JP6880636B2

JP6880636B2 - Image forming device and image forming method

Info

Publication number: JP6880636B2
Application number: JP2016201677A
Authority: JP
Inventors: 雅彦早川
Original assignee: Brother Industries Ltd
Current assignee: Brother Industries Ltd
Priority date: 2016-10-13
Filing date: 2016-10-13
Publication date: 2021-06-02
Anticipated expiration: 2036-10-13
Also published as: JP2018063359A

Description

本発明は，電子写真方式によって画像を形成する画像形成装置および画像形成方法に関する。 The present invention relates to an image forming apparatus and an image forming method for forming an image by an electrophotographic method.

電子写真方式によって感光体上に画像を形成する画像形成装置では，感光体の回転速度として，第１の回転速度と，第１の回転速度よりも遅い第２の回転速度と，があり，所定の条件によって感光体の回転速度を切り替える技術が知られている。例えば，特許文献１には，記録密度に応じて異なる回転速度となるよう感光体を制御する画像形成装置が開示されている。また，特許文献１には，感光体の回転速度が遅い場合に，感光体の回転速度が速い場合と比較して，帯電電圧を低くする構成が開示されている。 In an image forming apparatus that forms an image on a photoconductor by an electrophotographic method, there are a first rotation speed and a second rotation speed slower than the first rotation speed as the rotation speed of the photoconductor, which are predetermined. There is known a technique for switching the rotation speed of the photoconductor according to the above conditions. For example, Patent Document 1 discloses an image forming apparatus that controls a photoconductor so that the rotation speed differs depending on the recording density. Further, Patent Document 1 discloses a configuration in which the charging voltage is lowered when the rotation speed of the photoconductor is slow as compared with the case where the rotation speed of the photoconductor is high.

特開２００３−２１５８９２号公報Japanese Unexamined Patent Publication No. 2003-215892

しかしながら，前記した従来の技術には，次のような問題があった。すなわち，感光体と現像ローラとを接触させて現像を行う場合，現像剤の帯電量が低下することで，一部の現像剤が感光体の露光されていない部分に付着することがある。この現象は，感光体の回転速度が遅い場合，つまり現像ローラ上の現像剤が感光体と接触する時間が長い場合に顕著となる。 However, the above-mentioned conventional technique has the following problems. That is, when the photoconductor and the developing roller are brought into contact with each other for development, a part of the developing agent may adhere to the unexposed portion of the photoconductor because the charge amount of the developing agent decreases. This phenomenon becomes remarkable when the rotation speed of the photoconductor is slow, that is, when the developer on the developing roller is in contact with the photoconductor for a long time.

本発明は，前記した従来の技術が有する問題点を解決するためになされたものである。すなわちその課題とするところは，電子写真方式の画像形成装置において，感光体の露光されていない部分への現像剤の付着を低減する技術を提供することにある。 The present invention has been made to solve the problems of the above-mentioned conventional techniques. That is, the problem is to provide a technique for reducing the adhesion of the developer to the unexposed portion of the photoconductor in the electrophotographic image forming apparatus.

この課題の解決を目的としてなされた画像形成装置は，感光体と，前記感光体の表面を帯電させる帯電器と，前記感光体に接触して現像剤を前記感光体の表面に供給する現像ローラと，湿度センサと，制御部と，を備え，前記制御部は，前記感光体を第１の速度で回転させて画像を形成する場合，前記帯電器の印加電圧と前記現像ローラの印加電圧との差を，第１の差とし，前記感光体を前記第１の速度より遅い第２の速度で回転させて画像を形成する場合，前記湿度センサからの信号に基づく湿度が所定値よりも低い場合，前記帯電器の印加電圧と前記現像ローラの印加電圧との差を，前記第１の差よりも小さい第２の差とし，前記湿度センサからの信号に基づく湿度が前記所定値以上の場合，前記帯電器の印加電圧と前記現像ローラの印加電圧との差を，前記第２の差よりも小さい第３の差とする，特定電圧制御を実行する，ことを特徴としている。 The image forming apparatus made for the purpose of solving this problem includes a photoconductor, a charger that charges the surface of the photoconductor, and a developing roller that contacts the photoconductor and supplies a developer to the surface of the photoconductor. A humidity sensor and a control unit are provided, and the control unit uses the voltage applied by the charger and the voltage applied by the developing roller when the photoconductor is rotated at the first speed to form an image. When the photoconductor is rotated at a second speed slower than the first speed to form an image, the humidity based on the signal from the humidity sensor is lower than a predetermined value. In this case, the difference between the applied voltage of the charger and the applied voltage of the developing roller is set as a second difference smaller than the first difference, and the humidity based on the signal from the humidity sensor is equal to or higher than the predetermined value. It is characterized in that a specific voltage control is executed in which the difference between the applied voltage of the charger and the applied voltage of the developing roller is set as a third difference smaller than the second difference.

本明細書に開示される画像形成装置は，感光体が第２の速度での印字（低速印字）の際に，感光体が第１の速度での印字（高速印字）の際と比較して，帯電器の印加電圧と現像ローラの印加電圧との差を小さくする。これにより，現像ローラ上の帯電量が低下した現像剤が感光体の露光されていない部分に付着する，所謂，かぶりを低減し得る。 The image forming apparatus disclosed in the present specification is used when the photoconductor prints at the second speed (low-speed printing) as compared with the case where the photoconductor prints at the first speed (high-speed printing). ， Reduce the difference between the applied voltage of the charger and the applied voltage of the developing roller. As a result, the so-called fog, in which the developer having a reduced amount of charge on the developing roller adheres to the unexposed portion of the photoconductor, can be reduced.

さらに，本明細書に開示される画像形成装置は，高湿環境であった場合には低湿環境であった場合と比較してさらにその差を小さくする。これにより，現像剤の帯電量が低下し易い高湿環境にて，よりかぶりの発生を抑制し得る。つまり，本明細書に開示される画像形成装置は，感光体の回転速度に加え，湿度も条件として，帯電器の印加電圧および現像ローラの印加電圧を決定しており，感光体の回転速度のみを条件とする場合と比較して，感光体の露光されていない部分への現像剤の付着をより低減することが期待できる。 Further, the image forming apparatus disclosed in the present specification further reduces the difference in a high humidity environment as compared with a low humidity environment. As a result, the occurrence of fog can be further suppressed in a high humidity environment in which the charge amount of the developer tends to decrease. That is, the image forming apparatus disclosed in the present specification determines the applied voltage of the charger and the applied voltage of the developing roller on the condition of humidity in addition to the rotation speed of the photoconductor, and only the rotation speed of the photoconductor. It can be expected that the adhesion of the developer to the unexposed portion of the photoconductor can be further reduced as compared with the case where

上記装置の機能を実現するための制御方法，コンピュータプログラム，および当該コンピュータプログラムを格納するコンピュータにて読取可能な記憶媒体も，新規で有用である。 A control method for realizing the functions of the above device, a computer program, and a computer-readable storage medium for storing the computer program are also new and useful.

本発明によれば，電子写真方式の画像形成装置において，感光体の露光されていない部分への現像剤の付着を低減する技術が実現される。 According to the present invention, in an electrophotographic image forming apparatus, a technique for reducing adhesion of a developer to an unexposed portion of a photoconductor is realized.

実施の形態にかかるプリンタの概略構成を示す断面図である。It is sectional drawing which shows the schematic structure of the printer which concerns on embodiment. 実施の形態にかかるプリンタのプロセス部の概略構成を示す断面図である。It is sectional drawing which shows the schematic structure of the process part of the printer which concerns on embodiment. 実施の形態にかかるプリンタの電気的構成を示すブロック図である。It is a block diagram which shows the electrical structure of the printer which concerns on embodiment. 実施の形態における，動作モードがモードＡないしモードＣであった場合の，グリッド電圧および現像電圧の関係を示す図である。It is a figure which shows the relationship between the grid voltage and the development voltage when the operation mode is mode A to mode C in embodiment. 実施の形態における，動作モードがモードＢであった場合の，グリッド電圧および現像電圧の関係を示す図である。It is a figure which shows the relationship between the grid voltage and the development voltage when the operation mode is mode B in embodiment. 実施の形態にかかるプリンタが実行する印刷処理の手順を示すフローチャートである。It is a flowchart which shows the procedure of the printing process which a printer executes by this embodiment. 実施の形態にかかるプリンタが実行する電圧設定処理の手順を示すフローチャートである。It is a flowchart which shows the procedure of the voltage setting process which the printer performs by the embodiment. 応用形態における，動作モードがモードＡないしモードＣであった場合の，グリッド電圧および現像電圧の関係を示す図である。It is a figure which shows the relationship between the grid voltage and the development voltage when the operation mode is mode A to mode C in the application form. 応用形態における，湿度の閾値と温度との関係を示す図である。It is a figure which shows the relationship between the humidity threshold and temperature in an application form.

以下，本発明にかかる画像形成装置を具体化した実施の形態について，添付図面を参照しつつ詳細に説明する。本形態は，カラー画像の形成が可能なプリンタに本発明を適用したものである。 Hereinafter, embodiments in which the image forming apparatus according to the present invention is embodied will be described in detail with reference to the accompanying drawings. This embodiment is an application of the present invention to a printer capable of forming a color image.

本形態のプリンタ１００は，図１にその概略を示すように，いわゆるタンデム方式のカラーレーザプリンタである。プリンタ１００は，イエロー（Ｙ），マゼンタ（Ｍ），シアン（Ｃ），ブラック（Ｋ）の色ごとのプロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋを有している。そして，プロセス部１０Ｙは，感光ドラム１と，帯電器２と，現像器４と，を有している。なお，他色のプロセス部１０Ｍ，１０Ｃ，１０Ｋも同様の構成を有している。なお，本形態のプリンタ１００は，シートの搬送方向からプロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋの順に配置されているが，順番はこれに限定するものではない。 The printer 100 of this embodiment is a so-called tandem color laser printer, as outlined in FIG. The printer 100 has process units 10Y, 10M, 10C, and 10K for each color of yellow (Y), magenta (M), cyan (C), and black (K). The process unit 10Y includes a photosensitive drum 1, a charger 2, and a developer 4. The process units 10M, 10C, and 10K of other colors also have the same configuration. The printer 100 of this embodiment is arranged in the order of the process units 10Y, 10M, 10C, and 10K from the sheet transport direction, but the order is not limited to this.

また，プリンタ１００は，プロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋの上部に，全てのプロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋに共通の露光器６を有している。さらに，プリンタ１００は，転写ベルト７と，定着器８と，給紙トレイ９１と，排紙トレイ９２とを有している。 Further, the printer 100 has an exposure device 6 common to all the process units 10Y, 10M, 10C, and 10K above the process units 10Y, 10M, 10C, and 10K. Further, the printer 100 has a transfer belt 7, a fixing device 8, a paper feed tray 91, and a paper output tray 92.

具体的にプロセス部１０Ｙは，図２に示すように，感光ドラム１の周囲に，感光ドラム１の回転方向（図２中で時計回り方向）に沿って，帯電器２，現像器４，が配置されており，感光ドラム１の回転方向のうち，帯電器２よりも下流であって現像器４よりも上流の位置に，露光器６からの光ビームＬが感光ドラム１の表面に照射される。 Specifically, as shown in FIG. 2, the process unit 10Y has a charger 2, a developer 4, and a charger 2 around the photosensitive drum 1 along the rotation direction of the photosensitive drum 1 (clockwise in FIG. 2). The surface of the photosensitive drum 1 is irradiated with the light beam L from the exposure device 6 at a position downstream of the charger 2 and upstream of the developer 4 in the rotation direction of the photosensitive drum 1. To.

感光ドラム１は，導電性を有するドラム本体１１と，そのドラム本体１１の外周面に形成された筒状の感光層１２とを有する。ドラム本体１１は，接地されている。感光ドラム１は，感光体の一例である。 The photosensitive drum 1 has a conductive drum body 11 and a tubular photosensitive layer 12 formed on the outer peripheral surface of the drum body 11. The drum body 11 is grounded. The photosensitive drum 1 is an example of a photosensitive member.

帯電器２は，感光ドラム１の表面と非接触であり，かつ感光ドラム１の表面に並行するように配置されている。帯電器２は，ワイヤ電極２１とグリッド電極２２とを有するスコロトロン型の帯電器である。ワイヤ電極２１は，線形状の金属であり，感光ドラム１の軸方向に沿って配置されている。グリッド電極２２は，格子形状の金属であり，ワイヤ電極２１と感光ドラム１との間に配置されている。帯電器２は，ワイヤ電圧印加部２５からワイヤ電極２１に正極性のワイヤ電圧Ｖｗが印加されることでコロナ放電を発生させ，グリッド電極２２を介して，感光ドラム１の表面を正電位に一様に帯電させる。 The charger 2 is arranged so as to be non-contact with the surface of the photosensitive drum 1 and parallel to the surface of the photosensitive drum 1. The charger 2 is a scorotron type charger having a wire electrode 21 and a grid electrode 22. The wire electrode 21 is a linear metal and is arranged along the axial direction of the photosensitive drum 1. The grid electrode 22 is a grid-shaped metal and is arranged between the wire electrode 21 and the photosensitive drum 1. The charger 2 generates a corona discharge by applying a positive wire voltage Vw to the wire electrode 21 from the wire voltage applying portion 25, and makes the surface of the photosensitive drum 1 a positive potential via the grid electrode 22. It is charged like this.

また，帯電器２には，グリッド回路２３が接続される。グリッド回路２３は，定電圧素子としてのツェナーダイオード２３１と抵抗２３２とを有し，ツェナーダイオード２３１のカソード側がグリッド電極２２に接続され，ツェナーダイオード２３１のアノード側が抵抗２３２を介して接地されている。ツェナーダイオード２３１と抵抗２３２との接続点は，コントローラ３０と接続されている。この構成によって，ワイヤ電極２１からグリッド電極２２を介してツェナーダイオード２３１と抵抗２３２に流れたグリッド電流により，グリッド電極２２にグリッド電圧Ｖｇが生成される。ここで，ツェナーダイオード２３１と抵抗２３２との接続点の電圧Ｖｐは，グリッド電極２２のグリッド電圧Ｖｇに比例した値を示す。このため，コントローラ３０は，接続点の電圧Ｖｐに基づいてグリッド電圧Ｖｇを検出し，グリッド電圧Ｖｇが目標値になるように，ワイヤ電圧Ｖｗを調整する。 Further, a grid circuit 23 is connected to the charger 2. The grid circuit 23 has a Zener diode 231 and a resistor 232 as constant voltage elements, the cathode side of the Zener diode 231 is connected to the grid electrode 22, and the anode side of the Zener diode 231 is grounded via the resistor 232. The connection point between the Zener diode 231 and the resistor 232 is connected to the controller 30. With this configuration, a grid voltage Vg is generated in the grid electrode 22 by the grid current flowing from the wire electrode 21 to the Zener diode 231 and the resistor 232 via the grid electrode 22. Here, the voltage Vp at the connection point between the Zener diode 231 and the resistor 232 shows a value proportional to the grid voltage Vg of the grid electrode 22. Therefore, the controller 30 detects the grid voltage Vg based on the voltage Vp at the connection point, and adjusts the wire voltage Vw so that the grid voltage Vg becomes the target value.

露光器６（図１参照）は，不図示のレーザダイオードと，レーザダイオードから出射された光ビームを感光ドラム１に照射するための各種の光学部材とを有している。露光器６は，各種の光学部材として，例えば，ポリゴンミラー６１と，ｆθレンズ６５と，折り返しミラー６６，６７と，トーリックレンズ６８と，を備える。ポリゴンミラー６１は，ポリゴンモータ６２の駆動力によって回転する。露光器６では，レーザダイオードから出射された光ビームが，ポリゴンミラー６１に入射される。ポリゴンミラー６１は，上面視で正六角形をなし，画像形成時には，ポリゴンモータ６２によって一定速度で高速回転し，光ビームを反射する。そして，光ビームは，ポリゴンミラー６１の回転に伴って偏向され，感光ドラム１上に走査される。これにより，感光ドラム１の表面のうち光ビームが照射された箇所では電位の絶対値が下がり，感光ドラム１上には，静電潜像が形成される。 The exposure device 6 (see FIG. 1) includes a laser diode (not shown) and various optical members for irradiating the photosensitive drum 1 with a light beam emitted from the laser diode. The exposure device 6 includes, for example, a polygon mirror 61, an fθ lens 65, a folded mirror 66, 67, and a toric lens 68 as various optical members. The polygon mirror 61 is rotated by the driving force of the polygon motor 62. In the exposure device 6, the light beam emitted from the laser diode is incident on the polygon mirror 61. The polygon mirror 61 has a regular hexagonal shape when viewed from above, and at the time of image formation, the polygon motor 62 rotates at a high speed at a constant speed to reflect a light beam. Then, the light beam is deflected as the polygon mirror 61 rotates, and is scanned onto the photosensitive drum 1. As a result, the absolute value of the potential decreases at the portion of the surface of the photosensitive drum 1 irradiated with the light beam, and an electrostatic latent image is formed on the photosensitive drum 1.

現像器４は，正極性に帯電されたトナーを保持し，トナーを感光ドラム１の表面に供給する現像ローラ４１と，トナーを収容するトナータンク４２と，トナータンク４２に収容されているトナーを現像ローラ４１に供給するトナー供給ローラ４３と，を有している。現像ローラ４１は，感光ドラム１と接触している。現像器４は，現像電圧印加部４５から現像ローラ４１に正極性の現像電圧Ｖｂが印加されることで，正極性のトナーを現像ローラ４１を介して感光ドラム１に供給し，感光ドラム１に形成された静電潜像を現像する。これにより，感光ドラム１上には，トナー像が形成される。トナーは，現像剤の一例である。 The developing device 4 holds a developing roller 41 that holds the positively charged toner and supplies the toner to the surface of the photosensitive drum 1, a toner tank 42 that houses the toner, and a toner stored in the toner tank 42. It has a toner supply roller 43 for supplying to the developing roller 41. The developing roller 41 is in contact with the photosensitive drum 1. When the developing voltage Vb is applied to the developing roller 41 from the developing voltage application unit 45, the developing device 4 supplies positive toner to the photosensitive drum 1 via the developing roller 41 and supplies the positive toner to the photosensitive drum 1. The formed electrostatic latent image is developed. As a result, a toner image is formed on the photosensitive drum 1. Toner is an example of a developer.

また，現像器４は，プリンタ１００から着脱可能であり，現像器４を交換することでトナーを補充できる。なお，トナーの補充は，トナータンク４２が現像器４から着脱可能であれば，トナータンク４２のみを交換してもよい。また，現像器４が感光ドラム１等の他の部材と一体のユニットであれば，そのユニットを交換してもよい。 Further, the developing device 4 is removable from the printer 100, and toner can be replenished by replacing the developing device 4. To replenish the toner, if the toner tank 42 is removable from the developing device 4, only the toner tank 42 may be replaced. Further, if the developing device 4 is a unit integrated with other members such as the photosensitive drum 1, the unit may be replaced.

転写ベルト７は，プロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋの各感光ドラム１との接触位置の内側に転写ローラ５を備えている。転写ローラ５は，転写電圧印加部５５から負極性の転写電圧Ｖｔが印加されることで，感光ドラム１の表面にあるトナーを，転写ベルト７上を搬送されるシートあるいは転写ベルト７に転写する。 The transfer belt 7 includes a transfer roller 5 inside the contact position of each of the process units 10Y, 10M, 10C, and 10K with the photosensitive drum 1. The transfer roller 5 transfers the toner on the surface of the photosensitive drum 1 to the sheet or the transfer belt 7 conveyed on the transfer belt 7 by applying the negative transfer voltage Vt from the transfer voltage application unit 55. ..

プリンタ１００は，印刷命令を受け付けると，給紙トレイ９１に収納されているシートを１枚ずつ引き出し，転写ベルト７へ搬送する。そして，シートが感光ドラム１と転写ローラ５との間を通過する際に，転写ローラ５にて，感光ドラム１上に形成されたトナー像をシートへ転写する。さらに，プリンタ１００は，シートに転写されたトナー像を，定着器８にてシートに定着させる。その後，プリンタ１００は，定着器８を通過したシートを，排紙トレイ９２に排出する。 When the printer 100 receives a print command, it pulls out the sheets stored in the paper feed tray 91 one by one and conveys them to the transfer belt 7. Then, when the sheet passes between the photosensitive drum 1 and the transfer roller 5, the transfer roller 5 transfers the toner image formed on the photosensitive drum 1 to the sheet. Further, the printer 100 fixes the toner image transferred to the sheet to the sheet by the fixing device 8. After that, the printer 100 ejects the sheet that has passed through the fixing device 8 to the output tray 92.

なお，カラー印刷を実行する場合，プリンタ１００は，他色のプロセス部１０Ｍ，１０Ｃ，１０Ｋにてそれぞれの色のトナー像を形成し，順次シートに転写する。これにより，シート上でトナー像を重ね合わせる。そして，重ね合わされたトナー像をシートに定着させることにより，カラー画像が形成される。 When color printing is executed, the printer 100 forms toner images of each color in the process units 10M, 10C, and 10K of other colors, and sequentially transfers them to the sheet. As a result, the toner images are superimposed on the sheet. Then, a color image is formed by fixing the superimposed toner images on the sheet.

続いて，プリンタ１００の電気的構成について説明する。プリンタ１００は，図３に示すように，ＣＰＵ３１と，ＲＯＭ３２と，ＲＡＭ３３と，ＮＶＲＡＭ（不揮発性ＲＡＭ）３４と，ワイヤ電圧印加部２５と，現像電圧印加部４５と，転写電圧印加部５５と，を含むコントローラ３０を備えている。また，プリンタ１００は，各色のプロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋと，露光器６，定着器８，操作パネル３６と，通信インターフェイス３７と，湿度センサ８１と，搬送系７０と，を備え，これらがコントローラ３０に電気的に接続されている。 Subsequently, the electrical configuration of the printer 100 will be described. As shown in FIG. 3, the printer 100 includes a CPU 31, a ROM 32, a RAM 33, an NVRAM (nonvolatile RAM) 34, a wire voltage application unit 25, a development voltage application unit 45, a transfer voltage application unit 55, and the like. It includes a controller 30 including. Further, the printer 100 includes process units 10Y, 10M, 10C, 10K for each color, an exposure device 6, a fuser 8, an operation panel 36, a communication interface 37, a humidity sensor 81, and a transport system 70. These are electrically connected to the controller 30.

ＲＯＭ３２には，プリンタ１００を制御するための各種制御プログラムや各種設定，初期値等が記憶されている。ＲＡＭ３３およびＮＶＲＡＭ３４は，各種制御プログラムが読み出される作業領域として，あるいは，データを一時的に記憶する記憶領域として利用される。 The ROM 32 stores various control programs, various settings, initial values, and the like for controlling the printer 100. The RAM 33 and NVRAM 34 are used as a work area for reading various control programs or as a storage area for temporarily storing data.

ＣＰＵ３１は，ＲＯＭ３２から読み出した制御プログラムに従って，その処理結果をＲＡＭ３３またはＮＶＲＡＭ３４に記憶させながら，プリンタ１００の各構成要素を制御する。なお，図３中のコントローラ３０は，ＣＰＵ３１等，プリンタ１００の制御に利用されるハードウェアを纏めた総称であって，実際にプリンタ１００に存在する単一のハードウェアを表すとは限らない。ＣＰＵ３１は，制御部の一例である。なお，コントローラ３０が制御部の一例であってもよい。 The CPU 31 controls each component of the printer 100 while storing the processing result in the RAM 33 or the NVRAM 34 according to the control program read from the ROM 32. Note that the controller 30 in FIG. 3 is a general term for hardware used for controlling the printer 100, such as the CPU 31, and does not necessarily represent a single hardware that actually exists in the printer 100. The CPU 31 is an example of a control unit. The controller 30 may be an example of the control unit.

ワイヤ電圧印加部２５は，ワイヤ電極２１に接続されている。ワイヤ電圧印加部２５は，ＣＰＵ３１からの指示に応じて，トナーと同極性のワイヤ電圧Ｖｗをワイヤ電極２１に印加する。本形態では，グリッド電圧Ｖｇを目標値にするため，ワイヤ電圧Ｖｗが，例えば，＋５ｋＶ〜＋７ｋＶで調整される。本形態におけるグリッド電圧Ｖｇについては後述する。 The wire voltage application unit 25 is connected to the wire electrode 21. The wire voltage application unit 25 applies a wire voltage Vw having the same polarity as the toner to the wire electrode 21 in response to an instruction from the CPU 31. In this embodiment, in order to set the grid voltage Vg as the target value, the wire voltage Vw is adjusted, for example, from + 5 kV to + 7 kV. The grid voltage Vg in this embodiment will be described later.

現像電圧印加部４５は，現像ローラ４１に接続されている。現像電圧印加部４５は，ＣＰＵ３１からの指示に応じて，トナーと同極性の現像電圧Ｖｂを現像ローラ４１に印加する。本形態における現像電圧Ｖｂについては後述する。 The developing voltage application unit 45 is connected to the developing roller 41. The developing voltage application unit 45 applies a developing voltage Vb having the same polarity as the toner to the developing roller 41 in response to an instruction from the CPU 31. The development voltage Vb in this embodiment will be described later.

転写電圧印加部５５は，転写ローラ５に接続されている。転写電圧印加部５５は，ＣＰＵ３１からの指示に応じて，トナーと逆極性の転写電圧Ｖｔを印加する。本形態では，転写電圧Ｖｔの目標値を，例えば−１２００Ｖにする。なお，転写ローラ５は，電圧制御ではなく，転写ローラ５に流れる転写電流量を目標電流量に調整する電流制御を行ってもよい。 The transfer voltage application unit 55 is connected to the transfer roller 5. The transfer voltage application unit 55 applies a transfer voltage Vt having the opposite polarity to the toner in response to an instruction from the CPU 31. In this embodiment, the target value of the transfer voltage Vt is set to, for example, -1200V. The transfer roller 5 may perform current control for adjusting the amount of transfer current flowing through the transfer roller 5 to a target current amount instead of voltage control.

操作パネル３６は，プリンタ１００の外装に設けられ，ユーザからの入力操作を受け付ける各種のボタンや，メッセージや設定内容を表示するタッチパネルを有している。通信インターフェイス３７は，外部装置と通信を行うためのハードウェアである。具体的な通信インターフェイス３７としては，例えば，有線ＬＡＮインターフェイス，無線ＬＡＮインターフェイス，シリアル通信インターフェイス，パラレル通信インターフェイス，ファクシミリインターフェイスが該当する。 The operation panel 36 is provided on the exterior of the printer 100 and has various buttons for receiving input operations from the user and a touch panel for displaying messages and setting contents. The communication interface 37 is hardware for communicating with an external device. Specific examples of the communication interface 37 include a wired LAN interface, a wireless LAN interface, a serial communication interface, a parallel communication interface, and a facsimile interface.

湿度センサ８１は，湿度の値に応じて異なる信号をコントローラ３０に出力する。湿度センサ８１は，プリンタ１００のハウジング内の，プロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋの周囲の空気の湿度を取得する位置に配置されている。 The humidity sensor 81 outputs a different signal to the controller 30 according to the humidity value. The humidity sensor 81 is arranged in the housing of the printer 100 at a position where the humidity of the air around the process units 10Y, 10M, 10C, and 10K is acquired.

搬送系７０は，シートの搬送に用いられるものであり，給紙ローラ７１，レジストレーションローラ７２，転写ベルト７等，各種の搬送手段およびこれらの駆動手段によって構成される。プリンタ１００は，シートを搬送する態様として，高速搬送と，高速搬送の半分の速度で搬送する半速搬送とがある。半速搬送は，厚紙等の定着に時間がかかるシートを搬送する場合に，プリンタ１００によって自動的に選択される。また，ユーザによって静音印刷が指示された場合にも選択される。なお，半速搬送は，高速搬送よりも遅い搬送速度であればよく，必ずしも高速搬送の半分の速度である必要はない。半速搬送を行わない場合，プリンタ１００は高速搬送を行う。 The transport system 70 is used for transporting sheets, and is composed of various transport means such as a paper feed roller 71, a registration roller 72, a transfer belt 7, and a drive means thereof. The printer 100 has two modes of transporting sheets: high-speed transport and half-speed transport, which transports sheets at half the speed of high-speed transport. Half-speed transport is automatically selected by the printer 100 when transporting a sheet such as thick paper that takes a long time to fix. It is also selected when silent printing is instructed by the user. Note that the half-speed transfer may be slower than the high-speed transfer, and does not necessarily have to be half the speed of the high-speed transfer. When the half-speed transfer is not performed, the printer 100 performs high-speed transfer.

プリンタ１００は，シートの搬送速度を変更した場合，その変更に合わせて感光ドラム１の回転速度および現像ローラ４１の回転速度も変更する。すなわち，プリンタ１００は，シートの搬送速度を遅くした場合，その変更に合わせて感光ドラム１の回転速度を遅くし，さらに感光ドラム１の回転速度の変更に合わせて現像ローラ４１の回転速度も遅くする。感光ドラム１と現像ローラ４１とは，同一の駆動源によって所定のギア比で駆動される。これにより，プリンタ１００は，シートの搬送速度を変更した場合であっても，感光ドラム１と現像ローラ４１との周速比が同一になるように構成されている。 When the sheet transport speed is changed, the printer 100 also changes the rotation speed of the photosensitive drum 1 and the rotation speed of the developing roller 41 in accordance with the change. That is, when the sheet transport speed is slowed down, the printer 100 slows down the rotation speed of the photosensitive drum 1 in accordance with the change, and further slows down the rotation speed of the developing roller 41 in accordance with the change in the rotation speed of the photosensitive drum 1. To do. The photosensitive drum 1 and the developing roller 41 are driven by the same drive source at a predetermined gear ratio. As a result, the printer 100 is configured so that the peripheral speed ratio of the photosensitive drum 1 and the developing roller 41 is the same even when the sheet conveying speed is changed.

続いて，プロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋの動作モードについて説明する。プリンタ１００は，１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋの動作モードとして，モードＡ，モードＢ，モードＣ，の３つのモードを有している。この動作モードは，プロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋごとに設定され，プロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋごとの印刷量によって動作モードが決定される。 Subsequently, the operation modes of the process units 10Y, 10M, 10C, and 10K will be described. The printer 100 has three modes, mode A, mode B, and mode C, as operation modes of 10Y, 10M, 10C, and 10K. This operation mode is set for each of the process units 10Y, 10M, 10C, and 10K, and the operation mode is determined by the print amount for each of the process units 10Y, 10M, 10C, and 10K.

具体的に，モードＡは，トナー収容部である現像器４が新品に交換されてからの印刷回数が，新品状態か否かを判断するための新品閾値を超えていない場合の動作モードである。すなわち，現像器４が交換された直後，つまりトナーが新品状態である状態ではモードＡであり，プリンタ１００は，印刷回数が新品閾値に達するまではモードＡを継続する。新品閾値は，プロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋごとに設定してもよいし，全てのプロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋで共通としてもよい。本形態では，新品閾値を全てのプロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋで共通とし，その値を３００回とする。なお，上述したように本明細書に記載する「新品状態」は，現像器４が新品に交換されてからの印刷回数が新品閾値を超えていない状態を意味し，印刷が１回も行われていない状態を意味するものではない。 Specifically, the mode A is an operation mode in which the number of prints after the developer 4 which is the toner accommodating portion is replaced with a new one does not exceed the new threshold value for determining whether or not the state is new. .. That is, immediately after the developer 4 is replaced, that is, when the toner is in a new state, the mode A is set, and the printer 100 continues the mode A until the number of prints reaches the new threshold value. The new threshold value may be set for each process unit 10Y, 10M, 10C, 10K, or may be common to all process units 10Y, 10M, 10C, 10K. In this embodiment, the new threshold value is common to all process units 10Y, 10M, 10C, and 10K, and the value is set to 300 times. As described above, the "new state" described in the present specification means a state in which the number of printings since the developer 4 is replaced with a new one does not exceed the new threshold value, and printing is performed even once. It does not mean that the state is not printed.

また，モードＢは，現像器４が新品に交換されてからの印刷回数が，新品閾値以上であって，かつ劣化状態か否かを判断するための耐久閾値を超えていない場合の動作モードである。すなわち，プリンタ１００は，現像器４が新品状態でなくなった場合にモードＢに変更し，その後，印刷回数が耐久閾値に達するまではモードＢを継続する。耐久閾値は，プロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋごとに設定してもよいし，全てのプロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋで共通としてもよい。本形態では，耐久閾値を全てのプロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋで共通とし，その値を８０００回とする。 In addition, mode B is an operation mode in which the number of prints after the developer 4 is replaced with a new one is equal to or more than the new threshold value and does not exceed the durability threshold value for determining whether or not the developer is in a deteriorated state. is there. That is, the printer 100 changes to mode B when the developer 4 is no longer in a new state, and then continues mode B until the number of prints reaches the durability threshold. The durability threshold value may be set for each process unit 10Y, 10M, 10C, 10K, or may be common to all process units 10Y, 10M, 10C, 10K. In this embodiment, the durability threshold value is common to all process units 10Y, 10M, 10C, and 10K, and the value is set to 8000 times.

また，モードＣは，現像器４が新品に交換されてからの印刷回数が，耐久閾値以上であった場合の動作モードである。すなわち，プリンタ１００は，現像器４に収容されるトナーが劣化したと判断できる場合にモードＣに変更し，その後，現像器４が交換されるまではモードＣを継続する。 The mode C is an operation mode when the number of prints after the developer 4 is replaced with a new one is equal to or greater than the durability threshold. That is, the printer 100 changes to mode C when it can be determined that the toner contained in the developing device 4 has deteriorated, and then continues mode C until the developing device 4 is replaced.

プリンタ１００は，プロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋごとに，動作モードに応じて，グリッド電圧Ｖｇおよび現像電圧Ｖｂを決定する。図４は，動作モードがモードＡないしモードＣであった場合の，グリッド電圧Ｖｇおよび現像電圧Ｖｂを示している。現像電圧Ｖｂの絶対値は，グリッド電圧Ｖｇの絶対値よりも小さい値となっている。図５は，動作モードがモードＢであった場合の，グリッド電圧Ｖｇおよび現像電圧Ｖｂを示している。図４および図５中，「高速」は高速搬送を意味し，「半速低湿」は半速搬送かつ低湿状態を意味し，「半速高湿」は半速搬送かつ高湿状態を意味する。プリンタ１００は，例えば，湿度が７０％以上である場合に湿度が高い高湿状態と判断し，湿度が７０％未満である場合に湿度が低い低湿状態と判断する。 The printer 100 determines the grid voltage Vg and the development voltage Vb for each of the process units 10Y, 10M, 10C, and 10K according to the operation mode. FIG. 4 shows the grid voltage Vg and the developing voltage Vb when the operation mode is mode A to mode C. The absolute value of the developing voltage Vb is smaller than the absolute value of the grid voltage Vg. FIG. 5 shows the grid voltage Vg and the developing voltage Vb when the operation mode is mode B. In FIGS. 4 and 5, "high speed" means high speed transportation, "half speed low humidity" means half speed transportation and low humidity state, and "half speed high humidity" means half speed transportation and high humidity state. .. For example, when the humidity is 70% or more, the printer 100 determines that the humidity is high and high humidity, and when the humidity is less than 70%, it determines that the humidity is low and low humidity.

プリンタ１００では，現像ローラ４１を感光ドラム１に接触させて現像を行うため，感光ドラム１の表面電位の影響でトナーの帯電量が低下する場合がある。これにより，帯電量が相対的に少なくなったトナーの一部が感光ドラム１の露光されていない部分に付着する，所謂，かぶりが生じる。かぶりは，感光ドラム１の回転速度が遅い場合，つまり現像ローラ４１上のトナーが感光ドラム１と接触する時間が長い場合に顕著となる。 In the printer 100, since the developing roller 41 is brought into contact with the photosensitive drum 1 for development, the amount of toner charged may decrease due to the influence of the surface potential of the photosensitive drum 1. As a result, a part of the toner having a relatively small amount of charge adheres to the unexposed portion of the photosensitive drum 1, so-called fog occurs. Fogging becomes remarkable when the rotation speed of the photosensitive drum 1 is slow, that is, when the toner on the developing roller 41 is in contact with the photosensitive drum 1 for a long time.

そこで，プリンタ１００は，半速搬送時において，高速搬送時と比較して，グリッド電圧Ｖｇと現像電圧Ｖｂとの差Ｖｇ−Ｖｂを小さくする。これにより，現像ローラ４１上のトナーの帯電量の低下が抑制され，帯電量が少ないトナーが，感光ドラム１の露光されていない部分に付着し難くなる。具体的に図４に示した本形態のプリンタ１００の例では，イエローのプロセス部１０Ｙにおける，高速時と半速低湿ないし半速高湿との，差Ｖｇ−Ｖｂの関係が該当する。 Therefore, the printer 100 makes the difference Vg-Vb between the grid voltage Vg and the developing voltage Vb smaller in the half-speed transfer than in the high-speed transfer. As a result, the decrease in the charge amount of the toner on the developing roller 41 is suppressed, and the toner having a small charge amount is less likely to adhere to the unexposed portion of the photosensitive drum 1. Specifically, in the example of the printer 100 of the present embodiment shown in FIG. 4, the relationship of the difference Vg-Vb between the high speed and the half speed low humidity to the half speed high humidity in the yellow process unit 10Y corresponds.

また，かぶりは，感光ドラム１の低速回転の他，湿度が高い場合も生じ易い。つまり，湿度が高い場合もトナーの電荷が低下し易く，かぶりが生じ易い状態にある。そこで，プリンタ１００は，半速搬送時であって，さらに高湿状態の場合には，グリッド電圧Ｖｇと現像電圧Ｖｂとの差Ｖｇ−Ｖｂをさらに小さくして，帯電量が少ないトナーが感光ドラム１の露光されていない部分により付着し難くする。具体的に図４に示した本形態のプリンタ１００の例では，イエローのプロセス部１０Ｙにおける，半速低湿時と半速高湿時との，差Ｖｇ−Ｖｂの関係が該当する。 In addition to the low-speed rotation of the photosensitive drum 1, fog is likely to occur when the humidity is high. That is, even when the humidity is high, the charge of the toner is likely to decrease and fog is likely to occur. Therefore, in the printer 100 during half-speed transfer and in a higher humidity state, the difference Vg-Vb between the grid voltage Vg and the developing voltage Vb is further reduced, and the toner having a small amount of charge is charged to the photosensitive drum. The unexposed portion of 1 makes it difficult to adhere. Specifically, in the example of the printer 100 of the present embodiment shown in FIG. 4, the relationship of the difference Vg-Vb between the half-speed low humidity and the half-speed high humidity in the yellow process unit 10Y corresponds.

なお，半速搬送時におけるグリッド電圧Ｖｇおよび現像電圧Ｖｂの変更は，全ての色に対して行う必要はない。すなわち，かぶりの発生し易さは，トナーの特性によって異なる。本形態のプリンタ１００は，イエローでかぶりが発生し易く，他の色ではかぶりが発生し難いものとする。そのため，図４に示すように，イエロー以外の色では，プリンタ１００は，湿度に応じたグリッド電圧Ｖｇおよび現像電圧Ｖｂの変更を行っていない。言い換えると，プリンタ１００は，かぶりが発生し易いトナーを用いていることを条件として，湿度に応じたグリッド電圧Ｖｇおよび現像電圧Ｖｂの変更を行う。 It is not necessary to change the grid voltage Vg and the developing voltage Vb during half-speed transfer for all colors. That is, the susceptibility to fog differs depending on the characteristics of the toner. In the printer 100 of this embodiment, it is assumed that fog is likely to occur in yellow and fog is unlikely to occur in other colors. Therefore, as shown in FIG. 4, for colors other than yellow, the printer 100 does not change the grid voltage Vg and the developing voltage Vb according to the humidity. In other words, the printer 100 changes the grid voltage Vg and the developing voltage Vb according to the humidity on condition that a toner that easily causes fog is used.

また，トナーの帯電量が安定している場合，すなわちトナーの帯電量のばらつきが少ない場合も，かぶりは発生し難い。そのため，プリンタ１００は，モードＢで動作している場合，図５に示すように，湿度に応じたグリッド電圧Ｖｇおよび現像電圧Ｖｂの変更を行っていない。言い換えると，トナーが新品状態のときは，トナーの帯電量が上昇し難く，かぶりが発生し易い。また，トナーが耐久末期のときも，トナーの帯電量が上昇し難く，かぶりが発生し易い。そこで，プリンタ１００は，新品状態であることと，トナーが劣化していることと，のいずれか一方を満たすことを条件として，湿度に応じたグリッド電圧Ｖｇおよび現像電圧Ｖｂの変更を行う。 In addition, fog is unlikely to occur even when the charge amount of the toner is stable, that is, when the variation in the charge amount of the toner is small. Therefore, when the printer 100 is operating in the mode B, as shown in FIG. 5, the grid voltage Vg and the developing voltage Vb are not changed according to the humidity. In other words, when the toner is in a new state, the amount of charge in the toner is unlikely to increase, and fog is likely to occur. In addition, even when the toner is at the end of its durability, the amount of charge of the toner is unlikely to increase and fog is likely to occur. Therefore, the printer 100 changes the grid voltage Vg and the developing voltage Vb according to the humidity on condition that either the state of being new or the toner is deteriorated is satisfied.

続いて，前述した動作モードを実現するためにプリンタ１００が実行する印刷処理について，図６のフローチャートを参照しつつ説明する。印刷処理は，操作パネル３６や通信インターフェイス３７を介して印刷ジョブを受け付けたことを契機に，ＣＰＵ３１によって実行される。 Subsequently, the printing process executed by the printer 100 in order to realize the above-described operation mode will be described with reference to the flowchart of FIG. The print process is executed by the CPU 31 when a print job is received via the operation panel 36 or the communication interface 37.

印刷処理では，ＣＰＵ３１は先ず，シートの搬送態様や動作モードに基づいて，グリッド電圧Ｖｇおよび現像電圧Ｖｂを設定する電圧設定処理を実行する（Ｓ００１）。電圧設定処理の詳細は後述する。 In the printing process, the CPU 31 first executes a voltage setting process for setting the grid voltage Vg and the developing voltage Vb based on the sheet transport mode and the operation mode (S001). The details of the voltage setting process will be described later.

Ｓ００１の後，搬送系７０によって給紙トレイ９１からの給紙を開始し，シートをプロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋに向かって搬送させる（Ｓ０１１）。Ｓ０１１では，ＣＰＵ３１は，静音印刷の指示やシート種別に基づいて，高速搬送か半速搬送かを判断し，判断結果に応じた搬送態様によるシートの搬送を開始させる。 After S001, paper feeding from the paper feed tray 91 is started by the transport system 70, and the sheets are conveyed toward the process units 10Y, 10M, 10C, and 10K (S011). In S011, the CPU 31 determines whether to perform high-speed transfer or half-speed transfer based on the silent printing instruction and the sheet type, and starts the sheet transfer in the transfer mode according to the determination result.

また，ＣＰＵ３１は，プロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋに印刷ジョブに基づくトナー像を形成させる（Ｓ０１２）。Ｓ０１１の処理とＳ０１２の処理とは並行して実行され，どちらが先であってもよく同時に開始してもよい。Ｓ０１２によって形成されたトナー像は，Ｓ０１１によって給紙トレイ９１から搬送されてくるシートに転写され，その後，定着器８によって熱定着を受ける。そして，ＣＰＵ３１は，定着器８を通過したシートを，搬送系７０によって排紙トレイ９２に排紙させる。 Further, the CPU 31 causes the process units 10Y, 10M, 10C, and 10K to form a toner image based on the print job (S012). The processing of S011 and the processing of S012 are executed in parallel, and whichever comes first may be started at the same time. The toner image formed by S012 is transferred to the sheet conveyed from the paper feed tray 91 by S011, and then heat-fixed by the fixing device 8. Then, the CPU 31 discharges the sheet that has passed through the fixing device 8 to the paper discharge tray 92 by the transport system 70.

Ｓ０１２の後，ＣＰＵ３１は，カウンタＣをカウントアップする（Ｓ０１３）。カウンタＣは，プロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋごとに用意されたデータであり，それぞれ現像器４が新品に交換されてから印刷が行われた累積回数が記憶される。すなわち，新品の現像器４が装着された場合にその現像器４が装着されたプロセス部に対応するカウンタＣが０にリセットされる。そして，印刷が行われる度に，カラー印刷であれば全てのカウンタＣがカウントアップされ，モノクロ印刷であればプロセス部１０Ｋに対応するカウンタＣのみがカウントアップされる。カウンタＣは，ＮＶＲＡＭ３４に記憶される。 After S012, the CPU 31 counts up the counter C (S013). The counter C is data prepared for each of the process units 10Y, 10M, 10C, and 10K, and stores the cumulative number of times printing has been performed since the developer 4 was replaced with a new one. That is, when a new developer 4 is mounted, the counter C corresponding to the process unit to which the developer 4 is mounted is reset to 0. Then, every time printing is performed, all the counters C are counted up in the case of color printing, and only the counter C corresponding to the process unit 10K is counted up in the case of monochrome printing. The counter C is stored in the NVRAM 34.

Ｓ０１３の後，ＣＰＵ３１は，次の印刷が必要か否かを判断する（Ｓ０１４）。次の印刷が必要であれば（Ｓ０１４：ＹＥＳ），ＣＰＵ３１は，Ｓ０１１に移行して，次の印刷のための処理を行う。次の印刷が必要でなければ（Ｓ０１４：ＮＯ），ＣＰＵ３１は，印刷処理を終了する。 After S013, the CPU 31 determines whether or not the next printing is necessary (S014). If the next printing is required (S014: YES), the CPU 31 shifts to S011 and performs a process for the next printing. If the next printing is not required (S014: NO), the CPU 31 ends the printing process.

次に，Ｓ００１の電圧設定処理について，図７のフローチャートを参照しつつ説明する。なお，グリッド電圧Ｖｇおよび現像電圧Ｖｂは，プロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋごとに設定されるため，電圧設定処理は，プロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋごとに実行される。 Next, the voltage setting process of S001 will be described with reference to the flowchart of FIG. Since the grid voltage Vg and the development voltage Vb are set for each of the process units 10Y, 10M, 10C, and 10K, the voltage setting process is executed for each of the process units 10Y, 10M, 10C, and 10K.

電圧設定処理では，ＣＰＵ３１は先ず，新品状態か否かを判断する（Ｓ１０１）。具体的に新品状態であるか否かの判断は，カウンタＣをＮＶＲＡＭ３４から読み出し，その値が新品閾値を超えていなければ新品状態とする。 In the voltage setting process, the CPU 31 first determines whether or not it is in a new state (S101). Specifically, to determine whether or not the product is in a new state, the counter C is read from the NVRAM 34, and if the value does not exceed the new threshold value, the counter C is regarded as a new state.

新品状態でなければ（Ｓ１０１：ＮＯ），ＣＰＵ３１は，耐久劣化状態か否かを判断する（Ｓ１０２）。具体的に耐久劣化状態であるか否かの判断は，カウンタＣの値が耐久閾値以上であれば耐久劣化状態とする。Ｓ１０１とＳ１０２とは逆順であってもよい。 If it is not in a new state (S101: NO), the CPU 31 determines whether or not it is in a durable deterioration state (S102). Specifically, if the value of the counter C is equal to or greater than the durability threshold value, the durability deteriorated state is determined. S101 and S102 may be in reverse order.

耐久劣化状態でなければ（Ｓ１０２：ＮＯ），ＣＰＵ３１は，半速搬送が必要か否かを判断する（Ｓ１１１）。すなわち，新品状態でも耐久劣化状態でもなければ，動作モードがモードＢであり，モードＢでは図５に示したように，半速搬送か否かによってグリッド電圧Ｖｇおよび現像電圧Ｖｂが異なる。そこで，半速搬送が必要であれば（Ｓ１１１：ＹＥＳ），ＣＰＵ３１は，半速搬送用のグリッド電圧Ｖｇおよび現像電圧Ｖｂを設定する（Ｓ１１２）。一方，半速搬送が必要でなければ（Ｓ１１１：ＮＯ），ＣＰＵ３１は，高速搬送用のグリッド電圧Ｖｇおよび現像電圧Ｖｂを設定する（Ｓ１１３）。 If it is not in the endurance deterioration state (S102: NO), the CPU 31 determines whether or not half-speed transfer is necessary (S111). That is, if it is neither in a new state nor in a durable deterioration state, the operation mode is mode B, and in mode B, as shown in FIG. 5, the grid voltage Vg and the development voltage Vb differ depending on whether or not half-speed transfer is performed. Therefore, if half-speed transfer is required (S111: YES), the CPU 31 sets the grid voltage Vg and the development voltage Vb for half-speed transfer (S112). On the other hand, if half-speed transfer is not required (S111: NO), the CPU 31 sets the grid voltage Vg and the development voltage Vb for high-speed transfer (S113).

新品状態である場合（Ｓ１０１：ＹＥＳ），あるいは耐久劣化状態である場合（Ｓ１０２：ＹＥＳ），ＣＰＵ３１は，特定色か否かを判断する（Ｓ１２１）。特定色は，かぶりが生じ易い色が該当し，本形態ではイエローが該当する。すなわち，新品状態であれば，動作モードがモードＡであり，モードＡでは図４に示したように，イエローについては，搬送態様に加えて湿度によってグリッド電圧Ｖｇおよび現像電圧Ｖｂが異なる。また，劣化状態であれば，動作モードがモードＣであり，モードＣでもモードＡと同様に，イエローについては，搬送態様に加えて湿度によってグリッド電圧Ｖｇおよび現像電圧Ｖｂが異なる。一方で，イエロー以外の色であれば，グリッド電圧Ｖｇおよび現像電圧Ｖｂは，モードＢと同じ設定である。そこで，特定色でなければ（Ｓ１２１：ＮＯ），Ｓ１１１に移行して，ＣＰＵ３１は，モードＢと同様にグリッド電圧Ｖｇおよび現像電圧Ｖｂを設定する。 When it is in a new state (S101: YES) or in a durable deterioration state (S102: YES), the CPU 31 determines whether or not it is a specific color (S121). The specific color corresponds to a color that is prone to fogging, and yellow corresponds to this embodiment. That is, in the new state, the operation mode is mode A, and in mode A, as shown in FIG. 4, the grid voltage Vg and the development voltage Vb of yellow differ depending on the humidity in addition to the transport mode. Further, in the deteriorated state, the operation mode is mode C, and in mode C as in mode A, the grid voltage Vg and the development voltage Vb of yellow differ depending on the humidity in addition to the transport mode. On the other hand, if the color is other than yellow, the grid voltage Vg and the development voltage Vb are the same settings as in mode B. Therefore, if it is not a specific color (S121: NO), the process proceeds to S111, and the CPU 31 sets the grid voltage Vg and the development voltage Vb in the same manner as in mode B.

特定色であれば（Ｓ１２１：ＹＥＳ），ＣＰＵ３１は，湿度センサ８１からの信号に基づいて湿度を取得する（Ｓ１２２）。そして，ＣＰＵ３１は，半速搬送が必要か否かを判断する（Ｓ１３１）。半速搬送が必要でなければ（Ｓ１３１：ＮＯ），ＣＰＵ３１は，高速搬送用のグリッド電圧Ｖｇおよび現像電圧Ｖｂを設定する（Ｓ１３２）。 If it is a specific color (S121: YES), the CPU 31 acquires the humidity based on the signal from the humidity sensor 81 (S122). Then, the CPU 31 determines whether or not half-speed transfer is necessary (S131). If half-speed transfer is not required (S131: NO), the CPU 31 sets the grid voltage Vg and the development voltage Vb for high-speed transfer (S132).

一方，半速搬送が必要であれば（Ｓ１３１：ＹＥＳ），ＣＰＵ３１は，高湿状態か否かを判断する（Ｓ１４１）。Ｓ１４１では，ＣＰＵ３１は，Ｓ１２２にて取得した湿度が閾値湿度（本形態では７０％）を超えている場合に，高湿状態と判断する。高湿状態であれば（Ｓ１４１：ＹＥＳ），ＣＰＵ３１は，高湿状態かつ半速搬送用のグリッド電圧Ｖｇおよび現像電圧Ｖｂを設定する（Ｓ１４２）。一方，高湿状態でなければ（Ｓ１４１：ＮＯ），ＣＰＵ３１は，低湿状態かつ半速搬送用のグリッド電圧Ｖｇおよび現像電圧Ｖｂを設定する（Ｓ１４３）。 On the other hand, if half-speed transport is required (S131: YES), the CPU 31 determines whether or not the humidity is high (S141). In S141, the CPU 31 determines that the humidity is high when the humidity acquired in S122 exceeds the threshold humidity (70% in this embodiment). If the humidity is high (S141: YES), the CPU 31 sets the grid voltage Vg and the developing voltage Vb for half-speed transfer in the high humidity state (S142). On the other hand, if it is not in a high humidity state (S141: NO), the CPU 31 sets a grid voltage Vg and a developing voltage Vb for half-speed transfer in a low humidity state (S143).

Ｓ１１２の後，あるいはＳ１１３の後，あるいはＳ１３２の後，あるいはＳ１４２の後，あるいはＳ１４３の後，ＣＰＵ３１は，電圧設定処理を終了する。 After S112, after S113, after S132, after S142, or after S143, the CPU 31 ends the voltage setting process.

なお，プリンタ１００では，モードＡとモードＣとで同じグリッド電圧Ｖｇおよび現像電圧Ｖｂを設定するため，新品状態である場合（Ｓ１０１：ＹＥＳ）と，耐久劣化状態である場合（Ｓ１０２：ＹＥＳ）と，で同じ処理を行っているが，モードＡとモードＣとで異なるグリッド電圧Ｖｇおよび現像電圧Ｖｂを設定してもよい。この場合，新品状態である場合（Ｓ１０１：ＹＥＳ）と，耐久劣化状態である場合（Ｓ１０２：ＹＥＳ）と，で別々にグリッド電圧Ｖｇおよび現像電圧Ｖｂを設定する処理を設ければよい。 Since the same grid voltage Vg and development voltage Vb are set in the mode A and the mode C in the printer 100, there are cases where the printer is in a new state (S101: YES) and cases where the durability is deteriorated (S102: YES). , But the same processing is performed in, but different grid voltage Vg and development voltage Vb may be set in mode A and mode C. In this case, a process for setting the grid voltage Vg and the developing voltage Vb may be provided separately for the case of a new state (S101: YES) and the case of a durable deterioration state (S102: YES).

以上詳細に説明したようにプリンタ１００は，現像ローラ４１が感光ドラム１に接触して現像を行うものであって，半速搬送での印字の際に，高速搬送での印字の際と比較して，グリッド電圧Ｖｇと現像電圧Ｖｂとの差Ｖｇ−Ｖｂを小さくする。これにより，現像ローラ４１上のトナーの帯電量の低下が抑制され，かぶりを低減し得る。さらに，プリンタ１００は，高湿環境であった場合に，低湿環境であった場合と比較してさらにその差Ｖｇ−Ｖｂを小さくする。これにより，かぶりが発生し易い高湿環境にて，よりかぶりの発生を抑制し得る。つまり，プリンタ１００は，感光ドラム１の回転速度に加え，湿度も条件として，グリッド電圧Ｖｇおよび現像電圧Ｖｂを決定しており，シートの搬送態様のみを条件とする場合と比較して，かぶりをより低減することが期待できる。 As described in detail above, in the printer 100, the developing roller 41 comes into contact with the photosensitive drum 1 for development, and the printing in the half-speed transfer is compared with the printing in the high-speed transfer. Therefore, the difference Vg-Vb between the grid voltage Vg and the developing voltage Vb is reduced. As a result, a decrease in the amount of charge of the toner on the developing roller 41 can be suppressed, and fog can be reduced. Further, the printer 100 further reduces the difference Vg-Vb in the high humidity environment as compared with the case in the low humidity environment. As a result, the occurrence of fog can be further suppressed in a high-humidity environment where fog is likely to occur. That is, the printer 100 determines the grid voltage Vg and the developing voltage Vb on the condition of humidity in addition to the rotation speed of the photosensitive drum 1, and the fog is compared with the case where only the sheet transport mode is a condition. It can be expected to be further reduced.

なお，本実施の形態は単なる例示にすぎず，本発明を何ら限定するものではない。したがって本発明は当然に，その要旨を逸脱しない範囲内で種々の改良，変形が可能である。例えば，プリンタに限らず，複写機，ＦＡＸ等，電子写真方式による画像形成機能を備えるものであれば適用可能である。また，実施の形態に記載した各種電圧の数値は一例であって，適宜選択すればよい。 It should be noted that the present embodiment is merely an example and does not limit the present invention in any way. Therefore, as a matter of course, the present invention can be improved and modified in various ways without departing from the gist thereof. For example, it is applicable not only to a printer but also to a copier, a fax machine, or the like, which has an image forming function by an electrophotographic method. Further, the numerical values of various voltages described in the embodiment are examples, and may be appropriately selected.

また，実施の形態のプリンタ１００は，ワイヤ電極２１とグリッド電極２２とを有するスコロトロン型の帯電器であるが，これに限るものではない。例えば，電圧が印加される帯電ローラを有し，帯電ローラを感光ドラム１に接触させて感光ドラム１の表面を帯電させる帯電器であってもよい。 Further, the printer 100 of the embodiment is a scorotron type charger having a wire electrode 21 and a grid electrode 22, but is not limited thereto. For example, it may be a charger having a charging roller to which a voltage is applied and bringing the charging roller into contact with the photosensitive drum 1 to charge the surface of the photosensitive drum 1.

また，実施の形態では，プロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋごとに，ワイヤ電圧印加部２５，現像電圧印加部４５，転写電圧印加部５５，を備えているが，複数のプロセス部で共通の電圧印加部を備えていてもよい。例えば，プロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋの転写電圧Ｖｔが共通であれば，プロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋで共通の転写電圧印加部５５を備えればよい。 Further, in the embodiment, the wire voltage application unit 25, the development voltage application unit 45, and the transfer voltage application unit 55 are provided for each of the process units 10Y, 10M, 10C, and 10K, but they are common to a plurality of process units. A voltage application unit may be provided. For example, if the transfer voltage Vt of the process units 10Y, 10M, 10C, and 10K is common, the process unit 10Y, 10M, 10C, and 10K may be provided with a common transfer voltage application unit 55.

また，実施の形態では，現像器４が新品に交換されてからの印刷量として，印刷回数をカウントしているが，印刷量は印刷回数に限るものではない。例えば，現像器４を新品に交換してからの印字ドットや現像ローラ４１の回転数をカウントしてもよい。 Further, in the embodiment, the number of prints is counted as the print amount after the developer 4 is replaced with a new one, but the print amount is not limited to the number of prints. For example, the number of rotations of the printing dots and the developing roller 41 after the developer 4 is replaced with a new one may be counted.

また，実施の形態では，印刷ジョブを開始する度に，ＣＰＵ３１が，グリッド電圧Ｖｇおよび現像電圧Ｖｂを設定しているが，前の印刷ジョブと同じ種類のシートを連続搬送する場合，Ｓ００１の電圧設定処理を省略してもよい。すなわち，連続印字中は，グリッド電圧Ｖｇおよび現像電圧Ｖｂを変更しないようにしてもよい。 Further, in the embodiment, the CPU 31 sets the grid voltage Vg and the development voltage Vb each time the print job is started. However, when the same type of sheet as the previous print job is continuously conveyed, the voltage of S001 is obtained. The setting process may be omitted. That is, the grid voltage Vg and the development voltage Vb may not be changed during continuous printing.

また，実施の形態では，グリッド電圧Ｖｇと現像電圧Ｖｂとの差Ｖｇ−Ｖｂを変更する際，グリッド電圧Ｖｇと現像電圧Ｖｂとの両方を変更しているが，図８に示すように，現像電圧Ｖｂを変更せず，グリッド電圧Ｖｇのみを変更してもよい。あるいはグリッド電圧Ｖｇを変更せず，現像電圧Ｖｂのみを変更してもよい。一方の電圧のみを変更することで，他方の電圧の制御がシンプルになる。ただし，半速搬送すると感光ドラム１の表面の単位面積あたりの露光時間が長くなり，露光箇所の表面電位の絶対値が高速搬送の場合と比較して小さくなり易く，その結果として濃度が濃くなり易い。そのため，実施の形態のように現像電圧Ｖｂも小さくすることで，濃度変化も抑制し得る。 Further, in the embodiment, when the difference Vg-Vb between the grid voltage Vg and the development voltage Vb is changed, both the grid voltage Vg and the development voltage Vb are changed. Only the grid voltage Vg may be changed without changing the voltage Vb. Alternatively, only the development voltage Vb may be changed without changing the grid voltage Vg. By changing only one voltage, the control of the other voltage becomes simple. However, when half-speed transport is performed, the exposure time per unit area of the surface of the photosensitive drum 1 becomes long, and the absolute value of the surface potential of the exposed portion tends to be smaller than in the case of high-speed transport, resulting in a high density. easy. Therefore, the density change can be suppressed by reducing the developing voltage Vb as in the embodiment.

また，実施の形態では，イエローのみをかぶりが生じ易い特定色として，搬送態様に加えて湿度に応じて，グリッド電圧Ｖｇおよび現像電圧Ｖｂを設定しているが，特定色は，イエローに限るものではない。例えば，他の色を特定色としてもよい。また，特定色は，１つの色に限るものではなく，複数を特定色としてもよい。勿論，全ての色を特定色としてもよい。言い換えると，特定色か否かを判断せず，全てのプロセス部１０Ｙ，１０Ｍ，１０Ｃ，１０Ｋについて，湿度に応じて，グリッド電圧Ｖｇおよび現像電圧Ｖｂを設定してもよい。 Further, in the embodiment, the grid voltage Vg and the developing voltage Vb are set according to the humidity in addition to the transport mode as a specific color in which only yellow is likely to be fogged, but the specific color is limited to yellow. is not it. For example, another color may be used as a specific color. Further, the specific color is not limited to one color, and a plurality of specific colors may be used as specific colors. Of course, all colors may be designated as specific colors. In other words, the grid voltage Vg and the developing voltage Vb may be set according to the humidity for all the process units 10Y, 10M, 10C, and 10K without determining whether or not the color is a specific color.

また，実施の形態では，新品状態の場合（モードＡ）または耐久劣化状態の場合（モードＣ），湿度に応じてグリッド電圧Ｖｇおよび現像電圧Ｖｂを設定しているが，これらの状態を判断せず，全ての状態において，湿度に応じてグリッド電圧Ｖｇおよび現像電圧Ｖｂを設定してもよい。また，新品状態の場合（モードＡ）と耐久劣化状態の場合（モードＣ）とのいずれか一方のみを判断してもよい。 Further, in the embodiment, the grid voltage Vg and the developing voltage Vb are set according to the humidity in the case of a new state (mode A) or the durable deterioration state (mode C). Instead, the grid voltage Vg and the developing voltage Vb may be set according to the humidity in all states. Further, only one of the case of a new state (mode A) and the case of a durable deterioration state (mode C) may be determined.

また，実施の形態では，高湿状態か否かの湿度の閾値を固定値（本形態では７０％）としているが，可変値としてもよい。例えば，プリンタ１００がハウジング内の温度を検知するための温度センサを備え，図９に示すように，温度が高いほど，湿度の高低の閾値が低くなるようにしてもよい。 Further, in the embodiment, the humidity threshold value for high humidity or not is set to a fixed value (70% in this embodiment), but it may be a variable value. For example, the printer 100 may include a temperature sensor for detecting the temperature inside the housing, and as shown in FIG. 9, the higher the temperature, the lower the threshold value of humidity.

また，実施の形態では，半速搬送の際，低湿と高湿との２段階に分けて，グリッド電圧Ｖｇおよび現像電圧Ｖｂを設定しているが，３段階以上に分けてもよい。すなわち，湿度が高くなるほど，グリッド電圧Ｖｇと現像電圧Ｖｂとの差Ｖｇ−Ｖｂが小さくなるように構成すればよい。 Further, in the embodiment, the grid voltage Vg and the developing voltage Vb are set in two stages of low humidity and high humidity during half-speed transportation, but they may be divided into three or more stages. That is, the higher the humidity, the smaller the difference Vg-Vb between the grid voltage Vg and the developing voltage Vb may be.

また，実施の形態に開示されている処理は，単一のＣＰＵ，複数のＣＰＵ，ＡＳＩＣなどのハードウェア，またはそれらの組み合わせで実行されてもよい。また，実施の形態に開示されている処理は，その処理を実行するためのプログラムを記録した記録媒体，または方法等の種々の態様で実現することができる。 Further, the processing disclosed in the embodiment may be executed by a single CPU, a plurality of CPUs, hardware such as an ASIC, or a combination thereof. Further, the process disclosed in the embodiment can be realized in various modes such as a recording medium or a method in which a program for executing the process is recorded.

１感光ドラム
２帯電器
４１現像ローラ
８１湿度センサ
３０コントローラ
１００プリンタ 1 Photosensitive drum 2 Charger 41 Developing roller 81 Humidity sensor 30 Controller 100 Printer

Claims

Photoreceptor and
A charger that charges the surface of the photoconductor and
A developing roller that comes into contact with the photoconductor and supplies the developer to the surface of the photoconductor.
Humidity sensor and
Control unit and
With
The control unit
When the photoconductor is rotated at the first speed to form an image,
The difference between the applied voltage of the charger and the applied voltage of the developing roller is defined as the first difference.
When the photoconductor is rotated at a second speed slower than the first speed to form an image,
When the humidity based on the signal from the humidity sensor is lower than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is set as the second difference smaller than the first difference.
When the humidity based on the signal from the humidity sensor is equal to or higher than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is set as a third difference smaller than the second difference.
The peripheral speed ratio between the photoconductor and the developing roller is the same when the photoconductor is at the first speed and when the photoconductor is at the second speed.
An image forming apparatus characterized in that.

In the image forming apparatus according to claim 1,
With the plurality of the photoconductors
The charger and the developing roller corresponding to each of the plurality of photoconductors are provided.
The control unit
When the photoconductor is rotated at the second speed to form an image, with respect to at least one of the plurality of photoconductors.
When the humidity based on the signal from the humidity sensor is lower than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is defined as the second difference.
When the humidity based on the signal from the humidity sensor is equal to or higher than the predetermined value, the difference between the voltage applied by the charger and the voltage applied by the developing roller is defined as the third difference.
An image forming apparatus characterized in that.

Photoreceptor and
A charger that charges the surface of the photoconductor and
A developing roller that comes into contact with the photoconductor and supplies the developer to the surface of the photoconductor.
Humidity sensor and
A housing unit that houses the developer and
Control unit and
With
The control unit
The amount of printing after the housing is replaced with a new one is counted.
When the photoconductor is rotated at the first speed to form an image,
The difference between the applied voltage of the charger and the applied voltage of the developing roller is defined as the first difference.
When the photoconductor is rotated at a second speed slower than the first speed to form an image, the print amount count value does not exceed the first threshold value.
When the humidity based on the signal from the humidity sensor is lower than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is set as the second difference smaller than the first difference.
When the humidity based on the signal from the humidity sensor is equal to or higher than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is set as a third difference smaller than the second difference.
An image forming apparatus characterized in that.

Photoreceptor and
A charger that charges the surface of the photoconductor and
A developing roller that comes into contact with the photoconductor and supplies the developer to the surface of the photoconductor.
Humidity sensor and
A housing unit that houses the developer and
Control unit and
With
The control unit
The amount of printing after the housing is replaced with a new one is counted.
When the photoconductor is rotated at the first speed to form an image,
The difference between the applied voltage of the charger and the applied voltage of the developing roller is defined as the first difference.
When the photoconductor is rotated at a second speed slower than the first speed to form an image, the print amount count value exceeds the second threshold value.
When the humidity based on the signal from the humidity sensor is lower than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is set as the second difference smaller than the first difference.
When the humidity based on the signal from the humidity sensor is equal to or higher than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is set as a third difference smaller than the second difference.
An image forming apparatus characterized in that.

Photoreceptor and
A charger that charges the surface of the photoconductor and
A developing roller that comes into contact with the photoconductor and supplies the developer to the surface of the photoconductor.
Humidity sensor and
A housing unit that houses the developer and
Control unit and
With
The control unit
The amount of printing after the housing is replaced with a new one is counted.
When the photoconductor is rotated at the first speed to form an image,
The difference between the applied voltage of the charger and the applied voltage of the developing roller is defined as the first difference.
When the photoconductor is rotated at a second speed slower than the first speed to form an image, the count value of the print amount does not exceed the first threshold value or is larger than the first threshold value. On condition that the second threshold is exceeded
When the humidity based on the signal from the humidity sensor is lower than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is set as the second difference smaller than the first difference.
When the humidity based on the signal from the humidity sensor is equal to or higher than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is set as a third difference smaller than the second difference.
When the photoconductor is rotated at the second speed to form an image, and the count value of the print amount exceeds the first threshold value and does not exceed the second threshold value.
Regardless of the humidity value based on the signal from the humidity sensor, the difference between the applied voltage of the charger and the applied voltage of the developing roller is set as a fourth difference smaller than the first difference.
An image forming apparatus characterized in that.

In the image forming apparatus according to any one of claims 1 to 5.
The control unit
When reducing the difference between the applied voltage of the charger and the applied voltage of the developing roller, both the absolute value of the applied voltage of the developing roller and the absolute value of the applied voltage of the charger are reduced.
An image forming apparatus characterized in that.

In the image forming apparatus according to any one of claims 1 to 5.
The control unit
When reducing the difference between the applied voltage of the charger and the applied voltage of the developing roller, the applied voltage of the developing roller is not changed, and the absolute value of the applied voltage of the charger is reduced.
An image forming apparatus characterized in that.

In the image forming apparatus according to any one of claims 1 to 7.
The charger is
It is a corona charger equipped with a wire electrode and a grid electrode.
The control unit
The potential of the grid electrode is controlled as the applied voltage of the charger.
An image forming apparatus characterized in that.

Photoreceptor and
A charger that charges the surface of the photoconductor and
A developing roller that comes into contact with the photoconductor and supplies the developer to the surface of the photoconductor.
In the image forming method of the image forming apparatus provided with
The acquisition step to acquire the humidity and
When the photoconductor is rotated at the first speed to form an image, the difference between the applied voltage of the charger and the applied voltage of the developing roller is set as the first difference, and the first step.
When the photoconductor is rotated at a second speed slower than the first speed to form an image, a determination step for determining whether or not the humidity acquired in the acquisition step is lower than a predetermined value. ，
When it is determined in the determination step that the humidity is lower than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is a second difference smaller than the first difference. The second step and
When the humidity is determined to be equal to or higher than the predetermined value in the determination step, the difference between the applied voltage of the charger and the applied voltage of the developing roller is set as a third difference smaller than the second difference. The third step and
Only including,
The peripheral speed ratio between the photoconductor and the developing roller is the same when the photoconductor is at the first speed and when the photoconductor is at the second speed.
An image forming method of an image forming apparatus.

Photoreceptor and
A charger that charges the surface of the photoconductor and
A developing roller that comes into contact with the photoconductor and supplies the developer to the surface of the photoconductor.
A housing unit that houses the developer and
In the image forming method of the image forming apparatus provided with
A count step that counts the amount of printing after the housing is replaced with a new one, and
The acquisition step to acquire the humidity and
When the photoconductor is rotated at the first speed to form an image, the difference between the applied voltage of the charger and the applied voltage of the developing roller is set as the first difference, and the first step.
When the photoconductor is rotated at a second speed slower than the first speed to form an image, the acquisition step is performed on the condition that the count value of the print amount does not exceed the first threshold value. Judgment step to determine whether or not the acquired humidity is lower than the predetermined value, and
When it is determined in the determination step that the humidity is lower than the predetermined value, the difference between the applied voltage of the charger and the applied voltage of the developing roller is a second difference smaller than the first difference. The second step and
When the humidity is determined to be equal to or higher than the predetermined value in the determination step, the difference between the applied voltage of the charger and the applied voltage of the developing roller is set as a third difference smaller than the second difference. The third step and
A method for forming an image of an image forming apparatus, which comprises.