JP3961964B2 - Image reading control method, image reading apparatus, and image forming apparatus - Google Patents

Description

で示される。ここで、
ＤｐはＶｒｅｆｗ＊＊用Ｄ／Ａコンバータ設定値を変更後に期待するピークデータ、
Ｓｔｐはピーク値Ｄｗｐ＊＊を得たときのＤ／Ａコンバータ設定値
ＳｔｂはＶｒｅｆｂのＤ／Ａコンバータ設定値
である。
【００５４】
次いで、計算結果のＳｒｅｆｗ＊がＤ／Ａコンバータ５７の設定可能範囲（ＳｒｅｆｗＬ〜ＳｒｅｆｗＨ）内か否かを判断する(ステップ１０１２）。例えば、８ｂｉｔのＤ／Ａコンバータ５７であれば設定可能範囲は、０〜２５５といった具合である。設定可能範囲内の値であれば、実際に設定して(ステップ１０１３）、再度ステップ１０１０に戻り、ピークデータ：Ｄｗｐ＊ｅ、Ｄｗｐ＊ｏを読み取る。計算結果のＳｒｅｆｗがＤ／Ａコンバータの設定可能範囲外の場合はエラーであるが、設定可能範囲内で計算値に近い値を設定し(ステップ１０１４）、終了する。
【００５５】
一方、ステップ１０１０において、ピークデータ：Ｄｗｐ＊ｅ、Ｄｗｐ＊ｏが規格値：Ｄｐ±Ｃに入っている場合は、ステップ１００３からステップステップ１００７と同じ処理を行なう。すなわち、ゲインを決定する電圧：Ｖｇ＊＊を変更してピークデータ：Ｄｗｐ＊ｅ、Ｄｗｐ＊ｏを読み出し(ステップ１０１５）、それらピークデータが規格値：Ｄｐ±Ｂに入いるか否かを判断する(ステップ１０１６）。そして、ピークデータ：Ｄｗｐ＊ｅ、Ｄｗｐ＊ｏが規格値：Ｄｐ±Ｂに入っていない場合は、上記目標公差内に入るように、ゲインを決定する電圧：Ｖｇ＊＊を出力するためのＤ／Ａコンバータ５７の設定値：Ｓｖｇ＊＊を計算し(ステップ１０１７）、計算結果のＳｖｇがＤ／Ａコンバータ５７の設定可能範囲（ＳｖｇＬ〜ＳｖｇＨ）内か否かを判断し(ステップ１０１８）、設定可能範囲内の値であれば、実際にＤ／Ａコンバータ５７に設定値Ｓｖｇ＊＊を設定し(ステップ１０１９）、再度ピークデータ：Ｄｗｐ＊＊を読み取る。
【００５６】
ピークデータ：Ｄｗｐ＊ｅ、Ｄｗｐ＊ｏが規格値：Ｄｐ±Ｂに入った場合、Ｖｒｅｆｂを基準にした時にＶｒｅｆｗ＊が変更された割合だけ、Ｖｒｅｆｄ＊も変更する（ステップ１０２０）。変更前後の基準白板４１の読み取り用基準電圧を各々Ｖｒｅｆｗ＊’、Ｖｒｅｆｗ＊、変更前後の原稿読み取り用基準電圧を各々Ｖｒｅｆｄ＊’、Ｖｒｅｆｄ＊、下側基準電圧をＶｒｅｆｂとした時に、

になるようにＶｒｅｆｄを変更する。すなわち、Ｄ／Ａコンバータ５７の設定値は上式を満足するＳｒｅｆｄ＊を出力する設定値とする。また、Ｓｒｅｆｗ＊とＳｒｅｆｄ＊は不揮発性メモリ６２に保存する。
【００５７】
また、ステップ１０１６でピークデータ：Ｄｗｐ＊ｅ、Ｄｗｐ＊ｏが規格値：Ｄｐ±Ｂに入らなかった場合はエラーであるが、設定可能範囲内で計算値に近い値を設定し（ステップ１０２１）、終了する。
【００５８】
図１６は、上述した画像読取装置が設けられる画像形成装置の一例を図１６により説明する。図１６は図１の画像読取装置を備えた画像形成装置の一例の概略構成を示す図である。この例ではカラー複写機に適用した場合を例にとっている。
【００５９】
画像読取装置１で得られたR、G、B の色分解画像信号強度レベルを基にして、図示しない画像処理部で色変換処理を行い、ブラック（以下、Ｂｋと称する）、シアン（以下、Ｃと称する）、マゼンタ（以下、Ｍと称する）、イエロー（以下、Ｙと称する）の各カラー画像データを得る。これらのカラー画像データは、以下に説明するプリンタ部１００によって、Ｂｋ、Ｃ、Ｍ、Ｙの顕像化を行い、最終的なカラーコピーを得る。
【００６０】
プリンタ部１００では、書込光学ユニット８が、スキャナ１からのカラー画像データを光信号に変換して、原稿画像に対応した光書込みを行い、ドラム状の感光体９に静電潜像を形成する。書込光学ユニット８は、レーザー発光手段８a、図示しない発光駆動制御部、ポリゴンミラー８ｂ、このポリゴンミラー８ｂの回転モータ８ｃ、ｆθレンズ８ｄ、反射ミラー８ｅなどで構成されている。
【００６１】
感光体９は、矢印で示すように半時計方向へ回転するが、その周りには感光体クリーニングユニット１０、除電ランプ１１、帯電器１２、電位センサ１３、Ｂｋ現像器１４、Ｃ現像器１５、Ｍ現像器１６、Ｙ現像器１７、現像濃度パターン検知器１８、中間転写ベルト１９などが配置されている。
【００６２】
１４〜１７で示す各現像器は、静電潜像を現像するために現像剤を感光体９に対向させるように回転する現像スリーブ、現像剤を汲み上げて攪拌するために回転する現像パドル、及び現像剤のトナー濃度検知センサなどで構成されている。ここでは、現像動作の順序（カラー画像形成順序）をＢｋ、Ｃ、Ｍ、Ｙとして、以下に動作を説明する。（但し、画像形成装置はこれに限定されるものではない。）
コピー動作が開始されると、スキャナ１で所定のタイミングからＢＫ画像データの読取りがスタートし、この画像データに基づいて書込光学ユニット８のレーザー光による光書込み・潜像掲載が始まる（以下、Ｂｋ画像データによる静電潜像をＢｋ潜像と称する。C、M、Yについても同様にC潜像、M潜像、Y潜像と称する）。各現像器１４〜１７は、待機状態では現像不作動状態になっているが、Ｂｋ潜像の形成が行われるとこのＢｋ潜像の先端部から現像を行うため、Ｂｋ現像器１４の現像位置にＢｋ潜像の先端が到達する前に、Ｂｋ現像スリーブが回転を開始して、Ｂｋ潜像をＢｋトナーで現像する。その後、Ｂｋ潜像領域の現像動作を続けるが、Ｂｋ潜像の後端部がＢｋ現像位置を通過した時点で、速やかにＢｋ現像スリーブを不作動状態にする。これは少なくとも、次のＣ画像データによるＣ潜像の先端部が到達する前に完了させる。
【００６３】
ついで、感光体９上に形成したＢｋトナー像を、感光体９と同一周速で回転されている中間転写ベルト１９の表面に転写する（以下、感光体９から中間転写ベルト１９へのトナー像転写をベルト転写と称する）。ベルト転写は、感光体９と中間転写ベルト１９とが接触した状態において、ベルト転写バイアスローラ２０に所定のバイアス電圧を印可することで行う。なお、中間転写ベルト１９には感光体９に順次形成するＢｋ、Ｃ、Ｍ、Ｙのトナー像を同一面に順次位置合わせして、４色重ねのベルト転写画像を形成し、その後、用紙に一括転写を行う。
【００６４】
ここに、感光体９側では、Ｂｋ工程の次に、Ｃ工程に進むが、所定のタイミングからスキャナ１によるＣ画像データの読取りが始まり、そのＣ画像データに基づき、書込光学ユニット８が、レーザー光による光書き込み・Ｃ潜像の形成を開始する。Ｃ現像器１５はその現像位置に対して、Ｂｋ潜像の後端部が通過した後で、かつ、Ｃ潜像が到達する前にＣ現像スリーブの回転を開始し、Ｃ潜像をＣトナーで現像する。その後、Ｃ潜像領域の現像動作を続けるが、Ｃ潜像の後端部が通過した時点で、Ｂｋ現像器の場合と同様にＣ現像スリーブを不作動状態にする。これもやはり、次のＭ潜像の先端部が到達する前に完了させる。なお、Ｍ及びＹの工程については、それぞれの画像データの読取り・潜像形成・現像の動作が、ＢＫ、Ｃの工程と同じであるので、説明は省略する。
【００６５】
中間転写ベルトユニットは、複数のローラ群を中間転写ベルト１９で巻回した構成である。中間転写ベルト１９は、ベルト転写バイアスローラ２０、駆動ローラ２１、及び従動ローラに張られており、図示しない駆動モータにより駆動制御される。ベルトクリーニングユニット２２はブラシローラ、ゴムブレード、及び中間転写ベルト１９からの接離機構などで構成されており、１色目のＢｋ画像をベルト転写した後で、２、３、４色目をベルト転写している間は、ベルトクリーニングユニット２２を接離機構により、ベルト面から離間させておく。
【００６６】
紙転写ユニット２３は、紙転写バイアスローラ、ローラクリーニングブレード、及び上記中間転写ベルト１９からの接離機構などで構成されている。通常、紙転写バイアスローラは、中間転写ベルト１９面から離間しているが、中間転写ベルト１９面に形成された４色重ねのトナー像を用紙に一括転写する時に、タイミングを取って接離機構で押圧される。給紙バンク内の用紙カセット３０、３１、３２、３３には、各種サイズの用紙が収納されており、図示しない操作パネルで指定されたサイズの用紙カセットから、給紙コロによってレジストローラ２６の方向に給紙・搬送される。
【００６７】
画像形成が行われる時期に、用紙は、いずれかの用紙カセット３０、３１、３２、３３から給送され、レジストローラ２６のニップ部で待機している。そして、転写バイアスローラに中間転写ベルト１９上のトナー画像がさしかかるときに、ちょうど用紙の先端が、その画像先端に一致するようにレジストローラ２６が駆動され、用紙とトナー画像のレジスト合わせが行われる。ここで、転写バイアスローラに所定のバイアス電圧を印加して用紙への一括転写が行われる。中間転写ベルト１９から４色重ねのトナー像を一括転写された用紙は、搬送ベルトユニット２７上を定着装置２８方向へ搬送される。
【００６８】
搬送ベルトユニット２７は、２つのベルトローラ、搬送ベルト、２つの紙吸着用ファンなどで構成されており、２つのベルトローラのうちのいずれかが駆動ローラであり、この駆動ローラが駆動されると搬送ベルトが反時計方向に回転する。また、搬送ベルトのベルト面に多数の孔が設けられており、ベルト面が通気可能な構成となっている。
【００６９】
搬送ベルト２７ｃ内に設けられた２つの紙吸着用ファン２７ｄは、図示しない駆動手段により駆動されるものである。これらの紙吸着用ファン２７ｄは、その上下に位置する２枚のベルト面を通気させるようにファンが駆動され、搬送される用紙を搬送ベルトの面にひきつけるように吸着させてベルト面からの浮きを防止し、搬送力を高めるものである。
【００７０】
定着装置２８は、定着ローラ２８ａ、加圧ローラ２８ｂ、及びケース２８ｃなどにより構成されている。定着ローラ２８ａと加圧ローラ２８ｂは、それぞれの中空内部にハロゲンヒータなどで構成された熱発生手段が内装されており、図示しないサーミスタを介した温度制御により所定の高温に維持され、トナーを溶融可能としている。
【００７１】
搬送ベルトユニット２７により定着装置２８へ搬送された用紙は、所定の高温に維持された定着ローラ２８ａと加圧ローラ２８ｂとのニップ部でトナー像を溶融定着された後、排出ローラにより装置本体外に排出され、コピートレイ２９上に表向きにスタックされ最終的なフルカラーコピーを得ることができる。
【００７２】
なお、ベルト転写後の感光体９は、クリーニング前除電器、ブラシローラそしてゴムブレードなどで構成された感光体クリーニングユニット１０で表面をクリーニングされ、除電ランプ１１で均一に除電される。また、中間転写ベルト１９は、用紙へのトナー画像を転写した後、クリーニングユニット２２を再び接離機構で押圧され表面をクリーニングされる。
【００７３】
定着装置２８の近傍にサーモスタットスイッチ４０が配置されており、また、感光体９の近傍で電位センサ１３の近くにはサーモスタットスイッチ４１が設置されている。これらサーモスタットスイッチ４０，４１は周囲の温度変化により作動するスイッチである。
【００７４】
上述した画像形成動作の説明は、４色フルカラーを得るコピーモードの説明であったが、３色、又は２色モードの場合は、指定された色と回数の分について、上記と同様の動作を行う事になる。また、単色コピーモードの場合は、所定枚数が終了するまでの間、その色の現像器のみを現像作動状態にして、中間ベルト１９は、感光体９面に接触したまま往動方向に一定速度で駆動し、さらに、クリーニングユニット２２も中間転写ベルト１９に押圧した状態のまま連続してコピー動作を行う。
【００７５】
【発明の効果】
以上のように、本発明によれば、増幅回路の増幅範囲でデジタル信号を目標とする値に設定できない場合には、Ａ／Ｄ変換回路の特定の系統同士同じ割合でリファレンス電圧を変更するので、Ａ／Ｄ変換回路の性能を充分に引き出して使用することができ、地肌除去モードに於いてもデジタル信号のダイナミックレンジは大きく確保できるので、シェーディング補正演算結果の丸め込み量も小さくでき、これにより実効的な階調数が確保でき、ガサツキ感の無い綺麗な画像を得ることができる。
【図面の簡単な説明】
【図１】本発明の一実施形態における画像読取装置の概略構成を示す図である。
【図２】ＣＣＤの構成を示すもので、（ａ）はセンサ列を示す図、（ｂ）はＣＣＤの出力関係を説明するための図である。
【図３】読取基板と画像処理部の主要構成を示すブロック図である。
【図４】図３のゲインアンプの特性の一例を示すグラフである。
【図５】図３のオフセット設定部の特性の一例を示すグラフである。
【図６】図３のＤ／Ａコンバータの出力分圧の一例を示す回路図である。
【図７】アナログ画像信号の上限基準値と加減基準値の出力系統を示す回路図である。
【図８】主走査方向のタイミングチャートである。
【図９】副走査方向のタイミングチャートである。
【図１０】ＣＣＤにおける副走査方向を説明するための図である。
【図１１】ＷＴＧＴＧとＡＥの組合せによりＡ／Ｄコンバータに何を出力するか選択するための組合せの一例を示す表である。
【図１２】ＷＴＧＴ＊によりＡ／Ｄコンバータに何を出力するか選択するための組合せの一例を示す表である。
【図１３】本実施形態における処理過程を示すフローチャートである。
【図１４】図１３のＡに続くステップを示すフローチャートである。
【図１５】図１４のＢに続くステップを示すフローチャートである。
【図１６】図１の画像読取装置を備えた画像形成装置の一例の概略構成を示す図である。
【符号の説明】
１ 画像読取装置
４ 光源
８ 書込光学ユニット
８ａ レーザー発光手段
９ 感光体
１２ 帯電器
１４ Ｂｋ現像器
１５ Ｃ現像器
１６ Ｍ現像器
１７ Ｙ現像器
１９ 中間転写ベルト
２８ 定着装置
４１ 基準白板
４２ ＣＣＤ
４３ 画像処理部
５３ ゲインアンプ
５４ オフセット設定部
５５ Ｐ／Ｈ回路
５６ Ａ／Ｄコンバータ
５７ Ｄ／Ａコンバータ
５８ セレクタ
６１ ＣＰＵ
６２ 不揮発性メモリ
６３ オフセットレベル検出回路
６８ 画像処理回路
１００ プリンタ部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image reading control method for reading image information of an original by an optical reading element, an image reading apparatus that implements the method, and an image forming apparatus using the image reading apparatus.
[0002]
[Prior art]
In image forming apparatuses such as a printer, a scanner, a copying machine, and a facsimile, an image reading apparatus that optically reads a document image is used. In such an image reading apparatus, an analog image signal from a line sensor that has read an image is input to an A / D conversion circuit to obtain a digital signal. At this time, in order to sufficiently use the performance of the A / D conversion circuit, the analog image signal is input to the A / D conversion circuit with a large dynamic range within a range not exceeding the reference voltage of the A / D conversion circuit. Is desirable. For this reason, the analog image signal when the reference white plate is read by using an amplifier that can vary the amplification amount of the analog image signal is conventionally about 80% of the reference voltage of the A / D converter circuit (in accordance with the margin concept, the percentage is The input was amplified so that it would be different). However, the amplification amount variable width of the amplifier is finite, such as 2 to 10 times. The amount of amplification is determined by the magnitude of the analog image signal input to the A / D conversion circuit, but the magnitude of the analog image signal varies from machine to machine due to various factors. Factors include variations in the amount of light source, line sensor sensitivity, reference white plate density, mechanical dimensions, and the like.
[0003]
In the conventional method, an amplifier having a wide variable range is required so as to cover the minimum to maximum range of the analog image signal even if these variation factors are taken into consideration. The design of such an amplifier is technically difficult and costly. Recently, an IC in which processing up to inputting the line sensor output to the A / D conversion circuit is contained in one package is used. Since the variable range of the amplifier contained therein is determined in advance, it is necessary to add an amplifier serially outside in order to further widen the variable range.
[0004]
In Patent Document 1, a reading unit that reads reflected light from a document, a storage unit that stores temporal deterioration data of the light source, a timing unit that measures the cumulative lighting time of the light source, and a light source from the storage unit Compensation means is provided to compensate for the decrease in output of the reading means based on the deterioration data with time and the cumulative lighting time from the time measuring means for measuring the cumulative lighting time of the light source. It has been proposed that the white peak reference voltage of the A / D conversion means for converting to A is changed so as to suppress the influence of deterioration of the light source by the A / D conversion means.
[0005]
[Patent Document 1]
JP 2000-232579 A
[0006]
[Problems to be solved by the invention]
In the above-mentioned Patent Document 1, with respect to a light quantity decrease that is one of the variation factors, a light quantity reduction rate is predicted and the reference voltage of the A / D conversion circuit is changed. The reference voltage is changed based on this, and considering the variation in light source deterioration (there is a light quantity that is larger or smaller than the representative value after the same time elapses), there is a problem that is not necessarily an optimal correction. .
[0007]
The present invention has been made in view of the situation of the prior art as described above, and its purpose is to have an amplifier and an A / D conversion circuit having a variable range of an appropriate amount of amplification, and sufficiently draw out their performance. The purpose is to enable extraction of a highly accurate digital signal.
[0008]
[Means for Solving the Problems]
In order to achieve the object, the first means includes an illuminating means for irradiating the subject with light, a line sensor for outputting analog image signals corresponding to the reflected light or transmitted light of the subject divided into a plurality of systems, An amplification circuit that amplifies the analog image signal output from the line sensor by the designated amplification amount, an A / D conversion circuit that converts the output signal of the amplification circuit into a digital signal, and a reference voltage of the A / D conversion circuit In the image reading control method of the image reading apparatus having the means for changing the reference signal, the reference member for obtaining the subject and the correction data when the digital signal does not fall within the arbitrary range within the arbitrary amplification range of the amplification circuit The reference voltage of the A / D conversion circuit used when reading the signal is changed at the same rate for each of the specific systems. That is, for example, if the value of one system of green cannot be adjusted to an arbitrary value with a line sensor with a total of 6 outputs of 2 systems each of red, green, and black, the other system of green When the reference voltage of the A / D conversion circuit is changed at the same ratio together and the digital signal cannot be set to the target value within the amplification range of the amplification circuit, the specific systems of the A / D conversion circuit Since the reference voltage is changed at the same rate, the performance of the A / D converter circuit can be fully used and the digital signal dynamic range can be secured even in the background removal mode. The amount of rounding can be reduced. In addition, an effective number of gradations can be ensured, and a beautiful image with no roughness can be obtained.
[0009]
The second means is characterized in that, in the first means, only the set value related to the changed reference voltage of the A / D converter circuit is rewritten with the existing set value, and thereafter the set value is used. As a result, when the digital signal cannot be set to a target value within the amplification range of the amplifier circuit, the reference voltage of the A / D conversion circuit that reads the density reference member and the document image is changed at the same ratio, for example, a nonvolatile memory It can be saved in the time, and the time can be shortened when setting next time.
[0010]
A third means is characterized in that, in the second means, the existing set value is stored in a nonvolatile memory.
[0011]
A fourth means is characterized in that, in the first to third means, the system is constituted by providing a plurality of three systems of red, black and green.
[0012]
The fifth means includes an illuminating means for irradiating the subject with light, a line sensor for outputting an analog image signal corresponding to the reflected light or transmitted light of the subject in a plurality of systems, and an analog image signal from the line sensor. An amplification circuit that amplifies the output by the designated amplification amount, an A / D conversion circuit that converts an output signal of the amplification circuit into a digital signal, and means for changing a reference voltage of the A / D conversion circuit In the image reading apparatus, when the digital signal does not fall within an arbitrary range within an arbitrary amplification range of the amplification circuit, the A / D conversion used when reading the subject and a reference member for obtaining correction data It is characterized by having the change means which changes the reference voltage of a circuit at the same ratio between said specific systems. Thereby, an effect equivalent to that of the first means can be obtained.
[0013]
A sixth means is characterized in that the changing means of the fifth means rewrites only the set value related to the changed reference voltage of the A / D converter circuit with an existing set value, and thereafter uses the set value. An effect equivalent to that of the second means can be obtained.
[0014]
A seventh means is the sixth means, further comprising a non-volatile memory for storing the existing set value.
[0015]
The eighth means optically reads the image information of the subject as a document by the image reading device, forms a latent image on the image carrier by the optical scanning device, and develops the formed latent image. An image forming apparatus for forming an image, wherein the image reading apparatus uses image reading apparatuses of fifth to seventh means. As a result, the performance of the A / D conversion circuit can be fully utilized and used, and a large dynamic range of the digital signal can be secured even in the background removal mode, so that the rounding amount of the shading correction calculation result can be reduced. In addition, an effective number of gradations can be ensured, and a beautiful image without a feeling of roughness can be obtained.
[0016]
According to a ninth means, the image forming apparatus of the eighth means is such that the image carrier is composed of a photoconductive photosensitive member, and the photosensitive member is uniformly charged and then statically written by the optical scanning device. An electrostatic latent image is formed, the formed electrostatic latent image is developed to obtain a toner image, and the toner image is fixed on a recording medium to form an image.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0018]
FIG. 1 is a diagram showing a schematic configuration of an image reading apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing the configuration of a CCD, (a) is a diagram showing a sensor array, and (b) is a CCD output relationship. 3 is a block diagram showing the main configuration of the reading substrate and the image processing unit, FIG. 4 is a graph showing an example of the characteristics of the gain amplifier of FIG. 3, and FIG. 5 is a diagram of the offset setting unit of FIG. FIG. 6 is a circuit diagram showing an example of output voltage division of the D / A converter of FIG. 3, FIG. 7 is a circuit diagram showing an output system of an upper limit reference value and an adjustment reference value of an analog image signal, 8 is a timing chart in the main scanning direction, FIG. 9 is a timing chart in the sub scanning direction, and FIG. 10 is a diagram for explaining the sub scanning direction in the CCD.
[0019]
In the image reading apparatus 1, a contact glass 2 and a reference white plate 41 are disposed on the top thereof. The contact glass 2 is for setting an original on the original when reading the original. Although not shown in FIG. 1, the document is suppressed from floating from the contact glass 2 by a document pressing plate called a pressure plate from above. Of course, a known document feeder (ADF) may be provided. The reference white plate 41 is a substantially white member having a uniform density provided in the main scanning direction for obtaining correction data at the time of shading correction.
[0020]
Inside the image reading apparatus 1, a light source 4 that irradiates the reading surface at a certain angle with respect to the surface of the reference white plate 41 or the contact glass 2, and three first sheets that reflect the light reflected by the reference white plate 41 or the document. Second and third mirrors 5a, 5b, 5c, a lens 6 that forms an image of the reflected light from the third mirror 5c, and a line sensor that converts the reflected light into an analog image signal by the lens 6 (this embodiment) In the embodiment, a three-line CCD is used as a line sensor (hereinafter referred to as a CCD) 42, a reading board 7 provided with various circuits to be described later for converting an image signal from the CCD 42 into a digital signal, and a reading board 7 and an image processing unit 43 having various circuits to be described later for processing image data from 7. The light source 4 and the first, second, and third mirrors 5a, 5b, and 5c form first and second traveling bodies (not shown in FIG. 1), respectively, and the distance between the reading document surface and the CCD 42 is driven by the motor 44. It moves in the sub-scanning direction while keeping it constant. The CCD 42 outputs an analog image signal corresponding to the amount of incident light, converts it to a digital signal by the reading substrate 7, and then passes it to the image processing unit 11 as image data.
[0021]
As shown in FIG. 2A, the CCD 42 has three lines of sensor rows of R (red), G (green), and B (black) arranged in the sub-scanning direction, and 7300 sensors are arranged in the main scanning direction. A photo sensor is arranged. In addition, R, G, and B are systems for outputting even-numbered data and odd-numbered data (so-called E / O output system). In this embodiment, as shown in FIG. , Ge, Go, Be, and Bo have 6 outputs.
[0022]
The main components of the reading substrate and the image processing unit will be described with reference to FIG. In FIG. 3, the output from the CCD 42 is described as six systems, but any number of systems such as four or eight system output types may be used. The reading substrate 7 is provided with a buffer 51, a sampling circuit 52, a gain amplifier 53, an offset setting unit 54, a P / H circuit 55, an A / D converter 56, a D / A converter 57, and a selector 58. Each analog image signal output from the CCD 42 is driven by a buffer 51 and sampled and held by a sampling circuit 52 to remove high-frequency components such as reset noise.
[0023]
The gain amplifier 53 is a variable gain amplifier whose gain can be controlled by a voltage Vg ** applied to the control terminal, as shown in a characteristic example in FIG. Moreover, the offset setting part 54 has a function which provides an offset with the voltage: Vof ** applied to a control terminal so that the example of an offset setting characteristic may be shown in FIG. Vg ** and Vof ** are voltages determined by the CPU 61 described later by operating the D / A converter 57. For example, in the case of an 8-bit D / A converter, the CPU 61 sets any value from 0 to 255 to the D / A converter 57, and the D / A converter 57 outputs a corresponding voltage. In addition, ** of Vg ** and Vof ** is a subscript (Re, Ro, Ge, Go, Be, Bo) corresponding to the output of the CCD 42 in FIG. 2, and is set for each of the six systems. The Further, as shown in FIG. 3, the output voltage of the D / A converter 57: Vg **, Vof **, Vrefw *, and Vrefd * are directly used for the A / D converter via the gain amplifier 53, the offset setting unit 54, and the selector 58, respectively. However, as shown in FIG. 6, the output voltage of the D / A converter 57 may be finely controlled by dividing by a resistor or the like. However, in this case, since the variable range becomes narrow, it is necessary to consider the resistance constant.
[0024]
The P / H circuit 55 is a circuit for peak-holding the background level when using the background removal reading mode. The background removal mode is a reading method in which information such as characters is emphasized except for the background density of the original. In the present embodiment, only G data is handled in the background removal mode. Only the Ge system and Go system signals are connected to the P / H circuit 55, and a voltage obtained by multiplying the voltage corresponding to the reflectance of the background document by an arbitrary gain is peak-held.
[0025]
The A / D converter 56 converts the analog image signal into a digital image signal with a predetermined resolution (for example, 10 bits) based on the upper limit reference value: Vreft * and the lower limit reference value: Vrefb. The digital image signal from the A / D converter 56 is input to an offset level detection circuit 63 and an offset level subtraction circuit 64 of the image processing board 60 of the image processing unit 11 described later. Here, Vreft * and Vrefw * and Vrefd * described later are either R, G, or B, and will be described in detail later.
[0026]
The upper reference value of the A / D converter: Vreft * is the output of the selector 58. The selector 58 is configured to receive the Vrefw * and Vrefd * determined by the CPU 61 by operating the D / A converter 57 and the output of the P / H circuit 55: Vph.
[0027]
Here, the part paying attention to the reference voltage of the A / D converter will be described in detail with reference to FIG. Each output of the Ge, Go, Re, Ro, Be, and Bo systems of the CCD 42 is subjected to predetermined processing and input to the A / D converter 56. In FIG. 7, the A / D converter 56 is divided into six systems of Ge, Go, Re, Ro, Be, and Bo, and the selector 58 is also divided into three. The reference voltage lower limit reference value Vrefb is common to the A / D converters 56-1, 56-2,... 56-6, and uses the output of the D / A converter 57. Although the buffer is bitten to reduce the impedance, it is omitted here. Further, Vrefb may be a fixed voltage.
[0028]
The upper reference value of the reference voltage of the A / D converters 56-1 and 56-2 related to the Ge and Go systems is a connection that commonly uses the output of the selector 58-1 to which Vph, VrefwG, and VrefdG are input. The upper reference value of the reference voltage of the A / D converters 56-3 and 56-4 related to the Re and Ro systems is a connection that commonly uses the output of the selector 58-2 to which VrefwR and VrefdR are input. Similarly for the Be and Bo systems, the upper reference value of the reference voltage of the A / D converters 56-5 and 56-6 is a connection that commonly uses the output of the selector 58-3 to which VrefwB and VrefdB are input. The operation of the selector will be described later separately.
[0029]
An image processing board 43 of the image processing unit 11 includes a CPU 61, a nonvolatile memory 62, an offset level detection circuit 63, an offset level subtraction circuit 64, a white level detection circuit 65, a shading data storage circuit 66, and shading. A correction circuit 67 and an image processing circuit 68 are provided. The CPU 61 refers to the setting data stored in the nonvolatile memory 62 and sets data in the D / A converter 57. The D / A converter 57 outputs Vrefw * and Vrefd * according to the set data. Although not shown, the interface between the CPU 61 and the nonvolatile memory 62 is connected by a signal line related to address, data, and control, and data related to the value of Vrefw * or Vrefd * can be written and stored. It has a possible configuration.
[0030]
The offset level detection circuit 63 has a function of capturing and storing the output of the A / D converter 56 corresponding to the OPB pixel of the CCD 42 during the period when the xopb signal is asserted. FIG. 8 shows a timing chart in the main scanning direction. The stored offset level is an average value obtained by capturing a plurality of OPB pixels, and is stored for each output system of the CCD 42.
[0031]
The offset level subtraction circuit 64 is a circuit that subtracts the value stored in the offset level detection circuit 63 from the output value of the input A / D converter 56. The white level detection circuit 65 is a circuit that calculates and stores an average value of digital image signals input within a range in which the xlgate signal and the SMPL * signal are asserted, and timing examples are shown in FIGS. Show.
[0032]
The CPU 61 can obtain the latest offset level value and white level value by accessing the offset level detection circuit 63 and the white level detection circuit 65. Further, the shading data storage circuit 66 is a circuit that sequentially stores values read from the reference white plate 41 while performing processing such as averaging for each pixel, and the shading correction circuit 67 includes digital image data obtained by reading an image and This is a circuit that performs a correction operation on the reference whiteboard data stored in the shading data storage circuit 66. The CPU 61 can read the value of the specific pixel from the shading data storage circuit 66.
[0033]
The timing chart in the main scanning direction in FIG. 8 shows the relationship between the output of the CCD 42, the output of the sampling circuit 52, the output of the A / D converter 56, and xopb and xlgate in the main scanning direction. The CCD 42 has a sensor unit that is physically shielded called optical black (OPB), and then has a sensor unit that outputs a voltage proportional to the amount of incident light called an effective pixel. The data of the OPB portion and the effective pixel portion are repeatedly output every main scanning period. The output of the A / D converter 56 is output with a predetermined delay when digitized. xopb is an offset level data range instruction signal that is designed to be asserted for a predetermined period at the output timing of the A / D converter 56 corresponding to OPB. Usually, it is known from experience that the latter half of the OPB uses less noise, and this is also described in this embodiment. The last xlgate is a signal that is asserted in the area where the original in the effective pixel portion is read, and is used to specify a range when detecting the white level.
[0034]
The timing chart in the sub-scanning direction in FIG. 9 shows signals in the sub-scanning direction, SYNCB, WTGT *, AE, PHLD, and SMPL *. Here, * of WTGT * and SMPL * is any of R, G, and B. Because of the physical conditions of the CCD described in the lower part of FIG. 9, when reading a certain point on the reference white plate 41 or the original, it is read in the order of R, G, B shifted by the number of X lines. This is because the timing signal also needs to be shifted corresponding to R, G, and B. SYNCB is a timing signal for starting main scanning. WTGT * is a signal asserted at the timing when the CCD reads the reference white plate 41, and is used as a switching signal for the selector 58 in FIGS.
[0035]
AE is an enable signal for the P / H circuit 55, and is asserted only at the timing of reading the reference white plate 41 or reading the original as described by the solid line in the background removal reading mode. Further, when not in the background removal reading mode, it is negated even at the timing of reading the reference white plate 41 or reading the document as indicated by the dotted line. While this signal is negated, the P / H voltage is reset.
[0036]
PHLD is a signal for background processing of a specific portion of the document during the period when AE is asserted in the background removal reading mode, and is H: sampling and L: hold. Also in PHLD, the dotted line portion indicates the background removal reading mode, and the solid line portion indicates the background removal reading mode. SMPL * is asserted for all or part of the timing of reading the reference white plate 41 (WTGT *), and instructs the shading data storage circuit 66 to take in the data of the reference white plate 41. A is the number of lines corresponding to the time required to charge the peak hold circuit, B is X * N / 100 + A (line), and C is (X + Y) * N / 100 + A (line). Here, as shown in FIG. 11, X is the number of lines corresponding to rejection between R / G elements at the same magnification reading, and Y is a line corresponding to rejection between R / B elements at the same magnification reading. The number N is an equal magnification (for example, an arbitrary value between 25 and 400 [%]).
[0037]
As shown in FIGS. 3 and 7, the output (Vph) of the P / H circuit 55, VrefwG, and VrefdG are input to the selector 58 for the Ge and Go systems (58-1 in FIG. 7). , What is output to the A / D converter 56 is selected by a combination of WTGTG and AE. An example of the combination is shown in FIG.
[0038]
As described above, in the case of the background removal mode reading of the Ge and Go systems, the reference white plate 41 and the original are read by the upper reference voltage of the A / D converter 56: Vreft = Vph. When reading is not performed in the background removal mode, VrefG is selected when the reference white plate 41 is read, and VrefdG is selected when reading the document.
[0039]
On the other hand, the selector 58 for the Re, Ro system and the Be, Bo system (58-2, 58-3 in FIG. 7) does not receive the P / H output (Vph), but only Vrefw * and Vrefd *. What is to be output to the A / D converter 56 is selected by WTGT *. An example of the combination is shown in FIG.
[0040]
As described above, the Ge and Go systems, the Re and Ro systems, and the Be and Bo systems change in pairs when the upper reference voltage is changed.
[0041]
If (the upper reference voltage when reading the reference white plate 41−the lower reference voltage) and (the upper reference voltage when reading the original−the lower reference voltage) are not managed at a predetermined ratio, the balance of RGB after shading correction is achieved. When the upper reference voltage of one (for example, for reading the reference white plate 41) is changed, the upper reference voltage of the other (original reading side) is also changed. This is performed by data set in the D / A converter 57 by the CPU 61. In this case, the CPU 61 writes the changed upper reference data (for reading the reference white board 41 and for reading the document) into the nonvolatile memory 62 in order to set the next data in the D / A converter 57.
[0042]
As described above, even when the reference voltage is changed, specific systems (Ge and Go systems, Re and Ro systems, or Be and Bo systems) can be changed at the same rate.
[0043]
In order to obtain the digital image signal with high accuracy by fully exhibiting the accuracy of the A / D converter 56, the analog image signal uses a large difference between the upper limit reference value and the lower limit reference value of the A / D converter 56. Is advantageous. However, the size of the analog image signal before being converted into the digital image signal varies from machine to machine due to factors such as the light amount of the light source 4, the sensitivity of the CCD 42, the density of the reference white plate 41, and the mechanical dimensions. Therefore, even if the gain can be adjusted at the limit of the variable range at that time, the gain cannot be adjusted within the variable range if there is a change in the amount of light with time.
[0044]
Further, since the digital image data read from the document 3 is subjected to shading correction using the data of the reference white plate 41 stored in the shading data storage circuit 66, the size of the corrected digital image data is that of the reference white plate 41. It depends on the data. For this reason, if the ratio between the data of the reference white plate 41 and the digital image data obtained by reading the document 3 having the specified density is not standardized to a constant value, the corrected digital image data is obtained even when the document 3 having the same density is read. It is not preferable because it will vary between machines. This is called gray balance adjustment, and the reference voltage of the A / D converter 56 is adjusted when the reference white plate 41 is read and when the document 3 is read. Since this adjustment is performed using a document having a specified density, it is generally performed at the time of shipment from the factory, and the adjustment result is stored in the nonvolatile memory 62.
[0045]
Next, control for controlling the gain of the gain amplifier 53 and the reference voltage of the A / D converter 56 to set the output value of the A / D converter 56 to an appropriate level and maintaining the gray balance will be described. . Such control is control that can be used in the following cases.
[0046]
(1) Correction when the A / D converter output level deviates greatly from the standard value due to the light quantity, CCD sensitivity, and other factors before gray balance adjustment at the time of shipment from the factory.
[0047]
(2) Correction of A / D converter output drop due to light quantity drop over time.
[0048]
Hereinafter, control in the present embodiment will be described with reference to FIGS. 13 to 15. FIG. 13 is a flowchart showing the process in this embodiment, FIG. 13 is a flowchart showing the steps following A in FIG. 13, and FIG. 15 is a flowchart showing the steps following B in FIG. Here, the processing of each R, G, B E / O2 system when there are 6 CCD output systems of Re, Ro, Ge, Go, Be, Bo is described, and is performed for each color. . Further, at the start of FIG. 13, the output of the D / A converter 56: Vof ** is already set so that the offset level becomes a predetermined level with respect to the lower reference voltage: Vrefb of the A / D converter 56. It shall be. The predetermined level mentioned here is a value with a margin that does not become Vrefb or less (A / D converter output is 0 or less) even when noise and temperature fluctuations are taken into consideration.
[0049]
The CPU 61 sets values of gain: Vg ** and reference voltage for reading the reference white plate 41: Vrefw * (step 1001). Here, the reference voltage for reading: Vrefw * of the reference white plate 41 reflects the value set by the CPU 61 in the D / A converter 57 with reference to the contents of the nonvolatile memory 62. Next, WTGT * is asserted, AE is negated, Vrefw * is selected as the upper reference voltage of the A / D converter 57, and a carriage such as a light source is moved to the reference white plate 41 (step 1002). Then, the reference white plate 41 is read, and the CPU 61 reads the peak values Dwp * e and Dwp * o in the main scanning line from the white level detection circuit 65 (step 1003).
[0050]
Next, the CPU 61 determines whether the peak data: Dwp * e and Dwp * o are both within the standard value: Dp ± B (step 1004). Dp is an adjustment target value, which is a value with a slight margin so that the peak value of the analog image signal input to the A / D converter 56 does not exceed the upper reference voltage. This is because the performance of the A / D converter 56 is sufficiently extracted to extract a highly accurate digital signal. B is an adjustment tolerance. When the peak data: Dwp * e and Dwp * o are both within the standard value: Dp ± B, the processing ends because the target level is reached.
[0051]
On the other hand, when the peak data: Dwp * e and Dwp * o are not within the standard value: Dp ± B, D for outputting the voltage: Vg ** for determining the gain so as to be within the target tolerance. / Set value of A converter 57: Svg ** is calculated (step 1005). It is determined whether or not the calculated Svg is within the settable range (SvgL to SvgH) of the D / A converter 57 (step 1006). For example, in the case of an 8-bit D / A converter 57, the settable range is 0 to 255. If the value is within the settable range, the set value Svg ** is actually set in the D / A converter 57 (step 1007), and the peak data: Dwp ** is read again. If Svg ** is outside the range that can be set in the D / A converter 57, a value close to the calculated value within the settable range: SvgL or SvgH is set (step 1008), and the peak data: Dwp ** is read again (step 1008). Step 1009).
[0052]
It is determined whether or not the peak data: Dwp * e and Dwp * o are within the standard value: Dp ± C (step 1010). If not in Dp ± C, the CPU 61 calculates the upper reference voltage of the A / D converter 56 when reading the reference white plate 41 (step 1011). C is a tolerance and indicates a range in which peak data: Dwp * e and Dwp * o can be included in the target value: Dp ± B if the gain is changed.
[0053]
The relationship between the setting value of the D / A converter 57 and the reference voltage is represented by Vrefw * = f (D / AC setting value), and the inverse function of f (D / AC setting value) is D / AC setting value = g ( Vrefw *), the Vrefd D / A converter setting value to be changed: Srefw *

Indicated by here,
Dp is the peak data expected after changing the D / A converter set value for Vrefw **
Stp is the D / A converter setting value when the peak value Dwp ** is obtained
Stb is the D / A converter setting value of Vrefb
It is.
[0054]
Next, it is determined whether Srefw * of the calculation result is within a settable range (SrefwL to SrefwH) of the D / A converter 57 (step 1012). For example, in the case of an 8-bit D / A converter 57, the settable range is 0 to 255. If the value is within the settable range, it is actually set (step 1013), the process returns to step 1010 again, and peak data: Dwp * e and Dwp * o are read. If the calculation result Srefw is outside the settable range of the D / A converter, it is an error, but a value close to the calculated value is set within the settable range (step 1014), and the process ends.
[0055]
On the other hand, if the peak data: Dwp * e and Dwp * o are within the standard value: Dp ± C in step 1010, the same processing as step 1003 to step 1007 is performed. That is, the voltage that determines the gain: Vg ** is changed and the peak data: Dwp * e and Dwp * o are read (step 1015), and it is determined whether or not these peak data are within the standard value: Dp ± B. (Step 1016). When the peak data: Dwp * e and Dwp * o are not within the standard value: Dp ± B, D for outputting the voltage: Vg ** for determining the gain so as to fall within the target tolerance. / A converter 57 set value: Svg ** is calculated (step 1017), and it is determined whether or not the calculated Svg is within the settable range (SvgL to SvgH) of the D / A converter 57 (step 1018). If the value is within the settable range, the set value Svg ** is actually set in the D / A converter 57 (step 1019), and the peak data: Dwp ** is read again.
[0056]
When the peak data: Dwp * e and Dwp * o fall within the standard value: Dp ± B, Vrefd * is also changed by the rate at which Vrefw * is changed with reference to Vrefb (step 1020). When the reference voltage for reading of the reference white plate 41 before and after the change is Vrefw * ′ and Vrefw *, the reference voltage for reading the document before and after the change is Vrefd * ′ and Vrefd *, and the lower reference voltage is Vrefb, respectively.

Vrefd is changed so that That is, the set value of the D / A converter 57 is set to output Srefd * that satisfies the above equation. Further, Srefw * and Srefd * are stored in the nonvolatile memory 62.
[0057]
In step 1016, if the peak data: Dwp * e and Dwp * o do not fall within the standard value: Dp ± B, it is an error, but a value close to the calculated value is set within the settable range (step 1021). ,finish.
[0058]
FIG. 16 illustrates an example of an image forming apparatus provided with the image reading apparatus described above. FIG. 16 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including the image reading apparatus of FIG. In this example, a case where the present invention is applied to a color copying machine is taken as an example.
[0059]
Based on the color separation image signal intensity levels of R, G, and B obtained by the image reading device 1, color conversion processing is performed by an image processing unit (not shown), and black (hereinafter referred to as Bk), cyan (hereinafter referred to as “k”). Each color image data of C), magenta (hereinafter referred to as M), and yellow (hereinafter referred to as Y) is obtained. These color image data are visualized by Bk, C, M, and Y by a printer unit 100 described below to obtain a final color copy.
[0060]
In the printer unit 100, the writing optical unit 8 converts the color image data from the scanner 1 into an optical signal, performs optical writing corresponding to the original image, and forms an electrostatic latent image on the drum-shaped photoconductor 9. To do. The writing optical unit 8 includes a laser light emission means 8a, a light emission drive control unit (not shown), a polygon mirror 8b, a rotation motor 8c of the polygon mirror 8b, an fθ lens 8d, a reflection mirror 8e, and the like.
[0061]
The photoconductor 9 rotates counterclockwise as indicated by an arrow. Around the photoconductor 9, a photoconductor cleaning unit 10, a charge removal lamp 11, a charger 12, a potential sensor 13, a Bk developer 14, a C developer 15, An M developing device 16, a Y developing device 17, a developing density pattern detector 18, an intermediate transfer belt 19, and the like are arranged.
[0062]
Each of the developing devices 14 to 17 includes a developing sleeve that rotates so that the developer faces the photoconductor 9 in order to develop the electrostatic latent image, a developing paddle that rotates to pump up and stir the developer, and It is composed of a toner density detection sensor for the developer. Here, assuming that the order of developing operations (color image forming order) is Bk, C, M, and Y, the operation will be described below. (However, the image forming apparatus is not limited to this.)
When the copying operation is started, reading of the BK image data is started at a predetermined timing by the scanner 1, and optical writing / latent image posting by the laser beam of the writing optical unit 8 is started based on this image data (hereinafter, referred to as “below”). An electrostatic latent image based on Bk image data is referred to as a Bk latent image, and C, M, and Y are similarly referred to as a C latent image, an M latent image, and a Y latent image). Each of the developing units 14 to 17 is in a development inoperative state in the standby state, but when the Bk latent image is formed, the development is performed from the leading end of the Bk latent image. Before the leading edge of the Bk latent image arrives, the Bk developing sleeve starts to rotate and develops the Bk latent image with Bk toner. Thereafter, the developing operation of the Bk latent image area is continued, but when the rear end portion of the Bk latent image has passed the Bk developing position, the Bk developing sleeve is quickly deactivated. This is completed at least before the leading edge of the C latent image by the next C image data arrives.
[0063]
Next, the Bk toner image formed on the photoconductor 9 is transferred to the surface of the intermediate transfer belt 19 rotated at the same peripheral speed as the photoconductor 9 (hereinafter, the toner image from the photoconductor 9 to the intermediate transfer belt 19). Transfer is called belt transfer). The belt transfer is performed by applying a predetermined bias voltage to the belt transfer bias roller 20 in a state where the photoconductor 9 and the intermediate transfer belt 19 are in contact with each other. The intermediate transfer belt 19 sequentially aligns the Bk, C, M, and Y toner images formed on the photoconductor 9 on the same surface to form a four-color superimposed belt transfer image, and then onto the paper. Perform batch transfer.
[0064]
Here, on the photoconductor 9 side, the process proceeds to the C process after the Bk process. Reading of the C image data by the scanner 1 starts from a predetermined timing, and the writing optical unit 8 is based on the C image data. Starts optical writing with laser beam and formation of C latent image. The C developing unit 15 starts the rotation of the C developing sleeve after the rear end of the Bk latent image has passed with respect to the developing position and before the C latent image arrives. Develop with. Thereafter, the developing operation of the C latent image area is continued, but when the rear end portion of the C latent image passes, the C developing sleeve is made inoperative as in the case of the Bk developing device. This is also completed before the leading edge of the next M latent image arrives. The operations of M and Y are the same as the steps of BK and C, respectively, because the operations of reading image data, forming a latent image, and developing are the same as those of steps BK and C.
[0065]
The intermediate transfer belt unit has a configuration in which a plurality of roller groups are wound around an intermediate transfer belt 19. The intermediate transfer belt 19 is stretched around a belt transfer bias roller 20, a drive roller 21, and a driven roller, and is driven and controlled by a drive motor (not shown). The belt cleaning unit 22 includes a brush roller, a rubber blade, and a contact / separation mechanism from the intermediate transfer belt 19. After the first color Bk image is transferred onto the belt, the second, third, and fourth colors are transferred onto the belt. During this time, the belt cleaning unit 22 is separated from the belt surface by the contact / separation mechanism.
[0066]
The paper transfer unit 23 includes a paper transfer bias roller, a roller cleaning blade, and a contact / separation mechanism from the intermediate transfer belt 19. Normally, the paper transfer bias roller is separated from the surface of the intermediate transfer belt 19, but when the four-color superimposed toner images formed on the surface of the intermediate transfer belt 19 are collectively transferred onto the paper, the contact / separation mechanism is timed. Is pressed. Various sizes of paper are stored in the paper cassettes 30, 31, 32, and 33 in the paper supply bank. From the paper cassette of the size specified on the operation panel (not shown), the direction of the registration roller 26 by the paper supply roller. Is fed and transported.
[0067]
At the time when image formation is performed, the paper is fed from one of the paper cassettes 30, 31, 32, 33 and is waiting at the nip portion of the registration roller 26. When the toner image on the intermediate transfer belt 19 approaches the transfer bias roller, the registration roller 26 is driven so that the leading edge of the sheet coincides with the leading edge of the image, and the registration of the sheet and the toner image is performed. . Here, a predetermined bias voltage is applied to the transfer bias roller to perform batch transfer onto the sheet. The sheet onto which the four-color superimposed toner images have been collectively transferred from the intermediate transfer belt 19 is conveyed on the conveyance belt unit 27 toward the fixing device 28.
[0068]
The conveyor belt unit 27 includes two belt rollers, a conveyor belt, and two paper suction fans. One of the two belt rollers is a driving roller, and when the driving roller is driven. The conveyor belt rotates counterclockwise. In addition, a number of holes are provided in the belt surface of the conveyor belt so that the belt surface can be ventilated.
[0069]
The two paper suction fans 27d provided in the transport belt 27c are driven by a driving means (not shown). These paper suction fans 27d are driven so as to ventilate the two belt surfaces located above and below them, and suck the paper to be transported so as to attract the surface of the transport belt and lift it from the belt surface. Is to increase the conveying force.
[0070]
The fixing device 28 includes a fixing roller 28a, a pressure roller 28b, a case 28c, and the like. The fixing roller 28a and the pressure roller 28b have heat generation means composed of a halogen heater or the like inside each hollow, and are maintained at a predetermined high temperature by temperature control via a thermistor (not shown) to melt the toner. It is possible.
[0071]
The sheet conveyed to the fixing device 28 by the conveying belt unit 27 is melted and fixed on the toner image at the nip portion between the fixing roller 28a and the pressure roller 28b maintained at a predetermined high temperature. And is stacked on the copy tray 29 so that a final full-color copy can be obtained.
[0072]
The surface of the photoconductor 9 after the belt transfer is cleaned by a photoconductor cleaning unit 10 composed of a pre-cleaning static eliminator, a brush roller, a rubber blade, and the like, and is uniformly discharged by a static elimination lamp 11. Further, after transferring the toner image onto the paper, the intermediate transfer belt 19 is pressed again by the contact / separation mechanism with the cleaning unit 22 to clean the surface.
[0073]
A thermostat switch 40 is disposed in the vicinity of the fixing device 28, and a thermostat switch 41 is disposed in the vicinity of the photoreceptor 9 and in the vicinity of the potential sensor 13. These thermostat switches 40 and 41 are switches that are activated by changes in ambient temperature.
[0074]
The description of the image forming operation described above is the description of the copy mode for obtaining four full colors. In the case of the three-color or two-color mode, the same operation as described above is performed for the designated color and the number of times. Will do. Further, in the case of the single color copy mode, only the developing device for that color is in the developing operation state until the predetermined number of sheets is completed, and the intermediate belt 19 is kept in contact with the surface of the photosensitive member 9 at a constant speed in the forward movement direction. In addition, the cleaning unit 22 continuously performs the copying operation while being pressed against the intermediate transfer belt 19.
[0075]
【The invention's effect】
As described above, according to the present invention, when the digital signal cannot be set to the target value within the amplification range of the amplifier circuit, the reference voltage is changed at the same ratio between specific systems of the A / D converter circuit. , A / D converter circuit performance can be fully exploited, and the digital signal dynamic range can be secured even in the background removal mode, so that the rounding amount of the shading correction calculation result can be reduced. An effective number of gradations can be ensured, and a beautiful image with no roughness can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a schematic configuration of an image reading apparatus according to an embodiment of the present invention.
FIGS. 2A and 2B show a configuration of a CCD, in which FIG. 2A is a diagram showing a sensor array, and FIG. 2B is a diagram for explaining an output relationship of the CCD.
FIG. 3 is a block diagram illustrating main components of a reading substrate and an image processing unit.
4 is a graph showing an example of characteristics of the gain amplifier of FIG.
5 is a graph showing an example of characteristics of the offset setting unit in FIG. 3;
6 is a circuit diagram showing an example of output voltage division of the D / A converter of FIG. 3;
FIG. 7 is a circuit diagram showing an output system of an upper limit reference value and an adjustment reference value of an analog image signal.
FIG. 8 is a timing chart in the main scanning direction.
FIG. 9 is a timing chart in the sub-scanning direction.
FIG. 10 is a diagram for explaining a sub-scanning direction in a CCD.
FIG. 11 is a table showing an example of combinations for selecting what is output to the A / D converter by a combination of WTGTG and AE.
FIG. 12 is a table showing an example of combinations for selecting what is output to the A / D converter by WTGT *.
FIG. 13 is a flowchart showing a processing process in the present embodiment.
FIG. 14 is a flowchart showing steps subsequent to A in FIG. 13;
FIG. 15 is a flowchart showing steps subsequent to B in FIG. 14;
16 is a diagram illustrating a schematic configuration of an example of an image forming apparatus including the image reading apparatus of FIG.
[Explanation of symbols]
1 Image reader
4 Light source
8 Writing optical unit
8a Laser emission means
9 Photoconductor
12 Charger
14 Bk developer
15 C developer
16 M developer
17 Y developer
19 Intermediate transfer belt
28 Fixing device
41 standard white board
42 CCD
43 Image processing section
53 gain amplifier
54 Offset setting section
55 P / H circuit
56 A / D converter
57 D / A Converter
58 selector
61 CPU
62 Nonvolatile memory
63 Offset level detection circuit
68 Image processing circuit
100 Printer section

Claims (9)

A line sensor that outputs an analog image signal corresponding to the reflected light or transmitted light of the subject divided into a plurality of systems, an amplification circuit that amplifies the analog image signal output from the line sensor by an instructed amplification amount, and In an image reading control method for an image reading apparatus, comprising: an A / D conversion circuit that converts an output signal from an amplifier circuit into a digital signal; and a means for changing a reference voltage of the A / D conversion circuit.
When a digital signal does not fall within an arbitrary range within an arbitrary amplification range of the amplifier circuit, a reference voltage of the A / D conversion circuit used when reading a reference member for obtaining the subject and correction data is set as follows: An image reading control method, wherein each of the specific systems is changed at the same rate. 2. The image reading control method according to claim 1, wherein only the set value relating to the changed reference voltage of the A / D conversion circuit is rewritten with an existing set value, and thereafter the set value is used. 3. The image reading control method according to claim 2, wherein the existing set value is stored in a nonvolatile memory. The image reading control method according to claim 1, wherein the system is configured by providing a plurality of systems of three systems of red, black, and green. Illumination means for irradiating the subject with light, a line sensor for outputting analog image signals corresponding to the reflected light or transmitted light of the subject in a plurality of systems, and amplification instructed to output the analog image signal from the line sensor In an image reading apparatus comprising: an amplification circuit that amplifies by an amount; an A / D conversion circuit that converts an output signal of the amplification circuit into a digital signal; and means for changing a reference voltage of the A / D conversion circuit.
When the digital signal does not fall within an arbitrary range within an arbitrary amplification range of the amplifier circuit, a reference voltage of the A / D conversion circuit used when reading the reference member for obtaining the subject and correction data is set. An image reading apparatus comprising changing means for changing the specific systems at the same rate. 6. The image reading apparatus according to claim 5, wherein the changing unit rewrites only the set value related to the changed reference voltage of the A / D conversion circuit with an existing set value, and thereafter uses the set value. The image reading apparatus according to claim 6, further comprising a non-volatile memory for storing the existing setting value. Image formation in which image information of a subject that is a document is optically read by an image reading device, a latent image is formed on the image carrier by an optical scanning device, and the formed latent image is developed to form an image. An image forming apparatus using the image reading apparatus according to claim 5, wherein the image reading apparatus is an image forming apparatus. In the image forming apparatus, the image carrier is composed of a photoconductive photoconductor, and after the photoconductor is uniformly charged, an electrostatic latent image is formed by writing with the optical scanning device. The image forming apparatus according to claim 8, wherein the electrostatic latent image is developed to obtain a toner image, and the toner image is fixed on a recording medium to form an image.

Images