が生じる。
前記現像装置２は，前記感光体ドラム１にトナーを供給する現像ローラを備え，その現像ローラに印加された電位（現像バイアス電位）と前記感光体ドラム１表面の電位との電位ギャップに応じて，前記現像ローラ上のトナーが前記感光体ドラム１の面上に引き寄せられ，前記静電潜像がトナー像として顕像化される。
前記給紙部α２は，給紙カセット１１，給紙ローラ１２等を有して概略構成される。前記給紙カセット１１に予め収容された記録紙は，前記給紙ローラ１２が回転駆動することにより前記画像形成部α１に搬送される。
前記給紙部α２から送出された記録紙は，前記搬送ローラ４により搬送されつつ前記転写部４０で前記中間転写ベルト７からトナー像が転写され，前記定着装置１３を経て前記排紙部α３に搬送され，装置外の排紙トレーへ排出される。 The photosensitive drum 1 is, for example, an a-Si photosensitive member that is excellent in durability because of its high hardness and stable properties, while charging unevenness is likely to appear relatively remarkably in addition to sensitivity unevenness.
The charging device 3 uniformly charges the surface of the photosensitive drum 1 along its axial direction. If the photosensitive drum 1 is unevenly charged, Distribution occurs in the potential (initial potential) before exposure.
The developing device 2 includes a developing roller that supplies toner to the photosensitive drum 1, and corresponds to a potential gap between a potential (developing bias potential) applied to the developing roller and a potential on the surface of the photosensitive drum 1. The toner on the developing roller is attracted onto the surface of the photosensitive drum 1, and the electrostatic latent image is visualized as a toner image.
The paper feed unit α2 is schematically configured to have a paper feed cassette 11, a paper feed roller 12, and the like. The recording paper previously stored in the paper feed cassette 11 is conveyed to the image forming unit α1 when the paper feed roller 12 is driven to rotate.
The recording paper delivered from the paper feeding unit α2 is transferred by the transfer roller 40 while the toner image is transferred from the intermediate transfer belt 7 while being transported by the transport roller 4, and passes through the fixing device 13 to the paper discharge unit α3. It is transported and discharged to a discharge tray outside the device.

次に，図２に示す斜視図を用いて，前記往復スキャナ９によるビーム光の走査について説明する。なお，図２において，破線はビーム光の光路を表す。
静電潜像書き込み用の複数のビーム光は，それらを出力する複数の光源（レーザダイオード等）が組み込まれてユニット化された露光源Ｚから供給される。
前記露光源Ｚは，各々一の光源が実装されている電子基板が設けられた複数の（図２では４つ）の単光源ユニット２２（２２ＢＫ，２２Ｍ，２２Ｙ，２２Ｃ）と，それら単光源ユニット２２各々から出力される複数のビーム光（レーザ光）相互の位置関係（光路）を定める光学機器とが，一体成型された不図示の取付基材に一体に組み込まれたユニットである。
前記単光源ユニット２２各々から出射された４つのビーム光は，コリメータレンズ筒２４の内部に装着されたコリメータレンズを通過した後，反射ミラー２５〜２７により反射され，共通の反射ミラー２７に到達した段階で，４つのビーム光はほぼ鉛直方向（副走査方向）に１列に並んだ状態となっている。
前記共通の反射ミラー２７に反射された複数のビーム光の束は，シリンドリカルレンズ２８を通過し，それらビーム光各々を一括反射させる反射ミラー２９により，複数のビーム光を一括して往復走査させる前記往復スキャナ９の反射ミラー９ａに向けて反射される。
前記往復スキャナ９は，ビーム光を反射させる反射ミラー９ａと，その反射ミラーを所定の回動範囲において高速で往復回動させる駆動部９ｂとを備える。
この往復スキャナ９により往復走査される複数のビーム光各々は，図１に示した前記反射ミラー８により対応する前記感光体ドラム１各々に導かれ，前記感光体ドラム１各々の表面に対して往復走査される（光往復走査手段の一例）。
このようにして前記感光体ドラム１各々表面を走査されるビーム光は，図３の模式図を用いて前述したように，往路方向Ｒ１においては前記感光体ドラム１の回転軸に平行に走査され，復路方向Ｒ２においてはその回転軸に対して斜め方向に走査されることになる。
なお，往路方向において前記感光体ドラム１の回転軸に平行に走査し，復路方向においてはその回転軸に対して斜め方向に走査するものであってもかまわない。 Next, scanning of the beam light by the reciprocating scanner 9 will be described using the perspective view shown in FIG. In FIG. 2, the broken line represents the optical path of the beam light.
A plurality of light beams for writing an electrostatic latent image are supplied from an exposure source Z that is unitized by incorporating a plurality of light sources (laser diodes or the like) for outputting them.
The exposure source Z includes a plurality of (four in FIG. 2) single light source units 22 (22BK, 22M, 22Y, 22C) each provided with an electronic substrate on which one light source is mounted, and these single light source units. 22 is a unit in which a plurality of light beams (laser beams) output from each of the optical devices that determine the mutual positional relationship (optical path) are integrated into an integrally formed mounting base (not shown).
The four light beams emitted from each single light source unit 22 pass through the collimator lens mounted inside the collimator lens tube 24, are reflected by the reflection mirrors 25 to 27, and reach the common reflection mirror 27. At the stage, the four light beams are arranged in a line in the substantially vertical direction (sub-scanning direction).
A bundle of a plurality of light beams reflected by the common reflection mirror 27 passes through a cylindrical lens 28, and a plurality of light beams are collectively reciprocated by a reflection mirror 29 that collectively reflects each of the light beams. The light is reflected toward the reflection mirror 9 a of the reciprocating scanner 9.
The reciprocating scanner 9 includes a reflecting mirror 9a that reflects the beam light and a drive unit 9b that reciprocally rotates the reflecting mirror at a high speed within a predetermined rotation range.
Each of the plurality of beam lights reciprocally scanned by the reciprocating scanner 9 is guided to the corresponding photosensitive drum 1 by the reflecting mirror 8 shown in FIG. 1 and reciprocates with respect to the surface of the photosensitive drum 1. Scanned (an example of optical reciprocating scanning means).
The beam light scanned on the surface of each of the photosensitive drums 1 in this way is scanned in parallel with the rotation axis of the photosensitive drum 1 in the forward direction R1 as described above with reference to the schematic diagram of FIG. In the backward direction R2, scanning is performed obliquely with respect to the rotation axis.
Note that scanning may be performed in parallel with the rotation axis of the photosensitive drum 1 in the forward path direction, and scanning in an oblique direction with respect to the rotation axis in the backward path direction.

図４は，画像形成装置Ｘの主要部の概略構成を表すブロック図である。
画像形成装置Ｘは，前記帯電装置３，前記露光源Ｚ，前記現像装置２及び前記除電装置５に加え，ＭＰＵ及びその周辺装置であるＲＯＭ，ＲＡＭ等から構成され，当該画像形成装置Ｘの各構成要素を制御する制御部５０，利用者に対する情報の表示手段であるとともに，利用者の操作に従って情報を入力する手段でもある液晶タッチパネル等の表示操作部５１，各種画像処理を行う画像処理部５２，ＥＥＰＲＯＭ等の読み書き自在の記憶手段であり各種データを記憶するデータ記憶部５３及び前記感光体ドラム１各々の回転方向の位置を検出する回転位置検出部５４等を備えている。
前記画像処理部５２は，外部装置から不図示の通信制御部を介して入力される所定の画像データ（印刷ジョブ等）に基づいて，トナーの各色について画素ごとの濃淡レベルを表す画素階調をデジタル方式により決定する処理を実行する。
ここで，前記画像処理部５２は，前記画像データに基づいて，複数画素からなる画素群（以下，単位画素群という）の単位で，描画（印字）する画素の配列，及び描画する画素の前記画素階調を決定する誤差拡散方式やスクリーン方式等の面積階調方式によって画像の濃度階調表現を行う。
前記データ記憶部５３には，予め，前記感光体ドラム１各々について，その表面を複数に分割した分割領域ごとに，その分割領域における電位特性と全ての前記分割領域に共通の所定の基準電位特性との差分に応じた露光量調節情報が個別に記憶されている。例えば，前記分割領域各々の識別情報として，前記往復スキャナ９により検出される主走査方向（前記感光体ドラム１の回転軸方向）のビーム光走査位置（照射位置）と前記回転位置検出部５４の検出値との組み合わせを記憶しておき，さらにその組み合わせ（前記分割領域各々の識別情報）各々に対応づけて前記露光量調節情報を記憶しておく。その情報の具体的内容については後述する。
ここで，前記分割領域は，例えば，各画素に対応した領域（１画素分の幅（軸方向）×１ライン分の高さ（周方向））の領域や，前記画像処理部５２における面積階調方式での画像処理で採用される前記単位画素群に対応した領域とすること等が考えられる。
前記回転位置検出部５４の構成としては，例えば，前記感光体ドラム１の回転軸に回転式のポテンショメータを設けて回転位置を検出する構成や，前記感光体ドラム１の回転軸に突起部等の基準部を設け，その基準部の通過位置を接触型のスイッチやフォトカプラ等により検出し，その検出時点からの経過時間を計時する構成等が考えられる。 FIG. 4 is a block diagram illustrating a schematic configuration of a main part of the image forming apparatus X.
The image forming apparatus X includes an MPU and its peripheral devices such as ROM and RAM in addition to the charging device 3, the exposure source Z, the developing device 2 and the charge eliminating device 5. A control unit 50 that controls components, a display operation unit 51 such as a liquid crystal touch panel that is a unit for inputting information according to a user operation, and an image processing unit 52 that performs various types of image processing. , An EEPROM or the like, which is a readable / writable storage means, and includes a data storage unit 53 for storing various data, a rotation position detection unit 54 for detecting the position of each of the photosensitive drums 1 in the rotation direction, and the like.
The image processing unit 52 calculates a pixel gradation representing a gray level for each pixel for each color of toner based on predetermined image data (print job or the like) input from an external device via a communication control unit (not shown). The process determined by the digital method is executed.
Here, the image processing unit 52, based on the image data, arranges pixels to be drawn (printed) in units of a pixel group composed of a plurality of pixels (hereinafter referred to as a unit pixel group), and the pixel to be drawn. Density gradation expression of an image is performed by an area gradation method such as an error diffusion method or a screen method for determining pixel gradation.
In the data storage unit 53, for each of the photosensitive drums 1, the surface of each of the photosensitive drums 1 is divided into a plurality of divided areas, and the potential characteristics in the divided areas and predetermined reference potential characteristics common to all the divided areas are stored in advance. The exposure amount adjustment information corresponding to the difference is stored separately. For example, as identification information of each of the divided areas, a beam light scanning position (irradiation position) in the main scanning direction (rotational axis direction of the photosensitive drum 1) detected by the reciprocating scanner 9 and the rotational position detection unit 54 A combination with the detected value is stored, and the exposure amount adjustment information is stored in association with each combination (identification information of each divided region). Specific contents of the information will be described later.
Here, the divided region is, for example, a region corresponding to each pixel (a width of one pixel (axial direction) × a height of one line (circumferential direction)) or an area floor in the image processing unit 52. A region corresponding to the unit pixel group employed in the image processing in the gradation method may be considered.
As the configuration of the rotational position detector 54, for example, a rotational potentiometer is provided on the rotational axis of the photosensitive drum 1 to detect the rotational position, or a protrusion or the like is disposed on the rotational shaft of the photosensitive drum 1. A configuration in which a reference portion is provided, a passing position of the reference portion is detected by a contact-type switch, a photocoupler, or the like, and an elapsed time from the detection time point is measured.

前記制御部５０は，前記往復スキャナ９からはビーム光を往路の走査中であるか復路の走査中であるかを表す走査方向信号及びその走査位置を表す走査位置信号を，前記画像処理部５２からは画像処理により決定された前記画素階調を，前記回転位置検出部５４からは前記感光体ドラム１の回転位置信号を各々取得し，前記露光源Ｚを制御することによってビーム光の光量制御を行う。その際，前記制御部５０は，前記感光体ドラム１上における主走査方向（前記感光体ドラム１の回転軸方向）と副走査方向の各々におけるビーム光の照射位置を，前記走査位置信号及び前記感光体ドラム１の回転位置信号に基づいて認識し，これからビーム光を照射しようとしている位置（画素或いは前記分割領域）に対応する前記露光量調節情報を前記データ記憶部５３から抽出（検索）して読み出す。   The control unit 50 outputs a scanning direction signal indicating whether the beam light is being scanned forward or backward from the reciprocating scanner 9 and a scanning position signal indicating the scanning position to the image processing unit 52. The pixel gradation determined by image processing is acquired from the rotation position, and the rotation position signal of the photosensitive drum 1 is acquired from the rotation position detector 54, and the exposure light source Z is controlled to control the light amount of the beam light. I do. At this time, the control unit 50 determines the irradiation position of the beam light in the main scanning direction (rotational axis direction of the photosensitive drum 1) and the sub-scanning direction on the photosensitive drum 1, the scanning position signal, and the scanning position signal. Recognizing based on the rotational position signal of the photosensitive drum 1 and extracting (searching) the exposure amount adjustment information corresponding to the position (pixel or the divided region) from which the light beam is to be irradiated from the data storage unit 53. Read out.

本画像形成装置Ｘは，製造段階等において，それに組み込まれた前記感光体ドラム１個々の露光特性を得るための特性評価試験に供される。より具体的には，前記特性評価試験（予めの実測）は，前記帯電装置３により帯電された（帯電済みの）前記感光体ドラム１に対し，前記分割領域ごとに複数の露光量の条件下で前記露光源２による露光が行われるとともに，前記分割領域ごとの露光前の初期電位と露光後の電位とが実測され，前記分割領域各々の露光特性，即ち，露光量と露光後の電位との関係を表す特性（以下，実測露光特性という）が明らかにされる。図９（ａ）に示す太い破線グラフｇ０が，そのようにして明らかにされた露光特性の一例である。
ここで，前記分割領域各々の露光特性を測定する方法としては，例えば，前記分割領域各々について，密に露光量を切り替えて露光し，露光後の電位を測定すれば，正確な露光特性を測定できる。その他，図９（ａ）に示したように，露光特性の傾向（カーブの形）はある程度決まっており，係数のみ変更すれば共通の式で定式化できるのが一般的であるので，１又は複数の代表的な露光量で露光した後の電位を測定した結果に基づいて，露光特性を推定してもよい。
例えば，ａ−Ｓｉ感光体ドラムであれば，残留電位は前記感光体ドラム１の表面の位置によらずほぼ一定であるので，初期電位と，前記略線形特性の範囲の１つの露光量で露光した後の電位とを測定すれば，十分な精度で露光特性を推定できる。 The image forming apparatus X is subjected to a characteristic evaluation test for obtaining the exposure characteristics of each of the photosensitive drums 1 incorporated therein in the manufacturing stage. More specifically, the characteristic evaluation test (preliminarily measured) is performed on the photosensitive drum 1 charged (charged) by the charging device 3 under a condition of a plurality of exposure amounts for each divided region. The exposure source 2 performs exposure and the initial potential before exposure and the potential after exposure for each divided region are measured, and the exposure characteristics of each divided region, that is, the exposure amount and the potential after exposure, The characteristics representing the relationship (hereinafter referred to as measured exposure characteristics) are clarified. A thick broken line graph g0 shown in FIG. 9A is an example of the exposure characteristic thus clarified.
Here, as a method for measuring the exposure characteristics of each of the divided areas, for example, the exposure characteristics of each of the divided areas are densely switched and exposed, and the potential after exposure is measured to measure accurate exposure characteristics. it can. In addition, as shown in FIG. 9 (a), the tendency of exposure characteristics (curve shape) is determined to some extent, and it is general that it can be formulated by a common equation if only the coefficient is changed. The exposure characteristics may be estimated based on the result of measuring the potential after exposure with a plurality of representative exposure amounts.
For example, in the case of an a-Si photosensitive drum, the residual potential is almost constant regardless of the position of the surface of the photosensitive drum 1, so that the exposure is performed with the initial potential and one exposure amount within the range of the substantially linear characteristic. By measuring the potential after the exposure, the exposure characteristics can be estimated with sufficient accuracy.

以下，前述した図９及び図５〜図８を用いて，前記制御部５０によるビーム光の露光量制御について説明する。
ここで，前記制御部５０は，前記往復スキャナ９により往復走査されるビーム光のうち，前記感光体ドラム１の回転軸に平行な往路方向に走査されるビーム光（以下，第１ビーム光という）と，その反対方向である復路方向に走査されるビーム光（以下，第２ビーム光という）との各々について露光量制御を行う。
また，図５〜図８に示す例は，ａ−Ｓｉ感光体ドラム１の表面におけるある前記分割領域が，図９（ａ）に示した特性，即ち，帯電ムラと感度ムラとが併存する露光特性（ｇ０）を有する場合について，前記第１ビーム光及び前記第２ビーム光の各光量をどのように設定（制御）するかの実施例である。 Hereinafter, the exposure amount control of the beam light by the control unit 50 will be described with reference to FIGS. 9 and 5 to 8 described above.
Here, among the light beams scanned reciprocally by the reciprocating scanner 9, the control unit 50 scans light beams scanned in the forward direction parallel to the rotation axis of the photosensitive drum 1 (hereinafter referred to as first beam light). ) And the beam light scanned in the opposite direction (hereinafter referred to as second beam light).
Further, in the examples shown in FIGS. 5 to 8, the above-described divided area on the surface of the a-Si photosensitive drum 1 has an exposure in which the characteristics shown in FIG. 9A, that is, charging unevenness and sensitivity unevenness coexist. This is an example of how to set (control) the respective light amounts of the first beam light and the second beam light in the case of having the characteristic (g0).

＜第１実施例＞
図５（ｂ）は，図９（ａ）のグラフｇ０１に示した露光特性を有する前記分割領域について，第１実施例に係る前記画素階調とビーム光の光量との関係表すグラフであり，図５（ａ）は，図５（ｂ）の関係に従った露光を行った場合の前記画素階調と電位（初期電位及び露光後電位）との関係を表すグラフである。
前記制御部５０は，前記第１ビーム光による露光量について，前記画素階調に応じた露光量となるように前記露光源Ｚを制御する（第１露光量制御手段の一例）。
具体的には，図５（ｂ）に一点鎖線で示すように，前記第１ビーム光による画素ごとの露光量を，前記画素階調の値に比例した露光量（比例換算した露光量）となるように調節する。その際，前記画素階調と露光量との関係における比例係数ｋ０（傾き）は全ての前記分割領域について一定（共通）である。この線形特性（Ｅｉ＝ｋ０・Ｉ，Ｅｉは露光量，Ｉは画素階調，ｋ０は傾き）を，以下，第１ビーム基準光量設定特性という。
なお，図９（ａ）のグラフｇ０，ｇ０１に示した特性は，この第１ビーム基準光量設定特性（傾き＝ｋ０）に従ってビーム光の露光量設定が行われた場合の特性である。このことは，後述する図６〜図９においても同様である。
ここで，前記制御部５０は，前記露光源Ｚによるビーム光出力時間（以下，露光時間という）の調節によって前記第１ビーム光の露光量調節を行う。即ち，前記露光源Ｚにおけるビーム光の強度レベルは一定にしたままで，露光時間（発光時間）を前記画素階調に比例した時間に設定する。
但し，前記露光源Ｚにおけるビーム光出力開始時の立ち上がりロスがある場合には，その分を補うだけの露光時間は別途加算される。 <First embodiment>
FIG. 5B is a graph showing the relationship between the pixel gradation and the amount of beam light according to the first embodiment for the divided region having the exposure characteristics shown in the graph g01 in FIG. 9A. FIG. 5A is a graph showing the relationship between the pixel gradation and the potential (initial potential and post-exposure potential) when exposure is performed according to the relationship of FIG.
The control unit 50 controls the exposure source Z so that the exposure amount by the first beam light becomes an exposure amount corresponding to the pixel gradation (an example of first exposure amount control means).
Specifically, as shown by a one-dot chain line in FIG. 5B, the exposure amount for each pixel by the first light beam is set to an exposure amount proportional to the pixel gradation value (exposure amount converted proportionally). Adjust so that At that time, the proportionality coefficient k0 (slope) in the relationship between the pixel gradation and the exposure amount is constant (common) for all the divided regions. This linear characteristic (Ei = k0 · I, Ei is the exposure amount, I is the pixel gradation, and k0 is the slope) is hereinafter referred to as a first beam reference light amount setting characteristic.
The characteristics shown in the graphs g0 and g01 in FIG. 9A are characteristics when the exposure amount of the beam light is set according to the first beam reference light amount setting characteristic (slope = k0). This also applies to FIGS. 6 to 9 described later.
Here, the control unit 50 adjusts the exposure amount of the first beam light by adjusting the beam light output time (hereinafter referred to as exposure time) from the exposure source Z. That is, the exposure time (light emission time) is set to a time proportional to the pixel gradation while the intensity level of the beam light at the exposure source Z is kept constant.
However, if there is a rise loss at the start of beam light output at the exposure source Z, an exposure time sufficient to compensate for the rise loss is added separately.

さらに，前記制御部５０は，前記第２ビーム光による露光量が，前記分割領域ごとに前記データ記憶部５３に記憶された前記露光量調節情報に応じた露光量となるように前記露光源Ｚを制御する（第２露光量制御手段の一例）。これにより，前記第２ビーム光は，前記分割領域各々における電位特性と全ての前記分割領域に共通の所定の基準電位特性との差分に応じた露光量となるように制御される。
具体的には，以下の制御を行う。
まず，予め，全ての前記分割領域について共通のある基準電位Ｖｓ１とこれに対応する基準露光量Ｅｓ１とを予め定めておく。
例えば，全ての前記分割領域について共通のある基準露光電位特性（図９（ａ）のグラフｇ０）において，初期電位Ｖ０と残留電位ＶＬとの中点の電位Ｖｓ１（＝（Ｖ０＋ＶＬ）／２）を前記基準電位Ｖｓ１とし，その基準電位に対応する露光量を前記基準露光量Ｅｓ１とする。この基準露光量Ｅｓ１は，前記基準露光電位特性におけるいわゆる半減露光量である。
さらに，予め，前記露光量調節情報として，前記基準露光量Ｅｓ１と，前記分割領域各々における前記露光電位特性（図５（ａ）のｇ０１：露光量と露光後電位との対応関係を表す特性）に対し前記基準電位Ｖｓ１を適用して得られる露光量Ｅ１との差分露光量であるかさ上げ露光量ΔＥ１（＝Ｅ１−Ｅｓ１，かさ上げ露光量情報の一例）を前記分割領域ごとに前記データ記憶部５３に記憶しておく（かさ上げ露光量情報記憶手段の一例）。
その上で，前記制御部５０は，前記露光源Ｚを制御することにより，前記第２ビーム光（復路走査中のビーム光）について，前記分割領域ごとに，その分割領域に含まれる各画素の露光量を前記かさ上げ露光量ΔＥ１に設定して露光する（かさ上げ露光量設定手段の一例）。
これにより，各画素の合計露光量Ｅが，前記かさ上げ露光量ΔＥ１分だけかさ上げされ（Ｅ＝ｋ０・Ｉ＋ΔＥ１），図５（ａ）に示すように，前記分割領域各々における露光後電位の特性ｇｘ１を，露光量全範囲（即ち，前記画素階調の全範囲）に渡って全体的に近づくように露光することができる。その結果，帯電ムラや感度ムラが併存する前記感光体ドラム１についても画像の濃度ムラの発生を極力防止できる。 Further, the control unit 50 controls the exposure source Z so that the exposure amount by the second beam light becomes an exposure amount according to the exposure amount adjustment information stored in the data storage unit 53 for each divided region. (An example of second exposure amount control means). Thus, the second beam light is controlled so as to have an exposure amount corresponding to the difference between the potential characteristic in each of the divided areas and a predetermined reference potential characteristic common to all the divided areas.
Specifically, the following control is performed.
First, a reference potential Vs1 common to all the divided areas and a reference exposure amount Es1 corresponding to the reference potential Vs1 are determined in advance.
For example, in a reference exposure potential characteristic common to all the divided regions (graph g0 in FIG. 9A), the potential Vs1 (= (V0 + VL) / 2) at the midpoint between the initial potential V0 and the residual potential VL is obtained. The reference potential Vs1 is set, and the exposure amount corresponding to the reference potential is set as the reference exposure amount Es1. This reference exposure amount Es1 is a so-called half exposure amount in the reference exposure potential characteristic.
Further, as the exposure amount adjustment information, the reference exposure amount Es1 and the exposure potential characteristic in each of the divided regions (g01 in FIG. 5A: a characteristic indicating the correspondence between the exposure amount and the post-exposure potential). Is stored in the data for each of the divided areas as a raised exposure amount ΔE1 (= E1-Es1, an example of raised exposure amount information), which is a difference exposure amount from the exposure amount E1 obtained by applying the reference potential Vs1. This is stored in the unit 53 (an example of a raised exposure amount information storage unit).
In addition, the control unit 50 controls the exposure source Z, so that the second beam light (beam light during the backward scanning) is divided into each divided area for each pixel included in the divided area. Exposure is performed with the exposure amount set to the raised exposure amount ΔE1 (an example of a raised exposure amount setting unit).
As a result, the total exposure amount E of each pixel is increased by the increase exposure amount ΔE1 (E = k0 · I + ΔE1), and as shown in FIG. 5A, the post-exposure potential in each of the divided regions is increased. The exposure can be performed so that the characteristic gx1 approaches the entire exposure amount over the entire range (that is, the entire range of the pixel gradation). As a result, it is possible to prevent the occurrence of uneven image density as much as possible for the photosensitive drum 1 having uneven charging and uneven sensitivity.

ここで，前記基準露光量Ｅｓ１を半減露光量とすることで，露光量全範囲に渡って全体的に前記基準となる露光電位特性ｇ０に近づけることができる。これに対し，特定の露光量範囲内で露光する頻度が高いことが予めわかっている場合等には，前記基準となる露光電位特性ｇ０において，前記特定の露光量範囲内の露光量（例えば，その範囲の中心露光量）を前記基準露光量Ｅｓ１とし，これに対応する電位を前記基準電位Ｖｓ１とすることも考えられる。これにより，前記分割領域各々について，特に設定頻度の高い特定の露光量の範囲において前記基準となる露光電位特性ｇ０に対して近づくように露光することができ，画像の濃度ムラの発生を極力防止できる。
ここで，前記制御部５０は，前記露光源Ｚによる露光時間の調節若しくは露光強度の調節によって前記第２ビーム光の露光量調節を行う。即ち，前記露光源Ｚにおけるビーム光の強度レベルは一定にしたままで，露光時間（発光時間）を前記かさ上げ露光量ΔＥ１に比例した時間に設定するか，若しくは露光時間は一定にしたままで，露光強度（発光強度）をΔＥ１に比例した強度に設定する。この場合も，ビーム光出力開始時の立ち上がりロスがある場合には，その分を補うだけの露光時間若しくは露光強度は別途加算される。 Here, by setting the reference exposure amount Es1 to a half exposure amount, the exposure potential characteristic g0 as the reference can be approximated over the entire exposure amount range. On the other hand, when it is known in advance that the frequency of exposure within the specific exposure amount range is high, the exposure amount within the specific exposure amount range (for example, in the reference exposure potential characteristic g0, for example, It is also conceivable that the center exposure amount in that range is the reference exposure amount Es1, and the corresponding potential is the reference potential Vs1. Thus, each of the divided areas can be exposed so as to be close to the reference exposure potential characteristic g0 in a specific exposure amount range that is frequently set, and the occurrence of uneven density in the image is prevented as much as possible. it can.
Here, the controller 50 adjusts the exposure amount of the second beam light by adjusting the exposure time or exposure intensity by the exposure source Z. That is, the intensity level of the beam light in the exposure source Z is kept constant, and the exposure time (light emission time) is set to a time proportional to the raised exposure amount ΔE1, or the exposure time is kept constant. , The exposure intensity (emission intensity) is set to an intensity proportional to ΔE1. In this case as well, if there is a rise loss at the start of beam light output, the exposure time or exposure intensity sufficient to compensate for this is added separately.

＜第２実施例＞
図６（ｂ）は，図９（ａ）のグラフｇ０１に示した露光特性を有する前記分割領域について，第２実施例に係る前記画素階調とビーム光の光量との関係表すグラフであり，図６（ａ）は，図６（ｂ）の関係に従った露光を行った場合の前記画素階調と電位（初期電位及び露光後電位）との関係を表すグラフである。
この第２実施例では，前記第１ビーム光による露光量の制御については，前述の第１実施例と同じである。即ち，前記制御部５０により，全ての前記分割領域に共通の比例係数ｋ０に従って前記画素階調に比例した露光量（Ｅｉ＝ｋ０・Ｉ）となるように前記第１ビーム光の露光量が設定される（共通第１露光量制御手段の一例）。
一方，前記第２ビーム光の露光量制御が前述の第１実施例と異なる。
本第２実施例では，予め，前記露光量調節情報として，前記かさ上げ露光量ΔＥ１に加え，前記分割領域各々についての前記露光電位特性（図９（ａ）のｇ０１）のうちの残留電位ＶＬへの収束領域を除く部分である略線形の露光電位特性における傾きと，全ての前記分割領域に共通の基準となる傾きとの差分を表す差分傾きｋ２を前記分割領域ごとに予め前記データ記憶部５３に記憶しておく（差分傾き情報記憶手段の一例）。この差分傾きｋ２は，前記画素階調を補正露光量に比例換算する際の傾きｋ２（以下，感度補正係数ｋ２という）である。
即ち，この感度補正係数ｋ２は，当該分割領域の露光感度がｋ１（露光量変化に対する電位変化（絶対値）を表す傾き）で表される場合に，ｋ２＝ｋ１−ｋ０として求められ，前記第１ビーム光の露光量Ｅｉ（＝ｋ０・Ｉ）に，この感度補正係数ｋ２により前記画素階調を比例換算した露光量ΔＥ２（＝ｋ２・Ｉ）を画素ごとに加えれば，前記分割領域各々における感度ムラを補正できる。
そして，前記制御部５０は，前記露光源Ｚを制御することにより，前記第２ビーム光について，前記分割領域ごとに，その分割領域に含まれる各画素の露光量を，前記かさ上げ露光量ΔＥ１に，前記基準露光量Ｅｓ１に対応する基準画素階調Ｉｓ１（＝Ｅｓ１／ｋ０）に対する前記画素階調Ｉの差分（Ｉｓ１−Ｉ）を前記感度補正係数ｋ２により比例換算した感度補正分の露光量ΔＥ２（＝ｋ２・（Ｉｓ１−Ｉ））を加えた露光量（ΔＥ１＋ΔＥ２）を設定して露光する。即ち，前記第２ビーム光について，前記かさ上げ露光量ΔＥ１に対し，前記画素階調を前記差分傾きｋ２に基づき比例換算した露光量ΔＥ２分の補正を行う（露光感度補正手段の一例）。
この場合も，前記制御部５０は，前記露光源Ｚによる露光時間若しくは露光強度の調節によって前記第２ビーム光の露光量調節を行う。
これにより，図６（ａ）に示すように，前記分割領域各々における露光後電位の特性ｇｘ２を，全ての前記分割領域に共通の基準となる露光電位特性ｇ０にほぼ一致させることが可能となり，感度ムラ及び帯電ムラの両方をほぼ完全に補正することができる。 <Second embodiment>
FIG. 6B is a graph showing the relationship between the pixel gradation and the amount of beam light according to the second embodiment for the divided region having the exposure characteristics shown in the graph g01 in FIG. 9A. FIG. 6A is a graph showing the relationship between the pixel gradation and the potential (initial potential and post-exposure potential) when exposure is performed according to the relationship of FIG. 6B.
In the second embodiment, the control of the exposure amount by the first beam light is the same as that in the first embodiment. That is, the control unit 50 sets the exposure amount of the first light beam so that the exposure amount (Ei = k0 · I) is proportional to the pixel gradation in accordance with the proportional coefficient k0 common to all the divided regions. (An example of common first exposure amount control means).
On the other hand, the exposure amount control of the second beam light is different from that of the first embodiment.
In the second embodiment, as the exposure amount adjustment information, in addition to the raised exposure amount ΔE1, the residual potential VL in the exposure potential characteristic (g01 in FIG. 9A) for each of the divided regions is previously provided. A difference slope k2 representing a difference between a slope in a substantially linear exposure potential characteristic that is a portion excluding a convergence area and a reference slope common to all the divided areas is previously stored for each divided area. 53 (an example of difference inclination information storage means). The difference gradient k2 is a gradient k2 (hereinafter referred to as a sensitivity correction coefficient k2) when the pixel gradation is proportionally converted to the corrected exposure amount.
That is, this sensitivity correction coefficient k2 is obtained as k2 = k1−k0 when the exposure sensitivity of the divided area is represented by k1 (gradient representing potential change (absolute value) with respect to exposure amount change). If the exposure amount ΔE2 (= k2 · I) obtained by proportionally converting the pixel gradation by the sensitivity correction coefficient k2 is added to the exposure amount Ei (= k0 · I) of one beam light for each pixel, Sensitivity unevenness can be corrected.
Then, the control unit 50 controls the exposure source Z, thereby increasing the exposure amount of each pixel included in the divided region for the second beam light to the raised exposure amount ΔE1. Further, the exposure amount corresponding to the sensitivity correction obtained by proportionally converting the difference (Is1-I) of the pixel gradation I with respect to the reference pixel gradation Is1 (= Es1 / k0) corresponding to the reference exposure amount Es1 by the sensitivity correction coefficient k2. Exposure is performed by setting an exposure amount (ΔE1 + ΔE2) obtained by adding ΔE2 (= k2 · (Is1−I)). That is, for the second beam light, correction is performed for an exposure amount ΔE2 obtained by proportionally converting the pixel gradation based on the difference slope k2 with respect to the raised exposure amount ΔE1 (an example of an exposure sensitivity correction unit).
Also in this case, the controller 50 adjusts the exposure amount of the second beam light by adjusting the exposure time or exposure intensity by the exposure source Z.
As a result, as shown in FIG. 6A, the post-exposure potential characteristic gx2 in each of the divided regions can be made to substantially match the reference exposure potential characteristic g0 common to all the divided regions. Both sensitivity unevenness and charging unevenness can be corrected almost completely.

＜第３実施例＞
図７（ｂ）は，図９（ａ）のグラフｇ０１に示した露光特性を有する前記分割領域について，第３実施例に係る前記画素階調とビーム光の光量との関係表すグラフであり，図７（ａ）は，図７（ｂ）の関係に従った露光を行った場合の前記画素階調と電位（初期電位及び露光後電位）との関係を表すグラフである。
この第３実施例は，実質的に前述の第２実施例と同様の露光量制御を行うものであるが，前記基準露光量を０（即ち，露光無し）とし，前記基準電位を前記基準露光電位特性ｇ０における初期電位Ｖ０とした場合の例である。この場合，前記かさ上げ露光量ΔＥ１は，前記基準露光量（＝０）と，前記分割領域各々における前記露光電位特性に対し前記基準電位Ｖ０を適用して得られる露光量Ｅ１’との差分の露光量（＝Ｅ１’−０＝Ｅ１’）となる。
また，前記基準画素階調Ｉｓ１＝０となるので，図７（ｂ）に示すように，露光感度の補正分の露光量ΔＥ２＝ｋ２・Ｉとなる。
この場合も，前記制御部５０は，前記露光源Ｚによる露光時間若しくは露光強度の調節によって前記第２ビーム光の露光量調節を行う。
このような露光量制御によっても，図７（ａ）に示すように露光電位特性ｇｘ３を基準特性ｇ０にほぼ一致させることができ，前述の第２実施例と同様の作用効果を奏する。 <Third embodiment>
FIG. 7B is a graph showing the relationship between the pixel gradation and the amount of beam light according to the third embodiment for the divided region having the exposure characteristics shown in the graph g01 in FIG. 9A. FIG. 7A is a graph showing the relationship between the pixel gradation and the potential (initial potential and post-exposure potential) when exposure is performed according to the relationship of FIG. 7B.
In the third embodiment, the exposure amount control is performed in substantially the same manner as in the second embodiment, but the reference exposure amount is set to 0 (that is, no exposure), and the reference potential is set to the reference exposure. This is an example in which the initial potential V0 in the potential characteristic g0 is used. In this case, the raised exposure amount ΔE1 is the difference between the reference exposure amount (= 0) and the exposure amount E1 ′ obtained by applying the reference potential V0 to the exposure potential characteristic in each of the divided regions. The exposure amount (= E1′−0 = E1 ′).
Further, since the reference pixel gradation Is1 = 0, as shown in FIG. 7B, the exposure amount ΔE2 = k2 · I corresponding to the correction of the exposure sensitivity.
Also in this case, the controller 50 adjusts the exposure amount of the second beam light by adjusting the exposure time or exposure intensity by the exposure source Z.
Even with such exposure amount control, as shown in FIG. 7A, the exposure potential characteristic gx3 can be made substantially coincident with the reference characteristic g0, and the same effect as the second embodiment can be obtained.

＜第４実施例＞
図８は，図９（ａ）のグラフｇ０１に示した露光特性を有する前記分割領域について，第４実施例に係る前記画素階調とビーム光の光量との関係表すグラフである。
この第４実施例では，前記第２ビーム光による露光量については，前述の第１実施例と同様に，前記かさ上げ露光量ΔＥ１に設定する。但し，前記基準露光量Ｅｓ１を０とし，前記基準電位を基準特性ｇ０における初期電位Ｖ０とした場合の例である。
一方，前記第１ビーム光の露光量制御が前述の第１実施例と異なる。
即ち，前記データ記憶部５３に，前記分割領域各々の露光感度を表す情報として，前記画素階調を露光量に比例換算する際の傾きｋ１を前記分割領域ごとに予め記憶しておき（傾き情報記憶手段の一例），前記制御部５０により，前記第１ビーム光について，画素ごとに前記画像処理部５２により決定される前記画素階調を前記分割領域ごとの前記傾きｋ１に従って比例換算した露光量（Ｅｉ＝ｋ１・Ｉ）を前記第１ビーム光による露光量として設定する（個別第１露光量制御手段の一例）。
この場合，前記制御部５０が前記露光源Ｚを制御することにより，例えば，前記画素階調に応じて前記第１ビーム光の画素ごとの露光時間を調節するとともに，前記傾きｋ１に応じて前記第１ビーム光の前記分割領域ごとの露光強度を調節（基準強度の（ｋ１／ｋ０）倍に設定）すること等によって露光量を制御すればよい。
このような制御により，前記分割領域各々における感度ムラについては前記第１ビーム光（往路）により補正され，帯電ムラについては前記第２ビーム光（復路）により補正される結果，前述の第２実施例及び第３実施例と同様の作用効果を奏する。 <Fourth embodiment>
FIG. 8 is a graph showing the relationship between the pixel gradation and the amount of beam light according to the fourth embodiment for the divided region having the exposure characteristics shown in the graph g01 of FIG. 9A.
In the fourth embodiment, the exposure amount by the second beam light is set to the raised exposure amount ΔE1 as in the first embodiment. However, in this example, the reference exposure amount Es1 is set to 0, and the reference potential is set to the initial potential V0 in the reference characteristic g0.
On the other hand, the exposure amount control of the first beam light is different from that of the first embodiment.
That is, in the data storage unit 53, as information representing the exposure sensitivity of each of the divided areas, a gradient k1 when the pixel gradation is proportionally converted to the exposure amount is stored in advance for each divided area (inclination information). An example of storage means), the exposure amount obtained by proportionally converting the pixel gradation determined by the image processing unit 52 for each pixel with respect to the first light beam according to the inclination k1 for each divided region by the control unit 50 (Ei = k1 · I) is set as the exposure amount by the first light beam (an example of the individual first exposure amount control means).
In this case, the control unit 50 controls the exposure source Z, for example, to adjust the exposure time for each pixel of the first beam light according to the pixel gradation, and to adjust the exposure time according to the inclination k1. The exposure amount may be controlled by adjusting the exposure intensity of each divided region of the first beam light (set to (k1 / k0) times the reference intensity).
By such control, the sensitivity unevenness in each of the divided regions is corrected by the first beam light (outward path), and the charging unevenness is corrected by the second beam light (return path). The same effects as the example and the third embodiment are achieved.

以上示したように，本発明によれば，往復走査型のスキャナ９により往路と復路との双方向に走査されるビーム光の一方（往路又は復路のビーム光）を，前記画素階調に基づく静電潜像書き込みに用いるとともに，他方を電位特性の分布（基準特性との差分）の補正に用いて有効活用されるので，往復走査型のスキャナのメリット（小型化，省電力化，静音化及び起動時間の短縮）を活かした画像形成装置を構成することができるとともに，帯電ムラや感度ムラが併存する感光体についても画像の濃度ムラの発生を極力防止できる。
しかも，新たな露光源を追加する必要がないので，装置の大型化や高コスト化を招くこともない。
ところで，図３に示したように，往復走査されるビーム光における前記第１ビーム光（往路）の走査位置と前記第２ビーム光（復路）の走査位置とでは，副走査方向Ｒ２２において最大で半画素分のズレが存在する。即ち，静電潜像が書き込まれる位置（往路）と，帯電ムラ等を補正するための露光位置（復路）とにズレが生じる。
しかしながら，一般に，帯電ムラや感度ムラは，比較的空間周期の大きな分布を示し，さらに，帯電ムラ等の補正用の前記第２ビーム光による露光量は静電潜像書き込み用の前記第１ビーム光による露光量に比べて比較的低い露光量であるので，それらの副走査方向Ｒ２２におけるズレについて考慮しなくても特に問題はない。
また，本発明は，帯電ムラが顕著に表れることが多いａ−Ｓｉ感光体が用いられる場合，及び画像の濃度ムラが顕著に視認されるカラー画像形成装置に適用する場合に特に好適であるが，他の画像形成装置への適用も可能である。
また，前記分割領域は，前記感光体ドラム１表面をそのその軸方向及び周方向の両方に複数分割した領域とする場合に限らない。
例えば，主として前記感光体ドラム１の軸方向若しくは周方向のいずれかの帯電ムラや感度ムラが問題となる場合には，前記分割領域を前記感光体ドラム１の表面をその軸方向にのみ複数分割した領域（前記感光体ドラム１を輪切り状に分割した領域）若しくは周方向にのみ複数分割した領域とすることも考えられる。 As described above, according to the present invention, one of the light beams scanned in the forward and backward directions by the reciprocating scanner 9 (outward or backward beam light) is based on the pixel gradation. Since it is used for electrostatic latent image writing and the other is used effectively for correcting the distribution of potential characteristics (difference from the reference characteristics), the advantages of a reciprocating scanner (miniaturization, power saving, noise reduction) In addition, it is possible to configure an image forming apparatus that takes advantage of (and shortening of startup time), and it is possible to prevent the occurrence of uneven image density as much as possible even with respect to a photoconductor having uneven charging and uneven sensitivity.
In addition, since it is not necessary to add a new exposure source, the size and cost of the apparatus are not increased.
Incidentally, as shown in FIG. 3, the scanning position of the first beam light (outward path) and the scanning position of the second beam light (return path) in the reciprocatingly scanned beam light are maximum in the sub-scanning direction R22. There is a shift of half a pixel. That is, a deviation occurs between the position where the electrostatic latent image is written (outward path) and the exposure position (return path) for correcting uneven charging.
However, in general, the charging unevenness and the sensitivity unevenness show a distribution with a relatively large spatial period, and the exposure amount by the second beam light for correcting the charging unevenness or the like is the first beam for writing the electrostatic latent image. Since the exposure amount is relatively lower than the exposure amount by light, there is no particular problem even if the deviation in the sub-scanning direction R22 is not taken into consideration.
The present invention is particularly suitable when an a-Si photosensitive member, in which charging unevenness often appears remarkably, and when applied to a color image forming apparatus in which image density unevenness is remarkably visually recognized. , Application to other image forming apparatuses is also possible.
Further, the divided area is not limited to the case where the surface of the photosensitive drum 1 is divided into a plurality of areas both in the axial direction and in the circumferential direction.
For example, when charging unevenness or sensitivity unevenness mainly in the axial direction or circumferential direction of the photosensitive drum 1 is a problem, the divided region is divided into a plurality of parts only on the surface of the photosensitive drum 1 in the axial direction. It is also conceivable to use a region obtained by dividing the photosensitive drum 1 in a ring shape or a region obtained by dividing the photosensitive drum 1 in the circumferential direction.

本発明は，画像形成装置への利用が可能である。   The present invention can be used for an image forming apparatus.

本発明の実施形態に係る画像形成装置Ｘの概略断面図。1 is a schematic sectional view of an image forming apparatus X according to an embodiment of the present invention. 画像形成装置Ｘにおける往復スキャナによるビーム光の走査状態を表す斜視図。3 is a perspective view illustrating a scanning state of beam light by a reciprocating scanner in the image forming apparatus X. FIG. ドラム状の感光体の表面を平面として表したときの往復走査型のスキャナによるビームの走査経路を表す模式図。FIG. 3 is a schematic diagram showing a beam scanning path by a reciprocating scanning scanner when the surface of a drum-shaped photoconductor is represented as a plane. 画像形成装置Ｘの主要部の概略構成を表すブロック図。2 is a block diagram illustrating a schematic configuration of a main part of the image forming apparatus X. FIG. 第１実施例に係る画素階調とビーム光の光量との関係を表すグラフ及びそのときの画素階調と電位との関係を表すグラフ。The graph showing the relationship between the pixel gradation which concerns on 1st Example, and the light quantity of beam light, and the graph showing the relationship between the pixel gradation at that time, and an electric potential. 第２実施例に係る画素階調とビーム光の光量との関係を表すグラフ及びそのときの画素階調と電位との関係を表すグラフ。The graph showing the relationship between the pixel gradation which concerns on 2nd Example, and the light quantity of beam light, and the graph showing the relationship between the pixel gradation at that time, and an electric potential. 第３実施例に係る画素階調とビーム光の光量との関係を表すグラフ及びそのときの画素階調と電位との関係を表すグラフ。The graph showing the relationship between the pixel gradation which concerns on 3rd Example, and the light quantity of beam light, and the graph showing the relationship between the pixel gradation at that time, and an electric potential. 第４実施例に係る画素階調とビーム光の光量との関係を表すグラフ及びそのときの画素階調と電位との関係を表すグラフ。The graph showing the relationship between the pixel gradation which concerns on 4th Example, and the light quantity of beam light, and the graph showing the relationship between the pixel gradation at that time, and an electric potential. 帯電ムラと感度ムラとが並存する感光体表面における従来の画素階調と露光後の電位との関係の一例を表すグラフ。The graph showing an example of the relationship between the conventional pixel gradation and the potential after exposure on the surface of the photoreceptor where charging unevenness and sensitivity unevenness coexist.

符号の説明Explanation of symbols

Ｘ…本発明の実施形態に係る画像形成装置
Ｚ…露光源
１ＢＫ，１Ｍ，１Ｙ，１Ｃ…感光体ドラム
２ＢＫ，２Ｍ，２Ｙ，２Ｃ…現像装置
３ＢＫ，３Ｍ，３Ｙ，３Ｃ…帯電装置
５ＢＫ，５Ｍ，５Ｙ，５Ｃ…除電装置
７…中間転写ベルト
９…往復スキャナ
５０…制御部
５１…表示操作部
５２…画像処理部
５３…データ記憶部
５４…回転位置検出部 X: Image forming apparatus Z according to an embodiment of the present invention: Exposure sources 1BK, 1M, 1Y, 1C ... Photoconductor drums 2BK, 2M, 2Y, 2C ... Developing devices 3BK, 3M, 3Y, 3C ... Charging devices 5BK, 5M , 5Y, 5C ... neutralization device 7 ... intermediate transfer belt 9 ... reciprocating scanner 50 ... control unit 51 ... display operation unit 52 ... image processing unit 53 ... data storage unit 54 ... rotational position detection unit

Claims (11)

予め帯電済みの感光体の表面にビーム光を走査させることにより静電潜像を書き込む画像形成装置であって，
前記ビーム光を前記感光体表面に対し往復走査させる光往復走査手段と，
前記光往復走査手段により往復走査される前記ビーム光のうち往路若しくは復路のいずれか一方の方向に走査される第１ビーム光による露光量を制御することにより静電潜像書き込み用の露光制御を行う第１露光量制御手段と，
前記第１ビーム光と反対方向に走査される第２ビーム光による露光量を制御することにより前記感光体表面における特性分布を補正する露光制御を行う第２露光量制御手段と，
を具備してなる画像形成装置において，
前記第２露光量制御手段が，前記感光体の表面を複数に分割した分割領域ごとに該分割領域における電位特性と全ての前記分割領域に共通の所定の基準電位特性との差分に応じて前記第２ビーム光による露光量を制御してなるものであり，
前記第１露光量制御手段が，画素ごとの濃淡レベルを表す画素階調を全ての前記分割領域に共通の係数を用いて比例換算した露光量を前記第１ビーム光による露光量として設定する共通第１露光量制御手段であることを特徴とする画像形成装置。 An image forming apparatus for writing an electrostatic latent image by scanning a light beam on the surface of a pre-charged photoconductor,
Optical reciprocating scanning means for reciprocatingly scanning the beam light with respect to the surface of the photosensitive member;
The exposure control for writing the electrostatic latent image is performed by controlling the exposure amount of the first light beam scanned in either the forward or backward direction among the light beams scanned back and forth by the optical reciprocating scanning means. First exposure amount control means for performing;
Second exposure amount control means for performing exposure control for correcting a characteristic distribution on the surface of the photosensitive member by controlling an exposure amount by a second beam light scanned in a direction opposite to the first beam light;
In images forming apparatus ing comprises a,
The second exposure amount control means, for each divided region obtained by dividing the surface of the photosensitive member into a plurality of regions, according to a difference between a potential characteristic in the divided region and a predetermined reference potential characteristic common to all the divided regions. The exposure amount is controlled by the second beam light.
The first exposure amount control means sets the exposure amount obtained by proportionally converting the pixel gradation representing the gray level for each pixel using a common coefficient for all the divided regions as the exposure amount by the first beam light. An image forming apparatus which is a first exposure amount control means . 前記画素階調を露光量に比例換算する際の傾き情報を前記分割領域ごとに記憶する傾き情報記憶手段を具備し，
前記第１露光量制御手段が，画素ごとの濃淡レベルを表す画素階調を前記分割領域ごとの前記傾き情報に従って比例換算した露光量を前記第１ビーム光による露光量として設定する個別第１露光量制御手段である請求項１に記載の画像形成装置。 Inclination information storage means for storing, for each of the divided areas, inclination information when the pixel gradation is proportionally converted to an exposure amount;
Individual first exposure in which the first exposure amount control means sets, as the exposure amount by the first beam light, an exposure amount obtained by proportionally converting a pixel gradation representing a gray level for each pixel in accordance with the inclination information for each divided region. The image forming apparatus according to claim 1, wherein the image forming apparatus is an amount control unit. 前記第１露光量制御手段が，前記画素階調に応じて前記第１ビーム光の画素ごとの露光時間を調節するとともに，前記傾き情報に応じて前記第１ビーム光の前記分割領域ごとの露光強度を調節することにより露光量を制御してなる請求項２に記載の画像形成装置。 The first exposure amount control means adjusts an exposure time for each pixel of the first light beam according to the pixel gradation, and exposes the first light beam for each divided region according to the tilt information. The image forming apparatus according to claim 2 , wherein the exposure amount is controlled by adjusting the intensity. 全ての前記分割領域に共通の所定の基準露光量と，前記分割領域各々における露光量と電位との対応関係を表す露光電位特性に対し全ての前記分割領域に共通の所定の基準電位を適用して得られる露光量と，の差分露光量を特定するかさ上げ露光量情報を前記分割領域ごとに記憶するかさ上げ露光量情報記憶手段を具備し，
前記第２露光量制御手段が，前記分割領域ごとに前記かさ上げ露光量情報に基づいて前記第２ビーム光の露光量を設定するかさ上げ露光量設定手段を具備してなる請求項１〜３のいずれかに記載の画像形成装置。 A predetermined reference potential common to all the divided areas is applied to a predetermined reference exposure amount common to all the divided areas and an exposure potential characteristic representing a correspondence relationship between the exposure amount and the potential in each of the divided areas. A raised exposure amount information storage means for storing, for each of the divided areas, raised exposure amount information for specifying a difference exposure amount between the obtained exposure amount and
The second exposure control means, formed by including the exposure amount setting means raise the to set an exposure amount of said second light beam on the basis of the raising exposure information for each of the divided regions according to claim 1 to 3 The image forming apparatus according to any one of the above. 前記基準電位及び前記基準露光量が，全ての前記分割領域に共通の基準となる前記露光電位特性における初期電位と残留電位との略中点の電位及びその略中点の電位に対応する露光量である請求項４に記載の画像形成装置。 The reference potential and the reference exposure amount are approximately the midpoint potential between the initial potential and the residual potential in the exposure potential characteristics and the exposure amount corresponding to the approximately midpoint potential in the exposure potential characteristics that are common to all the divided regions. The image forming apparatus according to claim 4 . 前記第１露光量制御手段が前記共通第１露光量制御手段である場合に，
前記分割領域各々についての前記露光電位特性のうちの残留電位への収束領域を除く部分である略線形の露光電位特性における傾きと全ての前記分割領域に共通の基準となる傾きとの差分に関する差分傾き情報を前記分割領域ごとに記憶する差分傾き情報記憶手段を具備し，
前記第２露光量制御手段が，前記かさ上げ露光量設定手段により設定される前記第２ビーム光の露光量に対し，前記画像処理手段により決定される前記画素階調を前記差分傾き情報に基づいて比例換算した露光量分の補正を行う露光感度補正手段をさらに具備してな
る請求項４又は５のいずれかに記載の画像形成装置。 When the first exposure amount control means is the common first exposure amount control means,
The difference regarding the difference between the inclination in the substantially linear exposure potential characteristic that is the portion excluding the convergence area to the residual potential in the exposure potential characteristic for each of the divided areas and the reference inclination common to all the divided areas. Differential inclination information storage means for storing inclination information for each of the divided areas;
The second exposure amount control means determines the pixel gradation determined by the image processing means with respect to the exposure amount of the second beam light set by the raised exposure amount setting means based on the difference inclination information. the image forming apparatus according to any one of formed by further comprising an exposure sensitivity correction means for performing a proportional-converted exposure amount of correction according to claim 4 or 5 Te. 前記第２露光量制御手段が，前記第２ビーム光の露光時間又は露光強度を調節することにより露光量を制御してなる請求項１〜６のいずれかに記載の画像形成装置。 The second exposure control means, the image forming apparatus according to any one of claims 1 to 6 formed by controlling the exposure amount by adjusting the exposure time or the exposure intensity of the second light beam. 前記分割領域が，ドラム状の前記感光体の表面をその軸方向と周方向との一方又は両方に複数に分割した領域である請求項１〜７のいずれかに記載の画像形成装置。 The divided region, the image forming apparatus according to any one of claims 1 to 7, which is a region divided into a plurality of one or both of the the circumferential direction the axial direction of the surface of the drum-like of the photosensitive member. 前記感光体がａ−Ｓｉ感光体である請求項１〜８のいずれかに記載の画像形成装置。 The image forming apparatus according to any one of claims 1-8 wherein the photoconductor is an a-Si photosensitive member. 前記画像処理手段が，前記画像データに基づいて複数画素の前記画素階調の配列を決定する面積階調方式で階調表現を行うものである請求項１〜９のいずれかに記載の画像形成装置。 Wherein the image processing means, image formation according to any one of the image according to claim 1-9 in an area gray scale method is intended to perform gradation expression to determine the sequence of the pixel gray levels of a plurality of pixels based on the data apparatus. 複数色のトナーによりカラー画像形成を行うものである請求項１〜１０のいずれかに記載の画像形成装置。 The image forming apparatus according to any one of claims 1 to 1 0 by a plurality of colors of toner and performs color image formation.

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