JP2004309293A

JP2004309293A - Photosensor and image forming apparatus

Info

Publication number: JP2004309293A
Application number: JP2003102766A
Authority: JP
Inventors: Noboru Sawayama; 昇沢山; Kayoko Ikegami; 加余子池上; Katsuo Hatase; 勝夫畑瀬
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2003-04-07
Filing date: 2003-04-07
Publication date: 2004-11-04
Anticipated expiration: 2023-04-07
Also published as: JP4110027B2

Abstract

<P>PROBLEM TO BE SOLVED: To expand a range for detecting the amount of adhesion of a body for preventing light existing on an object to be irradiated for regularly reflecting light from being reflected regularly with improved sensitivity as compared with before. <P>SOLUTION: A P sensor 30 receives regular reflection light when incident light from a light-emitting element 31 is regularly reflected on the surface of a photoreceptor drum, and detects the amount of toner adhesion on the photoreceptor drum. The P sensor is composed so that the angle between the center line of an incident light path immediately before the incident light from the light-emitting element reaches the surface of the photoreceptor drum, and the center line of a regular reflection light path immediately after reflection by the photoreceptor drum becomes 25°, thus bringing the area of the photoreceptor drum surface section that does not contribute to the regular reflection light received by the light-receiving element fully closer to the area of the photoreceptor drum surface section that the toner adhering on the photoreceptor drum surface actually occupies and hence detecting even a large amount of toner adhesion with sufficient sensitivity. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、照射対象物に対して照射した入射光の正反射光を受光する光学センサ及びこの光学センサを用いた複写機、プリンタ、ファクシミリ等の画像形成装置に関するものである。
【０００２】
【従来の技術】
この種の画像形成装置においては、安定した画像濃度を得るために、感光体等の像担持体表面に濃度検知用トナーパッチ（基準パターン）を作成し、そのパッチの濃度を光学センサにより検出するものがある。この画像形成装置では、その光学センサによる検出結果に基づき、潜像形成用の書込光強度、帯電バイアス、現像バイアス等を変更して現像ポテンシャルを調節したり、２成分現像方式の場合には現像器内のトナー濃度の目標値を調節したりするような画像濃度制御を行う。この光学センサは、基準パターンを検出対象することからＰ（パターン）センサと呼ばれ、発光手段と受光手段とを備えた反射型光学センサが一般的に用いられる。
【０００３】
反射型光学センサには、照射対象物に照射した光が正反射したときの正反射光を検出するものがあり、このような反射型光学センサは、特許文献１等に開示されている。正反射光を検出する反射型光学センサをＰセンサとして用いたときの検出原理は、感光体ドラム上のトナー濃度（トナー付着量）を検出する場合を例に挙げて説明すれば、次のとおりである。
感光体ドラムの表面（照射対象物）にトナーが付着していない場合、入射光は、感光体ドラム表面で正反射し、その感光体ドラム表面の反射率に応じた正反射光が受光素子に受光される。これに対し、感光体ドラムの表面にトナーが付着している場合、入射光がトナーに吸収されたり、トナーによって乱反射したりする。そのため、入射光が感光体ドラム表面に到達する前にトナーに遮られたり、感光体ドラム表面からの正反射光が受光素子に到達する前にトナーに遮られたりすると、正反射光が受光素子で受光されない。よって、感光体ドラムの表面上のトナー付着量が多くなるにつれて、受光素子での受光量が減ることになる。したがって、受光素子での受光量に基づいて、感光体ドラム表面上のトナー付着量を検出することができる。
【０００４】
【特許文献１】
特開昭６４−３５４５５号公報
【０００５】
【発明が解決しようとする課題】
図１２（ａ）及び（ｂ）は、照射対象物である感光体ドラム５の表面に、トナーが付着している様子を示す模式図である。Ｐセンサの図示しない発光素子から入射光Ｌ_１が照射されると、トナーＴに邪魔されなければ、その入射光Ｌ_１が感光体ドラム表面で正反射し、その正反射光Ｌ_２が図示しない受光素子で受光される。しかし、図中斜線で示す領域の入射光は、トナーＴに邪魔されて受光素子に到達することができない。正反射光を検出する場合には、入射光の光路が感光体ドラム表面の法線方向Ｚに対して傾斜している必要がある。そのため、受光素子により受光される正反射光に寄与しない感光体ドラム表面部分の面積Ｓ_１は、感光体ドラム表面に対するトナーＴの正投影面積、すなわち、感光体ドラム表面を実際にトナーが占有している部分の面積Ｓ_０よりも大きくなる。すなわち、感光体ドラム表面を実際にトナーが占有している部分の面積Ｓ_０に対する、受光素子により受光される正反射光に寄与しない感光体ドラム表面部分の面積Ｓ_１の比率（以下、「シャドーファクター」という。）が大きくなる。よって、図１２（ｂ）に示すように、１個のトナーＴ_１に対して別のトナーＴ_２が近接していると、これらの間のスペースＳ_２については、トナーが存在していないにも関わらず、その正反射光が受光素子で受光されることはない。その結果、スペースＳ_２程度の間隔をあけて感光体ドラム上にトナーが付着した段階で、それ以上トナーが付着しても、これをＰセンサによって検出することが困難となる。したがって、感光体ドラム表面上のトナー付着量が多い領域に対しては、正反射光を検出するＰセンサの感度が低下し、その付着量を検出することは困難となる。
【０００６】
図１３は、感光体ドラム表面に付着した黒トナーの付着量と、正反射光を検出するＰセンサの出力電圧との関係を示すグラフである。また、図１４は、感光体ドラム表面に付着したカラートナーの付着量と、正反射光を検出するＰセンサの出力電圧との関係を示すグラフである。これらのグラフからわかるように、黒トナー及びカラートナーのいずれの場合も、付着量がおよそ０．３ｍｇ／ｃｍ^２程度になるまでは、トナー付着量の増加に対するＰセンサの出力電圧変化量が十分大きいので、トナー付着量を検出することが可能である。しかし、付着量がこれ以上多くなると、Ｐセンサの出力電圧の変化がほとんどなくなり、トナー付着量を検出することができない。なお、図１４に示すように、カラートナーの場合には、Ｐセンサの出力電圧がおよそ０．４ｍｇ／ｃｍ^２を境に単調減少から単調増加に転じている。これは、黒トナーの場合にはトナーが光を吸収するのに対し、カラートナーは光を乱反射させるという性質から生じた現象である。すなわち、カラートナーの場合、正反射光のほかトナーによる乱反射光も受光素子に受光されるが、その受光素子に受光される乱反射光の光量がトナー付着量の増加に伴って増加した結果の現象である。
【０００７】
特に、近年では、トナーの小粒径化が進み、また、トナーの円形度も向上していることから、正反射光を検出するＰセンサによるトナー付着量の検出限界が実質的に狭くなる状況となっている。すなわち、図１３や図１４に示したグラフで説明すれば、トナー付着量に対するＰセンサの出力電圧の変化がほとんどなくなる地点が、トナー付着量の低い方にシフトする状況にある。
詳しく説明すると、トナーの重量平均粒径が８μｍ以下という小粒径トナーの場合、１個のトナーが定着時の熱と圧力によって引き延ばされて記録紙表面を覆う面積は小さい。よって、同じ画像濃度を得る場合には、トナーの粒径が小さいほど多くのトナーが必要となるので、所望の画像濃度を得るために像担持体表面上のトナー付着量を検出するときには、トナーの粒径が小さいほどトナー付着量が多い領域を感度よく検出する必要がある。すなわち、トナーの粒径が小さくなるにつれて、Ｐセンサによるトナー付着量の検出範囲が高付着量側にシフトするため、Ｐセンサによるトナー付着量の検出限界が実質的に狭くなる。しかも、トナー付着量は、図１３や図１４に示したグラフのように、通常、単位面積当たりのトナー重量で表され、このトナー重量はトナーの体積に比例する。この場合、トナーの径が小さくなると、トナー半径をＲとすれば、トナーの体積は１／Ｒ^３に比例して小さくなるため、トナー重量も１／Ｒ^３に比例して小さくなる。そのため、トナー付着量に対するＰセンサの出力電圧の変化がほとんどなくなる地点は、トナー付着量の低い方にシフトする。したがって、Ｐセンサによるトナー付着量の検出限界が更に狭いものとなる。
また、平均円形度が０．９３以上という円形度の高いトナーの場合、一般に、上記シャドーファクターが大きくなる。そのため、感光体ドラム表面上のトナー付着量が多い領域に対しては、正反射光を検出するＰセンサの感度が低下し、その付着量を検出することは困難となる。
【０００８】
以上の説明では、感光体ドラム上のトナー付着量を検出するための光学センサについて説明したが、光を正反射させる照射対象物上に存在する光を正反射させない物体の量を正反射光の受光により検出する光学センサであれば、検出可能範囲が狭いという上記と同様の問題を有する。
【０００９】
本発明は、以上の背景に鑑みなされたものであり、その目的とするところは、光を正反射させる照射対象物上に存在する光を正反射させない物体の付着量を、感度よく検出できる範囲を従来に比べて広げることが可能な光学センサ及び画像形成装置を提供することである。
【００１０】
【課題を解決するための手段】
上記目的を達成するために、請求項１の発明は、少なくとも１つの発光手段と、該発光手段から照射された入射光が照射対象物により正反射したときの正反射光を受光する受光手段とを備えた光学センサにおいて、上記発光手段からの入射光が上記照射対象物に至るまでの入射光路のうち該照射対象物に至る直前における入射光路の中心線と、該照射対象物からの正反射光が上記受光手段に至るまでの正反射光路のうち該照射対象物での反射直後における正反射光路の中心線とのなす角が、２５°以下となるように構成したことを特徴とするものである。
また、請求項２の発明は、請求項１の光学センサにおいて、上記なす角が２０°以下となるように構成したことを特徴とするものである。
また、請求項３の発明は、請求項１又は２の光学センサにおいて、上記入射光路及び上記正反射光路のうちの少なくとも一方の光路に、光の進行方向を変更する進行方向変更手段を有することを特徴とするものである。
また、請求項４の発明は、請求項３の光学センサにおいて、上記進行方向変更手段を、光を反射する光反射部材で構成したことを特徴とするものである。
また、請求項５の発明は、請求項３の光学センサにおいて、上記進行方向変更手段を、光を屈折させる光屈折部材で構成したことを特徴とするものである。
また、請求項６の発明は、請求項３の光学センサにおいて、上記進行方向変更手段を、上記光路の中心線に対して光軸がズレるように配置した集光部材又は光放散部材で構成したことを特徴とするものである。
また、請求項７の発明は、請求項５の光学センサにおいて、上記進行方向変更手段を、上記少なくとも一方の光路の中心線に対して光軸が傾斜するように配置した集光部材又は光放散部材で構成したことを特徴とするものである。
また、請求項８の発明は、請求項１又は２の光学センサにおいて、上記入射光路及び上記正反射光路のうちの少なくとも一方の光路に、該光路の中心線に対して光軸が一致するように配置した集光部材を設けたことを特徴とするものである。
また、請求項９の発明は、請求項１又は２の光学センサにおいて、上記正反射光路に、光放散部材を設けたことを特徴とするものである。
また、請求項１０の発明は、請求項９の光学センサにおいて、上記入射光路に集光部材を設け、上記発光手段から該集光部材までの距離をａ_１とし、該集光部材から上記照射対象物までの距離をｂ_１とし、該集光部材の焦点距離をｆ_１とし、かつ、上記光放散部材から上記受光手段までの距離をａ_２とし、該照射対象物から該光放散部材までの距離をｂ_２とし、該光放散部材の焦点距離をｆ_２としたとき、次の２つの演算式のうちの少なくとも一方を満たすように、該集光部材及び該光放散部材を配置したことを特徴とするものである。
１／ａ_１＋１／（ｂ_１＋ｂ_２）＝１／ｆ_１
１／ａ_２＋１／（ｂ_１＋ｂ_２）＝１／ｆ_２
また、請求項１１の発明は、請求項１、２、３、４、５、６、７、８、９又は１０の光学センサにおいて、上記発光手段及び上記受光手段の少なくとも一方を、光学素子が基板上に表面実装された表面実装光学手段で構成したことを特徴とするものである。
また、請求項１２の発明は、少なくとも１つの発光手段と、該発光手段から照射された入射光が照射対象物によって正反射したときの正反射光を受光する受光手段とを備えた光学センサにおいて、上記発光手段からの入射光が上記照射対象物に至るまでの入射光路、及び、該照射対象物からの正反射光が上記受光手段に至るまでの正反射光路のうちの少なくとも一方の光路に、集光部材を設けたことを特徴とするものである。
また、請求項１３の発明は、請求項８又は１２の光学センサにおいて、上記集光部材を、上記入射光路及び上記正反射光路の両方に設けたことを特徴とするものである。
また、請求項１４の発明は、請求項８、１２又は１３の光学センサにおいて、上記少なくとも一方の光路の始点から上記集光部材までの距離をａとし、該集光部材から該光路の終点までの距離をｂとし、該集光部材の焦点距離をｆとしたとき、次の演算式を満たすように、該集光部材を配置したことを特徴とするものである。
１／ａ＋１／ｂ＝１／ｆ
また、請求項１５の発明は、請求項８、１２、１３又は１４の光学センサにおいて、上記正反射光路に、光放散部材を設けたことを特徴とするものである。
また、請求項１６の発明は、請求項１５の光学センサにおいて、上記入射光路に集光部材を設け、上記発光手段から該集光部材までの距離をａ_１とし、該集光部材から上記照射対象物までの距離をｂ_１とし、該集光部材の焦点距離をｆ_１とし、かつ、上記光放散部材から上記受光手段までの距離をａ_２とし、該照射対象物から該光放散部材までの距離をｂ_２とし、該光放散部材の焦点距離をｆ_２としたとき、次の２つの演算式のうちの少なくとも一方を満たすように、該集光部材及び該光放散部材を配置したことを特徴とするものである。
１／ａ_１＋１／（ｂ_１＋ｂ_２）＝１／ｆ_１
１／ａ_２＋１／（ｂ_１＋ｂ_２）＝１／ｆ_２
また、請求項１７の発明は、請求項６、７、８、９、１０、１２、１３、１４、１５又は１６の光学センサにおいて、上記集光部材及び上記光放散部材あるいは上記集光部材又は上記光放散部材における上記照射対象物に対向する側の面が平面であることを特徴とするものである。
また、請求項１８の発明は、少なくとも１つの発光手段と、該発光手段から照射された入射光が照射対象物によって正反射したときの正反射光を受光する受光手段とを備えた光学センサにおいて、上記発光手段及び上記受光手段の少なくとも一方を、光学素子が基板上に表面実装された表面実装光学手段で構成したことを特徴とするものである。
また、請求項１９の発明は、請求項１、２、３、４、５、６、７、８、９、１０、１１、１２、１３、１４、１５、１６、１７又は１８の光学センサにおいて、上記発光手段及び上記受光手段を、単一のパッケージに封入したことを特徴とするものである。
また、請求項２０の発明は、請求項１１又は１８の光学センサにおいて、上記発光手段の光学素子と上記受光手段の光学素子とを、互いに同一基板の反対面に実装したことを特徴とするものである。
また、請求項２１の発明は、請求項１１、１８又は１９の光学センサにおいて、上記発光手段及び上記受光手段の両方を上記表面実装光学手段で構成し、該発光手段の光学素子と該受光手段の光学素子とを、互いに同一基板の同一面に表面実装するとともに、これらの光学素子を結ぶ線分上に遮光手段を設けたことを特徴とするものである。
また、請求項２２の発明は、請求項２１の光学センサにおいて、上記遮光手段として、上記基板に実装された実装部品を用いたことを特徴とするものである。
また、請求項２３の発明は、請求項１１、１８又は１９の光学センサにおいて、上記発光手段及び上記受光手段の両方を上記表面実装光学手段で構成し、該発光手段の光学素子と該受光手段の光学素子とを、互いに同一基板の同一面に表面実装するとともに、これらの光学素子を結ぶ線分上の基板面に貫通孔を設けたことことを特徴とするものである。
また、請求項２４の発明は、請求項１１、１８、１９、２０、２１、２２又は２３の光学センサにおいて、上記表面実装光学手段として、実装部品が光路を遮らないように構成したことを特徴とするものである。
また、請求項２５の発明は、請求項１１、１８、１９、２０、２１、２２、２３又は２４の光学センサにおいて、上記表面実装光学手段は、光路に対向する基板上に表面実装部品が表面実装されたものを用いたことを特徴とするものである。
また、請求項２６の発明は、光を正反射させる表面を有する像担持体と、該像担持体上にトナー像を形成するトナー像形成手段と、該トナー像形成手段により該像担持体上にトナーを付着させたときの該トナーの付着量を検出するための光学センサと、該光学センサの検出結果に基づいて画像濃度制御を行う画像濃度制御手段とを備えた画像形成装置において、上記光学センサとして、請求項１、２、３、４、５、６、７、８、９、１０、１１、１２、１３、１４、１５、１６、１７、１８、１９、２０、２１、２２、２３、２４又は２５の光学センサを用いたことを特徴とするものである。
また、請求項２７の発明は、請求項２６の画像形成装置において、上記トナー像を構成するトナーとして、重量平均粒径が８μｍ以下のものを用いたことを特徴とするものである。
また、請求項２８の発明は、請求項２６又は２７の画像形成装置において、上記トナー像を構成するトナーとして、平均円形度が０．９３以上のものを用いたことを特徴とするものである。
【００１１】
請求項１乃至２５の光学センサ及び請求項２６乃至２８の画像形成装置に設けられるトナー付着量を検出するための光学センサは、入射光が照射対象物により正反射したときの正反射光を受光する。この光学センサは、その照射対象物上に、光を吸収したり、光を乱反射させたりする物体が付着したときの付着量の検出や、そのような物体の付着位置の検出などに利用することができる。
そして、請求項１の光学センサは、発光手段からの入射光が照射対象物に至る直前における入射光路の中心線と、その照射対象物での反射直後における正反射光路の中心線とのなす角が２５°以下となるように構成されている。好ましくは、請求項２の光学センサのように、この角度が２５°以下とする。この角度が２５°以下であれば、受光手段により受光される正反射光に寄与しない照射対象物部分の面積を、照射対象物上に付着する物体が実際に占有している照射対象物の面積に十分に近づけることができる。すなわち、シャドーファクターを小さくすることができる。よって、その物体の付着量が多くても、これを十分な感度で検出することができるようになり、その付着量を感度よく検出できる範囲が広がる。
なお、上記角度を狭くする方法としては、通常、光学センサの発光手段を構成する発光素子と受光手段を構成する受光素子とを互いに近接させる方法が採られる。しかし、各素子が互いに接触するまでしか近接させることができないため、近接させるにも限界がある。また、通常、発光素子と受光手段との間には、発光手段からの光が直接受光手段に受光されないように遮光部材を設ける必要もあるため、この理由からも、発光素子と受光手段とを近接させることは困難である。また、各素子を互いに近接させた状態で照射対象物から離せば、上記角度を更に狭くすることは可能である。しかし、各素子を照射対象物から離すほど、光量が不足し、結果的に光学センサの感度を落とす結果となる。このような理由から、従来の光学センサでは、上記角度を２５°以下とすることは困難であった。
【００１２】
また、請求項１２の光学センサは、照射対象物に対する入射光の入射光路及びその照射対象物からの正反射光の正反射光路のうちの少なくとも一方の光路に、集光部材が設けられている。上述のように、発光手段や受光手段を照射対象物から離すほど、光学センサの感度を落とす結果となる。しかし、本光学センサでは、集光部材の光軸を光路の中心線に一致するように集光部材を設ければ、入射光を照射対象物の照射目標位置に集光させたり、正反射光を受光手段の受光位置に集光させたりすることができる。したがって、発光手段や受光手段を照射対象物から離しても、光量の低下を抑制することができる。したがって、照射対象物に至る直前における入射光路の中心線と、照射対象物での反射直後における正反射光路の中心線とのなす角を、感度を落とさずに狭くすることができる。
また、本光学センサでは、集光部材の光軸を光路の中心線からズラしたり、傾けたりすれば、光を屈折させて光の進行方向を変更することができる。よって、発光手段と受光手段との間の距離が広くて、発光手段から入射光が照射された直後の入射光路の中心線と、受光手段で正反射光を受光する直前の正反射光路の中心線とのなす角が広い場合でも、照射対象物に至る直前における入射光路の中心線と、照射対象物での反射直後における正反射光路の中心線とのなす角については狭くすることが可能となる。この場合、発光手段や受光手段を照射対象物から離す必要がないので、光学センサの感度を落とすことはない。
【００１３】
また、請求項１８の光学センサは、発光手段及び受光手段の少なくとも一方を、光学素子が基板上に表面実装された表面実装光学手段で構成している。このような表面実装光学手段は、発光素子又は受光素子となる光学素子の間隔を狭くすることが可能であり、照射対象物に至る直前における入射光路の中心線と、照射対象物での反射直後における正反射光路の中心線とのなす角を、十分に狭くすることが可能となる。しかも、近年、このような表面実装される光学素子は、携帯電話機等の小型製品にも使用されるほど小型化が進んでおり、現状でも寸法が３ｍｍ以下という非常に小さな光学素子が実現されつつある。よって、表面実装される光学素子の間隔は、今後も、より狭くすることが可能で、上記なす角を十分に狭くすることが可能である。
【００１４】
【発明の実施の形態】
以下、本発明を、電子写真方式のカラーレーザプリンタ（以下、単に「プリンタ」という。）に適用した実施形態について説明する。
図２は、本実施形態に係るプリンタの概略構成を示す断面図である。このプリンタ１は、装置本体の下部に給紙部２が設けられ、その上方に作像部３を配置した構成となっている。装置上面には排紙トレイ６０が形成されている。図中破線は、記録材としての記録紙の搬送経路を示している。記録紙は、給紙部２から給紙され、作像部３にて形成した画像が表面に転写された後、定着装置５０で定着され、排紙トレイ６０に排紙される。なお、図中符号ｈで示すように、装置側面からは手差し給紙が可能となっている。また、装置本体の側面には両面装置９０が装着されている。記録紙の両面に画像を形成する場合、片方の面に画像を形成して定着した後、その記録紙を図中破線ｒで示すように搬送し、両面装置９０を介して記録紙の表裏を反転させた後、再搬送部４０を経て再給紙され、他方の面に画像が形成される。
【００１５】
上記作像部３には、給紙側を下に、排紙側を上となるように傾斜して配置された転写搬送ベルト装置２０が配設されている。この転写搬送ベルト装置２０の上部走行面に沿って、下から順にイエロー（Ｙ）、マゼンタ（Ｍ）、シアン（Ｃ）、黒（Ｂｋ）用の４つの作像ユニット４Ｙ，４Ｍ，４Ｃ，４Ｂｋが並んで配置されている。各作像ユニット４Ｙ，４Ｍ，４Ｃ，４Ｂｋの構成は同じであるので、以下、マゼンタ用の作像ユニット４Ｍを例に挙げて説明する。
【００１６】
図３は、マゼンタ用の作像ユニット４Ｍの詳細を示す拡大図である。作像ユニット４Ｍは、像担持体としての感光体ドラム５Ｍを備えており、感光体ドラム５Ｍは図示していない駆動手段によって図中時計方向へ回転駆動される。感光体ドラム５Ｍの周りには、帯電ロール６Ｍ、現像装置１０Ｍ、クリーニング装置９Ｍ、トナー付着量検出センサ（以下、「Ｐセンサ」という。）３０Ｍ等が設けられている。現像装置１０Ｍは、現像剤担持体としての現像スリーブ１１Ｍに担持したトナーを感光体ドラム５Ｍに付与する。潜像形成手段としての光書込装置８からのレーザ光は、図２に示すように、帯電ロール６Ｍと現像スリーブ１１Ｍとの間から感光体ドラム５Ｍに照射される。なお、Ｐセンサ３０Ｍの構成及び動作の詳細については、後述する。
【００１７】
転写搬送ベルト装置２０には、無端ベルト状の転写搬送ベルト２１が設けられている。この転写搬送ベルト２１は、駆動ローラ２２、従動ローラ２３及びテンションローラ２４，２５に張架されている。転写搬送ベルト２１の上部走行面の内側には、各色作像ユニット４Ｍ，４Ｃ，４Ｙ，４Ｂｋの感光体ドラム５Ｍ，５Ｃ，５Ｙ，５Ｂｋにそれぞれ対向する位置に、転写手段を構成する転写ブラシ２８が接触している。この転写ブラシ２８には、トナーの帯電極性（本実施形態ではマイナス極性）とは逆極性（プラス極性）の転写バイアスが印加される。また、従動ローラ２３の上部には、転写搬送ベルト２１を挟んで紙吸着ローラ２７が設けられている。記録紙は、従動ローラ２３と吸着ローラ２７の間から転写搬送ベルト２１上に送り出され、吸着ローラ２７に印加されたバイアス電圧によって静電的に転写搬送ベルト２１上に吸着された状態で搬送される。本実施形態では、プロセス線速が１２５ｍｍ／ｓｅｃに設定されており、この速度で記録紙が搬送される。
【００１８】
定着装置５０は、本実施形態ではベルト定着方式を採用しており、定着ローラ５２と加熱ローラ５３とに定着ベルト５４が巻き掛けられた構成となっている。定着ローラ５２と加圧ローラ５１は、互いに圧接しており、定着ニップを形成している。加熱ローラ５３及び加圧ローラ５１には図示しないヒータが内蔵されている。
【００１９】
次に、本プリンタ１におけるプリント動作について説明する。なお、以下の説明では、色分け符号Ｙ，Ｍ，Ｃ，Ｂｋについては、適宜省略する。
各色の作像ユニット４Ｙ，４Ｍ，４Ｃ，４Ｂｋにおいて、各感光体ドラム５Ｙ，５Ｍ，５Ｃ，５Ｂｋは、図示しないメインモータにより回転駆動される。そして、各感光体ドラム５Ｙ，５Ｍ，５Ｃ，５Ｂｋの表面は、まず、帯電ロール６に印加されたＡＣバイアス（ＤＣ成分はゼロ）により除電され、その表面電位が本実施形態では約−５０Ｖとなる。次に、各感光体ドラム５Ｙ，５Ｍ，５Ｃ，５Ｂｋは、ＡＣ電圧とＤＣ電圧とが重畳した電圧を帯電ロール６に印加することにより、そのＤＣ成分にほぼ等しい電位に均一に帯電され、その表面電位が本実施形態では約−５００Ｖ〜−７００Ｖに帯電される。なお、目標帯電電位は図示しないプロセス制御部により決定される。
【００２０】
このように帯電された各感光体ドラム５Ｙ，５Ｍ，５Ｃ，５Ｂｋの表面には、光書込装置８により各色に対応した静電潜像がそれぞれ形成される。光書込装置８は、パソコン等のホストマシンより送られた画像データに基づき、図示しないＬＤ（レーザダイオード）を駆動して、レーザ光をポリゴンミラー７に照射する。このレーザ光は、シリンダーレンズ等を介して、各感光体ドラム５Ｙ，５Ｍ，５Ｃ，５Ｂｋの表面上に導かれる。レーザ光が照射された部分の感光体表面電位は、約−５０Ｖとなり、この部分がトナーで現像すべき静電潜像となる。
【００２１】
この静電潜像に現像装置１０からトナーが付与されると、各感光体ドラム５Ｙ，５Ｍ，５Ｃ，５Ｂｋの表面には、それぞれの色のトナー像が形成される。本実施形態では、現像スリーブ１１に、ＤＣ電圧とＡＣ電圧とが重畳した現像バイアス（−３００Ｖ〜−５００Ｖ）が印加される。よって、現像スリーブ１１に担持されたマイナス極性のトナーは、現像電界により、光書き込みにより電位が低下した感光体ドラム５Ｙ，５Ｍ，５Ｃ，５Ｂｋの表面部分（静電潜像部分）にのみ付着し、光書き込みされずに電位が低下していない感光体ドラム５Ｙ，５Ｍ，５Ｃ，５Ｂｋの表面部分（非静電潜像部分）には付着しない。これにより、各感光体ドラム５Ｙ，５Ｍ，５Ｃ，５Ｂｋの静電潜像部分に、各色トナー像がそれぞれ形成される。
【００２２】
一方、給紙部２からは記録紙が給紙され、給紙された記録紙は転写搬送ベルト装置２０の搬送方向上流側に設けられたレジストローラ対４１に一旦突き当たる。そして、記録紙は、各色トナー像の転写タイミングに同期するようにして、転写搬送ベルト２１上により搬送され、各感光体ドラム５Ｙ，５Ｍ，５Ｃ，５Ｂｋに対向する転写位置に至る。この転写位置には、転写搬送ベルト２１の裏面側に配置された転写ブラシ２８に印加される転写バイアスの作用により転写電界が形成される。この転写電界により、各感光体ドラム５Ｙ，５Ｍ，５Ｃ，５Ｂｋ上の各色トナー像は、記録材上に互いに重ね合わさるように順次転写される。
なお、モノクロ画像をプリントする場合は、黒用の作像ユニット４Ｂｋの感光体ドラム５Ｂｋにのみ黒トナーによるトナー像を形成し、このトナー像の転写タイミングに同期するようにして転写搬送ベルト２１により記録紙を搬送して、黒トナー像のみ転写を行う。
【００２３】
このようにして、各色トナー像が転写された記録紙は、駆動ローラ２２の位置で転写搬送ベルト２１から曲率分離され定着装置５０に送られる。そして、定着装置５０の定着ニップを通過する際、熱と圧力により、各色トナー像が記録紙上に定着される。定着を終えた記録紙は、装置本体の上面に設けられた排紙トレイ６０に排紙されるか、図２中符号：ｒで示すように両面装置９０へ受け渡される。
【００２４】
以下、本発明の特徴部分である、各感光体ドラム５Ｙ，５Ｍ，５Ｃ，５Ｂｋの表面上のトナー付着量の検出について説明する。
本実施形態のプリンタ１においては、電源投入時あるいは所定枚数のプリントを行う度に、各色の画像濃度を適正化するためのプロセスコントロール動作（以下、「プロコン動作」という。）を実行する。このプロコン動作では、濃度検知用パッチ（以下、「基準パターン」という。）を、各感光体ドラム５Ｙ，５Ｍ，５Ｃ，５Ｂｋ上にそれぞれ形成する。各感光体ドラム５Ｙ，５Ｍ，５Ｃ，５Ｂｋ上にそれぞれ形成される基準パターンは、帯電バイアス及び現像バイアスを順次切り替えることにより、連続階調の基準パターンとする。すなわち、本実施形態では、トナー付着量が階調的に変化するライン状の基準パターンを、感光体ドラムの表面移動方向に沿って作成する。そして、この基準パターンを、図２に示すように、各作像ユニット４Ｙ，４Ｍ，４Ｃ，４Ｂｋに設けられたＰセンサ３０Ｙ，３０Ｍ，３０Ｃ，３０Ｂｋで検出する。
【００２５】
なお、本実施形態では、感光体ドラム上の基準パターンを検出する場合であるが、各感光体ドラム５Ｙ，５Ｍ，５Ｃ，５Ｂｋ上に形成した基準パターンを、転写搬送ベルト２１上に転写した後に検出する構成としてもよい。この場合、Ｐセンサ３０は、転写搬送ベルト２１に対向するように配置する。具体的には、例えば、図４に示すように、転写搬送ベルト装置２０のテンションローラ２４に対向する位置に配置する。記録紙を搬送する転写搬送ベルト２１の部分には作像ユニット４Ｙ，４Ｍ，４Ｃ，４Ｂｋが対向しているためＰセンサ３０を配置するスペース的に余裕が少ないが、図４に示すように記録紙を搬送しない転写搬送ベルト２１の部分にはスペース的に余裕があり、Ｐセンサの配置よるスペース増大あるいは機器配置の複雑化を防ぐことができる。なお、転写搬送ベルト２１上に転写した後に基準パターンを検出する構成とする場合には、各色の基準パターンが互いに重ならないように転写搬送ベルト２１上に転写する。
【００２６】
なお、Ｐセンサ３０を、転写搬送ベルト２１の位置ズレ検知手段として兼用することが可能である。すなわち、転写搬送ベルト２１に所定のマークを設け、これをＰセンサ３０で検出することにより、転写搬送ベルト２１の主走査方向のズレを検知することができる。
【００２７】
次に、本実施形態におけるＰセンサ３０の構成について説明する。
各作像ユニット４Ｙ，４Ｍ，４Ｃ，４Ｂｋに設けられたＰセンサの構成は同じであるので、以下、マゼンタ用の作像ユニット４Ｍに設けられたＰセンサ３０Ｍを例に挙げて説明する。なお、以下の説明では、色分け符号Ｙ，Ｍ，Ｃ，Ｂｋについては、適宜省略する。
【００２８】
図１は、本実施形態におけるＰセンサ３０の概略構成を示す断面図である。本実施形態におけるＰセンサ３０は、主に、発光手段としての発光素子３１と、正反射光を受光するための受光手段としての第１受光素子３２と、乱反射光を受光するための第２受光素子３３とからなる構成されている。各素子３１，３２，３３は、プリント基板３４上に実装されており、単一のパッケージ３５に封入されている。パッケージ３５には、発光素子３１から照射される入射光が感光体ドラム５の表面に至るまでの入射光路を確保するための通路、及び、感光体ドラム５の表面で正反射した正反射光が第１受光素子３２に至るまでの正反射光路を確保するための通路がそれぞれ形成されている。本実施形態では、発光素子３１として、ピーク発光波長が９５０ｎｍのＧａＡｓ発光ダイオードを用い、第１受光素子３２及び第２受光素子３３として、ピーク分光感度波長が８００ｎｍのＳｉフォトトランジスタを用いている。なお、第１受光素子３２及び第２受光素子３３としては、Ｓｉフォトトランジスタのほか、ＰＤ（フォトダイオード）などの他の受光素子を用いることもできる。
【００２９】
本実施形態では、各感光体ドラム５上に連続階調の基準パターンを作成し、トナー濃度が階調的に変化する基準パターンのトナー付着量をＰセンサ３０で連続的に検出する。Ｐセンサ３０における第１受光素子３２及び第２受光素子３３の出力は、図示しない制御部に送られる。この制御部では、これらの出力から得られる正反射光量及び乱反射光量に基づき、基準パターンのトナー付着量を連続的に把握し、この把握したトナー付着量と予め決められた目標付着量とを比較する。そして、この比較結果に基づいて、制御部は、画像濃度制御手段として機能し、光書込装置８のレーザ光の強度、帯電ロール６へ印加する帯電バイアス、現像スリーブ１１に印加する現像バイアス、現像器内へのトナー補給量などを適宜変更し、画像濃度が所望の濃度になるように調節する。
【００３０】
ところで、本実施形態では、重量平均粒径が８μｍ以下という小粒径のトナーを使用している。そのため、上述したように、トナー付着量が多い領域についてＰセンサによる検出を行う必要があるため、上記入射角θ_０と上記正反射角θ_１とを加算した角度を狭くして、トナー付着量の多い領域でも十分な感度で検出できるようにする必要がある。
なお、トナーの重量平均粒径は、種々の方法によって測定でき、例えばコールターカウンターを使用して測定することができる。このコールターカウンターとしては、例えばコールターカウンターＩＩ型（コールター社製）を利用することができる。そして、このようなコールターカウンターにより得られた測定結果に基づいて、例えば個数分布、体積分布といった特性について解析することにより、トナーの重量平均粒径を求めることができる。コールターカウンターによる測定で使用する電解液としては、１級塩化ナトリウムを使用して調節した１［％］塩化ナトリウム水溶液を用いることができる。
【００３１】
また、本実施形態で使用するトナーは、いわゆる重合法によって形成されたトナーであり、その形状は真球に近く、その平均円形度は０．９３以上である。そのため、上述したように、シャドーファクターが大きくなり、感光体ドラム表面上のトナー付着量が多い領域に対しては、正反射光を検出するＰセンサの感度が低下するため、トナー付着量の多い領域でも十分な感度で検出できるようにする必要がある。
なお、トナーの平均円形度は、各トナーの円形度の平均値であり、次の方法により測定したものである。各トナーの円形度の測定は、株式会社ＳＹＳＭＥＸ製フロー式粒子像分析装置ＦＰＩＡ−２１００を用いて行った。この測定では、まず、１級塩化ナトリウムを用いて、１［％］のＮａＣｌ水溶液を調整する。その後、このＮａＣｌ水溶液を０．４５のフィルターを通して５０〜１００［ｍｌ］の液を得て、これに分散剤として界面活性剤、好ましくはアルキルベンゼンスルフォン酸塩を０．１〜５［ｍｌ］加え、更に試料を１〜１０［ｍｇ］加える。これを、超音波分散機で分散処理を１分間行い、粒子濃度を５０００〜１５０００［個／μｌ］に調整し、分散液を得る。この分散液をＣＣＤカメラで撮像し、トナーの２次元投影画像の面積と同じ面積をもつ円の円周長を、そのトナーの２次元投影画像の周囲長で割った値を、各トナーの円形度として用いた。なお、ＣＣＤの画素の精度から、トナーの２次元投影画像の面積と同じ面積をもつ円の直径（円相当径）が０．６［μｍ］以上であるトナーを有効なものとした。トナーの平均円形度は、各トナーの円形度を得た後、測定範囲内にある全トナーの円形度をすべて足し合わせ、それをトナー個数で割った値を用いたものである。
【００３２】
そこで、本実施形態では、図１に示すように、感光体ドラム表面の法線方向における相対位置が互いにズレるように、発光素子３１及び第１受光素子３２を配置している。このように配置することで、発光素子３１と第１受光素子３２とを近接させても、互いが接触することがない。そして、図示のように、発光素子３１から照射される入射光の感光体ドラム５の表面に対する入射光路の中心線と感光体ドラム表面の法線方向Ｚとのなす角を入射角θ_０とし、感光体ドラム表面で正反射した正反射光の正反射光路の中心線と感光体ドラム表面の法線方向Ｚとのなす角を正反射角θ_１としたとき、本実施形態では、その入射角θ_０と正反射角θ_１とを加算した角度が、従来のＰセンサでは困難であった２５°以下、好ましくは２０°以下となるように設定することができる。
【００３３】
〔変形例１〕
次に、上記入射角θ_０と上記正反射角θ_１とを加算した角度が２５°以下となるように設定するための変形例（以下、本変形例を「変形例１」という。）について説明する。
図１に示した構成であっても、発光素子３１が正反射光路を遮るように配置することはできないので、発光素子３１と第１受光素子３２とを近接させるにも限界がある。そこで、本変形例１では、発光素子３１と第１受光素子３２との間を互いに近接させずに、入射光路及び正反射光路のうちの少なくとも一方の光路に、光の進行方向を変更する進行方向変更手段を設けた構成を採用し、上記入射角θ_０と上記正反射角θ_１とを加算した角度が２５°以下となるように設定する。
【００３４】
図５は、本変形例１におけるＰセンサ１３０の概略構成を示す断面図である。
本変形例１のＰセンサ１３０の発光素子３１、第１受光素子３２及び第３受光素子３３は、図１に示したＰセンサ３０と同様である。しかし、本変形例１のＰセンサ１３０では、感光体ドラム表面法線方向における相対位置との発光素子３１及び第１受光素子３２がズレていない。そのため、このままでは、上記入射角θ_０と上記正反射角θ_１とを加算した角度が２５°以下となるように設定することができない。そこで、本変形例１では、入射光路及び正反射光路の途中に、進行方向変更手段としての光反射部材である反射ミラー１３６ａ，１３６ｂがそれぞれ設けている。
【００３５】
このような構成により、発光素子３１から照射された入射光は、反射ミラー１３６ａに反射することでその進行方向が変更される。したがって、入射光は、反射ミラー１３６ａに至るまでの入射光路部分の中心線と感光体ドラム表面の法線方向Ｚとのなす角を任意に設定しても、感光体ドラム表面に到達する直前の入射光路部分の中心線と法線方向Ｚとのなす角を狭く設定することができる。また、感光体ドラム表面で正反射した正反射光も、反射ミラー１３６ｂに反射することでその進行方向が変更される。したがって、入射光の場合と同様、反射ミラー１３６ｂから第１受光素子３２に至るまでの正反射光路部分の中心線と感光体ドラム表面の法線方向Ｚとのなす角を任意に設定しても、感光体ドラム表面で正反射した直後の正反射光路部分の中心線と法線方向Ｚとのなす角を狭く設定することができる。したがって、本変形例１における構成によれば、発光素子３１及び第１受光素子３２の配置を任意に決定しても、反射ミラー１３６ａ，１３６ｂの位置及び姿勢を適宜設定すれば、上記入射角θ_０と上記正反射角θ_１とを加算した角度が２５°以下となるように設定することができる。
【００３６】
なお、本変形例１では、反射ミラー１３６ａ，１３６ｂにより、光を反射させて光の進行方向を変更する場合について説明したが、図６に示すように、光ファイバー等の光案内手段を光進行方向変更手段として用い、光の進行方向を変更するようにしてもよい。この場合、光案内手段の内部壁が光反射部材として機能する。また、回析格子等を光進行方向変更手段として用い、光の進行方向を変更するようにしてもよい。
【００３７】
〔変形例２〕
次に、上記入射角θ_０と上記正反射角θ_１とを加算した角度が２５°以下となるように設定するための他の変形例（以下、本変形例を「変形例２」という。）について説明する。
本変形例２は、上記変形例１と同様、発光素子３１と第１受光素子３２との間を互いに近接させずに、入射光路及び正反射光路のうちの少なくとも一方の光路に、光の進行方向を変更する進行方向変更手段を設けた構成を採用し、上記入射角θ_０と上記正反射角θ_１とを加算した角度が２５°以下となるように設定する。
【００３８】
図７は、本変形例２におけるＰセンサ２３０の概略構成を示す断面図である。
本変形例２のＰセンサ２３０の基本構成は、上記変形例１と同様である。しかし、本変形例２のＰセンサ２３０は、入射光路及び正反射光路の途中に、反射ミラー１３６ａ，１３６ｂの代わりに、進行方向変更手段としての光屈折部材である屈折レンズ２３６ａ，２３６ｂがそれぞれ設けている。
このような構成により、発光素子３１から照射された入射光は、屈折レンズ２３６ａを透過することで屈折され、その進行方向が変更される。したがって、入射光は、屈折レンズ２３６ａに至るまでの入射光路部分の中心線と感光体ドラム表面の法線方向Ｚとのなす角を任意に設定しても、感光体ドラム表面に到達する直前の入射光路部分の中心線と法線方向Ｚとのなす角を狭く設定することができる。また、感光体ドラム表面で正反射した正反射光も、屈折レンズ２３６ｂを透過することで屈折され、その進行方向が変更される。したがって、入射光の場合と同様、屈折レンズ２３６ｂから第１受光素子３２に至るまでの正反射光路部分の中心線と感光体ドラム表面の法線方向Ｚとのなす角を任意に設定しても、感光体ドラム表面で正反射した直後の正反射光路部分の中心線と法線方向Ｚとのなす角を狭く設定することができる。したがって、本変形例２における構成によれば、上記変形例１と同様に、発光素子３１及び第１受光素子３２の配置を任意に決定しても、屈折レンズ２３６ａ，２３６ｂの位置及び姿勢を適宜設定すれば、上記入射角θ_０と上記正反射角θ_１とを加算した角度が２５°以下となるように設定することができる。
【００３９】
なお、上記屈折レンズ２３６ａ，２３６ｂを配置した位置に、入射光路及び正反射光路のの中心線に対して光軸がズレるように、集光部材としての凸レンズや凹ミラー又は光放散部材としての凹ミラーや凸レンズを配置すれば、同様に光の進行方向を変更できるので、同様の効果を得ることができる。
また、上記屈折レンズ２３６ａ，２３６ｂを配置した位置に、入射光路及び正反射光路のの中心線に対して光軸が傾斜するように、集光部材としての凸レンズや凹ミラー又は光放散部材としての凹ミラーや凸レンズを配置しても、同様に光の進行方向を変更できるので、同様である。
【００４０】
〔変形例３〕
次に、上記入射角θ_０と上記正反射角θ_１とを加算した角度が２５°以下となるように設定するための更に他の変形例（以下、本変形例を「変形例３」という。）について説明する。
発光素子３１及び第１受光素子３２を感光体ドラム５の表面から離せば、図１に示したように感光体ドラム表面の法線方向における相対位置が互いにズレるように配置しなくても、上記入射角θ_０と上記正反射角θ_１とを加算した角度が２５°以下となるように設定することは可能である。しかし、この場合、第１受光素子３２で受光される光量が不足してしまうため、感度を落ちてしまう。そこで、本変形例３では、発光素子３１及び第１受光素子３２を感光体ドラム５の表面から離しても感度が落ちないよう、入射光路及び正反射光路のうちの少なくとも一方の光路に、その光路の中心線に対して光軸が一致するように集光部材を配置し、上記入射角θ_０と上記正反射角θ_１とを加算した角度が２５°以下となるように設定する。
【００４１】
図８は、本変形例３におけるＰセンサ３３０の概略構成を示す断面図である。
本変形例３のＰセンサ３３０の発光素子３１、第１受光素子３２及び第３受光素子３３は、図１に示したＰセンサ３０と同様である。しかし、本変形例３のＰセンサ３３０では、感光体ドラム表面法線方向における相対位置との発光素子３１及び第１受光素子３２がズレておらず、発光素子３１及び第１受光素子３２と感光体ドラム表面との距離が長い。そのため、このままでは、第１受光素子３２の受光量が不足し、感度が落ちてしまう。そこで、本変形例３では、入射光路の途中に、集光部材としての片面凸レンズ３３６ａを設け、正反射光路の途中に光放散部材としての片面凹レンズ３３６ｂがそれぞれ設けている。
【００４２】
本変形例３では、片面凸レンズ３３６ａ及び片面凹レンズ３３６ｂの平面側を感光体ドラム表面に対向するように、各レンズ３３６ａ，３３６ｂを配置している。これにより、各レンズ３３６ａ，３３６ｂが飛散トナーによって汚れても、そのクリーニングが容易となる。なお、ここでいう平面は、厳格なものではなく、クリーニングが容易となる程度に十分大きな曲率を有する面も含まれる。
また、本変形例３では、発光素子３１から片面凸レンズ３３６ａまでの距離をａ_１とし、その片面凸レンズ３３６ａから感光体ドラム表面までの距離をｂ_１とし、その片面凸レンズ３３６ａの焦点距離をｆ_１とし、かつ、片面凹レンズ３３６ｂから第１受光素子３２までの距離をａ_２とし、感光体ドラム表面から片面凹レンズ３３６ｂまでの距離をｂ_２とし、片面凹レンズ３３６ｂの焦点距離をｆ_２としたとき、下記の数１に示す２つの演算式を満たすように、片面凸レンズ３３６ａ及び片面凹レンズ３３６ｂが配置されている。これにより、発光素子３１からの入射光の正反射光を片面凹レンズ３３６ｂに集光させることができる。そして、その集光した正反射光は、片面凹レンズ３３６ｂにより第１受光素子３２に向かうように集光することができる。よって、第１受光素子３２に対する正反射光の伝達効率をより高めることができる。また、片面凸レンズ３３６ａや片面凹レンズ３３６ｂの取付角度等のバラツキに対する余裕度も広がるという効果も得られる。なお、これらの効果は、下記の数１に示す２つの演算式のうちのいずれか一方を満たせば、得ることが可能である。
【数１】
１／ａ_１＋１／（ｂ_１＋ｂ_２）＝１／ｆ_１
１／ａ_２＋１／（ｂ_１＋ｂ_２）＝１／ｆ_２
【００４３】
〔変形例４〕
次に、上記入射角θ_０と上記正反射角θ_１とを加算した角度が２５°以下となるように設定するための更に他の変形例（以下、本変形例を「変形例４」という。）について説明する。
図９は、本変形例４におけるＰセンサ４３０の概略構成を示す断面図である。
本変形例４のＰセンサ４３０の光学素子である発光素子４３１、第１受光素子４３２及び第３受光素子４３３は、表面実装用部品（ＳＭＤ：ＳｕｒｆａｃｅＭｏｕｎｔＤｅｖｉｃｅ）で構成されており、プリント基板３４上に表面実装されている。各素子４３１，４３２，４３３の素子面はプリント基板３４の面に対して法線方向に向いている。なお、各素子４３１，４３２，４３３は、その外形をＳＭＤとしただけで、中身は図１に示したＰセンサ３０と同様である。このように発光素子４３１と第１受光素子４３２をＳＭＤで構成することで、素子自体を小型化できるなどの効果が得られ、素子間の間隔を狭くすることができる。すなわち、上記入射角θ_０と上記正反射角θ_１とを加算した角度が２５°以下となるように設定することができる。
【００４４】
また、本変形例４のように各素子をＳＭＤ構成とした場合でも、発光素子４３１と第１受光素子４３２が互いに接触するまでしか近接させることができないため、これらを近接させるにも限界がある。そこで、上記入射角θ_０と上記正反射角θ_１とを加算した角度をより小さくすべく、本変形例４では、入射光路と正反射光路上に、進路変更手段としての光屈折部材である共通レンズ４３６を設けている。この共通レンズ４３６は、入射光路及び正反射光路の中心線に対して、その光軸がズレるように配置されているため、各光路を通る光の進行方向を変更できる。よって、本変形例４における構成では、発光素子４３１及び第１受光素子４３２を無理に近づけなくても、共通レンズ４３６の位置及び姿勢等を適宜設定すれば、上記入射角θ_０と上記正反射角θ_１とを加算した角度をより狭く設定することができる。
【００４５】
なお、本変形例４では、乱反射を受光するための第２受光素子４３３も表面実装されており、感光体ドラム表面から離れた位置に配置されている。そのため、第２受光素子４３３で受光される乱反射光量が不足するおそれがある。よって、本変形例４では、第２受光素子４３３で受光される乱反射光の乱反射光路上に、その光路の中心線に対して光軸をズラして配置した凸レンズ４３７を設けている。これにより、入射光がトナーにより乱反射したときの乱反射光を、凸レンズ４３７により第２受光素子４３３に向けて集光させることができる。したがって、第２受光素子４３３で受光される乱反射光量を十分に確保でき、適正な画像濃度制御が可能となる。
【００４６】
また、本変形例４では、発光素子４３１及び第１受光素子４３２を互いに同一のプリント基板３４の同一面に表面実装しているため、これらの光学素子を結ぶ線分上に遮蔽物がないと、発光素子４３１から照射される入射光が、直接、第１受光素子４３２に受光されてしまい、正確な検出ができなくなる。そこで、本変形例４では、発光素子４３１と第１受光素子４３２とを結ぶ線分上に、遮光手段としての遮光壁４３５ａが設けられている。なお、遮光壁４３５ａに代えて、プリント基板３４上に実装されたコンデンサやコイル等の実装部品を用いることもできる。また、このような遮光手段を設ける代わりに、発光素子４３１と第１受光素子４３２とを結ぶ線分上に存在するプリント基板面に貫通孔を設ける構成としても、発光素子４３１から照射される入射光が直接第１受光素子４３２に受光されるのを抑制できる。すなわち、このように構成すれば、発光素子４３１からの入射光がプリント基板面で反射したときの反射光が第１受光素子４３２に直接受光されることを抑制できる。よって、正確な検出が可能となる。
【００４７】
〔変形例５〕
次に、上記入射角θ_０と上記正反射角θ_１とを加算した角度が２５°以下となるように設定するための更に他の変形例（以下、本変形例を「変形例５」という。）について説明する。
図１０は、本変形例５におけるＰセンサ５３０を示す概略構成図である。
本変形例５のＰセンサ５３０の光学素子である発光素子５３１、第１受光素子５３２及び第３受光素子５３３は、上記変形例４と同様にＳＭＤで構成されており、プリント基板３４上に表面実装されているが、各素子面はプリント基板３４の面方向に対して平行な方向に向いている。なお、各素子５３１，５３２，５３３は、その外形をＳＭＤとしただけで、中身は図１に示したＰセンサ３０と同様である。このように発光素子５３１と第１受光素子５３２をＳＭＤで構成することで、上記変形例４と同様に、上記入射角θ_０と上記正反射角θ_１とを加算した角度が２５°以下となるように設定することができる。
【００４８】
また、本変形例４の場合と同様に、入射光路と正反射光路上に、進路変更手段としての光放散部材や集光部材を入射光路及び正反射光路の中心線に対してその光軸がズレるように配置してもよい。このような構成とすれば、発光素子５３１及び第１受光素子５３２を無理に近づけなくても、上記入射角θ_０と上記正反射角θ_１とを加算した角度をより狭く設定することが可能となる。
また、本変形例５では、発光素子５３１から照射される入射光が、直接、第１受光素子５３２に受光されないように、受光素子５３２を発光素子５３２の死角（入射光が直接届かない位置）に配置している。なお、本変形例４と同様に、発光素子５３１と第１受光素子５３２とを結ぶ線分上に、遮光壁や実装部品等の遮光手段を設けたり、発光素子５３１と第１受光素子５３２とを結ぶ線分上に存在するプリント基板面に貫通孔を設けたりして、発光素子４３１から照射される入射光が直接第１受光素子４３２に受光されるのを抑制するようにしてもよい。
【００４９】
また、本変形例５では、光路がプリント基板の面方向に対して平行であるため、その光路上に実装部品が搭載されると、その実装部品によって光が遮られてしまい、第１受光素子５３２の受光量が不足してしまう。そのため、本変形例５では、プリント基板３４上の実装部品は、入射光路及び正反射光路を遮らない位置に実装されている。また、本変形例５では、プリント基板３４上に、入射光路となる部分に切り欠きを有する遮光板５４８が設けられている。この切り欠きは、いわゆる光を絞る効果を奏する。
【００５０】
〔変形例６〕
次に、上記入射角θ_０と上記正反射角θ_１とを加算した角度が２５°以下となるように設定するための更に他の変形例（以下、本変形例を「変形例６」という。）について説明する。
図１１は、本変形例６におけるＰセンサ６３０の概略構成を示す断面図である。本変形例６のＰセンサ６３０の光学素子である発光素子５３１は、上記変形例５と同様にＳＭＤで構成されており、その素子面がプリント基板３４の面方向に対して平行な方向に向くように表面実装されている。また、本変形例６のＰセンサ６３０の光学素子である第１受光素子３２は、図１に示したＰセンサ３０の第１受光素子と同様である。なお、乱反射光を受光するための第２受光素子については図示を省略する。このような構成としても、上記入射角θ_０と上記正反射角θ_１とを加算した角度が２５°以下となるように設定することが可能である。
【００５１】
また、本変形例６では、入射光路上に、進路変更手段及び光屈折部材としての集光部材である集光レンズ６３６が配置されている。この構成においては、発光素子５３１からプリント基板３４の面に沿って進行した入射光は、集光レンズ６３６により屈折して、感光体ドラム表面の照射目標に集光される。また、正反射光路上にも、進路変更手段及び光屈折部材としての集光部材である集光レンズ６３７が配置されている。そして、本変形例６では、入射光路の始点すなわち発光素子５３１から集光レンズ６３６までの距離及び正反射光路の始点すなわち感光体ドラム表面から集光レンズ６３７までの距離をａとし、集光レンズ６３６から入射光路の終点すなわち感光体ドラム表面までの距離及び集光レンズ６３７から正反射光路の終点すなわち第１受光素子３２までの距離をｂとし、各集光レンズ６３６，６３７の焦点距離をｆとしたとき、下記の数２に示す演算式を満たすように、各集光レンズ６３６，６３７が配置されている。これにより、発光素子５３１から感光体ドラム表面の照射目標に対する入射光の伝達効率、感光体ドラム表面から第１受光素子３２に対する正反射光の伝達効率をそれぞれ高めることができる。
【数２】
１／ａ＋１／ｂ＝１／ｆ
【００５２】
このような構成により、発光素子５３１から照射された入射光は、集光レンズ６３６に至るまでに多少発散しても、集光レンズ６３６により感光体ドラム表面の照射目標に向けて集光される。したがって、発光素子５３１が感光体ドラム表面から離れていても、感光体ドラム表面の照射目標に十分な光量をもった入射光を照射することができる。また、感光体ドラム表面で正反射した正反射光も、集光レンズ６３７に至るまでに多少発散しても、集光レンズ６３７により第１受光素子３２に向けて集光される。したがって、第１受光素子３２が感光体ドラム表面から離れていても、第１受光素子３２に十分な光量をもった反射光を受光させることができる。したがって、本変形例６における構成によれば、発光素子５３１及び第１受光素子３２を感光体ドラム表面から離して配置しても、第１受光素子３２の受光量が不足することがない。その結果、感度を低下させることなく、上記入射角θ_０と上記正反射角θ_１とを加算した角度が２５°以下となるように設定することができる。
【００５３】
また、集光レンズ６３７から第１受光素子３２までに至る正反射光路部分は、プリント基板３４の表面及びケース６３５の内壁面に囲まれており、これらの面は光を反射させる反射面となる。よって、集光レンズ６３７から出た正反射光のうち第１受光素子３２に向かわない光も、プリント基板３４の表面やケース６３５の内壁面での反射を繰り返して、第１受光素子３２に受光される。よって、第１受光素子３２での受光量を十分に確保することができる。
【００５４】
また、本変形例６では、発光素子５３１と第１受光素子３２とを結ぶ線分上には、プリント基板３４が存在するため、発光素子５３１から照射される入射光が直接第１受光素子３２に受光されることはない。
また、本変形例６では、入射光路及び正反射光路がプリント基板３４の面方向に対してほぼ平行であるため、その光路上の実装部品によって光が遮られると、第１受光素子５３２の受光量が不足してしまう。そのため、本変形例６では、光路に対向するプリント基板上には、実装部品を載せないか、又は、その実装部品を平坦なＳＭＤ６３８で構成することとしている。
また、本変形例６では、プリント基板３４との間で光の絞り効果を得るために、ケース６３５の内壁面に凸部６３５ａが形成されている。よって、この凸部６３５ａとプリント基板との間で入射光を絞る効果が得られる。ここで、プリント基板３４の表面に対する発光素子５３１の発光位置は、ある程度の高さを必要とするため、入射光はプリント基板３４の表面から多少離れた位置を通ることになる。そのため、凸部６３５ａとプリント基板表面との間では、その絞り効果が不十分となる場合がある。そこで、本変形例６では、ケース６３５内壁の凸部６３５ａに対向するプリント基板３４の表面にＳＭＤ６３８を表面実装している。これにより、凸部６３５ａとＳＭＤ６３８の表面との間で、入射光の絞り効果を高めることができる。なお、このように絞り効果を高める効果は、プリント基板３４に実装される部品で代用せずに、別途遮光部材等をプリント基板３４に設けるようにしても同様に得ることができる。しかし、本変形例６のように、プリント基板３４に実装される部品であるＳＭＤ６３８により代用すれば、その遮光部材等を設けるためのコストを削減できる。
【００５５】
以上、本実施形態における光学センサとしてのＰセンサ３０，１３０，２３０，３３０，４３０，５３０，６３０は、少なくとも１つの発光手段である発光素子３１，４３１，５３１と、この発光素子から照射された入射光Ｌ_１が照射対象物である感光体ドラム表面により正反射したときの正反射光Ｌ_２を受光する受光手段としての第１受光素子３２，４３２，５３２を備えている。そして、発光素子３１，４３１，５３１からの入射光が感光体ドラム表面に至るまでの入射光路のうち感光体ドラム表面に至る直前における入射光路の中心線と、感光体ドラム表面からの正反射光が第１受光素子３２，４３２，５３２に至るまでの正反射光路のうち感光体ドラム表面での反射直後における正反射光路の中心線とのなす角が、２５°以下、好ましくは２０°以下となるように構成している。これにより、シャドーファクターが小さくなるため、感光体ドラム表面に付着するトナーの付着量が多くても、これを十分な感度で検出することができるようになり、その付着量を感度よく検出できる範囲が広がる。
また、上記変形例１、２、４及び６のＰセンサ１３０，２３０，４３０，６３０は、入射光路及び正反射光路のうちの少なくとも一方の光路に、光の進行方向を変更する進行方向変更手段を有している。例えば、上記変形例１では、その進行方向変更手段を、光を反射する光反射部材としての反射ミラー１３６ａ，１３６ｂで構成している。また、上記変形例２では、その進行方向変更手段を、光を屈折させる光屈折部材としての屈折レンズ２３６ａ，２３６ｂで構成している。また、上記変形例４では、その進行方向変更手段を、光路の中心線に対して光軸がズレるように配置した集光部材又は光放散部材である共通レンズ４３６で構成している。また、上記変形例６では、その進行方向変更手段を、光路の中心線に対して光軸が傾斜するように配置した集光部材である集光レンズ６３６，６３７で構成している。このように、光の進行方向を変更すれば、上記変形例１で説明したように、発光素子及び第１受光素子の配置を任意に決定しても、上記入射角θ_０と上記正反射角θ_１とを加算した角度を狭く設定できる。したがって、発光素子及び第１受光素子の配置の自由度が増すという効果が得られる。
また、上記変形例３のＰセンサ３３０は、入射光路及び正反射光路のうちの少なくとも一方の光路に、その光路の中心線に対して光軸が一致するように集光部材である片面凸レンズ３３６が配置されている。このような構成とすることで、上記変形例３で説明したように、発光素子３１及び第１受光素子３２を感光体ドラム表面から離して配置しても、感度を低下させることなく、上記入射角θ_０と上記正反射角θ_１とを加算した角度を狭く設定できる。
また、上記変形例３のＰセンサ３３０は、正反射光路に光放散部材である片面凹レンズ３３６ｂが設けられている。このような片面凹レンズ３３６ｂを正反射光路上に設けることで、レンズの取り付け角度のバラツキによる正反射光の「ケラレ」が発生するのを抑制できる。よって、レンズの取り付け角度の自由度が高まるという効果が得られる。
また、上記変形例３のＰセンサ３３０では、入射光路に片面凸レンズ３３６ａを設け、発光素子３１から片面凸レンズ３３６ａまでの距離をａ_１とし、その片面凸レンズ３３６ａから感光体ドラム表面までの距離をｂ_１とし、その片面凸レンズ３３６ａの焦点距離をｆ_１とし、かつ、片面凹レンズ３３６ｂから第１受光素子３２までの距離をａ_２とし、感光体ドラム表面から片面凹レンズ３３６ｂまでの距離をｂ_２とし、片面凹レンズ３３６ｂの焦点距離をｆ_２としたとき、下記の数１に示す２つの演算式の少なくとも一方を満たすように、片面凸レンズ３３６ａ及び片面凹レンズ３３６ｂが配置されている。これにより、上記変形例３で説明したように、第１受光素子３２に対する正反射光の伝達効率をそれぞれ高めることができる。
また、上記変形例４乃至６のＰセンサ４３０，５３０，６３０は、発光素子４３１，５３１及び第１受光素子４３２，５３２の少なくとも一方の素子が、プリント基板３４上に表面実装された表面実装光学手段で構成されている。このように発光素子と第１受光素子をＳＭＤで構成することで、素子間の間隔を狭くすることができる。すなわち、上記入射角θ_０と上記正反射角θ_１とを加算した角度を狭く設定できる。
また、上記変形例３や６のＰセンサ３３０，６３０のように、入射光路及び正反射光路のうちの少なくとも一方の光路に、集光部材である片面凸レンズ３３６ａや集光レンズ６３６，６３７を設ければ、感度を低下させることなく上記入射角θ_０と上記正反射角θ_１とを加算した角度を狭く設定できるという上記変形例３で説明した効果や、発光素子及び第１受光素子の配置の自由度が増すという上記変形例１で説明した効果等を得ることが可能となる。
また、上記変形例６のＰセンサ６３０のように、入射光路及び正反射光路の両方に集光部材である集光レンズ６３６，６３７を設ければ、感度を落とすことなく、発光素子５３１及び第１受光素子３２の両方を感光体ドラム表面から遠ざけることができるので、発光素子及び第１受光素子の配置の自由度が増す。
また、上記変形例６のＰセンサ６３０では、入射光路の始点すなわち発光素子５３１から集光レンズ６３６までの距離及び正反射光路の始点すなわち感光体ドラム表面から集光レンズ６３７までの距離をａとし、集光レンズ６３６から入射光路の終点すなわち感光体ドラム表面までの距離及び集光レンズ６３７から正反射光路の終点すなわち第１受光素子３２までの距離をｂとし、各集光レンズ６３６，６３７の焦点距離をｆとしたとき、上記数２に示す演算式を満たすように、各集光レンズが配置されている。これにより、発光素子から感光体ドラム表面の照射目標に対する入射光の伝達効率、感光体ドラム表面から第１受光素子３２に対する正反射光の伝達効率をそれぞれ高めることができる。
また、上記変形例３や上記変形例６のＰセンサ３３０，６３０のように、集光部材である片面凸レンズ３３６ａ及び集光レンズ６３６，６３７や、光放散部材である片面凹レンズ３３６ｂにおける感光体ドラム表面に対向する側の面が平面とすれば、上記変形例３で説明したように、レンズ面が飛散トナーによって汚れても、そのクリーニングが容易となる。
また、上記実施形態や上記変形例１、２、３及び４のＰセンサ３０，１３０，２３０，３３０，４３０は、発光素子３１，４３１及び第１受光素子３２，４３２を単一のパッケージに封入した構成となっているため、本Ｐセンサをプリント基板等の電気回路に接続する作業が容易となり、製造工程を簡略化できる。
また、上記変形例６のＰセンサ６３０のように、発光素子５３１及び第１受光素子３２が互いに同一基板３４の反対面に実装すれば、発光素子５３１から直接第１受光素子３２に向かう入射光を基板３４により遮ることができる。よって、発光素子５３１からの入射光が第１受光素子３２に直接受光されることがなくなるので、正確な検出が可能となる。
また、上記変形例４のＰセンサ４３０は、発光素子４３１及び第１受光素子４３２の両方が表面実装部品（ＳＭＤ）であって、基板３４の同一面に表面実装されている。そして、発光素子４３１と第１受光素子４３２とを結ぶ線分上には、遮光手段としての遮光壁４３５ａが設けられている。よって、発光素子４３１から直接第１受光素子４３２に向かう入射光が遮光壁４３５ａにより遮られ、発光素子５３１からの入射光が第１受光素子３２に直接受光されることがなくなるので、正確な検出が可能となる。なお、上記変形例４で説明したように、この遮光手段として基板３４に実装された実装部品を利用すれば、電子部品ではない部材を基板上に設ける必要がなくなるため、回路スペースを広く取ることができる。また、上記変形例４で説明したように、発光素子４３１と第１受光素子４３２とを結ぶ線分上の基板面に貫通孔を設けても、発光素子４３１から照射される入射光が基板面に反射して直接第１受光素子４３２に受光されるのを抑制できるため、正確な検出が可能となる。
また、上記変形例５及び６のＰセンサ５３０，６３０のように、実装部品が光路を遮らないように構成すれば、実装部品によって光が遮られて第１受光素子５３２の受光量が不足する事態を回避できる。
また、上記変形例６のＰセンサ６３０のように、光路に対向する基板上に表面実装部品を表面実装すれば、光の絞り効果を高めることができる。
また、上述した各変形例を含む本実施形態に係るプリンタは、光を正反射させる表面を有する像担持体としての感光体ドラム５と、感光体ドラム５上にトナー像を形成するトナー像形成手段としての帯電ロール６、光書込装置８及び現像装置１０と、このトナー像形成手段により感光体ドラム５上にトナーを付着させたときのトナー付着量を検出するための光学センサであるＰセンサと、このＰセンサの検出結果に基づいて画像濃度制御を行う画像濃度制御手段としての制御部とを備えている。そして、このＰセンサとして、上述したＰセンサ３０，１３０，２３０，３３０，４３０，５３０，６３０を用いるため、適正な画像濃度制御を行うことが可能となる。
また、本実施形態で使用するトナーは、重量平均粒径が８μｍ以下のものであるため、上述したように、トナー付着量の多い領域でも十分な感度でトナー付着量を検出できるようにする必要があるが、上述したＰセンサ３０，１３０，２３０，３３０，４３０，５３０，６３０を用いることで、トナー付着量の多い領域でも十分な感度でトナー付着量を検出することができるようになる。
また、本実施形態で使用するトナーは、平均円形度が０．９３以上のものであるため、上述したように、トナー付着量の多い領域でも十分な感度でトナー付着量を検出できるようにする必要があるが、上述したＰセンサ３０，１３０，２３０，３３０，４３０，５３０，６３０を用いることで、トナー付着量の多い領域でも十分な感度でトナー付着量を検出することができるようになる。
【００５６】
尚、本実施形態では、本発明を、感光体ドラム表面上のトナー付着量を検出するＰセンサを例に挙げて説明したが、他の光学センサに適用しても、同様の効果を得ることが可能である。例えば、トナー飛散の量を検出するために所定箇所に付着したトナーの付着量を検出するための光学センサなどにも適用することができる。また、画像形成装置に限らず、他の分野において、物体の付着量や物体の付着位置などを検出する光学センサにも同様に適用できる。
また、本実施形態では、４つの作像ユニット４Ｙ，４Ｍ，４Ｃ，４Ｂｋを備えたタンデム型の画像形成装置であって、各感光体ドラムから記録紙上に直接トナー像を転写する直接転写方式を採用しているが、これに限らず、種々の型又は方式の画像形成装置でも同様である。すなわち、作像ユニットを１つしか持たない１ドラム型の画像形成装置や、感光体ドラム上のトナーを一旦中間転写体に転写した後に記録紙上に転写する間接転写方式の画像形成装置などにも、本発明は同様に適用することができる。
【００５７】
【発明の効果】
請求項１乃至２８の発明によれば、光を正反射させる照射対象物上に存在する光を正反射させない物体の付着量を感度よく検出できる範囲を従来に比べて広げることができるという優れた効果がある。
【図面の簡単な説明】
【図１】実施形態に係るプリンタの各作像ユニットに設けられたＰセンサの概略構成を示す断面図。
【図２】同プリンタの概略構成を示す断面図。
【図３】同プリンタに設けられたマゼンタ用の作像ユニットの詳細を示す拡大図。
【図４】Ｐセンサの他の配置例を説明するためのプリンタの概略構成を示す断面図。
【図５】変形例１におけるＰセンサの概略構成を示す断面図。
【図６】同Ｐセンサの他の構成例を示す断面図。
【図７】変形例２におけるＰセンサの概略構成を示す断面図。
【図８】変形例３におけるＰセンサの概略構成を示す断面図。
【図９】変形例４におけるＰセンサの概略構成を示す断面図。
【図１０】変形例５におけるＰセンサを示す概略構成図。
【図１１】変形例６におけるＰセンサの概略構成を示す断面図。
【図１２】（ａ）及び（ｂ）は、感光体ドラムの表面にトナーが付着している様子を示す模式図。
【図１３】感光体ドラム表面に付着した黒トナーの付着量と、正反射光を検出するＰセンサの出力電圧との関係を示すグラフ。
【図１４】感光体ドラム表面に付着したカラートナーの付着量と、正反射光を検出するＰセンサの出力電圧との関係を示すグラフ。
【符号の説明】
１プリンタ
５Ｙ，５Ｍ，５Ｃ，５Ｂｋ感光体ドラム
１０Ｙ，１０Ｍ，１０Ｃ，１０Ｂｋ現像装置
２１転写搬送ベルト
２８転写ブラシ
３０，１３０，２３０，３３０，４３０，５３０，６３０Ｐセンサ
３１，４３１，５３１発光素子
３２，４３２，５３２第１受光素子
３３，４３３，５３３第２受光素子
３４プリント基板
３５パッケージ
１３６ａ，１３６ｂ反射ミラー
２３６ａ，２３６ｂ屈折レンズ
３３６ａ片面凸レンズ
３３６ｂ片面凹レンズ
４３５ａ遮光壁
４３６共通レンズ
４３７凸レンズ
５４８遮光板
６３５ケース
６３５ａ凸部
６３６，６３７集光レンズ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical sensor that receives specularly reflected light of incident light irradiated on an irradiation target, and an image forming apparatus using the optical sensor, such as a copying machine, a printer, and a facsimile.
[0002]
[Prior art]
In this type of image forming apparatus, in order to obtain a stable image density, a toner patch (reference pattern) for density detection is created on the surface of an image carrier such as a photoconductor, and the density of the patch is detected by an optical sensor. There is something. In this image forming apparatus, the developing potential is adjusted by changing the writing light intensity for forming a latent image, the charging bias, the developing bias, etc., based on the detection result of the optical sensor. Image density control is performed to adjust the target value of the toner density in the developing device. This optical sensor is called a P (pattern) sensor because it detects a reference pattern, and a reflection type optical sensor having a light emitting unit and a light receiving unit is generally used.
[0003]
Some reflective optical sensors detect specularly reflected light when light applied to an irradiation target is regularly reflected. Such a reflective optical sensor is disclosed in Patent Document 1 and the like. The principle of detection when a reflection type optical sensor for detecting specular reflection light is used as a P sensor will be described with reference to an example in which a toner concentration (toner adhesion amount) on a photosensitive drum is detected. It is.
If the toner is not adhered to the surface of the photoconductor drum (irradiation target), the incident light is specularly reflected on the photoconductor drum surface, and the specular reflection light corresponding to the reflectance of the photoconductor drum surface is transmitted to the light receiving element. Received. On the other hand, when toner adheres to the surface of the photosensitive drum, incident light is absorbed by the toner or is irregularly reflected by the toner. Therefore, if the incident light is blocked by the toner before reaching the photosensitive drum surface, or if the specularly reflected light from the photosensitive drum surface is blocked by the toner before reaching the light receiving element, the specularly reflected light is blocked by the light receiving element. No light is received. Therefore, as the amount of toner adhered on the surface of the photosensitive drum increases, the amount of light received by the light receiving element decreases. Therefore, it is possible to detect the amount of toner adhering on the surface of the photosensitive drum based on the amount of light received by the light receiving element.
[0004]
[Patent Document 1]
JP-A-64-35455
[0005]
[Problems to be solved by the invention]
FIGS. 12A and 12B are schematic diagrams illustrating a state in which toner is attached to the surface of the photosensitive drum 5 which is an irradiation target. Incident light L from a light emitting element (not shown) of the P sensor₁Is irradiated, the incident light L is not disturbed by the toner T.₁Is specularly reflected on the surface of the photosensitive drum, and the specularly reflected light L₂Are received by a light receiving element (not shown). However, the incident light in the hatched area in the drawing cannot reach the light receiving element because it is disturbed by the toner T. When detecting regular reflection light, the optical path of the incident light needs to be inclined with respect to the normal direction Z of the surface of the photosensitive drum. Therefore, the area S of the surface portion of the photosensitive drum that does not contribute to the regular reflection light received by the light receiving element₁Is the orthographic area of the toner T on the surface of the photosensitive drum, that is, the area S of the portion where the toner is actually occupied on the surface of the photosensitive drum.₀Larger than. That is, the area S of the portion where the toner actually occupies the photosensitive drum surface₀, The area S of the surface of the photosensitive drum that does not contribute to the specularly reflected light received by the light receiving element.₁(Hereinafter referred to as “shadow factor”). Therefore, as shown in FIG. 12B, one toner T₁To another toner T₂Are close together, the space S between them₂Regarding the above, the regular reflection light is not received by the light receiving element even though the toner is not present. As a result, the space S₂At a stage where the toner adheres to the photosensitive drum at a certain interval, even if the toner adheres further, it becomes difficult to detect the toner by the P sensor. Accordingly, the sensitivity of the P sensor for detecting the regular reflection light is reduced in an area where the toner adhesion amount is large on the surface of the photosensitive drum, and it becomes difficult to detect the adhesion amount.
[0006]
FIG. 13 is a graph showing the relationship between the amount of black toner adhering to the surface of the photosensitive drum and the output voltage of the P sensor that detects specularly reflected light. FIG. 14 is a graph showing the relationship between the amount of color toner adhering to the surface of the photoreceptor drum and the output voltage of a P sensor that detects specularly reflected light. As can be seen from these graphs, in both cases of the black toner and the color toner, the adhesion amount was approximately 0.3 mg / cm.²Until the change, the amount of change in the output voltage of the P sensor with respect to the increase in the amount of adhered toner is sufficiently large, so that the amount of adhered toner can be detected. However, if the amount of adhesion increases further, the output voltage of the P sensor hardly changes, and the amount of toner adhesion cannot be detected. As shown in FIG. 14, in the case of the color toner, the output voltage of the P sensor is about 0.4 mg / cm.²After that, it has changed from monotonous decrease to monotone increase. This is a phenomenon caused by the property that the black toner absorbs light while the color toner diffusely reflects light. That is, in the case of a color toner, irregularly reflected light due to toner in addition to specularly reflected light is received by the light receiving element. It is.
[0007]
In particular, in recent years, since the particle size of the toner has been reduced and the circularity of the toner has been improved, the detection limit of the amount of toner attached by the P sensor for detecting the regular reflection light has been substantially narrowed. It has become. In other words, referring to the graphs shown in FIGS. 13 and 14, the point where the change in the output voltage of the P sensor with respect to the toner adhesion amount is almost zero is shifted to the lower toner adhesion amount.
More specifically, in the case of a small particle size toner having a weight average particle size of 8 μm or less, one toner is stretched by heat and pressure at the time of fixing, and the area covering the recording paper surface is small. Therefore, in order to obtain the same image density, the smaller the particle size of the toner, the more toner is required. Therefore, when detecting the amount of toner adhering on the surface of the image carrier to obtain a desired image density, It is necessary to detect a region having a larger toner adhesion amount as the particle size of the toner is smaller, with high sensitivity. That is, as the particle size of the toner becomes smaller, the detection range of the toner adhesion amount by the P sensor shifts to the higher adhesion amount side, so that the detection limit of the toner adhesion amount by the P sensor becomes substantially narrower. In addition, the amount of toner adhered is usually represented by the toner weight per unit area as shown in the graphs of FIGS. 13 and 14, and this toner weight is proportional to the volume of the toner. In this case, if the diameter of the toner becomes smaller, the volume of the toner becomes 1 / R, where R is the toner radius.³, The toner weight is also 1 / R³Becomes smaller in proportion to. Therefore, the point where the output voltage of the P sensor hardly changes with respect to the toner adhesion amount shifts to the lower toner adhesion amount. Therefore, the detection limit of the toner adhesion amount by the P sensor is further narrowed.
In the case of a toner having a high circularity of 0.93 or more, the shadow factor generally increases. Therefore, the sensitivity of the P sensor for detecting the regular reflection light is reduced in a region where the amount of toner adhered on the surface of the photosensitive drum is large, and it is difficult to detect the amount of adhered toner.
[0008]
In the above description, the optical sensor for detecting the amount of toner adhering to the photosensitive drum has been described. However, the amount of the object that does not regularly reflect light existing on the irradiation target that regularly reflects light is defined as the amount of regular reflection light. An optical sensor that detects by light reception has the same problem that the detectable range is narrow.
[0009]
The present invention has been made in view of the above background, and an object of the present invention is to detect the amount of an object that does not regularly reflect light existing on an irradiation target object that regularly reflects light, in a range that can be detected with high sensitivity. The present invention provides an optical sensor and an image forming apparatus that can expand the size of the conventional optical sensor.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes at least one light emitting unit, and a light receiving unit that receives regular reflected light when incident light emitted from the light emitting unit is regularly reflected by an irradiation target. In the optical sensor provided with: a center line of the incident light path immediately before the incident light from the light emitting means to the irradiation object reaches the irradiation object; and a specular reflection from the irradiation object. The angle of the regular reflection light path to the center line of the regular reflection light path immediately after reflection on the irradiation object in the regular reflection light path until the light reaches the light receiving means is configured to be 25 ° or less. It is.
According to a second aspect of the present invention, in the optical sensor of the first aspect, the angle is 20 degrees or less.
According to a third aspect of the present invention, in the optical sensor according to the first or second aspect, at least one of the incident optical path and the regular reflection optical path includes a traveling direction changing unit that changes a traveling direction of light. It is characterized by the following.
According to a fourth aspect of the present invention, in the optical sensor of the third aspect, the traveling direction changing means is constituted by a light reflecting member that reflects light.
According to a fifth aspect of the present invention, in the optical sensor of the third aspect, the traveling direction changing means is constituted by a light refracting member that refracts light.
According to a sixth aspect of the present invention, in the optical sensor of the third aspect, the traveling direction changing means is constituted by a condensing member or a light dispersing member arranged such that an optical axis is shifted with respect to a center line of the optical path. It is characterized by the following.
According to a seventh aspect of the present invention, in the optical sensor of the fifth aspect, the traveling direction changing means is arranged so that an optical axis is inclined with respect to a center line of the at least one optical path. It is characterized by comprising a member.
According to an eighth aspect of the present invention, in the optical sensor according to the first or second aspect, at least one of the incident optical path and the regular reflection optical path has an optical axis coincident with a center line of the optical path. Wherein the light-collecting member disposed in the first position is provided.
According to a ninth aspect of the present invention, in the optical sensor of the first or second aspect, a light diffusion member is provided in the regular reflection optical path.
According to a tenth aspect of the present invention, in the optical sensor of the ninth aspect, a light collecting member is provided in the incident light path, and a distance from the light emitting means to the light collecting member is a.₁And the distance from the focusing member to the irradiation object is b₁And the focal length of the light collecting member is f₁And the distance from the light dispersing member to the light receiving means is a₂And the distance from the irradiation object to the light dissipating member is b₂And the focal length of the light dispersing member is f₂In this case, the light-collecting member and the light-dissipating member are arranged so as to satisfy at least one of the following two arithmetic expressions.
1 / a₁+ 1 / (b₁+ B₂) = 1 / f₁
1 / a₂+ 1 / (b₁+ B₂) = 1 / f₂
According to an eleventh aspect of the present invention, in the optical sensor according to the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, or tenth aspect, at least one of the light emitting unit and the light receiving unit is an optical element. It is characterized by comprising surface-mounting optical means surface-mounted on a substrate.
According to a twelfth aspect of the present invention, there is provided an optical sensor comprising at least one light emitting means and a light receiving means for receiving a regular reflection light when incident light emitted from the light emission means is regularly reflected by an irradiation object. The incident light path from the light emitting means to the irradiation target object, and at least one of the regular reflection light paths from the regular reflection light from the irradiation object to the light receiving means. And a light condensing member.
According to a thirteenth aspect of the present invention, in the optical sensor of the eighth or twelfth aspect, the light condensing member is provided on both the incident light path and the regular reflection light path.
According to a fourteenth aspect of the present invention, in the optical sensor according to the eighth, twelfth, or thirteenth aspect, a distance from the start point of the at least one optical path to the light collecting member is a, and the distance from the light collecting member to the end point of the light path. Where b is the distance of the light-collecting member and f is the focal length of the light-collecting member, the light-collecting member is arranged so as to satisfy the following arithmetic expression.
1 / a + 1 / b = 1 / f
According to a fifteenth aspect of the present invention, in the optical sensor according to the eighth, twelfth, thirteenth, or fourteenth aspect, a light diffusion member is provided in the regular reflection optical path.
According to a sixteenth aspect of the present invention, in the optical sensor according to the fifteenth aspect, a light collecting member is provided in the incident light path, and a distance from the light emitting unit to the light collecting member is a.₁And the distance from the focusing member to the irradiation object is b₁And the focal length of the light collecting member is f₁And the distance from the light dispersing member to the light receiving means is a₂And the distance from the irradiation object to the light dissipating member is b₂And the focal length of the light dispersing member is f₂In this case, the light-collecting member and the light-dissipating member are arranged so as to satisfy at least one of the following two arithmetic expressions.
1 / a₁+ 1 / (b₁+ B₂) = 1 / f₁
1 / a₂+ 1 / (b₁+ B₂) = 1 / f₂
The invention according to claim 17 is the optical sensor according to claim 6, 7, 8, 9, 10, 12, 13, 14, 15, or 16, wherein the light-collecting member and the light-dissipating member or the light-collecting member The surface of the light diffusion member on the side facing the irradiation object is a flat surface.
An invention according to claim 18 is an optical sensor comprising at least one light emitting means and a light receiving means for receiving regular reflection light when the incident light emitted from the light emission means is regularly reflected by the irradiation object. At least one of the light-emitting means and the light-receiving means is a surface-mounted optical means in which an optical element is surface-mounted on a substrate.
The invention according to claim 19 is the optical sensor according to claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 or 18. The light emitting means and the light receiving means are enclosed in a single package.
According to a twentieth aspect of the present invention, in the optical sensor according to the eleventh or eighteenth aspect, the optical element of the light emitting unit and the optical element of the light receiving unit are mounted on opposite surfaces of the same substrate. It is.
According to a twenty-first aspect of the present invention, in the optical sensor of the eleventh, eighteenth, or nineteenth aspect, both the light emitting means and the light receiving means are constituted by the surface mount optical means, and the optical element of the light emitting means and the light receiving means Are mounted on the same surface of the same substrate, and a light-shielding means is provided on a line connecting these optical elements.
According to a twenty-second aspect of the present invention, in the optical sensor according to the twenty-first aspect, a mounting component mounted on the substrate is used as the light shielding means.
According to a twenty-third aspect of the present invention, in the optical sensor of the eleventh, eighteenth or nineteenth aspect, both the light emitting means and the light receiving means are constituted by the surface mounting optical means, and the optical element of the light emitting means and the light receiving means Are mounted on the same surface of the same substrate, and a through hole is provided in the substrate surface on a line connecting these optical elements.
According to a twenty-fourth aspect of the present invention, in the optical sensor of the eleventh, eighteenth, nineteenth, twenty-first, twenty-second, twenty-second, or twenty-third aspect, the surface-mounting optical means is configured so that a mounted component does not block an optical path. It is assumed that.
According to a twenty-fifth aspect of the present invention, in the optical sensor according to the eleventh, eighteenth, nineteenth, twentieth, twenty-second, twenty-third, twenty-third, or twenty-fourth aspect, the surface-mounting optical means includes a surface-mount component on a substrate facing an optical path. It is characterized by using what is mounted.
According to a twenty-sixth aspect of the present invention, there is provided an image carrier having a surface for regularly reflecting light, a toner image forming means for forming a toner image on the image carrier, and an image carrier on the image carrier by the toner image forming means. An image forming apparatus comprising: an optical sensor for detecting an amount of toner adhered when toner is adhered to the image forming apparatus; and an image density control unit configured to perform image density control based on a detection result of the optical sensor. Claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 or 25 optical sensors are used.
According to a twenty-seventh aspect of the present invention, in the image forming apparatus of the twenty-sixth aspect, a toner having a weight average particle size of 8 μm or less is used as the toner constituting the toner image.
According to a twenty-eighth aspect of the present invention, in the image forming apparatus of the twenty-sixth or the twenty-seventh aspect, the toner constituting the toner image has an average circularity of 0.93 or more. .
[0011]
The optical sensor according to any one of claims 1 to 25 and the optical sensor provided in the image forming apparatus according to any one of claims 26 to 28 for detecting the amount of toner adhered receives specularly reflected light when incident light is specularly reflected by an irradiation target. I do. This optical sensor is used for detecting the amount of adhesion when an object that absorbs light or diffusely reflects light on the irradiation target, and for detecting the position of such an object. Can be.
The optical sensor according to claim 1, wherein the angle formed by the center line of the incident light path immediately before the incident light from the light emitting means reaches the irradiation target and the center line of the regular reflection light path immediately after reflection on the irradiation target object. Is 25 ° or less. Preferably, the angle is set to 25 ° or less as in the optical sensor of the second aspect. If this angle is 25 ° or less, the area of the irradiation target portion that does not contribute to the regular reflection light received by the light receiving means is the area of the irradiation target object that is actually occupied by the object attached to the irradiation target object. Can be brought close enough. That is, the shadow factor can be reduced. Therefore, even if the amount of the object attached is large, it can be detected with sufficient sensitivity, and the range in which the amount of the object can be detected with high sensitivity is widened.
In addition, as a method of narrowing the angle, a method of bringing a light emitting element forming a light emitting unit of the optical sensor and a light receiving element forming a light receiving unit of the optical sensor close to each other is usually adopted. However, since the elements can only be brought close to each other until they come into contact with each other, there is a limit to the approach. Further, usually, it is necessary to provide a light blocking member between the light emitting element and the light receiving means so that the light from the light emitting means is not directly received by the light receiving means. For this reason, the light emitting element and the light receiving means must be provided. It is difficult to get close. Further, if each element is separated from the irradiation target in a state where the elements are brought close to each other, it is possible to further narrow the angle. However, as each element is further away from the irradiation target, the light quantity becomes insufficient, and as a result, the sensitivity of the optical sensor is reduced. For these reasons, it has been difficult for the conventional optical sensor to set the angle to 25 ° or less.
[0012]
In the optical sensor according to the twelfth aspect, a light-condensing member is provided in at least one of an incident optical path of incident light to the irradiation target and a regular reflection optical path of regular reflection light from the irradiation target. . As described above, as the light emitting means and the light receiving means are moved away from the irradiation target, the sensitivity of the optical sensor decreases. However, in the present optical sensor, if the light collecting member is provided so that the optical axis of the light collecting member coincides with the center line of the optical path, the incident light can be condensed at the irradiation target position of the irradiation target or the specular reflection light can be collected. Can be focused on the light receiving position of the light receiving means. Therefore, even if the light emitting unit and the light receiving unit are separated from the irradiation target, a decrease in the light amount can be suppressed. Therefore, the angle between the center line of the incident light path immediately before reaching the irradiation object and the center line of the regular reflection light path immediately after reflection on the irradiation object can be reduced without lowering the sensitivity.
Further, in the present optical sensor, if the optical axis of the light collecting member is shifted or inclined from the center line of the optical path, the light can be refracted to change the traveling direction of the light. Therefore, the distance between the light emitting means and the light receiving means is large, and the center line of the incident light path immediately after the light is irradiated from the light emitting means and the center of the regular reflection light path immediately before the light receiving means receives the regular reflected light. Even when the angle between the beam and the line is wide, the angle between the center line of the incident light path immediately before reaching the irradiation object and the center line of the regular reflection light path immediately after reflection on the irradiation object can be reduced. Become. In this case, since it is not necessary to separate the light emitting means and the light receiving means from the irradiation target, the sensitivity of the optical sensor is not reduced.
[0013]
Further, in the optical sensor according to the eighteenth aspect, at least one of the light emitting means and the light receiving means is constituted by a surface mounting optical means in which an optical element is surface mounted on a substrate. Such a surface mounting optical means can reduce the interval between optical elements serving as light emitting elements or light receiving elements, the center line of the incident optical path immediately before reaching the irradiation target, and immediately after reflection on the irradiation target. Can be made sufficiently narrow with respect to the center line of the regular reflection optical path. Furthermore, in recent years, such surface-mounted optical elements have been miniaturized so as to be used for small products such as mobile phones, and at present, very small optical elements having dimensions of 3 mm or less are being realized. is there. Therefore, the distance between the optical elements to be surface-mounted can be further reduced in the future, and the angle formed can be sufficiently reduced.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to an electrophotographic color laser printer (hereinafter, simply referred to as a “printer”) will be described.
FIG. 2 is a sectional view illustrating a schematic configuration of the printer according to the present embodiment. The printer 1 has a configuration in which a paper feed unit 2 is provided at a lower portion of the apparatus main body, and an image forming unit 3 is disposed above the paper feed unit 2. A paper discharge tray 60 is formed on the upper surface of the apparatus. A broken line in the drawing indicates a conveyance path of a recording sheet as a recording material. The recording paper is fed from the paper feed unit 2, the image formed by the image forming unit 3 is transferred to the front surface, is fixed by the fixing device 50, and is discharged to the discharge tray 60. Note that, as indicated by reference numeral h in the figure, manual sheet feeding is possible from the side of the apparatus. A double-sided device 90 is mounted on a side surface of the device main body. When forming an image on both sides of a recording sheet, after forming and fixing an image on one side, the recording sheet is conveyed as shown by a dashed line r in the figure, and the front and back of the recording sheet are turned through a double-sided device 90. After the reversal, the sheet is fed again through the re-conveying unit 40, and an image is formed on the other surface.
[0015]
The image forming section 3 is provided with a transfer / conveyance belt device 20 which is arranged so as to be inclined such that the paper supply side is downward and the paper discharge side is upward. Four image forming units 4Y, 4M, 4C, and 4Bk for yellow (Y), magenta (M), cyan (C), and black (Bk) in this order from the bottom along the upper traveling surface of the transfer and transport belt device 20. Are arranged side by side. Since the configuration of each image forming unit 4Y, 4M, 4C, 4Bk is the same, the image forming unit 4M for magenta will be described below as an example.
[0016]
FIG. 3 is an enlarged view showing details of the magenta image forming unit 4M. The image forming unit 4M includes a photosensitive drum 5M as an image carrier, and the photosensitive drum 5M is driven to rotate clockwise in the figure by a driving unit (not shown). Around the photoconductor drum 5M, there are provided a charging roll 6M, a developing device 10M, a cleaning device 9M, a toner adhesion amount detection sensor (hereinafter, referred to as a "P sensor") 30M, and the like. The developing device 10M applies the toner carried on the developing sleeve 11M as a developer carrier to the photosensitive drum 5M. As shown in FIG. 2, the laser beam from the optical writing device 8 as a latent image forming means is applied to the photosensitive drum 5M from between the charging roll 6M and the developing sleeve 11M. The configuration and operation of the P sensor 30M will be described later in detail.
[0017]
An endless belt-shaped transfer conveyance belt 21 is provided in the transfer conveyance belt device 20. The transfer conveyance belt 21 is stretched around a driving roller 22, a driven roller 23, and tension rollers 24 and 25. On the inner side of the upper running surface of the transfer conveying belt 21, a transfer brush 28 constituting a transfer unit is provided at a position facing each of the photosensitive drums 5M, 5C, 5Y, 5Bk of the image forming units 4M, 4C, 4Y, 4Bk. Are in contact. The transfer brush 28 is applied with a transfer bias having a polarity (plus polarity) opposite to the charge polarity (minus polarity in this embodiment) of the toner. A paper suction roller 27 is provided above the driven roller 23 with the transfer conveyance belt 21 interposed therebetween. The recording paper is sent out onto the transfer conveyance belt 21 from between the driven roller 23 and the suction roller 27, and is conveyed while being electrostatically adsorbed on the transfer conveyance belt 21 by the bias voltage applied to the suction roller 27. You. In this embodiment, the process linear speed is set to 125 mm / sec, and the recording paper is conveyed at this speed.
[0018]
The fixing device 50 employs a belt fixing method in this embodiment, and has a configuration in which a fixing belt 54 is wound around a fixing roller 52 and a heating roller 53. The fixing roller 52 and the pressure roller 51 are in pressure contact with each other, and form a fixing nip. The heating roller 53 and the pressure roller 51 include a heater (not shown).
[0019]
Next, a printing operation in the printer 1 will be described. In the following description, the color-coded symbols Y, M, C, and Bk will be omitted as appropriate.
In the image forming units 4Y, 4M, 4C, and 4Bk of the respective colors, the photosensitive drums 5Y, 5M, 5C, and 5Bk are rotationally driven by a main motor (not shown). Then, the surface of each of the photoconductor drums 5Y, 5M, 5C, and 5Bk is first neutralized by an AC bias applied to the charging roll 6 (the DC component is zero). Become. Next, the photosensitive drums 5Y, 5M, 5C, and 5Bk are uniformly charged to a potential substantially equal to the DC component by applying to the charging roll 6 a voltage in which an AC voltage and a DC voltage are superimposed. In this embodiment, the surface potential is charged to about -500V to -700V. The target charging potential is determined by a process control unit (not shown).
[0020]
On the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5Bk charged in this way, an electrostatic latent image corresponding to each color is formed by the optical writing device 8. The optical writing device 8 drives an LD (laser diode) (not shown) based on image data sent from a host machine such as a personal computer to irradiate the polygon mirror 7 with laser light. This laser beam is guided onto the surface of each of the photosensitive drums 5Y, 5M, 5C, 5Bk via a cylinder lens or the like. The surface of the photosensitive member irradiated with the laser light has a potential of about -50 V, and this portion becomes an electrostatic latent image to be developed with toner.
[0021]
When toner is applied from the developing device 10 to the electrostatic latent image, toner images of respective colors are formed on the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5Bk. In the present embodiment, a developing bias (−300 V to −500 V) in which a DC voltage and an AC voltage are superimposed is applied to the developing sleeve 11. Therefore, the negative polarity toner carried on the developing sleeve 11 adheres only to the surface portions (electrostatic latent image portions) of the photosensitive drums 5Y, 5M, 5C, and 5Bk whose potential has been reduced by the optical writing due to the developing electric field. Does not adhere to the surface portions (non-electrostatic latent image portions) of the photosensitive drums 5Y, 5M, 5C, and 5Bk whose potentials have not been reduced without being written by light. As a result, a toner image of each color is formed on the electrostatic latent image portion of each of the photosensitive drums 5Y, 5M, 5C, and 5Bk.
[0022]
On the other hand, the recording paper is fed from the paper feeding unit 2, and the fed recording paper once strikes a pair of registration rollers 41 provided on the upstream side in the transport direction of the transfer transport belt device 20. Then, the recording paper is conveyed on the transfer conveyance belt 21 in synchronization with the transfer timing of each color toner image, and reaches the transfer position facing each of the photosensitive drums 5Y, 5M, 5C, and 5Bk. At this transfer position, a transfer electric field is formed by the action of a transfer bias applied to a transfer brush 28 disposed on the back side of the transfer conveyance belt 21. By this transfer electric field, the toner images of the respective colors on the photosensitive drums 5Y, 5M, 5C, 5Bk are sequentially transferred onto the recording material so as to be superimposed on each other.
In the case of printing a monochrome image, a toner image of black toner is formed only on the photosensitive drum 5Bk of the black image forming unit 4Bk, and the transfer conveyance belt 21 synchronizes with the transfer timing of the toner image. The recording paper is conveyed, and only the black toner image is transferred.
[0023]
The recording paper onto which the toner images of each color have been transferred in this manner is separated from the transfer conveyance belt 21 at the position of the drive roller 22 by a curvature and sent to the fixing device 50. Then, when passing through the fixing nip of the fixing device 50, the toner images of each color are fixed on the recording paper by heat and pressure. The recording paper on which the fixing has been completed is discharged to a paper discharge tray 60 provided on the upper surface of the apparatus main body, or transferred to a double-sided device 90 as indicated by a symbol r in FIG.
[0024]
Hereinafter, detection of the amount of toner adhering on the surface of each of the photosensitive drums 5Y, 5M, 5C, and 5Bk, which is a characteristic part of the present invention, will be described.
In the printer 1 according to the present embodiment, a process control operation (hereinafter, referred to as a “pro-control operation”) for optimizing the image density of each color is executed when the power is turned on or every time a predetermined number of prints are performed. In this procedure, a density detection patch (hereinafter, referred to as a “reference pattern”) is formed on each of the photosensitive drums 5Y, 5M, 5C, and 5Bk. The reference pattern formed on each of the photosensitive drums 5Y, 5M, 5C, and 5Bk is a continuous tone reference pattern by sequentially switching the charging bias and the developing bias. That is, in the present embodiment, a linear reference pattern in which the toner adhesion amount changes in a gradation manner is created along the surface movement direction of the photosensitive drum. Then, as shown in FIG. 2, this reference pattern is detected by P sensors 30Y, 30M, 30C, 30Bk provided in each of the image forming units 4Y, 4M, 4C, 4Bk.
[0025]
In this embodiment, the reference pattern on the photosensitive drum is detected. After the reference pattern formed on each of the photosensitive drums 5Y, 5M, 5C, and 5Bk is transferred onto the transfer / conveying belt 21, It may be configured to detect. In this case, the P sensor 30 is disposed so as to face the transfer / transport belt 21. Specifically, for example, as shown in FIG. 4, the transfer / transport belt device 20 is disposed at a position facing the tension roller 24. Since the image forming units 4Y, 4M, 4C, and 4Bk face the portion of the transfer / conveying belt 21 that conveys the recording paper, there is little room in the space for arranging the P sensor 30, but as shown in FIG. There is a space in the portion of the transfer conveyance belt 21 that does not convey the paper, and it is possible to prevent an increase in space due to the arrangement of the P sensor or a complicated arrangement of the devices. In the case where the reference pattern is detected after the transfer onto the transfer / transport belt 21, the transfer is performed on the transfer / transport belt 21 so that the reference patterns of the respective colors do not overlap each other.
[0026]
It should be noted that the P sensor 30 can also be used as a means for detecting the positional deviation of the transfer / transport belt 21. That is, by providing a predetermined mark on the transfer / transport belt 21 and detecting the mark with the P sensor 30, the shift of the transfer / transport belt 21 in the main scanning direction can be detected.
[0027]
Next, the configuration of the P sensor 30 in the present embodiment will be described.
Since the configuration of the P sensor provided in each of the image forming units 4Y, 4M, 4C, and 4Bk is the same, the P sensor 30M provided in the magenta image forming unit 4M will be described below as an example. In the following description, the color-coded symbols Y, M, C, and Bk will be omitted as appropriate.
[0028]
FIG. 1 is a cross-sectional view illustrating a schematic configuration of a P sensor 30 in the present embodiment. The P sensor 30 in the present embodiment mainly includes a light emitting element 31 as a light emitting unit, a first light receiving element 32 as a light receiving unit for receiving specularly reflected light, and a second light receiving unit for receiving diffusely reflected light. And an element 33. Each of the elements 31, 32, and 33 is mounted on a printed circuit board 34 and sealed in a single package 35. In the package 35, a path for securing an incident optical path until the incident light emitted from the light emitting element 31 reaches the surface of the photosensitive drum 5, and the regular reflection light regularly reflected on the surface of the photosensitive drum 5. Passages for securing a regular reflection optical path up to the first light receiving element 32 are formed. In this embodiment, a GaAs light emitting diode having a peak emission wavelength of 950 nm is used as the light emitting element 31, and a Si phototransistor having a peak spectral sensitivity wavelength of 800 nm is used as the first light receiving element 32 and the second light receiving element 33. Note that, as the first light receiving element 32 and the second light receiving element 33, other light receiving elements such as a PD (photodiode) can be used in addition to the Si phototransistor.
[0029]
In the present embodiment, a continuous tone reference pattern is created on each photoconductor drum 5, and the P sensor 30 continuously detects the toner adhesion amount of the reference pattern in which the toner density changes in tone. Outputs of the first light receiving element 32 and the second light receiving element 33 in the P sensor 30 are sent to a control unit (not shown). The control unit continuously grasps the toner adhesion amount of the reference pattern based on the regular reflection light amount and the irregular reflection light amount obtained from these outputs, and compares the grasped toner adhesion amount with a predetermined target adhesion amount. I do. Based on the comparison result, the control unit functions as an image density control unit, and controls the intensity of the laser beam of the optical writing device 8, the charging bias applied to the charging roll 6, the developing bias applied to the developing sleeve 11, The amount of toner replenished into the developing device is appropriately changed, and the image density is adjusted to a desired density.
[0030]
By the way, in this embodiment, a toner having a small particle diameter of 8 μm or less is used. Therefore, as described above, since it is necessary to perform detection by the P sensor in a region where the amount of toner adhesion is large, the incident angle θ₀And the specular reflection angle θ₁It is necessary to narrow the angle obtained by adding the above so that detection can be performed with sufficient sensitivity even in a region where the amount of toner adhesion is large.
The weight average particle size of the toner can be measured by various methods, for example, using a Coulter counter. As the coulter counter, for example, a Coulter counter type II (manufactured by Coulter Inc.) can be used. The weight average particle size of the toner can be determined by analyzing characteristics such as a number distribution and a volume distribution based on the measurement results obtained by such a Coulter counter. As the electrolytic solution used in the measurement by the Coulter counter, a 1% aqueous sodium chloride solution adjusted using primary sodium chloride can be used.
[0031]
The toner used in the present embodiment is a toner formed by a so-called polymerization method, and has a shape close to a true sphere and an average circularity of 0.93 or more. Therefore, as described above, the shadow factor increases, and the sensitivity of the P sensor for detecting the regular reflection light decreases in a region where the toner adhesion amount is large on the surface of the photosensitive drum. It is necessary to be able to detect with sufficient sensitivity even in the region.
Note that the average circularity of the toner is an average value of the circularity of each toner, and is measured by the following method. The circularity of each toner was measured using a flow particle image analyzer FPIA-2100 manufactured by SYSMEX CORPORATION. In this measurement, first, a 1% aqueous NaCl solution is prepared using primary sodium chloride. Thereafter, this NaCl aqueous solution was passed through a 0.45 filter to obtain a liquid of 50 to 100 [ml], and a surfactant, preferably an alkylbenzene sulfonate, of 0.1 to 5 [ml] was added thereto as a dispersant. Further, 1 to 10 [mg] of the sample is added. This is subjected to a dispersion treatment for 1 minute by an ultrasonic disperser, and the particle concentration is adjusted to 5000 to 15000 [particles / μl] to obtain a dispersion. This dispersion is imaged with a CCD camera, and the value obtained by dividing the circumference of a circle having the same area as the area of the two-dimensional projected image of the toner by the perimeter of the two-dimensional projected image of the toner is obtained. Used as a degree. Note that, from the accuracy of the pixels of the CCD, a toner having the same area as the area of the two-dimensional projected image of the toner and having a diameter (equivalent circle diameter) of 0.6 [μm] or more was regarded as effective. The average circularity of the toner is obtained by obtaining the circularity of each toner, adding all the circularities of all toners within the measurement range, and dividing the sum by the number of toners.
[0032]
Therefore, in the present embodiment, as shown in FIG. 1, the light emitting element 31 and the first light receiving element 32 are arranged such that the relative positions of the surface of the photosensitive drum in the normal direction are shifted from each other. With this arrangement, even when the light emitting element 31 and the first light receiving element 32 are brought close to each other, they do not come into contact with each other. As shown in the figure, the angle between the center line of the incident light path of the incident light emitted from the light emitting element 31 with respect to the surface of the photosensitive drum 5 and the normal direction Z of the photosensitive drum surface is defined as the incident angle θ.₀And the angle between the center line of the regular reflection optical path of the regular reflection light regularly reflected on the photosensitive drum surface and the normal direction Z of the photosensitive drum surface is the regular reflection angle θ.₁In this embodiment, the incident angle θ₀And the specular angle θ₁Can be set so as to be 25 ° or less, preferably 20 ° or less, which is difficult with the conventional P sensor.
[0033]
[Modification 1]
Next, the incident angle θ₀And the specular reflection angle θ₁A modification example (hereinafter, this modification example is referred to as “Modification Example 1”) for setting an angle obtained by adding the above to 25 ° or less will be described.
Even in the configuration shown in FIG. 1, since the light emitting element 31 cannot be arranged so as to block the regular reflection optical path, there is a limit to the approach between the light emitting element 31 and the first light receiving element 32. Therefore, in the first modification, the light-emitting element 31 and the first light-receiving element 32 are not brought close to each other, and the light traveling direction is changed to at least one of the incident optical path and the regular reflection optical path. The configuration in which the direction changing means is provided is adopted, and the incident angle θ is used.₀And the specular reflection angle θ₁Is set so that the angle obtained by adding the above is not more than 25 °.
[0034]
FIG. 5 is a cross-sectional view illustrating a schematic configuration of the P sensor 130 according to the first modification.
The light-emitting element 31, the first light-receiving element 32, and the third light-receiving element 33 of the P sensor 130 of the first modification are the same as the P sensor 30 shown in FIG. However, in the P sensor 130 of the first modification, the light emitting element 31 and the first light receiving element 32 do not deviate from the relative position in the normal direction of the photosensitive drum surface. Therefore, in this state, the incident angle θ₀And the specular reflection angle θ₁Cannot be set so that the angle obtained by adding the above is not more than 25 °. Therefore, in the first modification, reflection mirrors 136a and 136b, which are light reflection members as traveling direction changing means, are provided in the incident light path and the regular reflection light path, respectively.
[0035]
With such a configuration, the traveling direction of incident light emitted from the light emitting element 31 is changed by being reflected by the reflection mirror 136a. Therefore, even if the angle formed by the center line of the incident light path portion up to the reflection mirror 136a and the normal direction Z of the photosensitive drum surface is arbitrarily set, the incident light immediately before reaching the photosensitive drum surface can be used. The angle between the center line of the incident optical path and the normal direction Z can be set narrow. In addition, the direction of travel of the specularly reflected light that is specularly reflected on the surface of the photosensitive drum is changed by being reflected on the reflection mirror 136b. Therefore, similarly to the case of the incident light, the angle between the center line of the regular reflection optical path from the reflection mirror 136b to the first light receiving element 32 and the normal direction Z of the surface of the photosensitive drum can be arbitrarily set. The angle between the center line of the regular reflection optical path portion immediately after the regular reflection on the surface of the photosensitive drum and the normal direction Z can be set narrow. Therefore, according to the configuration of the first modification, even if the arrangement of the light emitting element 31 and the first light receiving element 32 is arbitrarily determined, if the positions and orientations of the reflection mirrors 136a and 136b are appropriately set, the incident angle θ₀And the specular reflection angle θ₁Can be set to be equal to or less than 25 °.
[0036]
In the first modification, the case where the light is reflected by the reflection mirrors 136a and 136b to change the traveling direction of the light has been described. However, as shown in FIG. It may be used as a changing means to change the traveling direction of light. In this case, the inner wall of the light guide functions as a light reflecting member. Further, a diffraction grating or the like may be used as the light traveling direction changing means to change the traveling direction of light.
[0037]
[Modification 2]
Next, the incident angle θ₀And the specular reflection angle θ₁Another modified example (hereinafter, this modified example will be referred to as “modified example 2”) for setting the angle obtained by adding the above to 25 ° or less will be described.
In the second modification, similarly to the first modification, the light travels along at least one of the incident optical path and the regular reflection optical path without bringing the light emitting element 31 and the first light receiving element 32 close to each other. A structure provided with a traveling direction changing means for changing the direction is adopted, and the incident angle θ₀And the specular reflection angle θ₁Is set so that the angle obtained by adding the above is not more than 25 °.
[0038]
FIG. 7 is a cross-sectional view illustrating a schematic configuration of the P sensor 230 according to the second modification.
The basic configuration of the P sensor 230 of the second modification is the same as that of the first modification. However, in the P sensor 230 of the second modification, refraction lenses 236a and 236b, which are light refraction members as traveling direction changing means, are provided in the middle of the incident light path and the regular reflection light path, instead of the reflection mirrors 136a and 136b. ing.
With such a configuration, incident light emitted from the light emitting element 31 is refracted by transmitting through the refraction lens 236a, and the traveling direction is changed. Therefore, even if the angle formed by the center line of the incident optical path portion up to the refractive lens 236a and the normal direction Z of the photosensitive drum surface is arbitrarily set, the incident light immediately before reaching the photosensitive drum surface can be used. The angle between the center line of the incident optical path and the normal direction Z can be set narrow. Also, the specularly reflected light that is specularly reflected on the surface of the photosensitive drum is refracted by passing through the refraction lens 236b, and its traveling direction is changed. Therefore, as in the case of the incident light, the angle between the center line of the regular reflection optical path from the refracting lens 236b to the first light receiving element 32 and the normal direction Z of the surface of the photosensitive drum can be arbitrarily set. The angle between the center line of the regular reflection optical path portion immediately after the regular reflection on the surface of the photosensitive drum and the normal direction Z can be set narrow. Therefore, according to the configuration of the second modification, similarly to the first modification, even if the arrangement of the light emitting element 31 and the first light receiving element 32 is arbitrarily determined, the positions and orientations of the refractive lenses 236a and 236b are appropriately adjusted. If set, the incident angle θ₀And the specular reflection angle θ₁Can be set to be equal to or less than 25 °.
[0039]
A convex lens or concave mirror as a light condensing member or a concave lens as a light dispersing member is provided at a position where the refractive lenses 236a and 236b are arranged so that the optical axis is deviated from the center line of the incident light path and the regular reflection light path. If a mirror or a convex lens is arranged, the traveling direction of light can be changed in the same manner, and the same effect can be obtained.
Further, a convex lens or a concave mirror as a condensing member or a light dispersing member as a light dispersing member is provided at a position where the refractive lenses 236a and 236b are arranged so that an optical axis is inclined with respect to a center line of an incident optical path and a regular reflection optical path. Even if a concave mirror or a convex lens is arranged, the traveling direction of light can be changed in the same manner.
[0040]
[Modification 3]
Next, the incident angle θ₀And the specular reflection angle θ₁Still another modification example (hereinafter, this modification example is referred to as "modification 3") for setting the angle obtained by adding? To 25 degrees or less will be described.
If the light emitting element 31 and the first light receiving element 32 are separated from the surface of the photoconductor drum 5, the relative positions in the normal direction of the photoconductor drum surface need not be displaced from each other as shown in FIG. Incident angle θ₀And the specular reflection angle θ₁Can be set so that the angle obtained by adding the above is not more than 25 °. However, in this case, the sensitivity decreases because the amount of light received by the first light receiving element 32 is insufficient. Therefore, in the third modification, the light-emitting element 31 and the first light-receiving element 32 are provided in at least one of the incident optical path and the regular reflection optical path so that the sensitivity does not decrease even when the light-emitting element 31 and the first light receiving element 32 are separated from the surface of the photosensitive drum 5. The light-collecting member is arranged so that the optical axis coincides with the center line of the optical path, and the incident angle θ₀And the specular reflection angle θ₁Is set so that the angle obtained by adding the above is not more than 25 °.
[0041]
FIG. 8 is a cross-sectional view illustrating a schematic configuration of the P sensor 330 according to the third modification.
The light emitting element 31, the first light receiving element 32, and the third light receiving element 33 of the P sensor 330 of the third modification are the same as the P sensor 30 shown in FIG. However, in the P sensor 330 according to the third modification, the light emitting element 31 and the first light receiving element 32 do not deviate from the relative position in the normal direction of the photosensitive drum surface, and the light emitting element 31 and the first light receiving element 32 Long distance from the drum surface. Therefore, in this state, the amount of light received by the first light receiving element 32 is insufficient, and the sensitivity is reduced. Therefore, in the third modification, a one-sided convex lens 336a as a light condensing member is provided in the middle of the incident optical path, and a one-sided concave lens 336b as a light diffusing member is provided in the middle of the regular reflection optical path.
[0042]
In the third modification, the lenses 336a and 336b are arranged such that the flat sides of the one-side convex lens 336a and the one-side concave lens 336b face the photosensitive drum surface. Thus, even if the lenses 336a and 336b are stained by the scattered toner, the cleaning is facilitated. The plane referred to here is not strict, and includes a plane having a curvature large enough to facilitate cleaning.
In the third modification, the distance from the light emitting element 31 to the one-side convex lens 336a is set to a₁And the distance from the one-side convex lens 336a to the surface of the photosensitive drum is b₁And the focal length of the one-side convex lens 336a is f₁And the distance from the single-sided concave lens 336b to the first light receiving element 32 is a₂And the distance from the photosensitive drum surface to the single-sided concave lens 336b is b₂And the focal length of the single-sided concave lens 336b is f₂In this case, the one-side convex lens 336a and the one-side concave lens 336b are arranged so as to satisfy the two arithmetic expressions shown in the following Expression 1. Thereby, the specularly reflected light of the incident light from the light emitting element 31 can be focused on the single-sided concave lens 336b. Then, the collected specularly reflected light can be collected by the one-side concave lens 336b so as to travel toward the first light receiving element 32. Therefore, the transmission efficiency of the specularly reflected light to the first light receiving element 32 can be further increased. In addition, the effect of increasing the margin for variations in the mounting angle and the like of the one-side convex lens 336a and the one-side concave lens 336b can be obtained. Note that these effects can be obtained if one of the two arithmetic expressions shown in the following Expression 1 is satisfied.
(Equation 1)
1 / a₁ + 1 / (b₁+ B₂) = 1 / f₁
1 / a₂ + 1 / (b₁+ B₂) = 1 / f₂
[0043]
[Modification 4]
Next, the incident angle θ₀And the specular reflection angle θ₁Still another modification example (hereinafter, this modification example is referred to as “modification example 4”) for setting the angle obtained by adding the above to 25 ° or less will be described.
FIG. 9 is a cross-sectional view illustrating a schematic configuration of the P sensor 430 according to the fourth modification.
The light-emitting element 431, the first light-receiving element 432, and the third light-receiving element 433, which are optical elements of the P sensor 430 according to the fourth modification, are formed of surface mount devices (SMDs), and include the printed circuit board 34. Surface mounted on top. The element surfaces of the elements 431, 432, and 433 are oriented in the normal direction to the surface of the printed circuit board 34. The contents of each of the elements 431, 432, and 433 are the same as those of the P sensor 30 shown in FIG. By configuring the light emitting element 431 and the first light receiving element 432 with the SMD in this manner, effects such as downsizing of the element itself can be obtained, and the distance between the elements can be reduced. That is, the incident angle θ₀And the specular reflection angle θ₁Can be set to be equal to or less than 25 °.
[0044]
Further, even when each element has the SMD configuration as in the fourth modification, the light-emitting element 431 and the first light-receiving element 432 can only be brought close to each other until they come into contact with each other. . Therefore, the incident angle θ₀And the specular reflection angle θ₁In the fourth modification, a common lens 436, which is a light refraction member as a course changing means, is provided on the incident light path and the regular reflection light path in order to further reduce the angle obtained by adding. Since the common lens 436 is disposed so that its optical axis is deviated from the center line of the incident optical path and the regular reflection optical path, the traveling direction of light passing through each optical path can be changed. Therefore, in the configuration of the fourth modification, the incident angle θ can be obtained by appropriately setting the position and posture of the common lens 436 without forcibly bringing the light emitting element 431 and the first light receiving element 432 close to each other.₀And the specular reflection angle θ₁Can be set narrower.
[0045]
In the fourth modification, the second light receiving element 433 for receiving diffuse reflection is also surface-mounted, and is arranged at a position away from the surface of the photosensitive drum. Therefore, there is a possibility that the amount of diffusely reflected light received by the second light receiving element 433 is insufficient. Therefore, in the fourth modification, the convex lens 437 is provided on the irregular reflection optical path of the irregular reflection light received by the second light receiving element 433, with the optical axis shifted from the center line of the optical path. Thereby, the irregularly reflected light when the incident light is irregularly reflected by the toner can be collected by the convex lens 437 toward the second light receiving element 433. Therefore, the amount of diffusely reflected light received by the second light receiving element 433 can be sufficiently ensured, and appropriate image density control can be performed.
[0046]
In the fourth modification, since the light emitting element 431 and the first light receiving element 432 are surface-mounted on the same surface of the same printed circuit board 34, there is no shielding on the line connecting these optical elements. In addition, the incident light emitted from the light emitting element 431 is directly received by the first light receiving element 432, and accurate detection cannot be performed. Therefore, in the fourth modification, a light-shielding wall 435a as light-shielding means is provided on a line connecting the light-emitting element 431 and the first light-receiving element 432. Note that, instead of the light shielding wall 435a, a mounted component such as a capacitor or a coil mounted on the printed circuit board 34 can be used. Further, instead of providing such a light shielding means, a configuration in which a through hole is provided in a printed circuit board surface existing on a line segment connecting the light emitting element 431 and the first light receiving element 432 may be employed. Light can be prevented from being directly received by the first light receiving element 432. That is, with such a configuration, it is possible to suppress that the reflected light when the incident light from the light emitting element 431 is reflected on the printed board surface is directly received by the first light receiving element 432. Therefore, accurate detection becomes possible.
[0047]
[Modification 5]
Next, the incident angle θ₀And the specular reflection angle θ₁Still another modification example (hereinafter, this modification example is referred to as "modification example 5") for setting the angle obtained by adding? To 25 degrees or less will be described.
FIG. 10 is a schematic configuration diagram showing a P sensor 530 in the fifth modification.
The light emitting element 531, the first light receiving element 532, and the third light receiving element 533, which are the optical elements of the P sensor 530 of the fifth modification, are formed of the SMD similarly to the fourth modification, and are formed on the printed circuit board 34. Although mounted, each element surface faces in a direction parallel to the surface direction of the printed circuit board 34. The contents of each of the elements 531, 532 and 533 are the same as those of the P sensor 30 shown in FIG. By configuring the light emitting element 531 and the first light receiving element 532 with the SMD in this manner, the incident angle θ is set in the same manner as in the fourth modification.₀And the specular reflection angle θ₁Can be set to be equal to or less than 25 °.
[0048]
Further, similarly to the case of the fourth modification, a light-dissipating member or a light-collecting member as a course changing means is provided on the incident optical path and the specular reflection optical path so that its optical axis is aligned with the center line of the incident optical path and the specular reflection optical path. You may arrange so that it may shift. With such a configuration, even if the light emitting element 531 and the first light receiving element 532 are not forcibly brought close to each other, the above incident angle θ can be obtained.₀And the specular reflection angle θ₁Can be set narrower.
In the fifth modification, the light receiving element 532 is placed at the blind spot of the light emitting element 532 (a position at which the incident light does not directly reach) so that the incident light emitted from the light emitting element 531 is not directly received by the first light receiving element 532. Has been placed. Note that, similarly to the fourth modification, a light-shielding unit such as a light-shielding wall or a mounting component is provided on a line connecting the light-emitting element 531 and the first light-receiving element 532, or the light-emitting element 531 and the first light-receiving element 532 are connected to each other. A through-hole may be provided in the printed circuit board surface existing on the line segment connecting the light-emitting elements 431, so that the incident light emitted from the light-emitting element 431 may be prevented from being directly received by the first light-receiving element 432.
[0049]
In the fifth modification, since the optical path is parallel to the surface direction of the printed circuit board, if a mounted component is mounted on the optical path, the light is blocked by the mounted component and the first light receiving element The light receiving amount of 532 becomes insufficient. For this reason, in the fifth modification, the mounted components on the printed circuit board 34 are mounted at positions that do not block the incident optical path and the regular reflection optical path. In the fifth modification, a light-shielding plate 548 having a cutout at a portion serving as an incident optical path is provided on the printed circuit board 34. The notch has a so-called light-squeezing effect.
[0050]
[Modification 6]
Next, the incident angle θ₀And the specular reflection angle θ₁Another modification example (hereinafter, this modification example will be referred to as “modification example 6”) for setting the angle obtained by adding the above to 25 ° or less will be described.
FIG. 11 is a cross-sectional view illustrating a schematic configuration of a P sensor 630 according to the sixth modification. The light emitting element 531 which is an optical element of the P sensor 630 of the sixth modification is configured by SMD similarly to the fifth modification, and its element surface faces in a direction parallel to the surface direction of the printed circuit board 34. So that it is surface mounted. Further, the first light receiving element 32, which is an optical element of the P sensor 630 of the sixth modification, is the same as the first light receiving element of the P sensor 30 shown in FIG. The illustration of the second light receiving element for receiving diffusely reflected light is omitted. Even with such a configuration, the incident angle θ₀And the specular reflection angle θ₁Can be set to be equal to or less than 25 °.
[0051]
In the sixth modification, a light-condensing lens 636 that is a light-condensing member serving as a path changing unit and a light refracting member is disposed on the incident optical path. In this configuration, incident light that has traveled along the surface of the printed circuit board 34 from the light emitting element 531 is refracted by the condenser lens 636 and is condensed on the irradiation target on the surface of the photosensitive drum. Also, on the regular reflection optical path, a path changing unit and a condenser lens 637 as a condenser member as a light refraction member are arranged. In the sixth modification, the start point of the incident optical path, that is, the distance from the light emitting element 531 to the condenser lens 636 and the start point of the regular reflection optical path, that is, the distance from the photosensitive drum surface to the condenser lens 637 are represented by a. The distance from 636 to the end point of the incident optical path, that is, the surface of the photosensitive drum, and the distance from the condenser lens 637 to the end point of the regular reflection optical path, that is, the first light receiving element 32 are represented by b, and the focal length of each condenser lens 636, 637 is f. In this case, the condenser lenses 636 and 637 are arranged so as to satisfy the arithmetic expression shown in Expression 2 below. Thereby, the transmission efficiency of the incident light from the light emitting element 531 to the irradiation target on the photosensitive drum surface and the transmission efficiency of the regular reflection light from the photosensitive drum surface to the first light receiving element 32 can be respectively increased.
(Equation 2)
1 / a + 1 / b = 1 / f
[0052]
With such a configuration, even if the incident light emitted from the light emitting element 531 slightly diverges before reaching the condenser lens 636, the incident light is collected by the condenser lens 636 toward the irradiation target on the surface of the photosensitive drum. . Therefore, even if the light emitting element 531 is separated from the surface of the photoconductor drum, it is possible to irradiate the irradiation target of the photoconductor drum surface with incident light having a sufficient light amount. In addition, even if the specularly reflected light that has been specularly reflected on the surface of the photoconductor drum slightly diverges before reaching the condenser lens 637, the light is also condensed toward the first light receiving element 32 by the condenser lens 637. Therefore, even if the first light receiving element 32 is separated from the photosensitive drum surface, the first light receiving element 32 can receive the reflected light having a sufficient light amount. Therefore, according to the configuration of Modification 6, even if the light emitting element 531 and the first light receiving element 32 are arranged apart from the photosensitive drum surface, the amount of light received by the first light receiving element 32 does not become insufficient. As a result, the incident angle θ can be reduced without lowering the sensitivity.₀And the specular reflection angle θ₁Can be set to be equal to or less than 25 °.
[0053]
In addition, the regular reflection optical path portion from the condenser lens 637 to the first light receiving element 32 is surrounded by the surface of the printed circuit board 34 and the inner wall surface of the case 635, and these surfaces are reflection surfaces for reflecting light. . Therefore, of the specularly reflected light emitted from the condenser lens 637, the light that does not go to the first light receiving element 32 is repeatedly reflected on the surface of the printed circuit board 34 or the inner wall surface of the case 635, and is received by the first light receiving element 32. Is done. Therefore, the amount of light received by the first light receiving element 32 can be sufficiently ensured.
[0054]
In the sixth modification, since the printed circuit board 34 exists on the line connecting the light emitting element 531 and the first light receiving element 32, the incident light emitted from the light emitting element 531 is directly transmitted to the first light receiving element 32. Is not received.
In the sixth modification, the incident light path and the specular reflection light path are substantially parallel to the surface direction of the printed circuit board 34. Therefore, when light is blocked by a mounted component on the light path, the first light receiving element 532 receives light. Insufficient quantity. Therefore, in the sixth modification, the mounted component is not mounted on the printed circuit board facing the optical path, or the mounted component is formed of a flat SMD 638.
In the sixth modification, a convex portion 635a is formed on the inner wall surface of the case 635 in order to obtain a light stop effect between the printed circuit board 34 and the printed circuit board 34. Therefore, an effect of reducing incident light between the convex portion 635a and the printed board can be obtained. Here, the light emitting position of the light emitting element 531 with respect to the surface of the printed circuit board 34 requires a certain height, so that the incident light passes through a position slightly away from the surface of the printed circuit board 34. Therefore, the aperture effect between the protrusion 635a and the surface of the printed circuit board may be insufficient. Therefore, in the sixth modification, the SMD 638 is surface-mounted on the surface of the printed circuit board 34 facing the convex portion 635a of the inner wall of the case 635. Thereby, the aperture effect of the incident light can be enhanced between the convex portion 635a and the surface of the SMD 638. Note that the effect of increasing the aperture effect can be similarly obtained by separately providing a light blocking member or the like on the printed circuit board 34 without substituting the component mounted on the printed circuit board 34. However, if the SMD 638, which is a component mounted on the printed circuit board 34, is used as in the sixth modification, the cost for providing the light shielding member and the like can be reduced.
[0055]
As described above, the P sensors 30, 130, 230, 330, 430, 530, and 630 as the optical sensors in the present embodiment emit light from the light emitting elements 31, 431, and 531 as at least one light emitting unit. Incident light L₁Is regularly reflected light L when the light is regularly reflected by the surface of the photosensitive drum as the irradiation target.₂Are provided as first light receiving elements 32, 432, and 532 as light receiving means for receiving light. The center line of the incident light path immediately before the incident light from the light emitting elements 31, 431, 531 reaches the surface of the photosensitive drum, and the regular reflection light from the surface of the photosensitive drum. Is 25 ° or less, preferably 20 ° or less, in the regular reflection optical path up to the first light receiving elements 32, 432 and 532, with the center line of the regular reflection optical path immediately after reflection on the photosensitive drum surface. It is constituted so that it may become. This reduces the shadow factor, so that even if the amount of toner adhering to the surface of the photosensitive drum is large, it can be detected with sufficient sensitivity, and the amount of toner that can be detected with high sensitivity can be detected. Spreads.
The P sensors 130, 230, 430, and 630 of Modifications 1, 2, 4, and 6 each include a traveling direction changing unit that changes a traveling direction of light to at least one of an incident optical path and a regular reflection optical path. have. For example, in the first modification, the traveling direction changing means is configured by the reflection mirrors 136a and 136b as light reflecting members that reflect light. In the second modification, the traveling direction changing means is constituted by refraction lenses 236a and 236b as light refraction members for refracting light. In the fourth modification, the traveling direction changing means is constituted by the common lens 436 which is a light-collecting member or a light-dissipating member arranged such that the optical axis deviates from the center line of the optical path. In the sixth modification, the traveling direction changing means is constituted by the condenser lenses 636 and 637 which are the condenser members arranged so that the optical axis is inclined with respect to the center line of the optical path. In this way, by changing the traveling direction of light, as described in the first modification, even if the arrangement of the light emitting element and the first light receiving element is arbitrarily determined, the incident angle θ₀And the specular reflection angle θ₁Can be set narrower. Therefore, the effect of increasing the degree of freedom in the arrangement of the light emitting element and the first light receiving element can be obtained.
Further, the P sensor 330 of the third modification has a single-sided convex lens 336 as a light condensing member so that at least one of the incident optical path and the regular reflection optical path has an optical axis coincident with the center line of the optical path. Is arranged. By adopting such a configuration, as described in the third modification, even if the light emitting element 31 and the first light receiving element 32 are arranged away from the surface of the photosensitive drum, the sensitivity can be reduced without lowering the sensitivity. Angle θ₀And the specular reflection angle θ₁Can be set narrower.
In the P sensor 330 of the third modification, a single-sided concave lens 336b, which is a light dispersing member, is provided on the regular reflection optical path. By providing such a one-sided concave lens 336b on the regular reflection optical path, it is possible to suppress the occurrence of “eclipse” of the regular reflection light due to a variation in the mounting angle of the lens. Therefore, the effect of increasing the degree of freedom of the lens mounting angle is obtained.
In the P sensor 330 of the third modification, the one-side convex lens 336a is provided in the incident optical path, and the distance from the light emitting element 31 to the one-side convex lens 336a is set to a.₁And the distance from the one-side convex lens 336a to the surface of the photosensitive drum is b₁And the focal length of the one-side convex lens 336a is f₁And the distance from the single-sided concave lens 336b to the first light receiving element 32 is a₂And the distance from the photosensitive drum surface to the single-sided concave lens 336b is b₂And the focal length of the single-sided concave lens 336b is f₂In this case, the one-side convex lens 336a and the one-side concave lens 336b are arranged so as to satisfy at least one of the two arithmetic expressions shown in the following Expression 1. Thereby, as described in the third modification, the transmission efficiency of the specularly reflected light to the first light receiving element 32 can be respectively increased.
Further, the P sensors 430, 530, and 630 of Modifications 4 to 6 are surface-mounted optical elements in which at least one of the light-emitting elements 431, 531 and the first light-receiving elements 432, 532 is surface-mounted on the printed circuit board 34. Means. By configuring the light emitting element and the first light receiving element with the SMD in this manner, the distance between the elements can be reduced. That is, the incident angle θ₀And the specular reflection angle θ₁Can be set narrower.
Further, as in the P sensors 330 and 630 of Modifications 3 and 6, a single-sided convex lens 336a or a condenser lens 636 or 637 serving as a condenser is provided on at least one of the incident optical path and the regular reflection optical path. Incident angle θ without lowering the sensitivity.₀And the specular reflection angle θ₁It is possible to obtain the effect described in Modification 3 in which the angle obtained by adding the above can be set to be small, the effect described in Modification 1 in which the degree of freedom in the arrangement of the light emitting element and the first light receiving element increases, and the like. Become.
Further, if the condenser lenses 636 and 637 as the condenser members are provided on both the incident light path and the regular reflection light path as in the P sensor 630 of the sixth modification, the light emitting element 531 and the Since both of the first light receiving elements 32 can be kept away from the photosensitive drum surface, the degree of freedom of arrangement of the light emitting elements and the first light receiving elements is increased.
In the P sensor 630 of Modification 6, the distance a from the start point of the incident light path, that is, the distance from the light emitting element 531 to the condenser lens 636, and the distance from the start point of the regular reflection light path, that is, the surface of the photosensitive drum to the condenser lens 637, are a. The distance from the condenser lens 636 to the end point of the incident light path, that is, the surface of the photosensitive drum, and the distance from the condenser lens 637 to the end point of the specular reflection light path, that is, the first light receiving element 32, are set to b, and each of the condenser lenses 636, 637 Assuming that the focal length is f, the respective condenser lenses are arranged so as to satisfy the arithmetic expression shown in Expression 2 above. Thereby, the transmission efficiency of the incident light from the light emitting element to the irradiation target on the surface of the photoconductor drum and the transmission efficiency of the regular reflection light from the surface of the photoconductor drum to the first light receiving element 32 can be respectively increased.
Also, as in the P sensors 330 and 630 of the third and sixth modifications, the photosensitive drum in the one-side convex lens 336a and the condensing lens 636, 637 as the light condensing member, and the one-side concave lens 336b as the light dispersing member. If the surface facing the surface is a flat surface, as described in the third modification, even if the lens surface is soiled by the scattered toner, the cleaning becomes easy.
Further, the P sensors 30, 130, 230, 330, and 430 of the embodiment and the modifications 1, 2, 3, and 4 enclose the light emitting elements 31, 431 and the first light receiving elements 32, 432 in a single package. With this configuration, the operation of connecting the present P sensor to an electric circuit such as a printed circuit board becomes easy, and the manufacturing process can be simplified.
Further, when the light emitting element 531 and the first light receiving element 32 are mounted on the opposite surfaces of the same substrate 34 as in the P sensor 630 of Modification Example 6, the incident light directly from the light emitting element 531 to the first light receiving element 32 is provided. Can be blocked by the substrate 34. Therefore, since the incident light from the light emitting element 531 is not directly received by the first light receiving element 32, accurate detection is possible.
In the P sensor 430 of the fourth modification, both the light emitting element 431 and the first light receiving element 432 are surface mount components (SMD), and are surface mounted on the same surface of the substrate 34. Further, a light-shielding wall 435a as light-shielding means is provided on a line connecting the light-emitting element 431 and the first light-receiving element 432. Therefore, the incident light directly from the light emitting element 431 to the first light receiving element 432 is blocked by the light shielding wall 435a, and the incident light from the light emitting element 531 is not directly received by the first light receiving element 32, so that accurate detection is possible. Becomes possible. As described in the fourth modification, if a component mounted on the board 34 is used as the light shielding means, it is not necessary to provide a member that is not an electronic component on the board. Can be. Further, as described in Modification 4, even if a through hole is provided in the substrate surface on the line connecting the light emitting element 431 and the first light receiving element 432, the incident light emitted from the light emitting element 431 does not Since it is possible to suppress the light from being reflected by the first light receiving element 432 and being directly received by the first light receiving element 432, accurate detection is possible.
Further, if the mounted components are configured so as not to block the optical path as in the P sensors 530 and 630 of Modifications 5 and 6, the light is blocked by the mounted components and the amount of light received by the first light receiving element 532 becomes insufficient. Things can be avoided.
Further, if the surface-mounted component is surface-mounted on the substrate facing the optical path as in the P sensor 630 of Modification Example 6, the light aperture effect can be enhanced.
The printer according to the present embodiment including each of the above-described modified examples includes a photoconductor drum 5 as an image carrier having a surface that regularly reflects light, and a toner image forming device that forms a toner image on the photoconductor drum 5. The charging roller 6, the optical writing device 8, and the developing device 10 as means, and an optical sensor P for detecting the amount of toner adhered when toner is adhered onto the photosensitive drum 5 by the toner image forming means. A sensor and a control unit as image density control means for performing image density control based on the detection result of the P sensor. Since the above-described P sensors 30, 130, 230, 330, 430, 530, and 630 are used as the P sensors, appropriate image density control can be performed.
Further, since the toner used in the present embodiment has a weight average particle diameter of 8 μm or less, it is necessary to detect the toner adhesion amount with sufficient sensitivity even in a region where the toner adhesion amount is large as described above. However, by using the above-described P sensors 30, 130, 230, 330, 430, 530, and 630, it becomes possible to detect the toner adhesion amount with sufficient sensitivity even in a region where the toner adhesion amount is large.
Further, since the toner used in the present embodiment has an average circularity of 0.93 or more, it is possible to detect the toner adhesion amount with sufficient sensitivity as described above even in a region where the toner adhesion amount is large. Although it is necessary, by using the above-described P sensors 30, 130, 230, 330, 430, 530, and 630, the toner adhesion amount can be detected with sufficient sensitivity even in a region where the toner adhesion amount is large. .
[0056]
In the present embodiment, the present invention has been described by taking as an example a P sensor for detecting the amount of toner adhering on the surface of the photosensitive drum, but the same effects can be obtained even when applied to other optical sensors. Is possible. For example, the present invention can be applied to an optical sensor or the like for detecting the amount of toner attached to a predetermined location to detect the amount of toner scattering. In addition, the present invention is not limited to the image forming apparatus, and can be similarly applied to an optical sensor that detects an amount of an object attached or an attached position of an object in other fields.
In the present embodiment, a tandem-type image forming apparatus including four image forming units 4Y, 4M, 4C, and 4Bk is used, which employs a direct transfer method in which a toner image is directly transferred from each photosensitive drum onto recording paper. However, the present invention is not limited to this, and the same applies to various types or types of image forming apparatuses. That is, a one-drum type image forming apparatus having only one image forming unit, an indirect transfer type image forming apparatus in which toner on a photosensitive drum is once transferred to an intermediate transfer body, and then transferred onto recording paper, etc. The present invention can be similarly applied.
[0057]
【The invention's effect】
According to the invention of claims 1 to 28, the range in which the amount of adhesion of an object that does not regularly reflect light existing on an irradiation target object that regularly reflects light can be detected with high sensitivity can be expanded as compared with the related art. effective.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a schematic configuration of a P sensor provided in each image forming unit of a printer according to an embodiment.
FIG. 2 is a cross-sectional view illustrating a schematic configuration of the printer.
FIG. 3 is an enlarged view showing details of a magenta image forming unit provided in the printer.
FIG. 4 is a cross-sectional view illustrating a schematic configuration of a printer for explaining another example of arrangement of a P sensor.
FIG. 5 is a sectional view showing a schematic configuration of a P sensor according to a first modification.
FIG. 6 is a sectional view showing another configuration example of the P sensor.
FIG. 7 is a cross-sectional view illustrating a schematic configuration of a P sensor according to a second modification.
FIG. 8 is a sectional view showing a schematic configuration of a P sensor according to a third modification.
FIG. 9 is a cross-sectional view illustrating a schematic configuration of a P sensor according to a fourth modification.
FIG. 10 is a schematic configuration diagram showing a P sensor according to a fifth modification.
FIG. 11 is a sectional view showing a schematic configuration of a P sensor according to a sixth modification.
FIGS. 12A and 12B are schematic diagrams illustrating a state in which toner adheres to the surface of a photosensitive drum.
FIG. 13 is a graph showing the relationship between the amount of black toner adhering to the surface of the photosensitive drum and the output voltage of a P sensor that detects specularly reflected light.
FIG. 14 is a graph showing the relationship between the amount of color toner adhering to the surface of the photoconductor drum and the output voltage of a P sensor that detects specularly reflected light.
[Explanation of symbols]
1 Printer
5Y, 5M, 5C, 5Bk Photoconductor drum
10Y, 10M, 10C, 10Bk developing device
21 Transfer conveyor belt
28 Transfer Brush
30, 130, 230, 330, 430, 530, 630 P sensor
31,431,531 Light emitting device
32,432,532 First light receiving element
33, 433, 533 second light receiving element
34 Printed circuit board
35 packages
136a, 136b Reflection mirror
236a, 236b Refractive lens
336a one side convex lens
336b one side concave lens
435a shading wall
436 Common lens
437 convex lens
548 shading plate
635 case
635a convex part
636,637 Condensing lens

Claims

At least one light emitting means;
An optical sensor comprising light receiving means for receiving regular reflection light when the incident light emitted from the light emitting means is regularly reflected by the irradiation object;
The center line of the incident light path immediately before the incident light from the light emitting means to the irradiation object reaches the irradiation object, and the specularly reflected light from the irradiation object reaches the light receiving means. An optical sensor characterized in that the angle formed by the center line of the regular reflection optical path immediately after reflection on the irradiation target object in the regular reflection optical path up to 25 ° is 25 ° or less.

The optical sensor according to claim 1,
An optical sensor characterized in that the angle is 20 degrees or less.

The optical sensor according to claim 1 or 2,
An optical sensor comprising: a traveling direction changing unit that changes a traveling direction of light in at least one of the incident optical path and the regular reflection optical path.

The optical sensor according to claim 3,
An optical sensor, wherein the traveling direction changing means is constituted by a light reflecting member that reflects light.

The optical sensor according to claim 3,
An optical sensor, wherein the traveling direction changing means is constituted by a light refraction member that refracts light.

The optical sensor according to claim 3,
An optical sensor, wherein the traveling direction changing means is constituted by a condensing member or a light dispersing member arranged such that an optical axis deviates from a center line of the optical path.

The optical sensor according to claim 5,
An optical sensor, wherein the traveling direction changing means is constituted by a light condensing member or a light dispersing member arranged so that an optical axis is inclined with respect to a center line of the at least one optical path.

The optical sensor according to claim 1 or 2,
An optical sensor, wherein a light-collecting member is provided on at least one of the incident optical path and the regular reflection optical path so that an optical axis is aligned with a center line of the optical path.

The optical sensor according to claim 1 or 2,
An optical sensor, wherein a light diffusing member is provided in the regular reflection optical path.

The optical sensor according to claim 9,
A light collecting member is provided in the incident light path,
The distance from the light emitting means to the light-collection member and a _1, a distance to the object to be irradiated and b ₁ from the condenser member, and the focal length of the condenser member and f _1, and the light emission Assuming that the distance from the member to the light receiving means is a ₂ , the distance from the irradiation target to the light radiating member is b _2, and the focal length of the light radiating member is f ₂ , the following two arithmetic expressions An optical sensor, wherein the light-collecting member and the light-emitting member are arranged so as to satisfy at least one of the following.
1 / a ₁ + 1 / (b ₁ + b ₂ ) = 1 / f ₁
1 / a ₂ + 1 / (b ₁ + b ₂ ) = 1 / f ₂

11. The optical sensor according to claim 1, wherein at least one of said light emitting means and said light receiving means is optically mounted on a substrate. An optical sensor comprising optical means.

At least one light emitting means;
An optical sensor comprising light receiving means for receiving specularly reflected light when the incident light emitted from the light emitting means is regularly reflected by the irradiation target;
The incident light path from the light emitting means to the irradiation target object, and at least one of the regular reflection light paths to the light receiving means, the regular reflection light from the irradiation object to the light receiving means, An optical sensor comprising a light collecting member.

The optical sensor according to claim 8 or 12,
An optical sensor, wherein the light collecting member is provided in both the incident light path and the regular reflection light path.

The optical sensor according to claim 8, 12, or 13,
When the distance from the start point of the at least one optical path to the light collecting member is a, the distance from the light collecting member to the end point of the light path is b, and the focal length of the light collecting member is f, An optical sensor, wherein the light-collecting member is arranged so as to satisfy an arithmetic expression.
1 / a + 1 / b = 1 / f

The optical sensor according to claim 8, 12, 13, or 14,
An optical sensor, wherein a light diffusing member is provided in the regular reflection optical path.

The optical sensor according to claim 15,
A light collecting member is provided in the incident light path,
The distance from the light emitting means to the light-collection member and a _1, a distance to the object to be irradiated and b ₁ from the condenser member, and the focal length of the condenser member and f _1, and the light emission Assuming that the distance from the member to the light receiving means is a ₂ , the distance from the irradiation target to the light radiating member is b _2, and the focal length of the light radiating member is f ₂ , the following two arithmetic expressions An optical sensor, wherein the light-collecting member and the light-emitting member are arranged so as to satisfy at least one of the following.
1 / a ₁ + 1 / (b ₁ + b ₂ ) = 1 / f ₁
1 / a ₂ + 1 / (b ₁ + b ₂ ) = 1 / f ₂

The optical sensor according to claim 6, 7, 8, 9, 10, 12, 13, 14, 15, or 16,
An optical sensor, wherein a surface of the light condensing member and the light dispersing member or a surface of the light condensing member or the light dispersing member facing the irradiation target is a flat surface.

At least one light emitting means;
An optical sensor comprising light receiving means for receiving specularly reflected light when the incident light emitted from the light emitting means is regularly reflected by the irradiation target;
An optical sensor, wherein at least one of the light-emitting means and the light-receiving means is constituted by a surface-mounted optical means in which an optical element is surface-mounted on a substrate.

The optical sensor according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, or 18.
An optical sensor characterized in that the light emitting means and the light receiving means are enclosed in a single package.

The optical sensor according to claim 11 or 18,
An optical sensor, wherein the optical element of the light emitting means and the optical element of the light receiving means are mounted on opposite surfaces of the same substrate.

20. The optical sensor according to claim 11, 18 or 19,
Both the light emitting means and the light receiving means are constituted by the surface mount optical means,
An optical sensor characterized in that the optical element of the light emitting means and the optical element of the light receiving means are surface-mounted on the same surface of the same substrate, and a light shielding means is provided on a line connecting these optical elements. .

The optical sensor according to claim 21,
An optical sensor, wherein a mounting component mounted on the substrate is used as the light blocking means.

20. The optical sensor according to claim 11, 18 or 19,
Both the light emitting means and the light receiving means are constituted by the surface mount optical means,
The optical element of the light emitting means and the optical element of the light receiving means are surface-mounted on the same surface of the same substrate, and a through hole is provided in a substrate surface on a line connecting these optical elements. Optical sensor.

24. The optical sensor according to claim 11, 18, 19, 20, 21, 22, or 23, wherein the surface mounting optical means is configured so that a mounted component does not block an optical path.

The optical sensor according to claim 11, 18, 19, 20, 21, 22, 23 or 24,
An optical sensor according to claim 1, wherein said surface-mounting optical means uses a surface-mounted component surface-mounted on a substrate facing an optical path.

An image carrier having a surface for regularly reflecting light,
Toner image forming means for forming a toner image on the image carrier,
An optical sensor for detecting the amount of toner adhered when the toner is adhered on the image carrier by the toner image forming means;
An image density control unit that performs image density control based on the detection result of the optical sensor,
Claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22 as the optical sensor. , 23, 24, or 25 using the optical sensor.

The image forming apparatus according to claim 26,
An image forming apparatus, wherein a toner having a weight average particle diameter of 8 μm or less is used as a toner constituting the toner image.

The image forming apparatus according to claim 26 or 27,
An image forming apparatus using a toner having an average circularity of 0.93 or more as a toner constituting the toner image.