JP4075424B2 - Image forming apparatus - Google Patents

Description

【００７４】
なお、湾曲の向きは、例えば図６において上方向を正方向、下方向を逆方向とする。表１に示したように、この場合は、湾曲方向が同じ方向のものについて、湾曲量が最も小さい色の走査線にその他の色の走査線を合わせる。これにより、画像全体の走査線湾曲を小さくすることができると共に、色ずれを抑えることができる。なお、各色の湾曲量の平均値を求め、この平均値に最も近い色の走査線にその他の色の走査線を合わせようにしてもよい。これにより、オフセット量を少なくすることができる。
【００７５】
また、湾曲の方向が混在する場合、湾曲が同じ方向の走査線については湾曲量の小さいものに合わせ、その後に湾曲が異なる方向の走査線について上記の逆方向の場合の補正を行うようにして全体を補正するようにしてもよい。
【００７６】
次に、本発明を適用した画像形成装置の回路構成について説明する。なお、説明の便宜上、分割位置に従って画像データを分割してＦＩＦＯに格納する回路ブロックと、格納した画像データをオフセット量に応じて読み出して補正された画像データを生成する回路ブロックとに分けて説明する。図８には前者の回路ブロックの概略構成を、図９には後者の回路ブロックの概略構成を示した。また、図１０には前者の回路ブロックにおけるタイミングチャートを、図１１には後者の回路ブロックにおけるタイミングチャートをそれぞれ示した。
【００７７】
図８に示す回路ブロックは、演算手段４６を備えている。演算手段４６には、湾曲量設定部４８Ｙ、４８Ｍ、４８Ｃ、４８Ｋが接続されている。湾曲量設定部４８Ｙ、４８Ｍ、４８Ｃ、４８Ｋには、Ｙ色、Ｍ色、Ｃ色、Ｋ色の走査線の形状データ、例えば走査線の左端位置、右端位置、中心位置の３点のデータが記憶されている。
【００７８】
演算手段４８は、湾曲量設定部４８Ｙ、４８Ｍ、４８Ｃ、４８Ｋに記憶された形状データから各走査線の湾曲量及び湾曲の方向を求め、これに基づいて補正の基準となる基準色及び補正対象となる補正色を定める。例えば、上記表１のパターン１の場合には、基準色はＫ色となり、補正色はＹ色及びＭ色となる。
【００７９】
そして、演算手段４８は、形状データに基づいて基準色の走査線の形状を表す近似式及び補正色の走査線の形状を表す近似式を算出し、これらの交点を演算する。近似式は、例えば２次式で表すことができる。そして、求めた交点に基づいて、前述したアルゴリズムによって走査領域を分割し、各分割走査領域の長さを各々求める。
【００８０】
なお、基準色の走査線が本発明の第１の走査線又は第２の走査線に相当し、補正色の走査線が本発明の第２の走査線に相当する。
【００８１】
演算手段４８は、各分割走査領域の長さに対応するカウント値を演算し、これをカウンタ５０Ｙ、５０Ｍ、５０Ｋ、５０Ｃにそれぞれ出力する。このカウント値は、予め定めた所定式によって算出してもよいし、ルックアップテーブルに各分割走査領域の長さとカウント値との対応関係を記憶しておき、これから求めてもよい。
【００８２】
カウンタ５０Ｙ、５０Ｍ、５０Ｋ、５０Ｃには、それぞれ分割回路５２Ｙ、５２Ｍ、５２Ｋ、５２Ｃがそれぞれ接続されている。なお、これらの分割回路は同一構成のため、分割回路５２Ｙについて説明し、他の分割回路の説明は省略する。なお、この分割回路は、本発明の分割手段に相当する。
【００８３】
分割回路５０Ｙは、ＥＮＢ発生器５４，セレクタ５６Ａ、セレクタ５６Ｂ、カウンタ５８、ＦＩＦＯ群６０を備えている。
【００８４】
ＦＩＦＯ群６０は、図８において左右方向及び上下方向にマトリクス上に配置されたｍ×ｎ個の先入れ先出しのメモリであるＦＩＦＯ６０_mnを備えている。前記左右方向が主走査方向に、上下方向が副走査方向にそれぞれ対応している。すなわち、１ライン当たりｎ個のＦＩＦＯをｍライン分備えた構成となっている。また、各ＦＩＦＯには、各分割走査領域の画素数分の画像データを記憶することができる。すなわち、各列が各分割走査領域に対応し、Ｙ画像データ６４は、分割走査領域の数と同じｎ個に分割され、各ＦＩＦＯに振り分けて記憶される。ＦＩＦＯの行数ｍは、湾曲量の大きさに応じて定められる。例えば、最も大きい湾曲量に相当する走査線の数だけ設けられる。
【００８５】
また、セレクタ５６ＡとＦＩＦＯ群６０との間には、各列のＦＩＦＯを同時に書き込み可能にするためのセレクト信号を出力するための配線がｎ列分配線されている。
【００８６】
また、セレクタ５６ＢとＦＩＦＯ群６０との間には、各行のＦＩＦＯを同時に書き込み可能にするためのセレクト信号を出力するための配線がｍ行分配線されている。
【００８７】
カウンタ５０Ｙは、演算手段４６によってセットされたカウント値のカウントが終了する毎に、終了信号をＥＮＢ発生器５４に通知する。なお、カウントの開始は、ＳＯＳセンサ６２からの開始信号によって開始する。ＥＮＢ発生器５４は、終了信号を受ける毎に、セレクタ５６Ａに対してセレクト信号の出力を指示するためのイネーブル信号を出力する。
【００８８】
セレクタ５６Ａは、ＥＮＢ発生器５４からイネーブル信号を受ける毎に、書き込み可能にするＦＩＦＯの列を切り替える。図１０では、上から順に１列目〜５列目のＦＩＦＯを書き込み可能にするためのセレクト信号を示しており、ｔ１〜ｔ４の各時点でイネーブル信号が出力される。すなわち、図１０に示すように、クロックに同期すると共に、イネーブル信号が出力される毎にハイレベルとなるセレクト信号が切り替わる。これにより、１列目のＦＩＦＯから順に書き込み可能となる。
【００８９】
一方、セレクタ５６Ｂは、Ｙ画像データ６４が入力されると共に、セレクタ５６Ａと同期して、各行のＦＩＦＯを選択するためのセレクト信号を出力する。このセレクト信号は、セレクタ５６Ａが出力するセレクト信号が１列目からｎ列目まで出力される毎に書き込み可能にするＦＩＦＯの行を切り替えるような信号である。なお、セレクタ５６Ａとセレクタ５６Ｂとの最初のセレクト信号出力のタイミングの同期は、カウンタ５８によって調整される。
【００９０】
これにより、セレクタ５６Ｂによって選択された行のＦＩＦＯが書き込み可能になると共に、各行のＦＩＦＯが選択されているときに、その行のＦＩＦＯが１列目から順に書き込み可能となる。従って、Ｙ画像データ６４は、分割走査領域に対応して分割され、図１０に示すように各ＦＩＦＯに振り分けて記憶される。
【００９１】
次に、ＦＩＦＯに格納された画像データを読み出すための回路ブロックについて図９を参照して説明する。なお、図８と同一部分には同一符号を付し、その詳細な説明は省略する。
【００９２】
図９に示す回路ブロックは、切替え設定回路６６Ｙ、６６Ｍ、６６Ｃ、６６Ｋを備えており、各切替え設定回路には、調整回路６８Ｙ、６８Ｍ、６８Ｃ、６８Ｋがそれぞれ接続されている。なお、これらの調整回路は同一構成のため、調整回路５２Ｙについて説明し、他の調整回路の説明は省略する。なお、この調整回路は、本発明の調整手段に相当する。
【００９３】
調整回路６８Ｙには、ＦＩＦＯ群６０、各列のＦＩＦＯに対応するセレクタ６９₁〜６９_n、合成回路７１が設けられている。
【００９４】
演算手段４８は、基準色の走査線と補正色の走査線との交点から前述したアルゴリズムによって走査領域を分割し、各分割走査領域のオフセット量Ｏｆｓ_iを各々求める。そして、各オフセット量Ｏｆｓ_iに対応するカウント値を演算し、これをセレクタ６９₁〜６９_nにそれぞれ出力する。このカウント値は、予め定めた所定式によって算出してもよいし、ルックアップテーブルに各分割走査領域のオフセット量Ｏｆｓ_iとカウント値との対応関係を記憶しておき、これから求めてもよい。
【００９５】
切替え設定回路６６Ｙからは、セレクタ６９₁〜６９_nを切り替えるための図１１に示すような切り替え設定信号が出力される。図１１では、上から順に１列目〜５列目に対応するセレクタ６９₁〜６９₅を選択するための切り替え設定信号が示されており、各切り替え設定信号は、各分割走査領域の長さ分ハイレベルとなる信号である。
【００９６】
セレクタ６９₁〜６９_nは、それぞれ設定されたカウント値に応じたタイミングでＦＩＦＯを１行目から順に選択する。各セレクタによって選択されたＦＩＦＯの画像データは、合成回路７１によって合成され、補正データとして後段の回路へ出力される。
【００９７】
これにより、合成された補正後の画像データは、オフセット量に応じて各分割走査領域の画像データが副走査方向に各々ずらされた画像データとなるため、各色画像を重ね合わせたときに色ずれの少ない画像を得ることができる。
【００９８】
次に、本実施形態の作用として、演算部４６で実行される制御ルーチンについて、図１２に示すフローチャートを参照して説明する。
【００９９】
図１２のステップ１００では、走査線の形状データから各走査線の湾曲量や湾曲の方向を求め、補正の基準となる基準色及び補正対象となる補正色の組み合わせを選択する。
【０１００】
次のステップ１０２では、選択した基準色の走査線の近似式及び補正色の走査線の近似式を求める。このステップ１０２の処理は、本発明の計測手段に相当する。
【０１０１】
次のステップ１０４では、選択した基準色及び補正色の組み合わせのうち、走査線の湾曲の方向が同方向の組み合わせが存在するか否かを判断し、存在しないばあいには、ステップ１１４へ移行し、存在する場合には、ステップ１０６へ移行する。
【０１０２】
ステップ１０６では、求めた近似式から基準色の走査線と補正色の走査線との交点を算出し、走査領域を分割する。この処理は、本発明の分割手段に相当する。
【０１０３】
ステップ１０８では、分割された分割走査領域毎に補正色の走査線が基準色の走査線に近づくように補正色の走査線を副走査方向にオフセットするためのオフセット量を求めてオフセットさせる。この処理は、本発明の演算手段に相当する。
【０１０４】
ステップ１１０では、基準色の走査線と補正色の走査線との離間距離が所定値（例えば走査線の解像度）以下であるか否かを判定し、所定値以下でない場合には、ステップ１０６へ戻って離間距離が所定値以下になるまで上記の処理を繰り返す。一方、離間距離が所定値以下になった場合には、ステップ１１２において、その他に走査線の湾曲の方向が同方向の補正すべき組み合わせが存在するか否かを判断する。なお、この所定値は、例えばプリンタの種類に応じて予め定められるが、所定値を設定するための設定手段を設けて、所定値を変更可能に構成してもよい。これにより、走査露光装置の種類等に応じて最適に補正することができる。
【０１０５】
そして、湾曲方向が同方向の補正すべき組み合わせが存在する場合には、ステップ１０６へ戻って上記と同様の処理を行い、存在しない場合には、ステップ１１４へ移行する。
【０１０６】
ステップ１１４では、走査線の湾曲の方向が逆方向の補正すべき組み合わせが存在するか否かを判断し、存在しない場合には、本ルーチンを終了し、存在する場合には、ステップ１１６へ移行する。
【０１０７】
ステップ１１６では、ステップ１０６と同様に、求めた近似式から基準色の走査線と補正色の走査線との交点を算出し、走査領域を分割する。
【０１０８】
ステップ１１８では、分割された分割走査領域毎に補正色の走査線が基準色の走査線に近づくように補正色の走査線を副走査方向にオフセットさせるためのオフセット量を求めてオフセットさせると共に、画像の連続性を維持させるために、基準色の走査線及び補正色の走査線を適宜副走査方向にオフセットさせる。
【０１０９】
ステップ１２０では、ステップ１１０と同様に、基準色の走査線と補正色の走査線との離間距離が所定値（例えば走査線の解像度）以下であるか否かを判定し、所定値以下でない場合には、ステップ１１６へ戻って離間距離が所定値以下になるまで上記の処理を繰り返す。一方、離間距離が所定値以下になった場合には、ステップ１２２において、その他に走査線の湾曲の方向が逆方向の補正すべき組み合わせが存在するか否かを判断する。
【０１１０】
そして、湾曲方向が逆方向の補正すべき組み合わせが存在する場合には、ステップ１１６へ戻って上記と同様の処理を行い、存在しない場合には、本ルーチンを終了する。
【０１１１】
このように、湾曲の方向が同方向のものについて補正を行い、次に逆方向のものについて補正を行う。各補正に伴う副走査方向のオフセット量は、一度レジスタに蓄えられて、各補正の処理が終わった後に一括して最終的なオフセット量として算出され、各列のＦＩＦＯの読み出しタイミングの制御に利用される。
【０１１２】
ところで、例えばパーソナルコンピュータなどの入力装置から入力された画像をプリンタ等の出力装置で出力する場合、入力装置の入力画像と出力装置の出力画像とマッチングを図って再現性を向上させるため、または、特徴的な画像出力とするため、図１３に示すように、画像処理が施されるのが一般的である。このため、図８、９に示した回路ブロックを、図１３に示すように画像処理した後のＡの位置に回路ブロックを挿入することが好ましいが、特に画像処理後のスクリーンデータ生成後のＢの位置に挿入することが好ましい。これにより、画像処理を有効としたままで走査線湾曲の補正を行うことができる。
【０１１３】
また、図１３に示すように、スクリーンデータの生成後には、実際に感光体に露光するためのビデオデータが生成されるので、そのビデオデータ生成後のＣの位置に回路ブロックを挿入するようにしてもよい。これにより、さらに画像処理の特徴を活かすことが可能となる。将来的には高解像化がさらに進み、ビデオデータ自身も完全に２値化となることが予想されるため、走査線湾曲を補正するための回路ブロックをビデオデータの処理に直接あてることが実用的には可能であり、この場合には、フルデジタル補正が可能になるというメリットがある。
【０１１４】
【発明の効果】
以上説明したように、本発明によれば、分割した一方の走査線の分割走査線の各々について、他方の走査線との変位量が小さくなる分割走査線の副走査方向のオフセット量を求め、該求めたオフセット量に基づいて、一方の走査線により前画像を形成するときの露光タイミングを調整するように構成したので、装置の耐久性を損なうことなく、簡単な構成で走査線湾曲を補正して高品質の画像を形成することができる、という優れた効果を有する。
【図面の簡単な説明】
【図１】 本発明の実施の形態に係る画像形成装置の概略構成図である。
【図２】 本発明の実施の形態に係る走査露光装置の概略構成図である。
【図３】 走査線湾曲について説明するための図である。
【図４】 走査線湾曲について説明するための図である。
【図５】 走査線湾曲について説明するための図である。
【図６】 同方向の走査線湾曲の補正アルゴリズムについて説明するための図である。
【図７】 逆方向の走査線湾曲の補正アルゴリズムについて説明するための図である。
【図８】 画像データを分割するための回路ブロックの概略構成図である。
【図９】 画像データの露光タイミングを調整するための回路ブロックの概略構成図である。
【図１０】 図８の回路ブロックのタイミングチャートである。
【図１１】 図９の回路ブロックのタイミングチャートである。
【図１２】 演算部で実行される制御ルーチンのフローチャートである。
【図１３】 画像データの処理の流れを示すブロック図である。
【図１４】 ４連タンデム方式の画像形成装置の概略構成図である。
【図１５】 走査線湾曲について説明するための図である。
【符号の説明】
１０ 画像形成装置
１１ 走査露光装置
１２ 感光体ドラム
３０ レーザダイオード
２２ ポリゴンミラー
１４ 帯電器
１６ 現像器
１８ 転写器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus, and in particular, includes a plurality of light sources and an image carrier, and sequentially scans the light beams modulated and emitted from the light sources based on a plurality of different image signals. The present invention relates to an image forming apparatus in which different original images are formed on the respective image carriers corresponding to image signals, and the original images are multiplex-transferred onto the same recording medium to form an image.
[0002]
[Prior art]
Conventionally, as an image forming apparatus such as a laser printer, a laser copier, and the like, an image forming apparatus is known in which a photosensitive member provided as an image carrier is scanned and exposed with a laser beam. In many cases, these image forming apparatuses are digitized and colorized.
[0003]
In these image forming apparatuses, in particular, when forming a color image, an original image corresponding to each of the four colors of black (K), yellow (Y), magenta (M), and cyan (C) is used. Finally, these four original images are superimposed to form a single color image. Compared to a conventional image forming apparatus that forms a black and white image, production in an image forming operation is performed. In some cases, the performance deteriorated.
[0004]
For this reason, so-called tandem image forming apparatuses capable of simultaneously forming original images corresponding to the respective colors K, Y, M, and C have been known. This tandem-type image forming apparatus has a plurality of photoconductors, and after exposing the photoconductors corresponding to each color with a laser beam emitted from the exposure device based on the image data signal separated for each color, Development is performed to form an original image for each color, and finally, an original image for each color is superimposed on the same transfer medium to form one color image. In this way, the tandem image forming apparatus significantly improves the productivity in the image forming operation that has been a problem in the past.
[0005]
However, in such a tandem-type image forming apparatus, positional deviation at the time of overlaying original images may occur due to variations in the optical characteristics of the laser beam corresponding to each color emitted from the exposure apparatus. In some cases, this reduces the quality of the formed image. Therefore, in order to solve this problem, it is necessary to perform appropriate alignment control between the original images of each color.
[0006]
In order to perform appropriate alignment between the original images in order to form a high-quality color image, a scanning line writing position in the main scanning direction (hereinafter referred to as a side register), and a scanning line writing position in the sub-scanning direction (hereinafter referred to as “side registration”). (Hereinafter referred to as “lead register”), writing end position or print width (hereinafter referred to as magnification) of the scanning line in the main scanning direction, curvature of the scanning line itself (hereinafter referred to as scanning line bending), and inclination of the scanning line (hereinafter referred to as scanning line). It is necessary to appropriately set the inclination).
[0007]
By the way, the tandem type image forming apparatus is roughly classified into two forms depending on the configuration of the scanning exposure apparatus that emits a laser beam for scanning exposure of each photosensitive member.
[0008]
In the first embodiment, as shown in FIG. 14, the scanning exposure apparatuses 72K, 72Y, 72M and 72C for deflecting and emitting one laser beam from a laser light source (not shown) by a rotating polygon mirror 73 The image forming apparatus 70 is in a form (hereinafter referred to as a quadruple tandem system) in which the K, Y, M, and C4 colors are separately arranged and provided. In the quadruple tandem image forming apparatus 70, the scanning exposure apparatuses 72K, 72Y, 72M, and 72C each have a rotating polygon mirror 73 that is rotated by a motor (not shown). By performing deflection scanning of the laser beam at 73, exposure of a monochrome image for each of the K, Y, M, and C colors is performed on the corresponding photosensitive member 74. Further, the single color images exposed on the photoreceptors 74 corresponding to the respective colors are developed by the respective developing units 76 and then transferred to the transfer belt 78 which is a common transfer member among the respective colors by the respective transfer units 77. It is designed to be transcribed. A fixing device 80 is disposed on the rearmost end side of the transfer belt 78. Here, a single color image for each color is sequentially superimposed on the recording medium P to finally form one color image. It has become.
[0009]
At this time, when superimposing each single color image at the time of color image formation (that is, alignment of the scanning exposure position in the laser beam corresponding to each color), the side registration, lead registration, magnification, scanning line curve, In addition to this, the quadruple tandem type image forming apparatus 70 rotates the rotating polygon mirror 73 in each of the scanning exposure apparatuses 72K, 72Y, 72M, and 72C. It is necessary to provide a special mechanism for controlling the rotational phase of each motor to be operated.
[0010]
On the other hand, in the second mode, for example, as in the technique described in Japanese Patent Laid-Open No. Hei 3-1442412, a laser beam modulated based on image signals corresponding to each of four colors is rotated by one rotation as a deflecting unit. A configuration in which a scanning exposure apparatus that performs exposure scanning in the main scanning direction by deflecting two-color mirrors in opposite directions around the rotating polygon mirror for each two colors (hereinafter referred to as a bidirectional spray paint method) This is an image forming apparatus. In this bidirectional spray paint type image forming apparatus, each photosensitive drum is exposed and scanned by deflecting a laser beam corresponding to each color by one rotating polygon mirror, so that the scanning exposure apparatus itself has a relatively compact configuration. be able to. Further, in the bidirectional spray paint type image forming apparatus, the multi-transfer operation of the single color image of each color at the time of color image formation is the same as the above-described quadruple tandem type image forming apparatus, but the laser beam by the rotating polygon mirror is used. In the deflection scanning operation, it is not necessary to provide a special rotation phase control mechanism between a plurality of motors as in the above-described four-tandem image forming apparatus.
[0011]
Therefore, in the quadruple tandem type image forming apparatus, each motor is independent, and therefore, with the rotational phase control of each motor, it is possible to perform alignment control with a high degree of freedom between each monochrome image, and almost all colors are controlled. It is possible to perform alignment to the same position. On the other hand, in the bidirectional spray paint type image forming apparatus, the laser beam of each color is deflected by a common rotary polygon mirror. Therefore, in the alignment control between the monochromatic images, the alignment is performed in units of scanning lines. . However, by adopting another technique, it becomes possible to control the scanning line unit or less. On the other hand, in recent high-resolution image forming apparatuses, color misregistration is not conspicuous even when alignment is performed in units of scanning lines. This is because in the case of control in units of scanning lines with a plurality of laser beams, the positional deviation amount is ½ line at the maximum.
[0012]
Here, a description will be given of formation position alignment control between single color images in each tandem image forming apparatus.
[0013]
When performing formation position alignment between single color images, it is necessary to correct side registration, lead registration, magnification, scanning line curvature, scanning line inclination, etc. as described above, and set them to appropriate values. In particular, correction of scanning line curvature related to the present invention will be described.
[0014]
The scanning line curve is caused by the optical system of the scanning exposure apparatus. For example, the incident angle of light to the polygon mirror mounted on the polygon motor which is the deflection means of the scanning optical system is relative to the reflection surface of the polygon mirror. This occurs when the angle is not right (see FIG. 15). This is because, when scanning light, the optical path length to the polygon mirror differs depending on the rotation angle of the polygon mirror, and the light reflection position on the reflection surface differs.
[0015]
Further, even if the reflecting surface is a plane mirror that simply reflects light, if the reflecting surface is curved in the scanning direction, the scanning path is curved because the optical path length is similarly different. Since the scanning line curve is caused by the alignment of the optical system as described above, it always occurs. When such a scanning line curve occurs, a color printer or the like that forms an image by overlapping the scanning lines for each color causes a color shift and cannot form a high-quality color image.
[0016]
Conventionally, as a means for correcting the scanning line curvature, the scanning mirror on the photosensitive member is corrected by mechanically deforming the plane mirror of the scanning exposure apparatus and bending it in a direction opposite to the scanning line bending direction. A method has been proposed. Furthermore, it is possible to correct by bending not only the plane mirror but also the cylindrical mirror in the same manner. Since such a method can correct the scanning line curve relatively easily, it has been widely used conventionally.
[0017]
Also, as an electrical correction method, image data to be printed is made to correspond to the scanning line curve, and each image data is arranged and converted in advance in the image memory, or the amount of laser light is changed. Thus, there is a method in which a latent image in which the pixel position is intentionally moved in the sub-scanning direction is formed on the photosensitive member, and the scanning line curve is made as small as possible. Further, Japanese Patent Laid-Open No. 4-326380 discloses that the scanning line curve is obtained by dividing the main scanning direction into fixed areas, detecting a deviation between the ideal exposure position and the actual exposure position, and correcting the exposure timing. There has been proposed a method for reducing the amount of bending.
[0018]
[Problems to be solved by the invention]
However, if the optical member such as a plane mirror is mechanically deformed as described above in order to correct the scanning line curvature, if the optical member is made of glass, it may be broken. A potential failure may occur. In particular, when the scanning line curvature is large, even if the optical member is deformed, the deformation necessary for the correction cannot be ensured, or a large force is applied for the correction.
[0019]
Even if the correction amount is small, it is necessary to maintain the corrected state, so that the state is maintained even if the temperature changes as in the case where the temperature inside the printer rises when the printer is operated. Must. To achieve this, the mechanism becomes large and costs and space are sacrificed.
[0020]
Furthermore, when the spray paint method is used as the scanning exposure apparatus, the direction of the scanning line curve may occur in the opposite direction depending on the color, and the correction amount becomes larger than usual. Therefore, the method of deforming a flat mirror or the like necessarily has a limit. In addition, in the correction by an image in the case of electrical correction, a temporary memory secured for correction becomes enormous depending on the printing resolution. That is, it is necessary to secure a certain memory area in the sub-scanning direction. In addition, since this memory area is required for each color, it is necessary to secure a further area. Further, since each image is used one by one, the algorithm for correction becomes complicated, and the time required for correction becomes long.
[0021]
Also, in the method of changing the pixel position by changing the light amount of the laser, it is effective when the scanning line bending amount is small, but when the scanning line bending amount is large, it cannot be corrected, and as a result Color shift cannot be resolved sufficiently.
[0022]
In addition, since the method of correcting by dividing the scanning direction into a fixed region is to perform correction in a pseudo manner, the correction becomes rough and the color misregistration cannot be corrected sufficiently. Furthermore, since the image data is processed, the print output may be affected.
[0023]
The present invention has been made to solve the above-described problems, and can form a high-quality image by correcting the scanning line curve with a simple configuration without impairing the durability of the apparatus. An object is to provide an apparatus.
[0024]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, an invention according to claim 1 is directed to an image forming apparatus that forms a plurality of color images by scanning each of a plurality of light beams in a main scanning direction and a sub-scanning direction intersecting the main scanning direction. The first scanning line formed by one main scanning of the first light beam of the plurality of light beams It is the amount of curvature, and is represented by the distance in the sub-scanning direction between the midpoint of the scanning line whose center is curved in the sub-scanning direction and the left end or right end of the scanning line. Measuring means for measuring a bending amount of the second scanning line formed by the same main scanning as the first main scanning for the second light beam, the first scanning line, and the first scanning line Each of the second scan lines The scan line is represented by a straight line that passes through the midpoint of the scan line and the midpoints of the line segments whose end points are the left and right ends of the scan line and parallel to the main scan direction. Find the average position The average position is matched so The one scanning line of the first scanning line and the second scanning line is divided in the main scanning direction at the intersection of the first scanning line and the second scanning line. First Split processing Each of the divided divided scanning lines in the sub-scanning direction and the other scanning line of the first scanning line and the second scanning line. And the maximum distance in the sub-scanning direction between the divided scanning lines In the direction that the separation distance decreases, Smaller than the separation distance Move to move the offset amount processing And After going , Each of the divided scanning lines is moved in the main scanning direction at an intersection position between each of the divided scanning lines newly generated by the moving process and the other scanning line of the first scanning line and the second scanning line. The second dividing process to divide and the moving process Repeat until the separation distance is equal to or less than a predetermined distance Much Split moving means and each of the divided scanning lines of the one scanning line when the separation distance is equal to or smaller than a predetermined distance from the offset amount when the divided scanning line of the one scanning line is moved by the dividing moving means. A calculating means for calculating a total offset amount for each divided scanning line, and the one of the one scanning lines when forming the color image based on the total offset amount of each divided scanning line of the one scanning line. Adjusting means for adjusting the exposure timing of the image of the portion corresponding to each divided scanning line of the scanning line.
[0025]
The present invention is applied to an image forming apparatus that scans each of a plurality of light beams in a main scanning direction and a sub-scanning direction intersecting the main scanning direction to form a plurality of color images, that is, a color image forming apparatus. Is. As such an image forming apparatus, for example, a plurality of image carriers and a plurality of light beams are scanned on the corresponding image carriers to form a color image for each color component on each image carrier. A plurality of color images formed on each image carrier so that the plurality of color images are sequentially transferred onto the transfer body so that a single image is transferred onto the transfer body. There is an image forming apparatus that forms an image.
[0026]
The measuring unit is configured to detect the first scanning line formed by one main scanning for the first light beam among the plurality of light beams. Bending amount And measuring the second scanning line of the second scanning line formed by the same main scanning as the one main scanning. Bending amount Measure. By grasping this bending amount for each of the plurality of light beams, it is possible to grasp the color shift between the respective colors.
[0027]
The shape of the first scanning line and the shape of the second scanning line may be measured in advance and stored in the storage unit.
[0028]
The split movement means One of the first scanning line and the second scanning line is divided in the main scanning direction based on the shape of the first scanning line and the shape of the second main scanning line. One of the scanning lines is a scanning line that is a correction target of color misregistration due to, for example, scanning line curvature, and the other scanning line is a scanning line that is a reference for correction.
[0029]
The calculation means obtains the offset amount in the sub-scanning direction of the divided scanning line for which the displacement amount with respect to the other scanning line becomes small for each of the divided scanning lines of the one scanning line. That is, the offset amount of the divided scanning line in the sub-scanning direction is determined so that the displacement amount (separation distance) between the divided scanning line and the other scanning line is equal to or less than a predetermined value (for example, the resolution of the scanning line). It is done. For this reason, the scanning line formed by the offset divided scanning lines can be approximated to the second scanning line.
[0030]
The adjusting unit adjusts the exposure timing when the color image is formed by one scanning line based on the offset amount of each of the divided scanning lines calculated by the calculating unit. That is, the exposure timing of the image corresponding to each divided scanning line is shifted in the sub-scanning direction by the set offset amount. As a result, since one scanning line can be apparently approximated to the other scanning line, color misregistration can be made inconspicuous.
[0031]
As described above, the adjustment of the exposure timing makes the color misregistration due to the scanning line curve inconspicuous, so that the durability is excellent. Further, since it is only necessary to shift the exposure timing by the image data corresponding to the divided scanning lines by the amount of the offset, the color shift can be suppressed with a relatively simple configuration.
[0032]
In addition The split moving means One scanning line can be divided based on the intersection of the first scanning line and the second scanning line. As described above, since the division position is not fixed by dividing at the intersection, correction at a position suitable for the shape of the scanning line is possible, and wasteful correction can be reduced.
[0033]
Claims 2 As described above, setting means may be further provided that sets the scanning line with the smallest amount of curvature as the other scanning line and sets the scanning lines other than the other scanning line as one scanning line. As a result, the exposure timing is adjusted so that the other scanning lines approximate the scanning line with the smallest amount of curvature, so that color misregistration can be made inconspicuous while reducing the amount of curvature of the entire image.
[0034]
Claims 3 As described above, a scanning line having a curve amount closest to the average value of the curve amounts of a plurality of scanning lines obtained from a plurality of light beams is set as the other scanning line, and scanning lines other than the other scanning line are set. You may make it set as one scanning line. As a result, the exposure timing is adjusted so that the other scanning lines approximate the scanning line whose curvature is closest to the average value, so that each offset amount can be reduced.
[0035]
Claims 4 As described above, the color image may be screen data. That is, by using a color image as image data after image processing, it is possible to suppress color misregistration due to scanning line curvature without impairing the effectiveness of image processing.
[0036]
Claims 5 As described above, the color image may be video data. That is, the influence on the print characteristics can be further reduced by using the color image as video data which is the final image data.
[0037]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0038]
FIG. 1 schematically shows an image forming apparatus 10 to which the present invention is applied. The image forming apparatus 10 includes four developing units (yellow developing unit Y, magenta developing unit M, cyan developing unit C, and black developing unit K) corresponding to each color signal constituting the color image signal, and each developing unit is the same. Each of which includes a photosensitive drum 12 as an image carrier.
[0039]
Further, the image forming apparatus 10 includes a scanning exposure device 11 for irradiating the photosensitive drum 12 included in each developing unit with a laser beam.
[0040]
FIG. 2 shows an outline of the scanning exposure apparatus 11 viewed from the direction of arrow A in FIG. The scanning exposure apparatus 11 includes an fθ lens 36 composed of a plano-convex lens and a plano-concave lens with a rotating polygon mirror (polygon mirror) 22 rotating at a constant speed in the direction of arrow (1) in FIG. They are arranged in the vertical direction. Further, the scanning exposure apparatus 11 has a laser beam corresponding to each color of Y (yellow), M (magenta), C (cyan), and K (black) modulated based on each color signal constituting the image data signal. Are provided with four laser diodes 30. The laser light emitted from each laser diode 30 is converted into parallel light by the corresponding collimator lens 34 and refracted in the optical path by the reflection mirror 29, and then transmitted through the fθ lens 36 to the polygon mirror 22. Each is incident.
[0041]
Each laser beam incident on the polygon mirror 22 is reflected by the reflecting surface of the polygon mirror 22, passes through the fθ lens 36 again, is refracted by the mirror 27 disposed on the optical path different from that at the time of incidence, and is incident on the cylindrical mirror 28. Each is guided (see FIG. 1). The laser light guided to the cylindrical mirror 28 is refracted by the cylindrical mirror 28 and irradiated to the exposure scanning position 13 on the surface of the photosensitive drum 12 (hereinafter referred to as the drum surface) of each developing unit. It has become. Therefore, the laser beam is scanned on the drum surface at a constant speed by the action of the fθ lens 36. The optical paths of the laser beams of the respective colors are indicated by arrows 15Y, 15M, 15C and 15K, respectively.
[0042]
In each developing unit, the photosensitive drum 12 is rotated at a predetermined speed in the direction of arrow (1) in FIG. 1 by a motor (not shown). As a result, each laser beam emitted from the scanning exposure device 11 is repeatedly scanned along the axial direction (main scanning direction) of the photosensitive drum 12 on the drum surface.
[0043]
In each developing unit, a charger 14 is provided slightly upstream of the exposure scanning position 13 along the drum rotation direction indicated by the arrow (1) in FIG. 1, so that the drum surface is uniformly charged. ing. As a result, the surface of the drum uniformly charged by the charger 14 is exposed and scanned with laser light, thereby removing the charged charges other than the image portion and leaving the charge in the image portion. A latent image is formed.
[0044]
Further, a developing device 16 is provided slightly downstream of the exposure scanning position 13 along the drum rotation direction indicated by the arrow (1) in FIG. The developing device 16 is filled with toner charged to a polarity opposite to that of the electrostatic latent image, and the electrostatic latent image formed on the drum surface is colored in each color (Y, M, C, K). A visible image (toner image) is formed by electrostatically adhering toner as charged fine particles.
[0045]
Further, a transfer unit 18 is provided below the photosensitive drum 12 in FIG. 1, and a transfer belt 18 </ b> A for transferring the toner image is sandwiched between the transfer unit 18 and the photosensitive drum 12. The transfer belt 18A is conveyed in order by the driving roller in the direction of arrow (2) in FIG. 1 through the developing units Y, M, C, and K. Further, the transfer unit 18 in each developing unit applies charges to the transfer belt 18A, and sequentially transfers the toner images for each color to the transfer belt 18A by the electrostatic force.
[0046]
Further, a fixing device 24 is disposed on the downstream side of the transfer belt 18A to which the toner image for each color is transferred in the direction indicated by the arrow (2) in FIG. In this fixing device 24, the toner image transferred to the transfer belt 18A by applying heat or pressure while sandwiching the recording medium 26 for recording an image and transporting it in the direction of arrow (3) in FIG. It is supposed to be fused.
[0047]
A cleaner 20 for removing toner remaining on the photosensitive drum 12 after transfer is provided at the rearmost end of the rotation direction of the photosensitive drum 12 of each developing unit (the direction indicated by the arrow (1) in FIG. 1). ing.
[0048]
In addition, as shown in FIG. 2, in the scanning exposure apparatus 11, laser light is respectively present near the scanning start position in the main scanning direction (arrows C and K in FIG. 2) of the laser light corresponding to C color and K color. SOS sensors 40C and 40K for detecting laser light are arranged in order to synchronize the timing of start of scanning (Start Of Scan; SOS). Further, in the main scanning direction (arrows Y and M in FIG. 2) of the laser light corresponding to the Y color and the M color, the SOS sensors 40Y and 40M are arranged in the vicinity of the scanning start position, respectively, and the scanning end position In the vicinity, EOS sensors 41Y and 41M for detecting the laser beam are arranged in order to synchronize the timing of the end of main scanning (End Of Scan; EOS) by the laser beam. In this case, the layout is such that EOS sensors are assigned for Y color and M color.
[0049]
These assignments are specific colors and need to be assigned to colors whose scanning direction is different from the specific color. In the present embodiment, since the C color is a specific color, EOS sensors are provided for the Y color and the M color, which are different from the C color scanning direction.
[0050]
Next, scanning line bending will be described.
[0051]
As described above, the color misregistration in the sub-scanning direction between the images of the respective colors generated by the scanning line curve is generated when the incident angle of the laser beam to the polygon mirror 22 is different for each color. The curve of the line has a shape as shown in FIGS. 3A and 3B, for example. As shown in FIGS. 3A and 3B, the scanning line bending amount is large for the inner M and C colors, and the bending direction is the same for the Y and M colors and for the C and K colors. However, Y and C colors, and M and K colors are in different directions.
[0052]
In order to make the color misregistration of each color due to the scanning line curve inconspicuous, first, it is necessary to know the scanning line curve amount of the scanning line of the laser light on the transfer belt 18A of each color, the recording material or the like. As described above, since the scanning line curve is usually generated due to the configuration of the optical system of the scanning exposure apparatus, the scanning line on the transfer target of each color laser beam at the time of manufacturing the scanning exposure apparatus. The shape of the scanning line may be obtained from the measurement result, and the scanning line shape may be obtained by forming a predetermined sample pattern on the transfer body and detecting it by a light receiving element such as a photodiode. And the scanning line bending amount may be obtained from the measurement result.
[0053]
As shown in FIG. 4, the scanning line A should be a straight line parallel to the arrow A direction that is the main scanning direction, but is curved in the arrow B direction that is the sub-scanning direction orthogonal to the main scanning direction. However, it does not have a complicated shape, and often has a simple shape in which the central portion of the scanning line swells.
[0054]
Accordingly, at least three positions of the left end 42L and the right end 42R of the scanning line A and the center position 42T between the left end 42L and the right end 42R in the main scanning direction are measured, and the scanning line bending amount can be obtained from the measured positions. . In the present embodiment, the distance H in the sub-scanning direction between the center position 42T and the left end 42L or the right end 42R is defined as the scanning line bending amount. Further, the curve characteristic of the entire scanning line can be estimated by obtaining a quadratic function from the above three point positions.
[0055]
By correcting the exposure timing of the image data of each color based on the scanning line curve amount measured in this way, it is possible to reduce the color misregistration between the respective colors. A description will be given of a case where correction is made (for example, a Y-color scanning line and an M-color scanning line shown in FIG. 3).
[0056]
FIGS. 5A and 5B show the scanning line 44M and the scanning line 44Y in which the scanning line bending amount is different and the bending direction is the same. As shown in FIGS. 5A and 5B, the bending amount of the scanning line 44M is larger than the bending amount of the scanning line 44Y. Therefore, by correcting the exposure timing of the Y image, the curvature amount of the scanning line 44Y is apparently increased to approach the curvature amount of the scanning line 44M, or the exposure timing of the M image is corrected to correct the scanning line 44M. By making the amount of bending of the scanning line 44Y closer to the amount of bending of the scanning line 44Y, the difference in the amount of bending between the scanning line 44M and the scanning line 44Y can be made apparently smaller. The color shift between them can be made inconspicuous.
[0057]
However, the closer the image of each line is to a straight line, the more faithfully the output image is reproduced with respect to the input image. Therefore, correcting the color misregistration by apparently increasing the amount of curvature is reasonable in terms of image quality. Not. For this reason, in the present embodiment, the color misregistration is corrected by correcting the exposure timing so that the bending amount of the scanning line having a large bending amount is apparently reduced. For example, in the example shown in FIG. 5, the amount of bending of the scanning line 44M shown in FIG. 5A approaches the amount of bending of the scanning line 44Y shown in FIG. 5B, that is, the shape of the scanning line 44M. Is apparently approximated to the scanning line shape of the scanning line 44Y, and the exposure timing of the M image is corrected.
[0058]
The scanning line curvature is corrected based on the average position of each scanning line (hereinafter referred to as the average position). In the present embodiment, for example, as shown by a one-dot chain line in FIG. 4, a center line indicating the center position in the sub-scanning direction between the center position 42T of the scanning line and the left end 42L or the right end 42R is defined as the average position 42D.
[0059]
Then, as shown in FIG. 5C, when the average positions 42D of the scanning line 44M and the scanning line 44Y are matched, intersections P1 and P2 at which the scanning line 44M and the scanning line 44Y intersect are displayed as M image images. As the data division position, an offset amount for correcting the exposure timing is calculated for each image data divided at this intersection. Then, the scanning line shape of the scanning line 44M can be approximated to the scanning line shape of the scanning line 44Y by shifting the exposure timing of the image data of the divided area by the corresponding offset amount. Thereby, the color shift between the Y image and the M image can be made inconspicuous, and the image quality can be improved.
[0060]
Next, an offset amount calculation algorithm for correcting the scanning line curvature will be described with reference to FIG. In FIG. 6, the scanning lines 44 </ b> M and 44 </ b> Y are approximated by straight lines to simplify the description.
[0061]
As shown in FIG. 6A, when the predetermined unit distance in the arrow B direction which is the sub-scanning direction is a, the bending amount of the scanning line 44M is 4a and the bending amount of the scanning line 44Y is 2a. is there. Further, since the correction is performed by matching the average position of the scanning line 44M and the average position of the scanning line 44Y, the distance in the sub-scanning direction at the position where the scanning line 44M and the scanning line 44Y are farthest apart, that is, the main scanning. The distance L between the both end positions and the center position of the region X is a. That is, the separation distance L is expressed by L = | H1−H2 | / 2, where H1 is the curvature of one scanning line and H2 is the curvature of the other scanning line.
[0062]
In calculating the offset amount, first, the intersections P1 and P2 between the scanning line 44M and the scanning line 44Y are set as division positions, and the main scanning area X is divided into the divided scanning areas X. ₁ , X ₂ , X _Three Divide into
[0063]
Then, a separation distance L between the scanning lines 44M and 44Y is obtained. For example, ½ of the separation distance L is set as an offset amount Ofs, and the divided scanning region X _i A scanning line 44M included in (i is a subscript indicating a divided scanning region). _i Scan line 44Y _i The scanning line 44M _i Are shifted in the sub-scanning direction by the offset amount ofs. That is, in FIG. 6A, the divided scanning region X ₁ Separation distance L ₁ Is a and the scanning line 44M ₁ Is the scanning line Y ₁ As shown in FIG. 6B, the scanning line 44M ₁ Up, ie, scanning line 44Y ₁ The offset amount Ofs ₁ Shift by (= a / 2). Similarly, the divided scanning region X ₂ Separation distance L ₂ Is a and the scanning line 44M ₂ Is the scanning line Y ₂ As shown in FIG. 6B, the scanning line 44M ₂ Down, that is, the scanning line 44Y ₂ The offset amount Ofs ₂ Shift by (= a / 2). Similarly, the divided scanning region X _Three Separation distance L _Three Is a and the scanning line 44M _Three Is the scanning line Y _Three As shown in FIG. 6B, the scanning line 44M _Three Up, ie, scanning line 44Y _Three The offset amount Ofs _Three Shift by (= a / 2).
[0064]
Then, as shown in FIG. 6B, the scanning line 44M _i Are newly generated by offsetting each of the scanning lines 44M. _i And scanning line 44Y _i With the intersections P3 to P6 and the intersections P1 and P2 as division positions, the main scanning area X is divided into the division scanning areas X. _Four ~ X _Ten Divide into
[0065]
Next, similarly to the above, the scanning line 44M _i And 44Y _i , And a scanning line 44M is obtained by setting 1/2 of the separation distance L as an offset amount Ofs. _i Scan line 44Y _i The scanning line 44M _i Is shifted in the sub-scanning direction by the offset amount ofs. In the case of FIG. 6B, each divided scanning region X _i Scan line 44M at _i And 44Y _i Distance L from _i Is a / 2, the offset amount ofs is a / 4. That is, the initial offset amount is 1/4 of the difference between the bending amount of the scanning line 44M and the bending amount of the scanning line 44Y.
[0066]
Each scanning line 44M with this offset amount _i Scan line 44Y _i FIG. 6C shows a state where the offset is made in the direction approaching. In this state, the total offset amount is 3a / 4. This is repeated until the separation distance L is equal to or less than the resolution of the scanning line, for example. It should be noted that since the quadruple tandem color printer can correct up to one scanning line or less, it is possible to set the correction completion time to one scanning line or less. Thereby, the shape of the scanning line 44M can be approximated to the shape of the scanning line 44Y.
[0067]
And each divided scanning region X _i Scan line 44M at _i The offset amounts themselves are the same, but since the offset directions are different, each scanning line 44M is based on a predetermined specific position, for example, the average position 42D. _i Each offset amount, and the offset amount Ofs _i And That is, the offset amount is normalized. In this way, each divided scanning region X _i The offset amount is calculated.
[0068]
Next, the case where the bending direction is the reverse direction will be described. Here, as shown in FIG. 7A, a case where the bending amount is the same and the directions are different will be described.
[0069]
In this case, the bending amount of the scanning line 44M is 4a and the bending amount of the scanning line 44Y is also 4a. However, since the bending directions are different, the difference in the bending amount is 8a.
[0070]
First, as in the case where the bending directions are the same, the intersection points P1 and P2 between the scanning line 44M and the scanning line 44Y are set as divided positions, and the main scanning area X is divided into the divided scanning areas X. ₁ , X ₂ , X _Three The distance L between the scanning lines 44M and 44Y is obtained. In this case, the separation distance L is 4a. Then, 1/2 of the separation distance L, that is, 2a is the offset amount Ofs, and the scanning line 44M _i Scan line 44Y _i The scanning line 44M _i Is shifted in the sub-scanning direction by the offset amount ofs.
[0071]
However, the scanning line 44M _i By offsetting the scanning line 44M at the positions of the divided positions P1 and p2. _i The continuity of will be lost. Therefore, for example, as shown in FIG. ₂ 44M included in ₂ And 44Y ₂ Is divided scanning region X ₁ 44M included in ₁ And 44Y ₁ Is offset in the opposite direction by the same offset amount 2a. Thereafter, in the same manner as described above, the scan area is divided by using the intersection newly generated by offsetting the scan line as a division position, and each scan line is appropriately offset, so that the result is finally as shown in FIG. In addition, the separation distance L is set to be equal to or less than the resolution of the scanning line, for example. Thereby, the scanning line 44M _i Shape and scanning line 44Y _i It can be made to substantially match the shape of the image, and the scanning line curve is corrected as a whole, and the continuity of the image is ensured. Even when the amount of bending is different, the offset amount is uniquely determined from the difference between the amounts of bending, so there is no case where correction is impossible.
[0072]
Here, a combination of scanning line bending will be described. As a scanning line curve pattern, for example, the following cases are conceivable.
[0073]
[Table 1]

[0074]
For example, the upward direction in FIG. 6 is the forward direction and the downward direction is the reverse direction in FIG. As shown in Table 1, in this case, the scanning lines of other colors are aligned with the scanning line of the color with the smallest amount of bending for the same bending direction. Thereby, the scanning line curve of the entire image can be reduced, and color misregistration can be suppressed. Note that an average value of the bending amount of each color may be obtained, and the scanning lines of other colors may be aligned with the scanning line of the color closest to the average value. Thereby, the offset amount can be reduced.
[0075]
In addition, when the directions of bending are mixed, the scanning lines having the same bending direction are adjusted to those having a small bending amount, and thereafter the scanning lines having different bending directions are corrected in the case of the above reverse direction. You may make it correct | amend the whole.
[0076]
Next, the circuit configuration of the image forming apparatus to which the present invention is applied will be described. For convenience of explanation, the description is divided into a circuit block that divides image data according to the division position and stores it in the FIFO, and a circuit block that reads the stored image data according to the offset amount and generates corrected image data. To do. FIG. 8 shows a schematic configuration of the former circuit block, and FIG. 9 shows a schematic configuration of the latter circuit block. FIG. 10 shows a timing chart in the former circuit block, and FIG. 11 shows a timing chart in the latter circuit block.
[0077]
The circuit block shown in FIG. The calculation means 46 is connected with bending amount setting sections 48Y, 48M, 48C, and 48K. In the bending amount setting sections 48Y, 48M, 48C, and 48K, Y-color, M-color, C-color, and K-color scanning line shape data, for example, data on three points of the scanning line left end position, right end position, and center position are stored. It is remembered.
[0078]
The calculation means 48 obtains the bending amount and the bending direction of each scanning line from the shape data stored in the bending amount setting units 48Y, 48M, 48C, and 48K, and based on this, the reference color and the correction target as the correction reference The correction color is determined. For example, in the case of pattern 1 in Table 1, the reference color is K and the correction colors are Y and M.
[0079]
Then, the computing unit 48 calculates an approximate expression representing the shape of the scanning line of the reference color and an approximate expression representing the shape of the scanning line of the correction color based on the shape data, and calculates an intersection of these. The approximate expression can be expressed by a quadratic expression, for example. Based on the obtained intersection, the scanning area is divided by the algorithm described above, and the length of each divided scanning area is obtained.
[0080]
The reference color scanning line corresponds to the first scanning line or the second scanning line of the present invention, and the correction color scanning line corresponds to the second scanning line of the present invention.
[0081]
The calculating means 48 calculates a count value corresponding to the length of each divided scanning region, and outputs it to the counters 50Y, 50M, 50K, and 50C. This count value may be calculated by a predetermined formula, or the correspondence between the length of each divided scanning region and the count value may be stored in a lookup table and obtained from this.
[0082]
Dividing circuits 52Y, 52M, 52K, and 52C are connected to the counters 50Y, 50M, 50K, and 50C, respectively. Since these divided circuits have the same configuration, only the divided circuit 52Y will be described, and description of the other divided circuits will be omitted. This dividing circuit corresponds to the dividing means of the present invention.
[0083]
The dividing circuit 50Y includes an ENB generator 54, a selector 56A, a selector 56B, a counter 58, and a FIFO group 60.
[0084]
The FIFO group 60 is a FIFO 60 which is m × n first-in first-out memories arranged on the matrix in the horizontal and vertical directions in FIG. _mn It has. The left-right direction corresponds to the main scanning direction, and the up-down direction corresponds to the sub-scanning direction. In other words, the configuration includes m FIFOs of n FIFOs per line. Also, each FIFO can store image data for the number of pixels in each divided scanning region. That is, each column corresponds to each divided scanning region, and the Y image data 64 is divided into n pieces equal to the number of divided scanning regions, and is distributed and stored in each FIFO. The number m of FIFO lines is determined according to the amount of bending. For example, the number of scanning lines corresponding to the largest amount of bending is provided.
[0085]
Further, between the selector 56A and the FIFO group 60, wiring for outputting a select signal for enabling writing of the FIFO of each column at the same time is wired for n columns.
[0086]
Further, between the selector 56B and the FIFO group 60, wiring for outputting a select signal for enabling writing of the FIFO of each row at the same time is wired for m rows.
[0087]
The counter 50Y notifies the ENB generator 54 of an end signal every time counting of the count value set by the computing means 46 is completed. The count is started by a start signal from the SOS sensor 62. Each time the ENB generator 54 receives the end signal, it outputs an enable signal for instructing the selector 56A to output a select signal.
[0088]
Each time the selector 56A receives an enable signal from the ENB generator 54, the selector 56A switches the FIFO column to be writable. FIG. 10 shows a select signal for enabling writing of the FIFOs in the first to fifth columns in order from the top, and an enable signal is output at each time point from t1 to t4. That is, as shown in FIG. 10, the select signal is switched to the high level every time the enable signal is output, in synchronization with the clock. As a result, writing can be performed sequentially from the FIFO in the first column.
[0089]
On the other hand, the selector 56B receives the Y image data 64 and outputs a select signal for selecting the FIFO of each row in synchronization with the selector 56A. This select signal is a signal for switching the FIFO row to enable writing every time the select signal output from the selector 56A is output from the first column to the n-th column. The synchronization of the timing of the first select signal output between the selector 56A and the selector 56B is adjusted by the counter 58.
[0090]
Thereby, the FIFO of the row selected by the selector 56B can be written, and when the FIFO of each row is selected, the FIFO of the row can be written in order from the first column. Therefore, the Y image data 64 is divided corresponding to the divided scanning areas, and is distributed and stored in each FIFO as shown in FIG.
[0091]
Next, a circuit block for reading image data stored in the FIFO will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to FIG. 8 and an identical part, and the detailed description is abbreviate | omitted.
[0092]
The circuit block shown in FIG. 9 includes switching setting circuits 66Y, 66M, 66C, and 66K, and adjustment circuits 68Y, 68M, 68C, and 68K are connected to the switching setting circuits, respectively. Since these adjustment circuits have the same configuration, the adjustment circuit 52Y will be described, and the description of the other adjustment circuits will be omitted. This adjusting circuit corresponds to the adjusting means of the present invention.
[0093]
The adjustment circuit 68Y includes a FIFO group 60 and a selector 69 corresponding to the FIFO in each column. ₁ ~ 69 _n A synthesis circuit 71 is provided.
[0094]
The calculation unit 48 divides the scanning area by the algorithm described above from the intersection of the scanning line of the reference color and the scanning line of the correction color, and the offset amount Ofs of each divided scanning area. _i Each is obtained. And each offset amount Ofs _i The count value corresponding to the ₁ ~ 69 _n Respectively. This count value may be calculated by a predetermined formula, or the offset amount Ofs of each divided scanning region is stored in the lookup table. _i The correspondence between the count value and the count value may be stored in advance.
[0095]
From the switching setting circuit 66Y, the selector 69 ₁ ~ 69 _n A switching setting signal as shown in FIG. In FIG. 11, selectors 69 corresponding to the first to fifth columns in order from the top. ₁ ~ 69 _Five A switching setting signal for selecting the signal is shown, and each switching setting signal is a signal that becomes a high level for the length of each divided scanning region.
[0096]
Selector 69 ₁ ~ 69 _n Selects the FIFO in order from the first row at the timing corresponding to the set count value. The FIFO image data selected by each selector is combined by the combining circuit 71 and output to the subsequent circuit as correction data.
[0097]
As a result, the combined corrected image data becomes image data in which the image data of each divided scanning area is shifted in the sub-scanning direction according to the offset amount. An image with less can be obtained.
[0098]
Next, as an operation of this embodiment, a control routine executed by the calculation unit 46 will be described with reference to a flowchart shown in FIG.
[0099]
In step 100 of FIG. 12, the curve amount and curve direction of each scanning line are obtained from the scanning line shape data, and a combination of a reference color as a correction reference and a correction color to be corrected is selected.
[0100]
In the next step 102, an approximate expression of the selected reference color scanning line and an approximate expression of the correction color scanning line are obtained. The processing in step 102 corresponds to the measuring means of the present invention.
[0101]
In the next step 104, it is determined whether or not there is a combination in which the direction of the curve of the scanning line is the same among the selected combinations of the reference color and the correction color. If not, the process proceeds to step 114. If it exists, the process proceeds to step 106.
[0102]
In step 106, the intersection of the scanning line of the reference color and the scanning line of the correction color is calculated from the obtained approximate expression, and the scanning area is divided. This process corresponds to the dividing means of the present invention.
[0103]
In step 108, an offset amount for offsetting the scanning line of the correction color in the sub-scanning direction is obtained and offset so that the scanning line of the correction color approaches the scanning line of the reference color for each divided scanning area. This process corresponds to the calculation means of the present invention.
[0104]
In step 110, it is determined whether or not the separation distance between the reference color scanning line and the correction color scanning line is equal to or less than a predetermined value (for example, the resolution of the scanning line). The above process is repeated until the separation distance becomes equal to or smaller than the predetermined value. On the other hand, if the separation distance is equal to or smaller than the predetermined value, it is determined in step 112 whether or not there is another combination that should be corrected in the same direction of the scanning line curvature. The predetermined value is determined in advance according to the type of printer, for example. However, a setting unit for setting the predetermined value may be provided so that the predetermined value can be changed. Thereby, it can correct | amend optimally according to the kind etc. of scanning exposure apparatus.
[0105]
If there is a combination to be corrected in the same bending direction, the process returns to step 106 to perform the same processing as above, and if not, the process proceeds to step 114.
[0106]
In step 114, it is determined whether or not there is a combination to be corrected in which the direction of curvature of the scanning line is opposite. If not, the routine is terminated. If there is, the routine proceeds to step 116. To do.
[0107]
In step 116, as in step 106, the intersection point between the scanning line of the reference color and the scanning line of the correction color is calculated from the obtained approximate expression, and the scanning area is divided.
[0108]
In step 118, an offset amount for offsetting the scanning line of the correction color in the sub-scanning direction is obtained and offset so that the scanning line of the correction color approaches the scanning line of the reference color for each divided scanning area. In order to maintain the continuity of the image, the reference color scanning line and the correction color scanning line are appropriately offset in the sub-scanning direction.
[0109]
In step 120, as in step 110, it is determined whether or not the distance between the scanning line of the reference color and the scanning line of the correction color is equal to or smaller than a predetermined value (for example, the resolution of the scanning line). In step S116, the above process is repeated until the separation distance becomes equal to or smaller than a predetermined value. On the other hand, if the separation distance is equal to or smaller than the predetermined value, it is determined in step 122 whether there is another combination to be corrected in which the direction of the scanning line curve is opposite.
[0110]
If there is a combination to be corrected whose bending direction is opposite, the process returns to step 116 to perform the same processing as above, and if not, the routine is terminated.
[0111]
In this way, correction is performed for the same direction of curvature, and then for the opposite direction. The amount of offset in the sub-scanning direction associated with each correction is once stored in a register, and is calculated as the final offset amount collectively after each correction process, and is used to control the FIFO read timing of each column. Is done.
[0112]
By the way, when an image input from an input device such as a personal computer is output by an output device such as a printer, the input image of the input device and the output image of the output device are matched to improve reproducibility, or In order to obtain a characteristic image output, image processing is generally performed as shown in FIG. For this reason, it is preferable to insert the circuit block at the position A after the image processing of the circuit block shown in FIGS. 8 and 9 as shown in FIG. It is preferable to insert at the position. Thereby, it is possible to correct the scanning line curvature while keeping the image processing effective.
[0113]
Further, as shown in FIG. 13, after the screen data is generated, video data for actually exposing the photoconductor is generated. Therefore, a circuit block is inserted at a position C after the video data is generated. May be. This makes it possible to further utilize the characteristics of image processing. In the future, the resolution will be further improved, and the video data itself is expected to be completely binarized. Therefore, a circuit block for correcting the scan line curvature may be directly applied to the processing of the video data. This is practically possible, and in this case, there is a merit that full digital correction is possible.
[0114]
【The invention's effect】
As described above, according to the present invention, for each of the divided scanning lines of one of the scanning lines, an offset amount in the sub-scanning direction of the divided scanning line with a smaller displacement amount from the other scanning line is obtained, Based on the obtained offset amount, it is configured to adjust the exposure timing when the previous image is formed by one scanning line, so that the scanning line curve is corrected with a simple configuration without impairing the durability of the apparatus. Thus, an excellent effect that a high-quality image can be formed is obtained.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic block diagram of a scanning exposure apparatus according to an embodiment of the present invention.
FIG. 3 is a diagram for explaining scanning line bending;
FIG. 4 is a diagram for explaining scanning line bending;
FIG. 5 is a diagram for explaining scanning line bending;
FIG. 6 is a diagram for explaining a scanning line curve correction algorithm in the same direction.
FIG. 7 is a diagram for explaining a scanning line curve correction algorithm in the reverse direction.
FIG. 8 is a schematic configuration diagram of a circuit block for dividing image data.
FIG. 9 is a schematic configuration diagram of a circuit block for adjusting the exposure timing of image data.
FIG. 10 is a timing chart of the circuit block of FIG.
FIG. 11 is a timing chart of the circuit block of FIG. 9;
FIG. 12 is a flowchart of a control routine executed by a calculation unit.
FIG. 13 is a block diagram showing a flow of processing of image data.
FIG. 14 is a schematic configuration diagram of a four-tandem image forming apparatus.
FIG. 15 is a diagram for explaining scanning line bending;
[Explanation of symbols]
10 Image forming apparatus
11 Scanning exposure equipment
12 Photosensitive drum
30 Laser diode
22 Polygon mirror
14 Charger
16 Developer
18 Transfer device

Claims (5)

In an image forming apparatus that forms a plurality of color images by scanning each of a plurality of light beams in a main scanning direction and a sub-scanning direction intersecting the main scanning direction.
The first light beam of the plurality of light beams is the amount of curvature of the first scanning line formed by one main scanning , and the center point of the scanning line whose center is curved in the sub-scanning direction and the scanning The amount of bending represented by the distance in the sub-scanning direction from the left end or the right end of the line is measured, and the bending of the second scanning line formed by the same main scanning as the first main scanning for the second light beam. A measuring means for measuring the quantity;
Among the scanning lines of each of the first scanning line and the second scanning line, the middle point of the scanning line and the line segment having the middle point of the line segment having the left end and the right end of the scanning line as end points, respectively. An average position represented by a straight line passing through the point and parallel to the main scanning direction is obtained, and at the intersection position between the first scanning line and the second scanning line in a state where these average positions are matched. First dividing processing for dividing one of the first scanning line and the second scanning line in the main scanning direction, and dividing each of the divided scanning lines in the sub-scanning direction and the first scanning line. An offset smaller than the separation distance in a direction in which the separation distance represented by the maximum distance in the sub-scanning direction between the other scanning line of the one scanning line and the second scanning line and the divided scanning line becomes smaller. after the movement process of the amount moved, the worth of newly generated by the mobile processing A second dividing process of dividing each of the divided scanning lines in the main scanning direction at an intersection position between each of the scanning lines and the other scanning line of the first scanning line and the second scanning line; the distance of the movement process and a split moving means to repeat until less than a predetermined distance,
The total offset amount of each divided scanning line of the one scanning line is divided from the offset amount when the divided scanning line of the one scanning line is moved by the division moving means when the separation distance is equal to or less than a predetermined distance. Computing means for computing for each scanning line;
Based on the total offset amount of each of the divided scanning lines of the one scanning line, exposure of an image of a portion corresponding to each divided scanning line of the one scanning line when the color image is formed by the one scanning line Adjusting means for adjusting the timing;
An image forming apparatus comprising: The apparatus further comprises setting means for setting the scanning line with the smallest amount of bending as the other scanning line and setting a scanning line other than the other scanning line as the one scanning line. 1 Symbol placing the image forming apparatus. A scanning line having a curvature amount closest to an average value of the curvature amounts of a plurality of scanning lines obtained from the plurality of light beams is set as the other scanning line, and scanning lines other than the other scanning line are set as the one scanning line. the image forming apparatus 請 Motomeko 2 wherein you and sets the scanning lines. The image forming apparatus according to claim 1, wherein the color image is screen data . Said color image, the image forming apparatus according to any one of claims 1 to 3, characterized in that the video data.

Images