JP2004181648A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of obtaining a high quality image at a low cost by correcting the curve of a scanning line appropriately in multibeam system. <P>SOLUTION: The image forming apparatus is arranged such that the beam spots W, X, Y, Z, A, B, C, D, E of a plurality of light beams in each row of a multibeam arranged in matrix become substantially linear on a surface to be scanned (photosensitive body) and the linear beam spots of each row have a specified angle θb with respect to the main scanning direction. When scanning is performed with scanning lines corresponding to the number of rows, a specified one of a plurality of light beams in each row is lighted by regulating the lighting timing in the main scanning direction. For example, a fifth dot (5) has a subscanning shift of 0.875-1 dot on the upper side and beam spots (W0-W3) in W row are used as lighting spots for correcting that shift. In this case, main scanning regulation amount becomes -8 clocks (being lighted 8 clocks earlier as compared with a case where spots in A row are used). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００３８】
さて、図８に戻り、主走査調整量演算回路２３で算出された主走査位置の調整量（クロック数）は、ビデオ制御部２４において主走査バッファ：Ｎｂｕｆｆに対して加算され、ビームスポットの点灯位置（主走査方向）がビームスポット毎に調整可能となる。なお、ビデオ制御部２４には、画像クロック，主走査バッファ：Ｎｂｕｆｆのほかに、同期検知信号や画像データ等が入力される。そして、ビデオ制御部２４は、これらの調整量や信号に基づいて、ドライバ２５を介して書き込み装置のレーザダイオード１１を制御・点灯する。
【００３９】
図７の下段には、上段右側に図示した走査線の各ドットをどのように補正するかをチャート状にして示してある。すなわち、第１ドット（図面中の▲１▼）は副走査ズレは僅少であり、点灯スポットとしてはＡ列ビームスポット（Ａ０〜Ａ３）を使用する。この場合の主走査調整量は０である。第２ドット（▲２▼）は上側に少しずれ（副走査ズレ）ており、これを補正するために点灯スポットとしてはＺ列ビームスポット（Ｚ０〜Ｚ３）を使用する。この場合の主走査調整量は−２クロックとなる（Ａ列スポットを使用する場合よりも２クロック早く点灯させる）。以下同様であり、第５ドット（▲５▼）は上側に０．８７５〜１ドットの副走査ズレがあり、これを補正するために点灯スポットとしてはＷ列ビームスポット（Ｗ０〜Ｗ３）を使用する。この場合の主走査調整量は−８クロック（Ａ列スポットを使用する場合よりも８クロック早く点灯させる）となる。第１９ドットの場合は下側への副走査ズレが少しあり、これを補正するために点灯スポットとしてはＢ列ビームスポット（Ｂ０〜Ｂ３）を使用する。この場合の主走査調整量は＋２クロックとなる（Ａ列スポットを使用する場合よりも２クロック遅れて点灯させる）。このようにして曲がり・傾きを補正した走査線を図９に示す。本例の場合、補正を行った結果、±０．１２５ドットの範囲内に走査線の曲がり・傾きを補正することができる。
【００４０】
ところで、本例においては上記の如く、直線状に配置された各行ビームスポットの傾き角θｂは１行の全ビームスポット（本例では９個）が副走査ピッチの２倍にちょうど合うような構成であった、これにより、１ドット以下の副走査ズレを良好に（精度良く）補正することができる。
【００４１】
これに対し、１行の全ビームスポットにより、走査線の曲がり・傾きによって発生する副走査ズレ量を包括するように、上記の角度θｂを設定するように構成しても良い。例えば、副走査ズレ量が１ドットより大きいような場合には、上記角度θｂをより大きく（副走査ピッチの２倍より大きく）設定することで、１ドット以上の副走査ズレの補正が可能となる。ただしこの場合、ビームスポットの数が同じであれば、角度θｂが小さい場合と比べて、副走査方向の最小補正量が大きくなるので、ビームスポットの数を増やすことにより（例えば、１１個、１３個等）、最小補正量の増大を抑えて精度を維持することができる。
【００４２】
図１０及び図１１は、本発明の第２の実施形態を示すもので、それぞれ画像形成装置の作像部付近を示す断面図、補正処理部を示すブロック図である。
図１０に示すように、本例の画像形成装置は、４つの感光体１０Ｍ，Ｃ，Ｙ，Ｂｋを搬送ベルト３０の上辺に沿って並設した、いわゆるタンデム型のフルカラー画像形成装置である。各感光体１０上に形成された各色画像が、搬送ベルト３０によって搬送される用紙上に重ね転写されて画像が形成される。各感光体に対する光書き込み部としては、例えば図１に示すものを使用することができ、単独の光学系は図３で説明したような構成である。
【００４３】
搬送ベルト３０は、３つのローラ３１〜３３に張設されているが、ローラ３３部の上方に曲がり・傾き検出部３４が設けられている。曲がり・傾き検出部３４は、複数組の発光素子からなる照明光源３５及び受光素子３６からなる反射型フォトセンサ、スリット部材３７、複数の集光レンズ３８を有している。なお、搬送ベルト３０としては、感光体１０からのトナー像を転写可能な構成のものを使用する。
【００４４】
スリット部材３７のスリットは、複数組の発光素子３５及び受光素子３６に対応して複数個設けられて搬送ベルト３０の幅方向（主走査方向）へ配列され、所定の測定パターンのライン幅、例えば０．１ｍｍ程度のラインと同程度のスリットとして設けられる。
【００４５】
例えば図１の光書き込み部において、各色レーザダイオード１１は、互いに異なる所定のタイミングで測定パターン発生回路からのＢＫ、Ｃ、Ｍ、Ｙの各測定パターン画像信号によりそれぞれ駆動制御されて各色測定パターン画像信号により強度変調されたレーザビームを出射させ、感光体ドラム１０に走査線として照射することにより、各色感光体ドラム１０にそれぞれ各色測定パターンを書き込んで各測定パターンの静電潜像を形成する。
【００４６】
感光体ドラム１０上の各測定パターンの静電潜像は、図示しない現像装置によりそれぞれ現像されて各色測定パターンの顕像となり、搬送ベルト３０に直接的に重ならないように転写される。搬送ベルト３０は各照明光源３５からスリット部材３７のスリットを通して光束が照射されてそれらの反射光がスリット部材３７の各スリット及び各集光レンズ３８を介して受光素子３６で受光され、搬送ベルト３０上の各色測定パターンの顕像の濃度が光学的に測定される。
【００４７】
図１１の補正量演算記憶部２６では、随時、受光素子３６の出力信号を演算して各色の走査線の曲がり・傾きを求め、例えばスリット部材３７の主走査方向へ配列された複数のスリットを通して受光する複数の受光素子の出力信号から各測定パターンの顕像の副走査方向への位置ずれを検出して光ビームの走査線の副走査方向への曲がり・傾きを検出する。なお、走査線の曲がり・傾きを検出する構成は、ここで例示したものに限定されるものではない。走査線の曲がり・傾きは、直接的に検出するものでも間接的に検出するものでも構わない。
【００４８】
本実施形態が前記実施形態と異なる点は、検出部３４及び演算記憶部２６で検出演算した走査線の曲がり・傾きに応じて動的に補正量が決定されることである。すなわち、図１１において、検出部３４及び演算記憶部２６で検出演算した走査線の曲がり・傾きに応じて点灯ドット選択回路２２にて点灯されるビームスポット列が決定され、それに応じた主走査方向の調整量が、主走査調整量演算回路２３で算出される。以下の処理は図８で説明した補正処理部の場合と同様である。なお、主走査方向の複数個（最低３個）のデータから、主走査方向に補間することによって全データの副走査補正量を求めるように構成することができる。また、走査線の曲がり・傾きの検出は、例えば紙間において、あるいは一定の時間ごとに、あるいは温度検知手段を設けて検知温度が所定の範囲外となったときなど、適時に検出し、補正量を更新する。
【００４９】
本実施形態においては、走査線の曲がり・傾きを検出する検出機構を備え、検出した走査線の曲がり・傾きに応じて動的に補正量が決定されるので、精度良く補正を行うことができる。また、経時あるいは環境変動による走査線の曲がり・傾き等に対応することが可能となる。
【００５０】
以上、本発明を図示例により説明したが、本発明はこれに限定されるものではない。例えば、マトリクス状に配置するビームスポットの行数や１行におけるビームスポットの個数、あるいは走査線に対する角度などは、適宜設定できるものである。また、ビームスポットの主走査方向の間隔も主走査ピッチの整数倍に限らない。また、光ビーム射出手段も半導体レーザに限らず、適宜な構成のものを使用することが可能である。走査線の曲がり・傾きを検出する検出機構を備える場合には、その構成も任意である。
【００５１】
【発明の効果】
以上説明したように、本発明の画像形成装置によれば、マルチビームを、複数の光ビームのビームスポットがマトリクス状に配置され、各行のビームスポットが被走査面上で略直線状となり、該直線状ビームスポットが主走査方向に対して所定の角度を有するように構成するとともに、マトリクスの行数本の走査線を走査する際に、各行の複数の光ビームの中の所定の光ビームを、主走査方向の点灯タイミングを調整して点灯させるので、マルチビーム光学系における走査線の曲がり・傾きを常に安定して適切に補正することができる。また、製造時に調整に時間がかかることもなく、レンズの歪みなどを生じることもない。
【００５２】
請求項２の構成により、マトリクスの各行における直線状ビームスポットの主走査方向に対する角度が、各行の複数の光ビームの全てのビームスポットが副走査ピッチの２倍以内に入る角度であるので、１ドット以下の走査線の曲がりを精度良く補正することができる。
【００５３】
請求項３の構成により、マトリクスの各行における直線状ビームスポットの主走査方向に対する角度が、各行の複数の光ビームの全てのビームスポットが走査線の曲がり・傾きによって発生する副走査ズレ量を包括する範囲内に入る角度であるので、１ドット以上の副走査ズレの補正が可能となる。
【００５４】
請求項４の構成により、被走査面上におけるマトリクス各行の直線状ビームスポットの各スポットの主走査方向の間隔が、主走査方向のドットピッチの整数倍となるように構成されているので、主走査方向の点灯タイミングの調整に際して位相の異なる複数の画像クロックを用意する必要がなく、調整が容易となる。また、処理回路の簡略化による低コスト化を図ることができる。
【００５５】
請求項５の構成により、走査線の曲がり・傾きを検出する検出機構を有し、マトリクスの行数本の走査線を走査する際に、検出機構によって検出した走査線の曲がり・傾きに応じてマトリクス各行の複数の光ビームの中の所定の光ビームを選択し、その選択された光ビームの主走査方向の点灯タイミングを調整するので、マルチビーム光学系において生じている走査線の曲がり・傾きを動的に補正して、より適切な補正を行うことができる。また、経時・環境変動に対応した補正を行うことができる。
【図面の簡単な説明】
【図１】本発明が適用される画像形成装置の一例における光書き込み部の概略構成を示す斜視図である。
【図２】本発明が適用される画像形成装置の別例における光書き込み部の概略構成を示す斜視図である。
【図３】単独の光学系の基本構成を示す斜視図である。
【図４】従来のマルチビーム方式での走査線の曲がりが発生している場合のビームの状況を示す模式図である。
【図５】本発明の実施例におけるマトリクスの各行の複数の光ビームのビームスポットが直線状になっている様子と、１つの光ビームによる走査線とを示す模式図である。
【図６】１行の９個のビームスポット毎の副走査補正量を示す模式図である。
【図７】本発明による走査線の曲がり・傾き補正を説明するための模式図で、１行の複数の光ビームのビームスポットが直線状になっている様子と、１つの光ビームによる走査線と、各ドットの補正状況をチャート状にして示したものである。
【図８】補正処理部の構成を示すブロック図である。
【図９】本発明により曲がり・傾きを補正した走査線を示す模式図である。
【図１０】本発明の第２の実施形態の画像形成装置の作像部付近を示す断面構成図である。
【図１１】その実施形態における補正処理部の構成を示すブロック図である。
【符号の説明】
１ レーザユニット
１０ 感光体
１１ レーザダイオード
２１ 曲がり・傾き補正量記憶部
２２ 点灯ビームスポット選択回路
２３ 主走査調整量演算回路
２４ ビデオ制御部
２６ 補正量演算記憶部
３０ 搬送ベルト
３４ 曲がり・傾き検出部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus that performs image recording by scanning a surface to be scanned such as a photoreceptor with a light beam, and more particularly, to a technique for correcting a bending or inclination of a scanning line.
[0002]
[Prior art]
[Patent Document 1] Japanese Patent Application Laid-Open No. 9-80338 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-177165 [Patent Document 3] Japanese Patent Application Laid-Open No. 9-90695 [0003]
In a color image forming apparatus having a plurality of photoconductors, an image is written on each photoconductor independently, and a color image is obtained by superimposing the images. The position accuracy of the writing beam with respect to each photoconductor, the scanning line bending / tilt / magnification error due to the variation of the lens of the optical system, the speed error of each photoconductor, the fluctuation of the writing position and magnification due to the temperature rise of the whole device, etc. In addition, color misregistration is likely to occur and appears as color unevenness or color misregistration in a final image, which is a factor of deteriorating image quality.
[0004]
Also, in an image forming apparatus in which a plurality of light beams are written to different positions in the sub-scanning direction on a single photoconductor to obtain a multi-color image, even if each scanning line has a bend or an inclination. In this case, when an image is superimposed, a color shift appears, and the image is significantly deteriorated.
[0005]
Further, even in the case of a single-color image forming apparatus, although it is not as serious as an apparatus that superimposes multiple colors, the bending and inclination of a scanning line are a bottleneck when forming an image such as a fine drawing.
[0006]
As a method of correcting the bending and the inclination of the scanning line, Japanese Patent Application Laid-Open No. 2003-133873 proposes to correct the bending by forcibly bending a plastic toroidal lens.
[0007]
Patent Document 2 proposes a method of correcting the curvature to one dot or less by rearranging image data in the sub-scanning direction according to the curvature of the scanning line.
Patent Document 3 proposes correcting a scan line bend by interpolating an image two-dimensionally in accordance with the bend.
[0008]
[Problems to be solved by the invention]
However, in the case of the above-mentioned Patent Document 1, it is necessary to individually adjust each one (one by one) at the manufacturing stage, which is a very time-consuming operation. In addition, there is a problem that, by forcibly bending the lens, a state in which distortion is always generated inside the lens, which adversely affects the imaging performance. In addition, it is expected that the bending state of the lens will change due to a change in temperature, and there is no compensation for performing stable correction over the entire environmental range.
[0009]
Further, in the case of the above-mentioned Patent Document 2, a step of one dot is formed at the position of the seam in the main scanning direction in which the image data is rearranged. Problems (called jaggies). In addition, the bending cannot be corrected to one dot or less.
[0010]
And the thing of the above-mentioned patent document 3 has a problem that the line width of a thin line varies.
[0011]
Further, in recent years, an image forming apparatus has been proposed which performs writing by a so-called multi-beam in which a plurality of light beams are arranged, and which is compatible with high speed and high density. Therefore, it is required to appropriately correct the scanning line bending even in such a multi-beam.
[0012]
The present invention solves the above-described problem in the conventional image forming apparatus, and provides an image forming apparatus capable of appropriately correcting the curvature of a scanning line and obtaining a high-quality image at low cost even in the case of multi-beam formation. The task is to
[0013]
[Means for Solving the Problems]
According to the present invention, there is provided an image forming apparatus which forms a latent image by scanning a surface to be scanned of an image carrier with a multi-beam composed of a plurality of light beams, and visualizes the latent image to record an image. In the multi-beam, the beam spots of a plurality of light beams are arranged in a matrix, the beam spots in each row are substantially linear on the surface to be scanned, and the linear beam spots are predetermined with respect to the main scanning direction. And having a certain angle, and when scanning several scanning lines of the matrix, a predetermined light beam among a plurality of light beams of each row, by adjusting the lighting timing in the main scanning direction. It is solved by turning on.
[0014]
In order to solve the above problem, the present invention proposes that the predetermined angle is an angle at which all beam spots of the plurality of light beams in the rows of the matrix fall within twice the sub-scanning pitch. I do.
[0015]
Further, in order to solve the above-mentioned problem, in the present invention, the predetermined angle includes a sub-scanning deviation amount in which all beam spots of a plurality of light beams in a row of the matrix are generated due to a curved or inclined scanning line. It is suggested that the angle be within the range of
[0016]
In order to solve the above-mentioned problem, according to the present invention, the interval between the linear beam spots in each row of the matrix on the surface to be scanned in the main scanning direction is an integral multiple of the dot pitch in the main scanning direction. It is proposed to be configured.
[0017]
Further, in order to solve the above-mentioned problem, the present invention has a detection mechanism for detecting a bending / inclination of a scanning line, and when scanning several scanning lines of the matrix, detection is performed by the detection mechanism. It is proposed that a predetermined light beam among a plurality of light beams in each row of the matrix is selected according to the bending / inclination of the scanning line, and the lighting timing of the selected light beam in the main scanning direction is adjusted.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view illustrating a schematic configuration of an optical writing unit in an example of an image forming apparatus to which the present invention is applied. The optical writing unit shown in this figure includes an LD (laser diode) unit 11, a two-layer fθ lens 12, a long WT lens 13, a polygon mirror 14, and the like. In addition, Bk, Y, C, and M after the sign indicate each color of black, yellow, cyan, and magenta, respectively. The laser light of each color from the optical writing unit is irradiated on the photoconductors 10Bk, 10Y, 10C, and 10M, respectively, and an electrostatic latent image is formed on each photoconductor. The electrostatic latent image formed on each photoconductor is visualized by applying toner from a developing device (not shown). The toner image is transferred from the photoreceptor 10 directly or via an intermediate transfer member (not shown) so as to be superimposed on a sheet to form a full-color image.
[0019]
FIG. 2 is a perspective view illustrating a schematic configuration of an optical writing unit in another example of the image forming apparatus to which the present invention is applied. The image forming apparatus shown in this figure is configured such that a wide scanning width is obtained by connecting two optical systems in the main scanning direction. The illustrated optical writing unit includes two sets (two colors) of a laser diode 11, a collimator lens 15, a cylinder lens 16, a polygon mirror 14, a first fθ lens 12a, a second fθ lens 12b, mirrors 17 to 19, and the like. . The two laser beams from the optical writing unit are irradiated onto the photoconductor 10 to form a wide electrostatic latent image. The latent image is visualized by applying toner from a developing device (not shown), and the toner image is directly transferred from the photoconductor 10 onto a sheet.
[0020]
Although not shown, the present invention is also applied to an image forming apparatus that obtains a multicolor image by scanning light beams from a plurality of writing systems at different positions in the sub-scanning direction on the same photosensitive member. be able to.
[0021]
In any of the above optical systems, each independent optical system is basically a single optical system as shown in FIG. 3, and therefore, the description of the present invention will be made with reference to FIG.
[0022]
In the optical system shown in FIG. 3, a laser beam (light beam) emitted from a laser unit 1 is condensed in a sub-scanning direction by a cylindrical lens 2 and is incident on a polygon mirror 3. Scan in the direction. Further, the laser light is focused and imaged as a beam spot on the surface to be scanned (photoconductor 10) by the fθ lens 4, the valet toroidal lens 5, and the like. The laser unit 1 has a plurality of light-emitting points in a matrix, and as shown in FIG. 3, a beam spot from each light-emitting point is configured such that each row of the matrix is substantially linear on the surface to be scanned. I have. Further, as described later, each line of the linear beam spot is configured to have a predetermined angle (θb) with respect to the scanning line.
[0023]
As a method for forming a matrix of a plurality of laser beams, a two-dimensional LD array (having a plurality of light-emitting points in a two-dimensional array in one LD package) is widely used, for example, as disclosed in Japanese Patent No. 29272284. It is proposed that such a known technique can be adopted. The use of a plurality of LDs and combining them by a prism or the like to form an array on the surface to be scanned is well known, for example, from Japanese Patent Application Laid-Open No. 7-72407, and such a technique can be adopted. Alternatively, a method of directly combining the optical axes by appropriately setting the angle of the optical axis without using a prism has been proposed, and such a technique can be adopted.
[0024]
Here, a description will be given of a state of a beam when a scanning line is bent in the conventional multi-beam system (simultaneous scanning of four lines) with reference to FIG. Note that the example shown in FIG. 4 shows a case where the bending is ± 1 dot or less in the sub-scanning direction.
[0025]
In FIG. 4, the beam is sequentially turned on and scanned from the leading dot 1 to form a scanning line (a series of beam spots). In the case of the illustrated example, the bend and the inclination are ± 1 dot or less, but since the bend of the scanning line in each color station occurs independently and randomly, when the beams are overlapped, a deviation of up to 2 dots may occur. become.
[0026]
Now, returning to the description of the present invention, as described above, each row of the beam spots from the laser unit 1 is configured to be substantially linear on the surface to be scanned, and the beam spots are defined with respect to the scanning lines. (Θb). This is shown in FIG. In this example, nine beam spots of W, X, Y, Z, A, B, C, D, and E are arranged in a substantially linear manner for each row. Are arranged in four rows and can be scanned by a total of 36 beam spots. In the example shown in FIG. 5, the inclination angle θb of the linearly arranged beam spots is a configuration example in which all the beam spots W to E in each row exactly match the double scanning pitch.
[0027]
Assuming that the beam spot interval on one straight line is Pb, the beam spot interval Pfb in the sub-scanning direction and the beam spot interval Psb in the main scanning direction are Pfb = Pb × sin θb and Psb = Pb × cos θb, respectively.
[0028]
By arranging the beam spots in this manner, the interval twice as large as the sub-scanning pitch Pf is evenly divided by the number of beam spots N-1 (9-1 = 8 in this example). That is, scanning can be performed by dividing the sub-scanning interval by (N-1) / 2. When the number of beam spots in this example is nine, the sub-scanning pitch can be divided into four. The greater the number of beam spots, the greater the number of beam spots that can be divided, and it is possible to perform bending and tilt correction with high accuracy.
[0029]
The right part of FIG. 5 is the same as that of FIG. 4, but shows a scanning line when the lighting is performed using only the beam spot in column A of the beam spot matrix (9 × 4 rows). It is.
[0030]
Next, FIG. 6 is a schematic diagram showing the amount of sub-scanning correction for each of the nine beam spots in each row arranged in a straight line. Here, for the sake of convenience, the + and-signs of the correction amount are corrected to + for correction of a value shifted upward with reference to the center line of the sub-scanning pitch in FIG. 4 or FIG. 5 and for correction of a value shifted downward. The case in which it is performed is indicated by-. However, the sign may be reversed.
[0031]
In this drawing, the correction amount (correction range) for each spot is indicated by a straight line connecting a black circle and a white circle. Here, an example is shown in which one dot in the sub-scanning direction is divided into four (-1 divided by +1 dot into eight) to perform correction. For example, a sub-scan shift within -0.125 to +0.125 dots indicates that the beam spot A row (A0 to A3) is turned on. In addition, the amount of deviation is shown by adding a + sign to the upper deviation and a-sign to the lower deviation with respect to the center line of the sub-scanning pitch.
[0032]
When the sub-scan shift amount is −0.125 to −0.375 dots (shift below the center line), the beam spot B row (B0 to B3) is turned on. Similarly, for example, in the case of the fifth dot in FIG. 5 (5 in the drawing), there is a displacement close to +1 dot (displacement above the center line), so that the beam spot W row is turned on. Actually, the correction amount corresponding to the deviation amount is stored in the form of a table. However, instead of being stored as a table, it may be calculated by an arithmetic expression such as INT (2f (nd) / (N-1)).
[0033]
FIG. 7 is a schematic diagram for explaining the correction of the bending / tilt of the scanning line. The left side of the upper part of FIG. 7 shows nine beam spots for one row arranged in a substantially straight line. In this example, as described with reference to FIG. 5, a matrix of 9 × 4 rows is used. However, since the row direction is the same, only one row is shown in FIG. For simplicity of description, the optical system is set so that the beam spot interval Psb in the main scanning direction is an integral multiple (Nck: N clocks, twice in this example) of the main scanning pitch Ps (see FIG. 5). Is assumed to be set. However, bend / tilt correction is possible even if it is not an integral multiple, but by using an integral multiple, the correction process, that is, the circuit configuration for performing the correction process can be simplified, and cost reduction can be achieved. it can. The right side of the upper part of FIG. 7 shows a scanning line when lighting is performed using only the A spot among the nine beam spots for one row. The lower part of FIG. 7 will be described later.
[0034]
FIG. 8 is a block diagram illustrating a configuration of a correction processing unit that performs a process of correcting a scan line for bend and tilt.
In this figure, the bend / tilt correction amount storage unit 21 stores a bend / tilt correction amount f (nd) in the sub-scanning direction of all dots in the main scanning direction. In this example, it is assumed that the amount of bending and inclination is individually measured and stored at the stage of manufacturing the device. It should be noted that the correction amount may be obtained by calculating the correction amount of each dot by interpolation from the values of the deviation amounts in the sub-scanning direction (not all dots) in the main scanning direction.
[0035]
When the lighting beam spot is determined by the selection circuit 22 based on the correction amount (as described with reference to FIG. 6), the adjustment amount in the main scanning direction corresponding thereto is calculated by the main scanning adjustment amount calculation circuit 23. As shown on the right side of the upper part of FIG. 7, when the beam spot W is used to correct, for example, the fifth dot (5 in the drawing) of the scanning line that illuminated the beam spot A, the upper part of FIG. As shown on the left side, the beam spots A and W are shifted by 2 × 4 = 8 clocks in the main scanning direction (as described above, Psb is an integral multiple of the main scanning pitch Ps in this example, and in this example, Therefore, adjustment in the main scanning direction is necessary.
[0036]
Table 1 below shows the main scanning adjustment amount for each beam spot. The main scanning adjustment amount for each column beam spot is represented by “Nck × spot number”, and is shown in the rightmost column of Table 1. In this example, Nck = 2 as described above. The sign of +/− of the adjustment amount (spot number) is attached with + on the left side and − on the right side with reference to the spot A at the center of the nine beam spots in the main scanning direction in FIG. You can reverse it. Table 1 also shows the sub-scanning correction amount (movement amount) for each column beam spot shown in FIG.
[0037]
[Table 1]

[0038]
Returning to FIG. 8, the adjustment amount (clock number) of the main scanning position calculated by the main scanning adjustment amount calculation circuit 23 is added to the main scanning buffer: Nbuff in the video control unit 24, and the beam spot is turned on. The position (main scanning direction) can be adjusted for each beam spot. The video control unit 24 receives a synchronization detection signal, image data, and the like in addition to the image clock and the main scanning buffer: Nbuff. Then, the video control unit 24 controls and lights the laser diode 11 of the writing device via the driver 25 based on these adjustment amounts and signals.
[0039]
The lower part of FIG. 7 shows, in a chart form, how to correct each dot of the scanning line shown on the right side of the upper part. That is, the first dot ((1) in the drawing) has a small sub-scanning deviation, and the A-th row beam spot (A0 to A3) is used as the lighting spot. The main scanning adjustment amount in this case is zero. The second dot ((2)) is slightly displaced upward (sub-scan deviation), and in order to correct this, a Z-row beam spot (Z0 to Z3) is used as a lighting spot. The main scanning adjustment amount in this case is -2 clocks (lights up two clocks earlier than in the case of using the column A spot). The same applies to the following. The fifth dot ([5]) has a sub-scanning deviation of 0.875 to 1 dot on the upper side, and a W-line beam spot (W0 to W3) is used as a lighting spot to correct this. I do. In this case, the main scanning adjustment amount is -8 clocks (lights up eight clocks earlier than in the case of using the spot in column A). In the case of the nineteenth dot, there is a slight downward sub-scanning deviation, and in order to correct this, a B-line beam spot (B0 to B3) is used as a lighting spot. In this case, the main scanning adjustment amount is +2 clocks (lighting is delayed by two clocks as compared with the case of using the A-row spot). FIG. 9 shows a scanning line in which the bending and the inclination have been corrected in this manner. In the case of this example, as a result of performing the correction, it is possible to correct the bending and inclination of the scanning line within the range of ± 0.125 dots.
[0040]
By the way, in this example, as described above, the inclination angle θb of each line beam spot arranged linearly is such that all the beam spots (nine in this example) of one line exactly match the double scanning pitch. This makes it possible to satisfactorily (accurately) correct the sub-scanning deviation of one dot or less.
[0041]
On the other hand, the angle θb may be set so as to cover the amount of sub-scan shift caused by the bending or tilt of the scanning line by all the beam spots in one row. For example, if the amount of sub-scanning deviation is larger than one dot, setting the angle θb to be larger (greater than twice the sub-scanning pitch) makes it possible to correct sub-scanning deviation of one dot or more. Become. However, in this case, if the number of beam spots is the same, the minimum correction amount in the sub-scanning direction is larger than in the case where the angle θb is small, so that the number of beam spots is increased (for example, 11 or 13). , Etc.), and the accuracy can be maintained while suppressing an increase in the minimum correction amount.
[0042]
FIGS. 10 and 11 show a second embodiment of the present invention, and are a cross-sectional view showing the vicinity of an image forming unit of an image forming apparatus and a block diagram showing a correction processing unit, respectively.
As shown in FIG. 10, the image forming apparatus of this example is a so-called tandem type full-color image forming apparatus in which four photoconductors 10M, C, Y, and Bk are arranged side by side along the upper side of the conveyor belt 30. Each color image formed on each photoconductor 10 is overlaid and transferred onto a sheet conveyed by the conveyance belt 30 to form an image. As the optical writing unit for each photoconductor, for example, the one shown in FIG. 1 can be used, and a single optical system has the configuration as described in FIG.
[0043]
The transport belt 30 is stretched around three rollers 31 to 33, and a bend / tilt detection unit 34 is provided above the roller 33. The bend / tilt detector 34 has an illumination light source 35 composed of a plurality of sets of light emitting elements, a reflective photosensor composed of a light receiving element 36, a slit member 37, and a plurality of condenser lenses 38. Note that the transport belt 30 has a configuration capable of transferring a toner image from the photoconductor 10.
[0044]
A plurality of slits of the slit member 37 are provided corresponding to a plurality of sets of the light emitting element 35 and the light receiving element 36 and are arranged in the width direction (main scanning direction) of the transport belt 30, and a line width of a predetermined measurement pattern, for example, It is provided as a slit of the same degree as a line of about 0.1 mm.
[0045]
For example, in the optical writing unit of FIG. 1, each laser diode 11 is driven and controlled by each of the measurement pattern image signals BK, C, M, and Y from the measurement pattern generation circuit at predetermined timings different from each other, so that each color measurement pattern image By emitting a laser beam intensity-modulated by a signal and irradiating the photosensitive drum 10 as a scanning line, each color measurement pattern is written on each color photosensitive drum 10 to form an electrostatic latent image of each measurement pattern.
[0046]
The electrostatic latent image of each measurement pattern on the photoconductor drum 10 is developed by a developing device (not shown) to become a visible image of each color measurement pattern, and is transferred so as not to directly overlap the transport belt 30. The conveying belt 30 is irradiated with a light beam from each illumination light source 35 through a slit of a slit member 37, and the reflected light is received by a light receiving element 36 via each slit of the slit member 37 and each condensing lens 38. The density of the visible image of each color measurement pattern is optically measured.
[0047]
In the correction amount calculation storage unit 26 of FIG. 11, the output signal of the light receiving element 36 is calculated at any time to determine the bending / inclination of the scanning line of each color, and, for example, through a plurality of slits of the slit member 37 arranged in the main scanning direction. The positional deviation of the visualized image of each measurement pattern in the sub-scanning direction is detected from the output signals of the plurality of light-receiving elements that receive light, and the bending and inclination of the scanning line of the light beam in the sub-scanning direction are detected. Note that the configuration for detecting the bending / inclination of the scanning line is not limited to the configuration illustrated here. The bending / inclination of the scanning line may be detected directly or indirectly.
[0048]
The present embodiment is different from the above-described embodiment in that the correction amount is dynamically determined according to the curvature / inclination of the scanning line detected and calculated by the detection unit 34 and the calculation storage unit 26. That is, in FIG. 11, a beam spot array to be lit by the lighting dot selection circuit 22 is determined in accordance with the curvature / inclination of the scanning line detected and calculated by the detection unit 34 and the calculation storage unit 26, and the main scanning direction corresponding thereto is determined. Is calculated by the main scanning adjustment amount calculation circuit 23. The following processing is the same as in the case of the correction processing unit described with reference to FIG. It should be noted that it is possible to obtain a sub-scanning correction amount of all data by interpolating in the main scanning direction from a plurality of (at least three) data in the main scanning direction. In addition, the detection of the bending / inclination of the scanning line can be detected and corrected in a timely manner, for example, between sheets, at regular intervals, or when a detected temperature is out of a predetermined range by providing a temperature detecting means. Update the quantity.
[0049]
In the present embodiment, a detection mechanism is provided for detecting the curvature / inclination of the scanning line, and the correction amount is dynamically determined according to the detected curvature / inclination of the scanning line, so that the correction can be performed with high accuracy. . In addition, it is possible to cope with a bending or inclination of a scanning line due to aging or environmental change.
[0050]
Although the present invention has been described with reference to the illustrated examples, the present invention is not limited thereto. For example, the number of rows of beam spots arranged in a matrix, the number of beam spots in one row, the angle with respect to a scanning line, and the like can be appropriately set. Further, the interval between the beam spots in the main scanning direction is not limited to an integral multiple of the main scanning pitch. Further, the light beam emitting means is not limited to the semiconductor laser, but may have an appropriate configuration. When a detection mechanism for detecting the bending / inclination of the scanning line is provided, its configuration is also arbitrary.
[0051]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, the multi-beams are arranged such that the beam spots of a plurality of light beams are arranged in a matrix, and the beam spots of each row are substantially linear on the surface to be scanned. The linear beam spot is configured so as to have a predetermined angle with respect to the main scanning direction, and when scanning several scanning lines of the matrix, a predetermined light beam among a plurality of light beams of each row is scanned. Since the lighting is performed by adjusting the lighting timing in the main scanning direction, the bending and inclination of the scanning line in the multi-beam optical system can always be stably and appropriately corrected. In addition, no time is required for adjustment at the time of manufacture, and no distortion of the lens or the like occurs.
[0052]
According to the configuration of claim 2, the angle of the linear beam spot in each row of the matrix with respect to the main scanning direction is an angle at which all the beam spots of the plurality of light beams in each row fall within twice the sub-scanning pitch. The curvature of the scanning line below the dot can be corrected with high accuracy.
[0053]
According to the configuration of the third aspect, the angle of the linear beam spot in each row of the matrix with respect to the main scanning direction includes the amount of sub-scanning deviation caused by bending or tilting of the scanning line in all the beam spots of the plurality of light beams in each row. Since the angle falls within the range, the sub-scanning deviation of one or more dots can be corrected.
[0054]
According to the configuration of the fourth aspect, the interval between the linear beam spots in each row of the matrix on the scanned surface in the main scanning direction is configured to be an integral multiple of the dot pitch in the main scanning direction. When adjusting the lighting timing in the scanning direction, it is not necessary to prepare a plurality of image clocks having different phases, which facilitates the adjustment. Further, cost reduction can be achieved by simplifying the processing circuit.
[0055]
According to the configuration of the fifth aspect, there is provided a detecting mechanism for detecting the bending / inclination of the scanning line, and when scanning several scanning lines of the matrix, according to the bending / inclination of the scanning line detected by the detecting mechanism. Since a predetermined light beam among a plurality of light beams in each row of the matrix is selected and the lighting timing of the selected light beam in the main scanning direction is adjusted, the bending and inclination of the scanning line generated in the multi-beam optical system Can be dynamically corrected to perform more appropriate correction. Further, it is possible to perform correction corresponding to aging and environmental fluctuation.
[Brief description of the drawings]
FIG. 1 is a perspective view illustrating a schematic configuration of an optical writing unit in an example of an image forming apparatus to which the present invention is applied.
FIG. 2 is a perspective view illustrating a schematic configuration of an optical writing unit in another example of the image forming apparatus to which the present invention is applied.
FIG. 3 is a perspective view showing a basic configuration of a single optical system.
FIG. 4 is a schematic view showing a state of a beam when a scanning line is bent in a conventional multi-beam system.
FIG. 5 is a schematic diagram showing a state in which beam spots of a plurality of light beams in each row of a matrix are linear in one embodiment of the present invention, and scanning lines formed by one light beam.
FIG. 6 is a schematic diagram illustrating a sub-scanning correction amount for each of nine beam spots in one row.
FIG. 7 is a schematic diagram for explaining the correction of the bending and inclination of the scanning line according to the present invention, in which the beam spots of a plurality of light beams in one row are linear, and the scanning line is formed by one light beam. And the correction status of each dot is shown in the form of a chart.
FIG. 8 is a block diagram illustrating a configuration of a correction processing unit.
FIG. 9 is a schematic view showing a scanning line in which a bend and a tilt are corrected according to the present invention.
FIG. 10 is a cross-sectional configuration diagram illustrating the vicinity of an image forming unit of an image forming apparatus according to a second embodiment of the present invention.
FIG. 11 is a block diagram illustrating a configuration of a correction processing unit according to the embodiment.
[Explanation of symbols]
Reference Signs List 1 laser unit 10 photoconductor 11 laser diode 21 bend / tilt correction amount storage unit 22 lighting beam spot selection circuit 23 main scanning adjustment amount calculation circuit 24 video control unit 26 correction amount calculation storage unit 30 transport belt 34 bend / tilt detection unit

Claims (5)

An image forming apparatus that scans a surface to be scanned of an image carrier with a multi-beam composed of a plurality of light beams to form a latent image and visualizes the latent image to record an image.
In the multi-beam, the beam spots of a plurality of light beams are arranged in a matrix, the beam spots in each row are substantially linear on the surface to be scanned, and the linear beam spots are at a predetermined angle with respect to the main scanning direction. And having
An image forming apparatus that, when scanning several scanning lines of the matrix, emits a predetermined light beam among a plurality of light beams in each row by adjusting lighting timing in a main scanning direction; . 2. The image forming apparatus according to claim 1, wherein the predetermined angle is an angle at which all the beam spots of the plurality of light beams in the rows of the matrix fall within twice the sub-scanning pitch. Wherein the predetermined angle is an angle in which all beam spots of the plurality of light beams in the rows of the matrix fall within a range including a sub-scanning deviation amount generated by the bending / inclination of the scanning line. The image forming apparatus according to claim 1. The linear beam spot of each row of the matrix on the surface to be scanned is configured such that intervals between the spots in the main scanning direction are integer multiples of a dot pitch in the main scanning direction. The image forming apparatus according to any one of claims 1 to 3. Has a detection mechanism to detect the bending and inclination of the scanning line,
When scanning several rows of scanning lines of the matrix, select a predetermined light beam from a plurality of light beams of each row of the matrix according to the bending and inclination of the scanning lines detected by the detection mechanism, The image forming apparatus according to any one of claims 1 to 4, wherein a lighting timing of the selected light beam in the main scanning direction is adjusted.

Images