JP7545656B2

JP7545656B2 - Transfer device and image forming apparatus

Info

Publication number: JP7545656B2
Application number: JP2020100430A
Authority: JP
Inventors: 啓司渡辺
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2020-06-09
Filing date: 2020-06-09
Publication date: 2024-09-05
Anticipated expiration: 2040-06-09
Also published as: JP2021196398A

Description

この発明は、感光体ドラム、中間転写ベルトなどの像担持体の表面に担持されたトナー像をシートに転写する転写装置と、それを備えた複写機、プリンタ、ファクシミリ、又は、それらの複合機等の画像形成装置と、に関するものである。 This invention relates to a transfer device that transfers a toner image carried on the surface of an image carrier such as a photosensitive drum or an intermediate transfer belt onto a sheet, and an image forming device equipped with the transfer device, such as a copier, printer, facsimile, or a combination machine of these.

従来から、複写機やプリンタ等の画像形成装置において、感光体ドラム、中間転写ベルト等の像担持体の表面に形成されたトナー像をシートに転写する転写工程前に、そのシートの電荷を除電する技術が用いられている（例えば、特許文献１参照。）。 Conventionally, in image forming devices such as copiers and printers, a technique has been used to remove the charge from a sheet before the transfer process in which a toner image formed on the surface of an image carrier such as a photosensitive drum or intermediate transfer belt is transferred to the sheet (see, for example, Patent Document 1).

一方、特許文献１には、感光体ドラムと転写ローラとが当接する転写ニップに対して被記録体（シート）の搬送方向上流側であって、被記録体の転写面に対向する位置に、電気的にフロート状態の除電器（除電部材）を設置する技術が開示されている。 Meanwhile, Patent Document 1 discloses a technology in which an electrically floating static eliminator (static eliminator member) is installed upstream in the transport direction of the recording medium (sheet) from the transfer nip where the photosensitive drum and transfer roller come into contact, and in a position facing the transfer surface of the recording medium.

従来の技術は、転写工程前にシートが除電部材によって除電されるときに、シートの帯電量によって除電状態が安定しないことがあった。そして、そのようにシートの除電不良が生じることにより、転写工程によってシートに形成される転写画像に、転写ムラ、チリ、黒スジ、転写不良などが生じてしまっていた。 In conventional technology, when the sheet is neutralized by a neutralizing member before the transfer process, the neutralization state is sometimes unstable depending on the amount of charge on the sheet. Such poor neutralization of the sheet can result in uneven transfer, dust, black streaks, and transfer defects in the transferred image formed on the sheet by the transfer process.

この発明は、上述のような課題を解決するためになされたもので、転写工程前にシートを良好に除電することができる、転写装置、及び、画像形成装置を提供することにある。 This invention was made to solve the above-mentioned problems, and aims to provide a transfer device and an image forming device that can effectively remove static electricity from a sheet before the transfer process.

この発明における転写装置は、像担持体の表面に担持されたトナー像を、転写位置に搬送されるシートの転写面に転写する転写装置であって、前記転写位置に対してシートの搬送方向上流側であって、シートの前記転写面に対向する位置に配置されて、シートの電荷を除電可能な第１除電部材と、前記転写位置に対してシートの搬送方向上流側であって、シートの非転写面に対向する位置に配置されて、シートの電荷を除電可能な第２除電部材と、前記第１除電部材と前記第２除電部材とのうち少なくとも一方を、電気的に接地状態とフロート状態とのいずれかに切替可能な切替手段と、を備え、前記切替手段は、前記転写位置に搬送されるシートの前記転写面の帯電量が所定値よりも大きい場合には前記第１除電部材を前記接地状態にして、前記転写位置に搬送されるシートの前記転写面の帯電量が前記所定値以下である場合には前記第１除電部材を前記フロート状態にするものである。 The transfer device of the present invention is a transfer device that transfers a toner image carried on the surface of an image carrier to a transfer surface of a sheet transported to a transfer position, and is equipped with a first de-electrifying member that is arranged upstream of the transfer position in the sheet transport direction and facing the transfer surface of the sheet, and is capable of de-electrifying the charge of the sheet, a second de-electrifying member that is arranged upstream of the transfer position in the sheet transport direction and facing the non-transfer surface of the sheet, and is capable of de-electrifying the charge of the sheet, and a switching means that is capable of electrically switching at least one of the first de-electrifying member and the second de-electrifying member between a grounded state and a floating state , and the switching means switches the first de-electrifying member to the grounded state when the charge amount of the transfer surface of the sheet transported to the transfer position is greater than a predetermined value, and switches the first de-electrifying member to the floating state when the charge amount of the transfer surface of the sheet transported to the transfer position is less than the predetermined value .

本発明によれば、転写工程前にシートを良好に除電することができる、転写装置、及び、画像形成装置を提供することができる。 The present invention provides a transfer device and an image forming device that can effectively remove static electricity from a sheet before the transfer process.

この発明の実施の形態における画像形成装置を示す全体構成図である。1 is an overall configuration diagram showing an image forming apparatus according to an embodiment of the present invention; 転写装置の近傍を示す拡大図である。FIG. 除電部材を示す構成図である。FIG. 2 is a diagram showing the configuration of a static eliminator. 除電部材を幅方向に示す図である。FIG. 4 is a view showing the static eliminator in the width direction. 両面印刷時の切替スイッチの制御を示す表図である。FIG. 13 is a table showing the control of the changeover switch during double-sided printing. 変形例１としての、切替スイッチの制御を示す表図である。FIG. 11 is a table showing control of a changeover switch according to a first modified example. 変形例２としての、切替スイッチの制御を示す表図である。FIG. 11 is a table showing control of a changeover switch according to a second modified example. 変形例３としての、切替スイッチの制御を示す表図である。FIG. 13 is a table showing control of the changeover switch according to Modification 3. 変形例４としての、切替スイッチの制御を示す表図である。FIG. 13 is a table showing control of the changeover switch according to the fourth modified example. 変形例５としての、転写装置の近傍を示す拡大図である。FIG. 13 is an enlarged view showing the vicinity of a transfer device according to a fifth modified example. 図１０の転写装置でおこなわれる切替スイッチの制御を示す表図である。11 is a table showing control of a changeover switch performed in the transfer device of FIG. 10.

以下、この発明を実施するための形態について、図面を参照して詳細に説明する。なお、各図中、同一又は相当する部分には同一の符号を付しており、その重複説明は適宜に簡略化ないし省略する。 The following describes in detail the embodiments of the present invention with reference to the drawings. Note that in each drawing, the same or corresponding parts are given the same reference numerals, and the repeated explanations will be appropriately simplified or omitted.

まず、図１にて、画像形成装置における全体の構成・動作について説明する。
図１において、１００は画像形成装置としてのプリンタ、６は像担持体としての感光体ドラム１上にトナー像（画像）を形成するプロセスカートリッジ（作像部）、７はパソコンなどの入力装置から入力された画像情報に基いた露光光Ｌを感光体ドラム１上に照射する露光部（書込み部）、９は感光体ドラム１に当接して転写ニップ（転写位置）を形成する転写部材としての転写ローラ、を示す。
また、１０は画像形成装置１００における種々の操作をユーザーが入力したり種々の情報を確認したりするための操作表示パネル、１２は用紙等のシートＰが収納された給紙装置（給紙カセット）、２０はシートＰ上の未定着画像を定着する定着装置、２１は定着装置２０に設置された定着ローラ、２２は定着装置２０に設置された加圧ローラ、２５は定着ローラを加熱する赤外線ヒータ、を示す。
また、３０Ａ、３０Ｂは転写工程前のシートＰを除電する除電部材、４５は感光体ドラム１と転写ローラ９とが当接する転写位置（転写ニップ）に向けてシートＰを搬送するレジストローラ対（タイミングローラ対）、９０は感光体ドラム１（像担持体）の表面に形成されたトナー像を転写ニップ（転写位置）に搬送されるシートＰの転写面に転写する転写装置、を示す。
画像形成装置１００には、シートＰを搬送するための複数の搬送経路Ｋ１～Ｋ４が設けられていて、それらの搬送経路Ｋ１～Ｋ４には複数の搬送ローラ対が設置されている。これらの搬送ローラ対や、後述する給紙ローラ４１などは、軸部にローラ部が形成されたものであって、ローラ部の表面には絶縁性ゴム層が形成されている。 First, the overall configuration and operation of an image forming apparatus will be described with reference to FIG.
In FIG. 1, reference numeral 100 denotes a printer as an image forming apparatus, 6 denotes a process cartridge (imaging unit) that forms a toner image (image) on a photosensitive drum 1 as an image carrier, 7 denotes an exposure unit (writing unit) that irradiates the photosensitive drum 1 with exposure light L based on image information input from an input device such as a personal computer, and 9 denotes a transfer roller as a transfer member that comes into contact with the photosensitive drum 1 to form a transfer nip (transfer position).
In addition, reference numeral 10 denotes an operation display panel through which a user inputs various operations in the image forming apparatus 100 and checks various information, reference numeral 12 denotes a paper feeding device (paper feeding cassette) in which sheets P such as paper are stored, reference numeral 20 denotes a fixing device that fixes an unfixed image on the sheet P, reference numeral 21 denotes a fixing roller installed in the fixing device 20, reference numeral 22 denotes a pressure roller installed in the fixing device 20, and reference numeral 25 denotes an infrared heater that heats the fixing roller.
In addition, 30A and 30B indicate de-electrifying members that de-electrify the sheet P before the transfer process, 45 indicates a pair of registration rollers (a pair of timing rollers) that transport the sheet P toward a transfer position (transfer nip) where the photosensitive drum 1 and the transfer roller 9 abut, and 90 indicates a transfer device that transfers the toner image formed on the surface of the photosensitive drum 1 (image carrier) to the transfer surface of the sheet P transported to the transfer nip (transfer position).
The image forming apparatus 100 is provided with a plurality of transport paths K1 to K4 for transporting the sheet P, and a plurality of transport roller pairs are installed on the transport paths K1 to K4. These transport roller pairs and a paper feed roller 41, which will be described later, are each formed with a roller portion on the shaft portion, and an insulating rubber layer is formed on the surface of the roller portion.

ここで、図１及び図２を参照して、プロセスカートリッジ６は、像担持体としての感光体ドラム１と、帯電装置４（帯電ローラ）と、現像装置５と、クリーニング装置２と、が一体的にユニットとして構成されている。このプロセスカートリッジ６は、画像形成装置本体１００に対して、着脱可能（交換可能）に設置されている。 Now, referring to Figures 1 and 2, the process cartridge 6 is configured as a unit that includes a photosensitive drum 1 as an image carrier, a charging device 4 (charging roller), a developing device 5, and a cleaning device 2. This process cartridge 6 is installed in the image forming apparatus main body 100 so as to be detachable (replaceable).

さらに詳しくは、像担持体としての感光体ドラム１は、負帯電性の有機感光体であって、ドラム状導電性支持体上に感光層等を設けたものである。図示は省略するが、感光体ドラム１は、基層としての導電性支持体上に、絶縁層である下引き層、感光層としての電荷発生層及び電荷輸送層が順次積層されている。また、感光体ドラム１は、不図示の駆動モータによる回転駆動によって、図１の反時計方向に回転する。
帯電装置４は、導電性芯金の外周に中抵抗の弾性層を被覆してなる帯電ローラであって、感光体ドラム１に当接している。帯電装置４には不図示の電源部から所定の電圧（帯電バイアス）が印加されて、これにより対向する感光体ドラム１の表面を一様に帯電する。 More specifically, the photoconductor drum 1 as an image carrier is a negatively charged organic photoconductor, and is configured by providing a photosensitive layer and the like on a drum-shaped conductive support. Although not shown, the photoconductor drum 1 is configured by sequentially laminating an undercoat layer as an insulating layer, a charge generating layer as a photosensitive layer, and a charge transport layer as a photosensitive layer on a conductive support as a base layer. The photoconductor drum 1 is rotated counterclockwise in FIG. 1 by being driven to rotate by a drive motor (not shown).
The charging device 4 is a charging roller made of a conductive core metal covered with a medium resistance elastic layer, and is in contact with the photosensitive drum 1. A predetermined voltage (charging bias) is applied to the charging device 4 from a power source unit (not shown), thereby uniformly charging the surface of the opposing photosensitive drum 1.

現像装置５は、主として、感光体ドラム１に対向する現像ローラ５１と、仕切部材を介して並設された２つの現像搬送スクリュ５３、現像ローラ５１に対向するドクターブレード５２と、で構成される。現像ローラ５１は、内部に固設されてローラ周面に磁極を形成するマグネットと、マグネットの周囲を回転するスリーブと、で構成される。マグネットによって現像ローラ５１（スリーブ）上に複数の磁極が形成されて、現像ローラ５１上に現像剤が担持されることになる。現像装置５内には、キャリアとトナーとからなる２成分現像剤が収容されている。また、図示は省略するが、現像装置５の上方には、プロセスカートリッジ６とは別に着脱可能に設置されたトナー容器（新品のトナーが収容されている。）が接続されている。 The developing device 5 mainly consists of a developing roller 51 facing the photosensitive drum 1, two developing and transporting screws 53 arranged side by side with a partition member, and a doctor blade 52 facing the developing roller 51. The developing roller 51 consists of a magnet that is fixed inside and forms a magnetic pole on the roller surface, and a sleeve that rotates around the magnet. The magnet forms multiple magnetic poles on the developing roller 51 (sleeve), and the developer is carried on the developing roller 51. The developing device 5 contains a two-component developer consisting of a carrier and a toner. Although not shown in the figure, a toner container (containing new toner) that is installed separately from the process cartridge 6 and can be removed is connected above the developing device 5.

このように構成された現像装置５は、次のように動作する。
現像ローラ５１のスリーブは、図１の時計方向に回転している。そして、マグネットにより形成された磁界によって現像ローラ５１上に担持された現像剤は、スリーブの回転にともない現像ローラ５１上を移動する。ここで、現像装置５内の現像剤は、現像剤中のトナーの割合（トナー濃度）が所定の範囲内になるように調整される（トナー容器から不図示のトナー補給口を介して適宜にトナーが補給される）。
その後、現像剤収容部内に補給されたトナーは、２つの現像搬送スクリュ５３によって、現像剤とともに混合・撹拌されながら、仕切部材によって幅方向の両端部以外が隔絶された２つの現像剤収容部を循環する（図１の紙面垂直方向の移動である。）。そして、現像剤中のトナーは、キャリアとの摩擦帯電によりキャリアに吸着して、現像ローラ５１上に形成された磁力によりキャリアとともに現像ローラ５１上に担持される。 The developing device 5 configured in this manner operates as follows.
The sleeve of the developing roller 51 rotates in the clockwise direction in Fig. 1. The developer carried on the developing roller 51 by the magnetic field generated by a magnet moves on the developing roller 51 as the sleeve rotates. Here, the developer in the developing device 5 is adjusted so that the ratio of toner in the developer (toner concentration) falls within a predetermined range (toner is appropriately replenished from a toner container through a toner refill port (not shown)).
Thereafter, the toner replenished in the developer storage compartment is mixed and stirred with the developer by the two developer transport screws 53, while circulating through the two developer storage compartments separated at all sides except for both ends in the width direction by the partition members (movement in the direction perpendicular to the paper surface of FIG. 1). The toner in the developer is attracted to the carrier by frictional charging with the carrier, and is carried on the developing roller 51 together with the carrier by the magnetic force formed on the developing roller 51.

現像ローラ５１上に担持された現像剤は、図１中の時計方向に搬送されて、ドクターブレード５２の位置に達する。そして、現像ローラ５１上の現像剤は、この位置で現像剤量が適量化された後に、感光体ドラム１との対向位置（現像領域である。）まで搬送される。そして、現像領域に形成された電界（現像ローラ５１に印可される現像バイアスと、感光体ドラム１上の潜像電位と、によって形成される電界である。）によって、感光体ドラム１上に形成された潜像にトナーが吸着される。その後、現像ローラ５１上に残った現像剤はスリーブの回転にともない現像剤収容部の上方に達して、この位置で現像ローラ５１から離脱される。 The developer carried on the developing roller 51 is transported in the clockwise direction in FIG. 1 until it reaches the position of the doctor blade 52. The developer on the developing roller 51 is then adjusted to an appropriate amount at this position, and then transported to a position facing the photosensitive drum 1 (the developing area). The toner is then attracted to the latent image formed on the photosensitive drum 1 by the electric field formed in the developing area (the electric field formed by the developing bias applied to the developing roller 51 and the latent image potential on the photosensitive drum 1). The developer remaining on the developing roller 51 then reaches the top of the developer storage section as the sleeve rotates, and is released from the developing roller 51 at this position.

図１を参照して、クリーニング装置２には、感光体ドラム１に当接して感光体ドラム１の表面に付着した未転写トナー（シートＰから生じる紙粉、未転写トナー同士が凝集したもの（凝集トナー）、帯電装置４による放電時に感光体ドラム１上に生じる放電生成物、トナーに添加されている添加剤、等の付着物も含むものとする。）を除去するクリーニングブレード２ａや、クリーニング装置２で除去・回収された未転写トナーを不図示の廃トナー回収容器に向けて搬送する搬送スクリュ２ｂ、などが設置されている。 Referring to FIG. 1, the cleaning device 2 is equipped with a cleaning blade 2a that comes into contact with the photosensitive drum 1 to remove untransferred toner (including paper dust generated from the sheet P, aggregates of untransferred toner (aggregated toner), discharge products generated on the photosensitive drum 1 during discharge by the charging device 4, additives added to the toner, and other deposits) that have adhered to the surface of the photosensitive drum 1, and a transport screw 2b that transports the untransferred toner removed and collected by the cleaning device 2 to a waste toner collection container (not shown).

クリーニングブレード２ａは、ウレタンゴム、ヒドリンゴム、シリコーンゴム、フッ素ゴム等のゴム材料からなる板状のブレード本体が保持板に保持されたものであって、感光体ドラム１の表面に所定角度かつ所定圧力で当接している。これにより、感光体ドラム１上に付着する未転写トナーが機械的に掻き取られてクリーニング装置２内に回収されることになる。
不図示の駆動モータからの駆動力を受けて所定方向に回転する。
搬送スクリュ２ｂは、回転軸部にスクリュ部が螺旋状に巻装されたものであって、不図示の駆動モータからの駆動力を受けて所定方向に回転する。 The cleaning blade 2a is a plate-shaped blade body made of a rubber material such as urethane rubber, hydrin rubber, silicone rubber, or fluororubber, held by a holding plate, and is in contact with the surface of the photosensitive drum 1 at a predetermined angle and with a predetermined pressure. As a result, untransferred toner adhering to the photosensitive drum 1 is mechanically scraped off and collected in the cleaning device 2.
It receives a driving force from a driving motor (not shown) and rotates in a predetermined direction.
The conveying screw 2b has a screw portion wound in a spiral shape around a rotating shaft portion, and rotates in a predetermined direction upon receiving a driving force from a driving motor (not shown).

図１を参照して、画像形成装置１００における、通常の画像形成時の動作について説明する。
まず、パソコン等の入力装置から画像形成装置１の露光部７に画像情報が送信されると、露光部７からその画像情報に基づいた露光光Ｌ（レーザ光）が、感光体ドラム１の表面に向けて発せられる。
一方、感光体ドラム１は、矢印方向（反時計方向）に回転している。そして、まず、感光体ドラム１の表面は、帯電装置４との対向部で、一様に帯電される（帯電工程である。）。こうして、感光体ドラム１上には、帯電電位（－９００Ｖ程度である。）が形成される。その後、帯電された感光体ドラム１の表面は、それぞれの露光光Ｌの照射位置に達する。そして、露光光Ｌが照射された部分の電位が潜像電位（０～－１００Ｖ程度である。）となって、感光体ドラム１の表面に静電潜像が形成される（露光工程である。）。すなわち、感光体ドラム１の表面において、露光光Ｌが照射された部分は画像部（静電潜像）として潜像電位（画像部電位）が形成されて、それ以外の部分は非画像部（地肌部）として帯電電位（非画像電位）が維持される。 With reference to FIG. 1, the operation of image forming apparatus 100 during normal image formation will be described.
First, when image information is sent from an input device such as a personal computer to the exposure unit 7 of the image forming apparatus 1 , exposure light L (laser light) based on the image information is emitted from the exposure unit 7 toward the surface of the photosensitive drum 1 .
Meanwhile, the photosensitive drum 1 rotates in the direction of the arrow (counterclockwise). First, the surface of the photosensitive drum 1 is uniformly charged at the portion facing the charging device 4 (charging process). Thus, a charging potential (about -900V) is formed on the photosensitive drum 1. After that, the charged surface of the photosensitive drum 1 reaches the irradiation position of each exposure light L. Then, the potential of the portion irradiated with the exposure light L becomes a latent image potential (about 0 to -100V), and an electrostatic latent image is formed on the surface of the photosensitive drum 1 (exposure process). That is, on the surface of the photosensitive drum 1, the portion irradiated with the exposure light L forms a latent image potential (image portion potential) as an image portion (electrostatic latent image), and the other portion is maintained as a non-image portion (background portion) at a charging potential (non-image potential).

その後、静電潜像が形成された感光体ドラム１の表面は、現像装置５（現像ローラ５１）との対向位置に達する。そして、現像装置５から感光体ドラム１上にトナーが供給されて、感光体ドラム１上の潜像が現像されてトナー像が形成される（現像工程である。）。
その後、現像工程後の感光体ドラム１の表面は、転写部材としての転写ローラ９との転写ニップ（転写位置）に達する。そして、転写ローラ９との転写ニップで、転写ローラ９に印可された転写バイアス（トナーの極性とは異なる極性のバイアスである。）によって、レジストローラ対４５により搬送されたシートＰ上に、感光体ドラム１上に形成されたトナー像が転写される（転写工程である。）。なお、転写ローラ９は、図１の時計方向に回転している。 Thereafter, the surface of the photoconductor drum 1 on which the electrostatic latent image has been formed reaches a position facing the developing device 5 (developing roller 51). Then, toner is supplied from the developing device 5 onto the photoconductor drum 1, and the latent image on the photoconductor drum 1 is developed to form a toner image (developing process).
Thereafter, the surface of the photosensitive drum 1 after the development process reaches a transfer nip (transfer position) with a transfer roller 9 as a transfer member. Then, in the transfer nip with the transfer roller 9, the toner image formed on the photosensitive drum 1 is transferred onto the sheet P conveyed by the pair of registration rollers 45 by a transfer bias (a bias with a polarity different from that of the toner) applied to the transfer roller 9 (transfer process). The transfer roller 9 rotates clockwise in FIG. 1.

その後、転写工程後の感光体ドラム１の表面は、クリーニング装置２との対向位置に達する。そして、この位置で、クリーニングブレード２ａによって感光体ドラム１上に残存する未転写トナー（紙粉、凝集トナー等の、その他の付着物も含まれる。）が機械的に除去されて、クリーニング装置２内に回収される（クリーニング工程である。）。
そして、クリーニング工程後の感光体ドラム１の表面は、除電装置３０の照射部３２から射出される除電光Ｋ（光）による除電により表面電位がほぼ０Ｖにリセットされる。そして、感光体ドラム１における一連の作像プロセスが終了する。 Thereafter, the surface of the photoconductor drum 1 after the transfer process reaches a position facing the cleaning device 2. At this position, the untransferred toner (including other deposits such as paper powder and aggregated toner) remaining on the photoconductor drum 1 is mechanically removed by the cleaning blade 2a and collected in the cleaning device 2 (cleaning process).
After the cleaning process, the surface of the photoconductor drum 1 is reset to a surface potential of approximately 0 V by discharging the surface with the discharging light K (light) emitted from the irradiation unit 32 of the discharging device 30. Then, a series of image forming processes on the photoconductor drum 1 is completed.

一方、感光体ドラム１と転写ローラ９との転写ニップ（転写位置）に搬送されるシートＰは、次のように動作する。
まず、給紙装置１２に収納されたシートＰの最上方の１枚が、給紙ローラ４１によって、搬送経路Ｋ１に向けて給送される。
その後、シートＰは、レジストローラ対４５の位置に達する。そして、レジストローラ対４５の位置に達したシートＰは、感光体ドラム１上に形成された画像と位置合わせをするためにタイミングを合わせて、転写ニップ（転写ローラ９）に向けて搬送される。 On the other hand, the sheet P conveyed to the transfer nip (transfer position) between the photosensitive drum 1 and the transfer roller 9 operates as follows.
First, the uppermost sheet of the sheets P stored in the sheet feeding device 12 is fed by the sheet feeding roller 41 toward the transport path K1.
Thereafter, the sheet P reaches the position of the registration roller pair 45. Then, the sheet P that has reached the position of the registration roller pair 45 is transported toward the transfer nip (transfer roller 9) in time for alignment with the image formed on the photosensitive drum 1.

そして、転写工程後のシートＰは、転写ニップ（転写ローラ９）の位置を通過した後に、転写ガイド板４６や定着ガイド板４７によって形成される搬送経路を経て定着装置２０に達する。定着装置２０に達したシートＰは、定着ローラ２１と加圧ローラ２２との間に送入されて、定着ローラ２１（内部に設置された赤外線ヒータ２５によって加熱されている。）から受ける熱と双方の部材２１、２２から受ける圧力とによって画像が定着される。画像が定着されたシートＰは、定着ローラ２１と加圧ローラ２２との間（定着ニップ部である。）から送出された後に、排出経路Ｋ２を通過して、画像形成装置本体１００から排出される。
こうして、一連の画像形成プロセス（「片面印刷モード」による印刷動作である。）が完了する。 After the transfer process, the sheet P passes through the transfer nip (transfer roller 9) and then reaches the fixing device 20 via a transport path formed by a transfer guide plate 46 and a fixing guide plate 47. The sheet P that has reached the fixing device 20 is fed between the fixing roller 21 and the pressure roller 22, and the image is fixed by the heat from the fixing roller 21 (heated by an infrared heater 25 installed inside) and the pressure from both members 21 and 22. The sheet P with the fixed image is sent out from between the fixing roller 21 and the pressure roller 22 (the fixing nip portion), passes through a discharge path K2, and is discharged from the image forming apparatus main body 100.
Thus, a series of image forming processes (printing operations in the "single-sided printing mode") is completed.

なお、図１を参照して、シートＰの両面（オモテ面とウラ面とである。）へのプリントをおこなう「両面印刷モード」が選択されている場合には、オモテ面への定着工程が終了したシートＰは、不図示の切替爪の動作により、上述した「片面印刷モード」が選択されているときのようにそのまま画像形成装置１００から排出されることなく、反転搬送経路Ｋ３に導かれる。そして、反転搬送経路Ｋ３に導かれたシートＰは、その搬送方向が反転された後に、不図示の切替爪の動作により、両面搬送経路Ｋ４に導かれる。そして、両面搬送経路Ｋ４に導かれたシートＰは、再び転写ニップ（転写位置）に向けて搬送される。そして、転写ニップ（転写位置）で先に説明したものと同様の画像形成プロセス（画像形成動作）によってシートＰのウラ面への画像形成がおこなわれ、その後に定着部１９での定着工程を経て、排出搬送経路Ｋ２を経由して、画像形成装置１００から排出される。
なお、「片面印刷モード」、「両面印刷モード」は、ユーザーによる操作表示パネル１０（画像形成装置１００の外装部に設置されている。）の操作によって選択される。 1, when a "duplex printing mode" is selected in which printing is performed on both sides (front and back sides) of the sheet P, the sheet P after the fixing process on the front side is not discharged from the image forming apparatus 100 as it is when the above-mentioned "single-sided printing mode" is selected, but is guided to the reverse conveying path K3 by the operation of a switching claw (not shown). Then, the sheet P guided to the reverse conveying path K3 has its conveying direction reversed, and is guided to the double-sided conveying path K4 by the operation of a switching claw (not shown). Then, the sheet P guided to the double-sided conveying path K4 is conveyed again toward the transfer nip (transfer position). Then, an image is formed on the back side of the sheet P by the image forming process (image forming operation) similar to that described above at the transfer nip (transfer position), and then the sheet P is subjected to a fixing process at the fixing unit 19 and discharged from the image forming apparatus 100 via the discharge conveying path K2.
The "single-sided printing mode" and "double-sided printing mode" are selected by the user through operation of the operation display panel 10 (installed on the exterior of the image forming apparatus 100).

以下、本実施の形態における画像形成装置１００において、特徴的な転写装置９０について詳述する。
図２を参照して、転写装置９０は、像担持体としての感光体ドラム１の表面に担持されたトナー像を、転写位置としての転写ニップＮに搬送されるシートＰの転写面に転写する装置である。
ここで、本実施の形態における転写装置９０には、転写部材としての転写ローラ９、２つの除電部材（第１除電部材３０Ａと第２除電部材３０Ｂとである。）、切替手段としての切替スイッチ３１Ａ、３１Ｂ（切替装置）、などで構成されている。転写ローラ９は、感光体ドラム１に当接して、転写位置としての転写ニップＮを形成している。 The transfer device 90, which is a characteristic feature of the image forming apparatus 100 according to the present embodiment, will be described in detail below.
2, transfer device 90 is a device that transfers a toner image carried on the surface of photosensitive drum 1 serving as an image carrier, onto a transfer surface of sheet P transported to transfer nip N serving as a transfer position.
Here, the transfer device 90 in this embodiment is composed of a transfer roller 9 as a transfer member, two charge removing members (a first charge removing member 30A and a second charge removing member 30B), changeover switches 31A and 31B (switching devices) as switching means, etc. The transfer roller 9 abuts against the photosensitive drum 1 to form a transfer nip N as a transfer position.

図２に示すように、第１除電部材３０Ａは、転写ニップＮ（転写位置）に対してシートＰの搬送方向上流側（図２の下方である。）であって、シートＰの転写面（感光体ドラム１に対向する側の面である。）に対向する位置に配置されていて、シートＰの電荷を除電可能に構成されている。
これに対して、第２除電部材３０Ｂは、転写ニップＮ（転写位置）に対してシートＰの搬送方向上流側であって、シートＰの非転写面（転写面に対して反対側の面であって、転写ローラ９に対向する側の面である。）に対向する位置に配置されていて、シートＰの電荷を除電可能に構成されている。 As shown in Figure 2, the first de-ionizing member 30A is positioned upstream (lower in Figure 2) of the transfer nip N (transfer position) in the transport direction of the sheet P, facing the transfer surface of the sheet P (the surface facing the photosensitive drum 1), and is configured to be able to de-ionize the electric charge of the sheet P.
In contrast, the second de-ionizing member 30B is positioned upstream of the transfer nip N (transfer position) in the transport direction of the sheet P, facing the non-transfer surface of the sheet P (the surface opposite the transfer surface, the surface facing the transfer roller 9), and is configured to be able to de-ionize the charge of the sheet P.

特に、本実施の形態において、第１除電部材３０Ａと第２除電部材３０Ｂとは、シートＰの搬送経路（図２において一点鎖線矢印で示している。）を挟んで互いに対向するように配置されている。
具体的に、図２において、搬送経路に対して左側に第１除電部材３０Ａが配置され、搬送経路に対して右側に第２除電部材３０Ｂが配置されている。
また、第１除電部材３０Ａと第２除電部材３０Ｂとは、レジストローラ対４５に対して、搬送方向下流側（図２の上方である。）に配置されている。 In particular, in this embodiment, the first charge removing member 30A and the second charge removing member 30B are disposed to face each other across the transport path of the sheet P (indicated by the dashed dotted arrow in FIG. 2).
Specifically, in FIG. 2, the first charge removing member 30A is disposed on the left side of the transport path, and the second charge removing member 30B is disposed on the right side of the transport path.
The first charge removing member 30A and the second charge removing member 30B are disposed downstream in the transport direction with respect to the pair of registration rollers 45 (upper side in FIG. 2).

また、第１除電部材３０Ａと第２除電部材３０Ｂとは、同じ材質で形成されている。
具体的に、第１除電部材３０Ａと第２除電部材３０Ｂとは、同一部品であって、いずれも、図３に示すようにステンレスなどの金属材料からなる複数本の除電ブラシ３０ａが金属板３０ｂに挟まれて保持されたものである。除電ブラシ３０ａは、金属板３０ｂからの突出し量が５ｍｍ程度に設定され、ブラシ繊維の太さが１２μｍ/本程度に設定されている。また、第１除電部材３０Ａと第２除電部材３０Ｂとは、いずれも、図４に示すようにシートＰの幅方向（白矢印で示す搬送方向に直交する方向であって、図２の紙面垂直方向である。）の全域に接触（又は、隙間をあけて対向）するように形成されている。 The first charge removing member 30A and the second charge removing member 30B are formed from the same material.
Specifically, the first charge removing member 30A and the second charge removing member 30B are the same part, and each of them is formed by sandwiching and holding a plurality of charge removing brushes 30a made of a metal material such as stainless steel between metal plates 30b as shown in Fig. 3. The charge removing brushes 30a are set to protrude from the metal plate 30b by about 5 mm, and the thickness of the brush fibers is set to about 12 µm per brush. In addition, each of the first charge removing member 30A and the second charge removing member 30B is formed to contact (or face each other with a gap) the entire width direction of the sheet P (the direction perpendicular to the conveying direction indicated by the white arrow and perpendicular to the paper surface of Fig. 2) as shown in Fig. 4.

そして、転写ニップＮに向けて搬送されるシートＰが、第１、第２除電部材３０Ａ、３０Ｂの位置で、第１、第２除電部材３０Ａ、３０Ｂ（除電ブラシ３０ａ）に接触することにより、シートＰに蓄積された電荷が除去（除電）されることになる。
具体的に、転写ニップＮに向けて搬送されるシートＰは、給紙装置１２から搬送経路Ｋ１を経由することになるが、その間に給紙ローラ４１や複数の搬送ローラ対などに接触することで、摩擦帯電してしまう。そして、そのように帯電した状態のシートＰに転写工程をおこなうことで、転写画像に転写ムラ、チリ、黒スジ、転写不良などが生じてしまう。しかし、本実施の形態では、転写工程前に第１、第２除電部材３０Ａ、３０ＢによってシートＰの除電をおこなっているため、そのような不具合が生じにくくなる。 Then, as the sheet P is transported toward the transfer nip N, it comes into contact with the first and second charge-eliminating members 30A and 30B (charge-eliminating brush 30a) at the positions of the first and second charge-eliminating members 30A and 30B, thereby removing (discharging) the electric charge accumulated on the sheet P.
Specifically, the sheet P transported toward the transfer nip N passes through the transport path K1 from the paper feed device 12, and becomes frictionally charged during the process by contacting the paper feed roller 41 and the multiple transport roller pairs. Then, when the transfer process is performed on the sheet P in such a charged state, uneven transfer, dust, black streaks, transfer failures, and the like occur in the transferred image. However, in the present embodiment, the sheet P is neutralized by the first and second charge eliminating members 30A and 30B before the transfer process, so that such problems are less likely to occur.

ここで、本実施の形態では、第１除電部材３０Ａと第２除電部材３０Ｂとによって除電されたシートＰは、転写ニップＮ（転写位置）に達するまで、他の部材に接触しないように構成している。
すなわち、第１、第２除電部材３０Ａ、３０Ｂから転写ニップＮに至る搬送経路には、シートＰに接触可能ないかなる部材も設置されていない。これにより、第１、第２除電部材３０Ａ、３０Ｂの位置から転写ニップＮに達するまでに、シートＰが他の部材に摺接して摩擦帯電してしまう不具合を防止することができる。 Here, in this embodiment, the sheet P that has been neutralized by the first and second neutralizing members 30A and 30B is configured not to come into contact with other members until it reaches the transfer nip N (transfer position).
That is, no member capable of contacting the sheet P is provided on the transport path from the first and second charge removing members 30A and 30B to the transfer nip N. This makes it possible to prevent the sheet P from coming into sliding contact with other members and becoming frictionally charged before reaching the transfer nip N from the positions of the first and second charge removing members 30A and 30B.

ここで、転写装置９０には、第１除電部材３０Ａと第２除電部材３０Ｂとのうち少なくとも一方を、電気的に接地状態とフロート状態とのいずれかに切替可能な切替手段が設けられている。
詳しくは、本実施の形態では、第１除電部材３０Ａを電気的に接地状態とフロート状態とのいずれかに切替可能な第１切替スイッチ３１Ａ（第１切替装置）と、第２除電部材３０Ｂを電気的に接地状態とフロート状態とのいずれかに切替可能な第２切替スイッチ３１Ｂ（第２切替装置）と、が設けられている。そして、これらの第１、第２切替スイッチ３１Ａ、３１Ｂが切替手段として機能している。
なお、「フロート状態」とは、接地状態でも、所定の電圧が印加された状態でもなく、電気が自由に流れ得る状態である。 The transfer device 90 is provided with a switching means capable of switching at least one of the first charge removing member 30A and the second charge removing member 30B between an electrically grounded state and a floating state.
In detail, in this embodiment, a first changeover switch 31A (first switching device) capable of switching the first static elimination member 30A between an electrically grounded state and a floating state, and a second changeover switch 31B (second switching device) capable of switching the second static elimination member 30B between an electrically grounded state and a floating state are provided. These first and second changeover switches 31A and 31B function as a switching means.
The "floating state" refers to a state in which electricity can flow freely, neither in a grounded state nor in a state in which a specific voltage is applied.

さらに具体的に、図２に示すように、第１切替スイッチ３１Ａは、第１除電部材３０Ａをフロート状態のフレーム（本実施の形態では、現像装置５の現像ケース５０である。）に電気的に接続したり、第１除電部材３０Ａを接地状態のフレーム（例えば、画像形成装置本体１００の本体フレームである。）に電気的に接続したり、制御部６０の制御によって切替えられるように構成されている。
同様に、第２切替スイッチ３１Ｂは、第２除電部材３０Ｂをフロート状態のフレーム（本実施の形態では、転写装置９０の転写ケース９１である。）に電気的に接続したり、第２除電部材３０Ｂを接地状態のフレーム（例えば、画像形成装置本体１００の本体フレームである。）に電気的に接続したり、制御部６０の制御によって切替えられるように構成されている。
なお、図２は、第１、第２除電部材３０Ａ、３０Ｂが接地された状態を示している。 More specifically, as shown in FIG. 2, the first changeover switch 31A is configured to be switched under the control of the control unit 60 to electrically connect the first de-ionizing member 30A to a frame in a floating state (in this embodiment, the developing case 50 of the developing device 5) or to electrically connect the first de-ionizing member 30A to a frame in a grounded state (for example, the main body frame of the image forming apparatus main body 100).
Similarly, the second changeover switch 31B is configured to be switched under the control of the control unit 60 to electrically connect the second de-ionizing member 30B to a frame in a floating state (in this embodiment, the transfer case 91 of the transfer device 90) or to electrically connect the second de-ionizing member 30B to a frame in a grounded state (for example, the main body frame of the image forming apparatus main body 100).
FIG. 2 shows a state in which the first and second charge removing members 30A and 30B are grounded.

ここで、本実施の形態において、切替手段としての第１切替スイッチ３１Ａや第２切替スイッチ３１Ｂは、転写ニップＮ（転写位置）に搬送されるシートＰの状態と、周囲環境と、のうちいずれか一方（本実施の形態では、シートＰの状態である。）に基づいて、第１除電部材３０Ａと第２除電部材３０Ｂとのうち少なくとも一方を、電気的に接地状態とフロート状態とのいずれかに切替可能に構成されている。 In this embodiment, the first changeover switch 31A and the second changeover switch 31B serving as the switching means are configured to be able to switch at least one of the first charge removal member 30A and the second charge removal member 30B between an electrically grounded state and a floating state based on either the state of the sheet P being transported to the transfer nip N (transfer position) or the surrounding environment (in this embodiment, the state of the sheet P).

詳しくは、本実施の形態において、切替手段としての第１切替スイッチ３１Ａは、制御部６０による制御によって、転写ニップＮ（転写位置）に搬送されるシートＰの転写面の帯電量が所定値Ｘよりも大きい場合には第１除電部材３０Ａを接地状態にして、転写ニップＮに搬送されるシートＰの転写面の帯電量が所定値Ｘ以下である場合には第１除電部材３０Ａをフロート状態にしている。
また、本実施の形態において、切替手段としての第２切替スイッチ３１Ｂは、制御部６０による制御によって、転写ニップＮ（転写位置）に搬送されるシートＰの非転写面の帯電量が所定の値Ｙより大きい場合には第２除電部材３０Ｂを接地状態にして、転写ニップＮに搬送されるシートＰの非転写面の帯電量が所定の値Ｙ以下である場合には第２除電部材３０Ｂをフロート状態にしている。 In detail, in this embodiment, the first changeover switch 31A as a switching means, under the control of the control unit 60, places the first de-ionization member 30A in a grounded state when the amount of charge on the transfer surface of the sheet P transported to the transfer nip N (transfer position) is greater than a predetermined value X, and places the first de-ionization member 30A in a floating state when the amount of charge on the transfer surface of the sheet P transported to the transfer nip N is equal to or less than the predetermined value X.
In addition, in this embodiment, the second changeover switch 31B as a switching means, under the control of the control unit 60, places the second de-ionization member 30B in a grounded state when the amount of charge on the non-transfer surface of the sheet P transported to the transfer nip N (transfer position) is greater than a predetermined value Y, and places the second de-ionization member 30B in a floating state when the amount of charge on the non-transfer surface of the sheet P transported to the transfer nip N is equal to or less than the predetermined value Y.

すなわち、本実施の形態において、第１切替スイッチ３１Ａ（切替手段）は、転写ニップＮ（転写位置）に搬送されるシートＰの転写面の帯電量が大きい場合には第１除電部材３０Ａを接地状態にして、転写ニップＮに搬送されるシートＰの転写面の帯電量が小さい場合には第１除電部材３０Ａをフロート状態にするように制御部６０によって制御される。
同様に、第２切替スイッチ３１Ｂ（切替手段）は、転写ニップＮ（転写位置）に搬送されるシートＰの非転写面の帯電量が大きい場合には第２除電部材３０Ｂを接地状態にして、転写ニップＮに搬送されるシートＰの非転写面の帯電量が小さい場合には第２除電部材３０Ｂをフロート状態にするように制御部６０によって制御される。 That is, in this embodiment, the first changeover switch 31A (switching means) is controlled by the control unit 60 to place the first de-ionizing member 30A in a grounded state when the amount of charge on the transfer surface of the sheet P transported to the transfer nip N (transfer position) is large, and to place the first de-ionizing member 30A in a floating state when the amount of charge on the transfer surface of the sheet P transported to the transfer nip N is small.
Similarly, the second changeover switch 31B (switching means) is controlled by the control unit 60 to place the second de-ionizing member 30B in a grounded state when the amount of charge on the non-transfer surface of the sheet P transported to the transfer nip N (transfer position) is large, and to place the second de-ionizing member 30B in a floating state when the amount of charge on the non-transfer surface of the sheet P transported to the transfer nip N is small.

このような制御をおこなうのは、シートＰの表面の帯電量の大きさよって、シートＰの除電状態が変化するためである。
詳しくは、シートＰの除電は、除電部材とシートＰとの間で適当な放電を発生させる必要がある。過剰な放電がされてしまうと、転写工程時に必要な電流まで除電部材に流れ込んでしまい、転写不足により必要な画像濃度の転写画像が形成されないことになる。また、充分な放電がされないと、シートＰの除電が不足して、シートＰ上の転写画像にチリや黒スジ等の異常画像が発生してしまう。
このようなことから、シートＰの帯電量がある程度高くなるような状態では、充分な放電がおこなわれるように、除電部材３０Ａ、３０Ｂを積極的に接地して、除電効率を上げる必要がある。これに対して、シートＰの帯電量が低くなるような状態で、除電部材３０Ａ、３０Ｂを接地してしまうと、転写電流が除電部材３０Ａ、３０Ｂに流れ込んでしまい、過剰な放電により転写電流不足となり、シートＰ上で必要な画像濃度が得られず薄くなったり、転写ムラ（濃淡）が発生したりする不具合が生じやすくなる。そのため本実施の形態では、シートＰの帯電量が低くなるようなときに、切替スイッチ３１Ａ、３１Ｂによる切替によって除電部材３０Ａ、３０Ｂをフロート状態にしている。これにより、除電部材３０Ａ、３０Ｂに転写電流が必要以上に流れ込むことが防止されて、適切な除電効果を得られ、転写画像上に転写ムラ、黒スジ（ブラシ跡）、転写不足、転写ムラなどの異常画像が生じにくくなる。
すなわち、転写工程前にシートＰを良好に除電することができる。 The reason why such control is performed is that the state of charge removal from the sheet P changes depending on the amount of charge on the surface of the sheet P.
More specifically, to eliminate the charge on the sheet P, it is necessary to generate an appropriate discharge between the charge eliminating member and the sheet P. If excessive discharge occurs, even the current required during the transfer process will flow into the charge eliminating member, and the transfer will be insufficient, resulting in a transfer image not having the required image density. Furthermore, if sufficient discharge is not performed, the charge on the sheet P will be insufficient, and abnormal images such as dust and black streaks will occur in the transferred image on the sheet P.
For this reason, when the charge amount of the sheet P is relatively high, it is necessary to positively ground the charge removing members 30A and 30B to increase the charge removing efficiency so that sufficient discharge is performed. On the other hand, when the charge amount of the sheet P is low, if the charge removing members 30A and 30B are grounded, the transfer current flows into the charge removing members 30A and 30B, and the transfer current becomes insufficient due to excessive discharge, and the necessary image density on the sheet P is not obtained and becomes thin, or uneven transfer (shading) is likely to occur. Therefore, in this embodiment, when the charge amount of the sheet P is low, the charge removing members 30A and 30B are put into a floating state by switching the changeover switches 31A and 31B. This prevents the transfer current from flowing into the charge removing members 30A and 30B more than necessary, thereby obtaining an appropriate charge removing effect, and making it difficult for abnormal images such as uneven transfer, black streaks (brush marks), insufficient transfer, and uneven transfer to occur on the transferred image.
That is, the sheet P can be effectively neutralized before the transfer step.

特に、本実施の形態では、搬送経路を挟むように２つの除電部材３０Ａ、３０Ｂを配置しているため、転写工程前にシートＰが除電部材３０Ａ、３０Ｂによって除電されるときに、２つの除電部材３０Ａ、３０ＢによってシートＰが挟まれた状態になる。そのため、１つの除電部材のみをシートＰの片面に接触させるように構成する場合に比べて、除電時にシートＰがバタついたり撓んだりしにくくなり、シートＰを充分に除電しやすくなる。そのため、転写工程によってシートＰに形成される転写画像に、転写ムラ、チリ、黒スジ、転写不良などが生じにくくなる。すなわち、転写工程前にシートＰを良好に除電することができる。
特に、２つの除電部材３０Ａ、３０Ｂによって、シートＰをオモテ面側からとウラ面側とから除電しているため、除電効率が高くなる。また、２つの除電部材３０Ａ、３０Ｂは、同等に構成されていて、同等の除電効果を発揮することになるため、転写工程前にシートＰを良好に除電することができる。 In particular, in this embodiment, since the two charge removing members 30A and 30B are arranged to sandwich the conveying path, when the sheet P is neutralized by the charge removing members 30A and 30B before the transfer process, the sheet P is sandwiched between the two charge removing members 30A and 30B. Therefore, compared with a configuration in which only one charge removing member is in contact with one side of the sheet P, the sheet P is less likely to flutter or bend during neutralization, and the sheet P can be easily neutralized sufficiently. Therefore, the transfer image formed on the sheet P by the transfer process is less likely to have transfer unevenness, dust, black streaks, transfer failures, etc. In other words, the sheet P can be satisfactorily neutralized before the transfer process.
In particular, the two charge eliminating members 30A and 30B eliminate the charge from the front surface side and the back surface side of the sheet P, thereby improving the charge eliminating efficiency. In addition, the two charge eliminating members 30A and 30B are configured in the same way and exert the same charge eliminating effect, so that the sheet P can be satisfactorily charged before the transfer process.

ここで、本実施の形態において、第１、第２切替スイッチ３１Ａ、３１Ｂ（切替手段）は、図５に示すように、両面印刷時において、シートＰのオモテ面（第１面）を転写面として転写ニップＮ（転写位置）でトナー像を転写するときには、第１除電部材３０Ａと第２除電部材３０Ｂとをそれぞれフロート状態にする。そして、第１、第２切替スイッチ３１Ａ、３１Ｂ（切替手段）は、オモテ面にトナー像が転写されたシートＰのウラ面（第２面）を転写面として転写ニップＮでトナー像を転写するときには、第１除電部材３０Ａと第２除電部材３０Ｂとをそれぞれ接地状態にする。
すなわち、両面印刷モード時において、シートＰのオモテ面に対する転写工程前の除電はフロート状態の第１、第２除電部材３０Ａ、３０Ｂによっておこなわれ、シートＰのウラ面に対する転写工程前の除電は接地状態の第１、第２除電部材３０Ａ、３０Ｂによっておこなわれる。 5, in this embodiment, the first and second changeover switches 31A and 31B (switching means) respectively put the first charge removing member 30A and the second charge removing member 30B into a floating state when a toner image is transferred at a transfer nip N (transfer position) with the front side (first side) of a sheet P as a transfer surface during double-sided printing.Then, the first and second changeover switches 31A and 31B (switching means) respectively put the first charge removing member 30A and the second charge removing member 30B into a grounded state when a toner image is transferred at a transfer nip N with the back side (second side) of the sheet P with the toner image transferred on its front side as a transfer surface.
That is, in double-sided printing mode, the de-electrification of the front side of the sheet P before the transfer process is performed by the first and second de-electrification members 30A and 30B in a floating state, and the de-electrification of the back side of the sheet P before the transfer process is performed by the first and second de-electrification members 30A and 30B in a grounded state.

このような制御をおこなうのは、両面印刷時において、オモテ面に転写画像を形成するときのシートＰの帯電量と、ウラ面に転写画像を形成するときのシートＰの帯電量と、が大きく異なるためである。
詳しくは、オモテ面に転写画像を形成するときのシートＰは、給紙装置１２に収納されていたものがそのまま搬送されたものであるため、その含水量はある程度多くて、帯電量は小さくなる。そのため、転写電流が除電部材３０Ａ、３０Ｂに流れ込まないように、第１、第２除電部材３０Ａ、３０Ｂをフロート状態にする。
これに対して、ウラ面に転写画像を形成するときのシートＰは、オモテ面に対する定着工程時に定着装置２０によって熱を受けているため、水分が蒸発して含水分量が低くなって、帯電量が大きくなる。そのため、充分な除電をおこなうために、第１、第２除電部材３０Ａ、３０Ｂを接地状態に切替える。
具体例として、常温常湿環境（２３℃、５０ＲＨ％）にて普通紙（５５ｋｇ紙）をシートＰとして用いる場合、オモテ面に転写画像を形成するときのシートＰの含水分量は６％程度であるのに対して、ウラ面に転写画像を形成するときのシートＰの含水分量は２％程度になる。
このような制御をおこなうことで、両面印刷時においてオモテ面に対してもウラ面に対しても転写工程前にシートＰを良好に除電することができて、良好な両面画像を形成することができる。 Such control is performed because, during double-sided printing, the amount of charge on the sheet P when a transfer image is formed on the front side differs greatly from the amount of charge on the sheet P when a transfer image is formed on the back side.
Specifically, the sheet P when a transfer image is formed on the front surface is the one that is transported as it is from the sheet feeder 12, so that the sheet P has a relatively large amount of moisture and a small amount of charge. Therefore, the first and second charge removing members 30A and 30B are set in a floating state so that the transfer current does not flow into the charge removing members 30A and 30B.
On the other hand, when a transfer image is formed on the back side of the sheet P, the sheet P is heated by the fixing device 20 during the fixing process for the front side, so that the moisture evaporates, the moisture content decreases, and the amount of charge increases. Therefore, in order to perform sufficient static elimination, the first and second static elimination members 30A and 30B are switched to a grounded state.
As a specific example, when ordinary paper (55 kg paper) is used as sheet P in a normal temperature and humidity environment (23°C, 50 RH%), the moisture content of sheet P when a transfer image is formed on the front side is approximately 6%, whereas the moisture content of sheet P when a transfer image is formed on the back side is approximately 2%.
By carrying out such control, it is possible to satisfactorily remove static electricity from the sheet P before the transfer process on both the front and back sides during double-sided printing, and it is possible to form a good double-sided image.

このように、シートＰの帯電量はシートＰの含水分量に関係するため、シートＰの含水状態を検知する含水検知手段としての含水分測定器６２（図２参照）を設置して、含水分測定器６２（含水分検知手段）の検知結果に基づいて、第１除電部材３０Ａと第２除電部材３０Ｂとをそれぞれ接地状態とフロート状態とのいずれかに切替えるように、制御部６０によって第１、第２切替スイッチ３１Ａ、３１Ｂ（切替手段）を制御しても良い。
特に、含水分測定器６２の検知結果に基づいて、第１除電部材３０Ａと第２除電部材３０Ｂとを、それぞれ、接地状態とフロート状態とのいずれかに同じように切替えても良い。すなわち、含水分測定器６２の検知結果に基づいて、第１除電部材３０と第２除電部材３０Ｂとがいずれも接地状態となる第１の状態と、第１除電部材３０と第２除電部材３０Ｂとがいずれもフロート状態となる第２の状態と、を切替可能に構成しても良い。
具体的に、含水分測定器６２によって検知された含水分量が所定値Ａ以下である場合には第１、第２除電部材３０Ａ、３０Ｂを接地状態にして、含水分測定器６２によって検知された含水分量が所定値Ａを超える場合には第１、第２除電部材３０Ａ、３０Ｂをフロート状態にする。
なお、含水分測定器６２は、第１、第２除電部材３０Ａ、３０Ｂの上流側近傍に設置されることが好ましいが、その測定時間を確保できないような場合には、給紙装置１２の近傍に設置して、給紙装置１２に収納されたシートＰの含水分量を測定するように構成することもできる。そのような場合には、定着装置２０を通過した後のシートＰの含水分量は、通過前のものから一定の割合で減ずるものとして推定値として扱うことになる。 As such, since the amount of charge on the sheet P is related to the moisture content of the sheet P, a moisture content meter 62 (see Figure 2) may be provided as a moisture content detection means for detecting the moisture state of the sheet P, and the control unit 60 may control the first and second changeover switches 31A, 31B (switching means) to switch the first de-ionization member 30A and the second de-ionization member 30B to either a grounded state or a floating state, respectively, based on the detection result of the moisture content meter 62 (moisture content detection means).
In particular, the first and second static elimination members 30A and 30B may be switched between a grounded state and a floating state in the same manner, based on the detection result of the moisture content meter 62. That is, the first and second static elimination members 30A and 30B may be configured to be switchable between a first state in which both the first and second static elimination members 30A and 30B are in a grounded state and a second state in which both the first and second static elimination members 30A and 30B are in a floating state, based on the detection result of the moisture content meter 62.
Specifically, when the moisture content detected by the moisture content meter 62 is equal to or less than a predetermined value A, the first and second de-ionization members 30A, 30B are grounded, and when the moisture content detected by the moisture content meter 62 exceeds the predetermined value A, the first and second de-ionization members 30A, 30B are floated.
The moisture content meter 62 is preferably installed near the upstream side of the first and second charge removing members 30A and 30B, but if the measurement time cannot be secured, it may be installed near the paper feeder 12 to measure the moisture content of the sheets P stored in the paper feeder 12. In such a case, the moisture content of the sheet P after passing through the fixing device 20 is treated as an estimated value, assuming that it is reduced at a constant rate from the moisture content before passing through.

また、本実施の形態において、シートＰの帯電量を直接的に検知できるような場合には、その検知結果に基づいて、第１、第２除電部材３０Ａ、３０Ｂを接地状態とフロート状態とのいずれかに切替えても良い。
具体的に、シートＰの帯電量が所定値Ｂ以下である場合には第１、第２除電部材３０Ａ、３０Ｂをフロート状態にして、帯電量が所定値Ｂを超える場合には第１、第２除電部材３０Ａ、３０Ｂを接地状態にする。 In addition, in this embodiment, if the amount of charge on the sheet P can be directly detected, the first and second charge removal members 30A, 30B may be switched between a grounded state and a floating state based on the detection results.
Specifically, when the amount of charge on the sheet P is equal to or less than a predetermined value B, the first and second charge eliminating members 30A, 30B are placed in a floating state, and when the amount of charge on the sheet P exceeds the predetermined value B, the first and second charge eliminating members 30A, 30B are placed in a grounded state.

ここで、本実施の形態において、第１除電部材３０Ａと第２除電部材３０Ｂとを、画像形成装置本体１００に対して着脱可能に設置しても良い。
具体例として、転写ニップＮ（転写位置）に対してシートＰの搬送方向上流側であって、シートＰの転写面に対向する位置に配置された転写面側ユニットとしての現像装置５に、第１除電部材３０Ａを着脱可能に設置しても良い。
また、転写ニップＮ（転写位置）に対してシートＰの搬送方向上流側であって、シートＰの非転写面に対向する位置に配置された非転写面側ユニットとしての転写装置９０に、第２除電部材３０Ｂを着脱可能に設置しても良い。
そのように構成することで、第１、第２除電部材３０Ａ、３０Ｂのメンテナンス時の作業性を向上させることができる。 In this embodiment, the first charge removing member 30A and the second charge removing member 30B may be detachably installed in the image forming apparatus main body 100.
As a specific example, the first de-ionizing member 30A may be removably installed in the developing device 5 as a transfer surface side unit arranged upstream of the transfer nip N (transfer position) in the transport direction of the sheet P and in a position opposite the transfer surface of the sheet P.
In addition, the second de-ionizing member 30B may be removably installed in the transfer device 90 as a non-transfer surface side unit arranged upstream of the transfer nip N (transfer position) in the transport direction of the sheet P and in a position opposite the non-transfer surface of the sheet P.
Such a configuration can improve the workability during maintenance of the first and second charge eliminating members 30A and 30B.

＜変形例１＞
変形例１において、切替手段としての第１切替スイッチ３１Ａや第２切替スイッチ３１Ｂは、転写ニップＮ（転写位置）に搬送されるシートＰの状態と、周囲環境と、のうち、周囲環境に基づいて、第１除電部材３０Ａと第２除電部材３０Ｂとのうち少なくとも一方を、電気的に接地状態とフロート状態とのいずれかに切替可能に構成されている。
詳しくは、図６に示すように、変形例１では、画像形成装置１００の周囲環境（温湿度）に応じて第１、第２切替スイッチ３１Ａ、３１Ｂの切替制御をおこなっている。
詳しくは、画像形成装置１００には、周囲の温湿度（特に、給紙装置１２の周囲の温湿度である。）を検知する温湿度検知手段としての温湿度センサ６１（図１、図２参照）が設置されている。
そして、温湿度センサ６１（温湿度検知手段）の検知結果に基づいて、第１除電部材３０Ａと第２除電部材３０Ｂとをそれぞれ接地状態とフロート状態とのいずれかに切替えるように、制御部６０によって第１、第２切替スイッチ３１Ａ、３１Ｂ（切替手段）を制御している。
特に、温湿度センサ６１の検知結果に基づいて、第１除電部材３０Ａと第２除電部材３０Ｂとを、それぞれ、接地状態とフロート状態とのいずれかに同じように切替えている。すなわち、温湿度センサ６１の検知結果に基づいて、第１除電部材３０と第２除電部材３０Ｂとがいずれも接地状態となる第１の状態と、第１除電部材３０と第２除電部材３０Ｂとがいずれもフロート状態となる第２の状態と、を切替可能に構成している。
詳しくは、夏環境（高温高湿）などであって、温湿度センサ６１の検知結果に基づいて絶対湿度が高いものと判断された場合には、シートＰの含水量が多くて、シートＰの帯電量は小さくなる。そのため、転写電流が除電部材３０Ａ、３０Ｂに流れ込まないように、第１、第２除電部材３０Ａ、３０Ｂをフロート状態にする。
これに対して、冬環境（低温低湿）などであって、温湿度センサ６１の検知結果に基づいて絶対湿度が低いものと判断された場合には、シートＰの含水量が少なくて、シートＰの帯電量は大きくなる。そのため、充分な除電をおこなうために、第１、第２除電部材３０Ａ、３０Ｂを接地状態にする。 <Modification 1>
In variant example 1, the first changeover switch 31A and the second changeover switch 31B serving as a switching means are configured to be able to switch at least one of the first de-ionizing member 30A and the second de-ionizing member 30B between an electrically grounded state and a floating state based on the state of the sheet P transported to the transfer nip N (transfer position) and the surrounding environment.
More specifically, as shown in FIG. 6, in the first modification, the first and second changeover switches 31A and 31B are controlled to be changed over depending on the ambient environment (temperature and humidity) of the image forming apparatus 100. In the first modification, as shown in FIG.
More specifically, the image forming apparatus 100 is provided with a temperature and humidity sensor 61 (see FIGS. 1 and 2) as a temperature and humidity detection unit that detects the surrounding temperature and humidity (particularly, the temperature and humidity around the paper feeder 12).
Based on the detection results of the temperature and humidity sensor 61 (temperature and humidity detection means), the control unit 60 controls the first and second change-over switches 31A, 31B (switching means) to switch the first de-ionization member 30A and the second de-ionization member 30B between either a grounded state or a floating state.
In particular, the first and second charge removing members 30A and 30B are switched between a grounded state and a floating state in the same manner, based on the detection results of the temperature and humidity sensor 61. That is, based on the detection results of the temperature and humidity sensor 61, the first and second charge removing members 30A and 30B are configured to be switchable between a first state in which both the first and second charge removing members 30A and 30B are in a grounded state, and a second state in which both the first and second charge removing members 30A and 30B are in a floating state.
More specifically, in a summer environment (high temperature and humidity) where the absolute humidity is determined to be high based on the detection result of the temperature and humidity sensor 61, the water content of the sheet P is high and the charge amount of the sheet P is small. Therefore, the first and second charge removing members 30A and 30B are put into a floating state so that the transfer current does not flow into the charge removing members 30A and 30B.
On the other hand, in a winter environment (low temperature and low humidity) where the absolute humidity is determined to be low based on the detection result of the temperature and humidity sensor 61, the moisture content of the sheet P is low and the amount of charge on the sheet P is large. Therefore, in order to perform sufficient charge removal, the first and second charge removing members 30A and 30B are grounded.

さらに、変形例１では、図６に示すように、上述した温湿度センサ６１の検知結果に基づく第１、第２切替スイッチ３１Ａ、３１Ｂの切替制御に加えて、両面印刷モード時の第１、第２切替スイッチ３１Ａ、３１Ｂの切替制御もおこなっている。
具体的に、片面印刷モード時や、両面印刷モード時におけるオモテ面への印刷時には、温湿度センサ６１の検知結果に基づいて絶対湿度が所定値（６ｇ／ｍ³）未満であると判断された場合には、第１、第２除電部材３０Ａ、３０Ｂを接地状態にして、絶対湿度が所定値（６ｇ／ｍ³）以上であると判断された場合には、第１、第２除電部材３０Ａ、３０Ｂをフロート状態にする。
これに対して、両面印刷モード時におけるウラ面への印刷時には、温湿度センサ６１の検知結果に関わらず、シートＰの含水分量が減ぜられるものとして、第１、第２除電部材３０Ａ、３０Ｂを接地状態にする。
このような制御をおこなった場合にも、転写工程前にシートＰを良好に除電することができる。 Furthermore, in variant example 1, as shown in FIG. 6, in addition to controlling the switching of the first and second changeover switches 31A, 31B based on the detection results of the temperature and humidity sensor 61 described above, switching control of the first and second changeover switches 31A, 31B in double-sided printing mode is also performed.
Specifically, when in single-sided printing mode or when printing on the front side in double-sided printing mode, if the absolute humidity is determined to be less than a specified value (6 g/ ^m3 ) based on the detection results of the temperature and humidity sensor 61, the first and second de-ionizing members 30A, 30B are grounded, and if the absolute humidity is determined to be equal to or greater than the specified value (6 g/ ^m3 ), the first and second de-ionizing members 30A, 30B are floated.
In contrast, when printing on the back side in double-sided printing mode, the moisture content of the sheet P is assumed to be reduced regardless of the detection result of the temperature and humidity sensor 61, and the first and second charge removing members 30A and 30B are placed in a grounded state.
Even when such control is performed, the sheet P can be satisfactorily neutralized before the transfer step.

＜変形例２＞
変形例２では、切替手段としての第１切替スイッチ３１Ａや第２切替スイッチ３１Ｂは、転写ニップＮ（転写位置）に搬送されるシートＰの状態と、周囲環境と、のうち、シートの状態に基づいて、第１除電部材３０Ａと第２除電部材３０Ｂとのうち少なくとも一方を、電気的に接地状態とフロート状態とのいずれかに切替可能に構成されている。
詳しくは、図７に示すように、変形例２では、シートＰの表面の電気抵抗値に応じて第１、第２切替スイッチ３１Ａ、３１Ｂの切替制御をおこなっている。
詳しくは、画像形成装置１００には、シートＰの表面の電気抵抗値を検知する抵抗検知手段としての表面抵抗測定器６３（図２参照）が、給紙装置１２の近傍に設置されている。この表面抵抗測定器６３（抵抗検知手段）は、給紙装置１２に収納されたシートＰの電気抵抗値を直接的に検知するものである。
そして、表面抵抗測定器６３（抵抗検知手段）の検知結果に基づいて、第１除電部材３０Ａと第２除電部材３０Ｂとをそれぞれ接地状態とフロート状態とのいずれかに切替えるように、制御部６０によって第１、第２切替スイッチ３１Ａ、３１Ｂ（切替手段）を制御している。
特に、表面抵抗測定器６３の検知結果に基づいて、第１除電部材３０Ａと第２除電部材３０Ｂとを、それぞれ、接地状態とフロート状態とのいずれかに同じように切替えている。すなわち、表面抵抗測定器６３の検知結果に基づいて、第１除電部材３０と第２除電部材３０Ｂとがいずれも接地状態となる第１の状態と、第１除電部材３０と第２除電部材３０Ｂとがいずれもフロート状態となる第２の状態と、を切替可能に構成している。
詳しくは、表面抵抗が小さなシートＰは、シートＰの帯電量は小さくなる。そのため、転写電流が除電部材３０Ａ、３０Ｂに流れ込まないように、第１、第２除電部材３０Ａ、３０Ｂをフロート状態にする。
これに対して、表面抵抗が大きなシートＰは、シートＰの帯電量は大きくなる。そのため、充分な除電をおこなうために、第１、第２除電部材３０Ａ、３０Ｂを接地状態にする。
このようなシートＰの表面抵抗は、シートＰの種類によって異なるため、表面抵抗測定器６３で直接的に検知しなくても、ユーザーによって操作表示パネル１０に入力されるシートＰに関する情報に基づいて間接的に検知しても良い。その場合、操作表示パネル１０が抵抗検知手段として機能することになる。 <Modification 2>
In variant example 2, the first changeover switch 31A and the second changeover switch 31B serving as a switching means are configured to be able to switch at least one of the first de-ionizing member 30A and the second de-ionizing member 30B between an electrically grounded state and a floating state based on the state of the sheet P transported to the transfer nip N (transfer position) and the surrounding environment, whichever is the state of the sheet.
More specifically, as shown in FIG. 7, in the second modification, the first and second changeover switches 31A and 31B are controlled to be switched in accordance with the electrical resistance value of the surface of the sheet P. In the second modification, as shown in FIG.
More specifically, in the image forming apparatus 100, a surface resistance meter 63 (see FIG. 2 ) serving as resistance detection means for detecting the electrical resistance value of the surface of the sheet P is installed near the sheet feeding device 12. This surface resistance meter 63 (resistance detection means) directly detects the electrical resistance value of the sheet P stored in the sheet feeding device 12.
Based on the detection results of the surface resistance meter 63 (resistance detection means), the control unit 60 controls the first and second change-over switches 31A, 31B (switching means) so as to switch the first de-ionization member 30A and the second de-ionization member 30B to either a grounded state or a floating state, respectively.
In particular, the first and second static elimination members 30A and 30B are switched between a grounded state and a floating state in the same manner, based on the detection result of the surface resistance meter 63. That is, based on the detection result of the surface resistance meter 63, a first state in which the first and second static elimination members 30A and 30B are both in a grounded state, and a second state in which the first and second static elimination members 30A and 30B are both in a floating state can be switched.
Specifically, a sheet P having a small surface resistance has a small amount of charge on the sheet P. Therefore, the first and second charge removing members 30A and 30B are set in a floating state so that the transfer current does not flow into the charge removing members 30A and 30B.
On the other hand, a sheet P having a large surface resistance has a large amount of charge on the sheet P. Therefore, in order to perform sufficient charge removal, the first and second charge removing members 30A and 30B are grounded.
Since the surface resistance of such a sheet P differs depending on the type of sheet P, it does not have to be detected directly by the surface resistance measuring device 63, but may be detected indirectly based on information about the sheet P input by the user to the operation display panel 10. In this case, the operation display panel 10 functions as a resistance detection means.

さらに、変形例２では、図７に示すように、上述した抵抗検知手段の検知結果に基づく第１、第２切替スイッチ３１Ａ、３１Ｂの切替制御に加えて、両面印刷モード時の第１、第２切替スイッチ３１Ａ、３１Ｂの切替制御もおこなっている。
具体的に、片面印刷モード時や、両面印刷モード時におけるオモテ面への印刷時には、シートＰの電気抵抗が所定値（１０¹²Ω）未満であると判断された場合には、第１、第２除電部材３０Ａ、３０Ｂをフロート状態にして、電気抵抗が所定値（１０¹²Ω）以上であると判断された場合には、第１、第２除電部材３０Ａ、３０Ｂを接地状態にする。
これに対して、両面印刷モード時におけるウラ面への印刷時には、抵抗検知手段の検知結果に関わらず、シートＰの含水分量が減ぜられるものとして、第１、第２除電部材３０Ａ、３０Ｂを接地状態にする。
このような制御をおこなった場合にも、転写工程前にシートＰを良好に除電することができる。 Furthermore, in variant example 2, as shown in FIG. 7, in addition to controlling the switching of the first and second changeover switches 31A, 31B based on the detection results of the resistance detection means described above, switching control of the first and second changeover switches 31A, 31B in double-sided printing mode is also performed.
Specifically, in single-sided printing mode or when printing on the front side in double-sided printing mode, if the electrical resistance of sheet P is determined to be less than a predetermined value (10 ¹² Ω), the first and second de-ionizing members 30A, 30B are set to a floating state, and if the electrical resistance is determined to be equal to or greater than the predetermined value (10 ¹² Ω), the first and second de-ionizing members 30A, 30B are set to a grounded state.
In contrast, when printing on the back side in the double-sided printing mode, the moisture content of the sheet P is assumed to be reduced regardless of the detection result of the resistance detection means, and the first and second charge removing members 30A, 30B are placed in a grounded state.
Even when such control is performed, the sheet P can be satisfactorily neutralized before the transfer step.

ここで、シートＰの帯電量は、シートＰの材質（又は、種類）によって異なるため、シートＰの材質（又は、種類）に基づいて、第１除電部材３０Ａと第２除電部材３０Ｂとをそれぞれ接地状態とフロート状態とのいずれかに切替えるように、制御部６０によって第１、第２切替スイッチ３１Ａ、３１Ｂ（切替手段）を制御しても良い。
特に、シートＰの材質（又は、種類）に基づいて、第１除電部材３０Ａと第２除電部材３０Ｂとを、それぞれ、接地状態とフロート状態とのいずれかに同じように切替えても良い。すなわち、シートＰの材質（又は、種類）に基づいて、第１除電部材３０と第２除電部材３０Ｂとがいずれも接地状態となる第１の状態と、第１除電部材３０と第２除電部材３０Ｂとがいずれもフロート状態となる第２の状態と、を切替可能に構成しても良い。
具体的に、同じ条件（環境条件や搬送条件などである。）であっても、帯電しやすい材質（又は、種類）のシートＰが用いられる場合には第１、第２除電部材３０Ａ、３０Ｂを接地状態にして、帯電しにくい材質（又は、種類）のシートＰが用いられる場合には第１、第２除電部材３０Ａ、３０Ｂをフロート状態にする。
なお、シートＰの材質や種類は、ユーザーによって操作表示パネル１０に入力されるシートＰに関する情報に基づいて判断することができる。その場合、操作表示パネル１０が、シートＰの材質や種類を検知する検知手段として機能することになる。 Here, since the amount of charge on the sheet P varies depending on the material (or type) of the sheet P, the first and second changeover switches 31A, 31B (switching means) may be controlled by the control unit 60 so as to switch the first charge removal member 30A and the second charge removal member 30B between either a grounded state or a floating state, respectively, based on the material (or type) of the sheet P.
In particular, the first and second charge eliminating members 30A and 30B may be switched between a grounded state and a floating state in the same manner, based on the material (or type) of the sheet P. That is, the sheet P may be configured to be switchable between a first state in which the first and second charge eliminating members 30A and 30B are both in a grounded state and a second state in which the first and second charge eliminating members 30A and 30B are both in a floating state, based on the material (or type) of the sheet P.
Specifically, even under the same conditions (environmental conditions, transport conditions, etc.), when a sheet P made of a material (or type) that easily becomes charged is used, the first and second charge-eliminating members 30A, 30B are in a grounded state, and when a sheet P made of a material (or type) that does not easily become charged is used, the first and second charge-eliminating members 30A, 30B are in a floating state.
The material and type of the sheet P can be determined based on information about the sheet P input by the user to the operation display panel 10. In this case, the operation display panel 10 functions as a detection unit that detects the material and type of the sheet P.

＜変形例３＞
変形例３では、オモテ面の材質とウラ面の材質とが異なるシートＰが搬送される場合に、それぞれの材質に基づいて、第１除電部材３０Ａと第２除電部材３０Ｂとをそれぞれ接地状態とフロート状態とのいずれかに切替えるように、制御部６０によって第１、第２切替スイッチ３１Ａ、３１Ｂ（切替手段）を制御している。
具体的に、オモテ面の材質とウラ面の材質とが異なるシートＰが搬送される場合に、それぞれの材質に基づいて、第１除電部材３０と第２除電部材３０Ｂとがいずれも接地状態となる第１の状態と、第１除電部材３０と第２除電部材３０Ｂとがいずれもフロート状態となる第２の状態と、第１除電部材３０が接地状態で第２除電部材３０Ｂがフロート状態となる第３の状態と、第１除電部材３０がフロート状態で第２除電部材３０Ｂが接地状態となる第４の状態と、を切替可能に構成している。
図８は、そのような場合の一例を示すものであって、片面印刷モードにてシートＰとしてコート紙（普通紙のオモテ面にコート層が形成されたシートである。）が用いられたときの第１、第２切替スイッチ３１Ａ、３１Ｂの切替制御を示す。
コート紙は、コート層が形成されたオモテ面の表面抵抗が、コート層が形成されていないウラ面の表面抵抗に比べて高くなる。そのため、図８に示すように、表面抵抗が大きくて帯電量が大きくなるオモテ面を除電する第１除電部材３０Ａは接地状態にして、表面抵抗が小さくて帯電量が小さくなるウラ面を除電する第２除電部材３０Ｂはフロート状態にする。
このような制御をおこなった場合にも、転写工程前にシートＰを良好に除電することができる。 <Modification 3>
In variant example 3, when a sheet P having different materials on its front and back sides is transported, the control unit 60 controls the first and second changeover switches 31A, 31B (switching means) so as to switch the first charge-eliminating member 30A and the second charge-eliminating member 30B between a grounded state and a floating state, respectively, based on the respective materials.
Specifically, when a sheet P having different materials on its front and back sides is transported, the sheet is configured to be switchable between a first state in which the first charge removal member 30 and the second charge removal member 30B are both in a grounded state, a second state in which the first charge removal member 30 and the second charge removal member 30B are both in a floating state, a third state in which the first charge removal member 30 is in a grounded state and the second charge removal member 30B is in a floating state, and a fourth state in which the first charge removal member 30 is in a floating state and the second charge removal member 30B is in a grounded state, based on the respective materials.
Figure 8 shows an example of such a case, and illustrates the switching control of the first and second changeover switches 31A, 31B when coated paper (a sheet of plain paper with a coating layer formed on the front side) is used as the sheet P in single-sided printing mode.
In coated paper, the surface resistance of the front side on which the coating layer is formed is higher than the surface resistance of the back side on which the coating layer is not formed. Therefore, as shown in Fig. 8, the first charge eliminating member 30A, which eliminates electricity from the front side, which has a large surface resistance and a large amount of charge, is in a grounded state, and the second charge eliminating member 30B, which eliminates electricity from the back side, which has a small surface resistance and a small amount of charge, is in a floating state.
Even when such control is performed, the sheet P can be satisfactorily neutralized before the transfer step.

＜変形例４＞
変形例４では、第１除電部材３０Ａと第２除電部材３０Ｂとのうちいずれか一方を、接地状態とフロート状態とのうちいずれかの状態に固定している。すなわち、変形例４では、第１除電部材３０Ａと第２除電部材３０Ｂとのうち一方のみが、電気的に接地状態とフロート状態とのいずれかに切替可能に構成されている。
図９は、そのような場合の一例を示すものであって、第１除電部材３０Ａを接地状態とフロート状態とのいずれかに切替可能に構成しているのに対して、第２除電部材３０Ｂをフロート状態に固定している。
詳しくは、片面印刷モードにて、シートＰとしてコート紙（普通紙のオモテ面にコート層が形成されたシートである。）が用いられるときには第１除電部材３０Ａが接地状態にされて、シートＰとして普通紙（非コート紙であって、表面抵抗が１０¹²Ω未満のシートである。）が用いられるときには第１除電部材３０Ａがフロート状態にされる。コート紙については図８にて説明した理由により、普通紙については図７にて説明した理由により、上述した第１除電部材３０Ａの切替がおこなわれる。
このような制御をおこなった場合にも、転写工程前にシートＰを良好に除電することができる。特に、このような制御は、使用されるシートＰの種類が限定されている場合や、片面印刷に限定されている場合などに有用である。また、変形例４のように構成した場合には、第２切替スイッチ３１Ｂが不要になるため、装置を小型化、低コスト化することができる。 <Modification 4>
In the fourth modification, either the first charge removing member 30A or the second charge removing member 30B is fixed to either the grounded state or the floating state. That is, in the fourth modification, only one of the first charge removing member 30A or the second charge removing member 30B is configured to be electrically switchable between either the grounded state or the floating state.
Figure 9 shows an example of such a case, in which the first de-ionization member 30A is configured to be switchable between a grounded state and a floating state, while the second de-ionization member 30B is fixed in a floating state.
More specifically, in the single-sided printing mode, when coated paper (a sheet of plain paper with a coating layer formed on the front side) is used as the sheet P, the first charge removing member 30A is grounded, and when plain paper (uncoated paper with a surface resistance of less than ¹⁰ Ω) is used as the sheet P, the first charge removing member 30A is floated. The above-mentioned switching of the first charge removing member 30A is performed for the reasons explained in Fig. 8 for coated paper, and for the reasons explained in Fig. 7 for plain paper.
Even when such control is performed, the sheet P can be satisfactorily destaticized before the transfer process. This type of control is particularly useful when the type of sheet P used is limited, or when printing is limited to one side. Furthermore, when configured as in Modification 4, the second changeover switch 31B is not required, which allows the device to be made smaller and less expensive.

＜変形例５＞
図１０に示すように、変形例５における転写装置９０は、第１除電部材３０Ａと第２除電部材３０Ｂとが、シートＰの搬送経路において、互いに対向する位置ではなくて、搬送方向にズレた位置に配置されている（搬送方向の異なる位置に配置されている）。
詳しくは、第１除電部材３０Ａと第２除電部材３０Ｂとは、いずれも、レジストローラ対４５の搬送方向下流側であって、転写ニップＮの搬送方向上流側に配置されている。しかし、第２除電部材３０Ｂは、第１除電部材３０Ａに対して、搬送方向下流側に配置されている。
このように構成することで、時間をずらした２段階の除電動作がおこなわれることになり、除電効果（除電能力）を細かく調整することが可能になる。詳しくは、図１１に示すように、「１」は、第１除電部材３０Ａを接地状態にするとともに、第２除電部材３０Ｂも接地状態にするモードであって、除電効果が大きくなる。これに対して、「２」は、第１除電部材３０Ａを接地状態（又は、フロート状態）にするのに対して、第２除電部材３０Ｂをフロート状態（又は、接地状態）にするモードであって、除電効果が中程度になる。さらに、「３」は、第１除電部材３０Ａをフロート状態にするととも、に第２除電部材３０Ｂもフロート状態にするモードであって、除電効果が小さくなる。
このように構成して制御をおこなった場合にも、転写工程前にシートＰを良好に除電することができる。特に、このような構成は、２つの除電部材３０Ａ、３０Ｂによって挟んだ状態でシートＰの除電をおこなわなくても、シートＰに大きなバタツキや撓みが生じにくい場合であって、除電効果を細かく調整したい場合に有用である。 <Modification 5>
As shown in Figure 10, in the transfer device 90 of variant example 5, the first de-ionization member 30A and the second de-ionization member 30B are not positioned opposite each other on the transport path of the sheet P, but are positioned offset in the transport direction (positioned at different positions in the transport direction).
More specifically, the first charge removing member 30A and the second charge removing member 30B are both disposed downstream in the transport direction of the pair of registration rollers 45 and upstream in the transport direction of the transfer nip N. However, the second charge removing member 30B is disposed downstream in the transport direction of the first charge removing member 30A.
By configuring in this way, two-stage static elimination operation is performed with a time lag, and it is possible to finely adjust the static elimination effect (static elimination ability). More specifically, as shown in FIG. 11, "1" is a mode in which the first static elimination member 30A is in a grounded state and the second static elimination member 30B is also in a grounded state, and the static elimination effect is large. In contrast, "2" is a mode in which the first static elimination member 30A is in a grounded state (or a floating state) and the second static elimination member 30B is in a floating state (or a grounded state), and the static elimination effect is medium. Furthermore, "3" is a mode in which the first static elimination member 30A is in a floating state and the second static elimination member 30B is also in a floating state, and the static elimination effect is small.
Even when the control is performed by configuring in this manner, the sheet P can be satisfactorily neutralized before the transfer process. In particular, such a configuration is useful when the sheet P is unlikely to flutter or bend significantly even if the sheet P is not neutralized while sandwiched between the two neutralizing members 30A and 30B, and when it is desired to finely adjust the neutralization effect.

以上説明したように、本実施の形態における転写装置は、感光体ドラム１（像担持体）の表面に担持されたトナー像を転写ニップＮ（転写位置）に搬送されるシートＰの転写面に転写する転写装置９０である。そして、シートＰの電荷を除電可能な第１除電部材３０Ａが、転写ニップＮに対してシートＰの搬送方向上流側であって、シートＰの転写面に対向する位置に配置されている。また、シートＰの電荷を除電可能な第２除電部材３０Ｂが、転写ニップＮに対してシートＰの搬送方向上流側であって、シートＰの非転写面に対向する位置に配置されている。さらに、第１除電部材３０Ａと第２除電部材３０Ｂとのうち少なくとも一方を、電気的に接地状態とフロート状態とのいずれかに切替可能な切替スイッチ３１Ａ、３１Ｂ（切替手段）が設けられている。
これにより、転写工程前にシートＰを良好に除電することができる。 As described above, the transfer device in this embodiment is a transfer device 90 that transfers a toner image carried on the surface of the photosensitive drum 1 (image carrier) to a transfer surface of a sheet P transported to a transfer nip N (transfer position). A first charge removing member 30A capable of removing charge from the sheet P is disposed upstream of the transfer nip N in the transport direction of the sheet P and at a position facing the transfer surface of the sheet P. A second charge removing member 30B capable of removing charge from the sheet P is disposed upstream of the transfer nip N in the transport direction of the sheet P and at a position facing the non-transfer surface of the sheet P. Furthermore, changeover switches 31A, 31B (switching means) are provided that can electrically switch at least one of the first charge removing member 30A and the second charge removing member 30B between a grounded state and a floating state.
This allows the sheet P to be satisfactorily neutralized before the transfer step.

なお、本実施の形態では、像担持体としての感光体ドラム１の表面に担持されたトナー像をシートＰに転写する直接転写方式の画像形成装置１００に対して本発明を適用した。しかし、本発明の適用はこれに限定されることなく、例えば、複数の感光体ドラムの表面に担持されたトナー像を中間転写ベルトなどの中間転写体に１次転写した後に、像担持体としての中間転写体に担持されたトナー像をシートに転写（２次転写）する間接転写方式の画像形成装置に対しても本発明を適用することができる。
そして、そのような場合であっても、本実施の形態のものと同様の効果を得ることができる。 In this embodiment, the present invention is applied to a direct transfer type image forming apparatus 100 in which a toner image carried on the surface of a photosensitive drum 1 serving as an image carrier is transferred to a sheet P. However, the application of the present invention is not limited to this, and the present invention can also be applied to an indirect transfer type image forming apparatus in which, for example, toner images carried on the surfaces of a plurality of photosensitive drums are primarily transferred to an intermediate transfer body such as an intermediate transfer belt, and then the toner images carried on the intermediate transfer body serving as an image carrier are transferred (secondary transfer) to a sheet.
Even in such a case, the same effects as those of the present embodiment can be obtained.

また、本実施の形態では、感光体ドラム１（像担持体）と、帯電装置４と、現像装置５と、クリーニング装置２と、を一体化してプロセスカートリッジ６を構成したが、感光体ドラム（像担持体）と、帯電装置と、現像装置と、クリーニング装置と、をそれぞれ別々のユニットとして、画像形成装置本体に対して着脱可能（交換可能）に構成することもできる。
なお、「プロセスカートリッジ」とは、像担持体を帯電する帯電装置と、像担持体上に形成された潜像を現像する現像装置（現像装置）と、像担持体上をクリーニングするクリーニング装置（クリーニング装置）とのうち、少なくとも１つと、像担持体とが、一体化されて、画像形成装置本体に対して着脱可能に設置されるユニットと定義する。 In addition, in this embodiment, the photosensitive drum 1 (image carrier), charging device 4, developing device 5, and cleaning device 2 are integrated to form the process cartridge 6, but the photosensitive drum (image carrier), charging device, developing device, and cleaning device can also be configured as separate units that are detachable (replaceable) from the image forming apparatus main body.
In addition, a "process cartridge" is defined as a unit in which at least one of a charging device that charges an image carrier, a developing device (developing device) that develops a latent image formed on the image carrier, and a cleaning device (cleaning device) that cleans the image carrier is integrated with an image carrier, and is detachably installed in the main body of an image forming apparatus.

なお、本発明が本実施の形態に限定されず、本発明の技術思想の範囲内において、本実施の形態の中で示唆した以外にも、本実施の形態は適宜変更され得ることは明らかである。また、前記構成部材の数、位置、形状等は本実施の形態に限定されず、本発明を実施する上で好適な数、位置、形状等にすることができる。 It is clear that the present invention is not limited to this embodiment, and that within the scope of the technical concept of the present invention, this embodiment may be modified as appropriate in ways other than those suggested in this embodiment. Furthermore, the number, position, shape, etc. of the components are not limited to this embodiment, and may be any number, position, shape, etc. that is suitable for implementing the present invention.

１感光体ドラム（像担持体）、
５現像装置（転写面側ユニット）、
９転写ローラ（転写部材）、
１０操作表示パネル、
３０Ａ第１除電部材、
３０Ｂ第２除電部材、
３０ａ除電ブラシ、３０ｂ金属板、
３１Ａ第１切替スイッチ（切替手段）、
３１Ｂ第２切替スイッチ（切替手段）、
５０現像ケース、
６１温湿度センサ（温湿度検知手段）、
６２含水分量測定器（含水分検知手段）、
６３表面抵抗測定器（抵抗検知手段）、
９０転写装置（非転写面側ユニット）、
９１転写ケース、
１００画像形成装置（画像形成装置本体）、
Ｐシート、Ｎ転写ニップ（転写位置）。 1 Photoconductor drum (image carrier),
5 Developing device (transfer surface side unit),
9 Transfer roller (transfer member),
10 Operation display panel,
30A first static elimination member,
30B second static elimination member,
30a: static elimination brush; 30b: metal plate;
31A first changeover switch (changeover means),
31B second changeover switch (changeover means),
50 developing case,
61 temperature and humidity sensor (temperature and humidity detection means),
62 Moisture content measuring device (moisture content detection means),
63 Surface resistance measuring instrument (resistance detection means),
90 Transfer device (non-transfer surface side unit),
91 Transfer case,
100 Image forming device (image forming device main body),
P sheet, N transfer nip (transfer position).

特開平１１－８４９０３号公報Japanese Patent Application Publication No. 11-84903

Claims

A transfer device that transfers a toner image carried on a surface of an image carrier onto a transfer surface of a sheet that is transported to a transfer position,
a first charge removing member that is disposed upstream of the transfer position in a sheet transport direction and opposed to the transfer surface of the sheet, and that is capable of removing charge from the sheet;
a second charge removing member that is disposed upstream of the transfer position in a sheet conveying direction and opposed to a non-transfer surface of the sheet, and that is capable of removing electric charge from the sheet;
a switching means for switching at least one of the first and second charge removing members between an electrically grounded state and a floating state;
Equipped with
The transfer device is characterized in that the switching means sets the first charge removal member to the grounded state when the charge amount of the transfer surface of the sheet transported to the transfer position is greater than a predetermined value, and sets the first charge removal member to the floating state when the charge amount of the transfer surface of the sheet transported to the transfer position is equal to or less than the predetermined value .

A transfer device that transfers a toner image carried on a surface of an image carrier onto a transfer surface of a sheet that is transported to a transfer position,
a first charge removing member that is disposed upstream of the transfer position in a sheet transport direction and opposed to the transfer surface of the sheet, and that is capable of removing charge from the sheet;
a second charge removing member that is disposed upstream of the transfer position in a sheet conveying direction and opposed to a non-transfer surface of the sheet, and that is capable of removing electric charge from the sheet;
a switching means for switching at least one of the first and second charge removing members between an electrically grounded state and a floating state;
Equipped with
The transfer device is characterized in that the switching means sets the second charge removal member to the grounded state when the charge amount of the non-transfer surface of the sheet transported to the transfer position is greater than a predetermined value, and sets the second charge removal member to the floating state when the charge amount of the non-transfer surface of the sheet transported to the transfer position is equal to or less than the predetermined value.

A transfer device that transfers a toner image carried on a surface of an image carrier onto a transfer surface of a sheet that is transported to a transfer position,
a first charge removing member that is disposed upstream of the transfer position in a sheet transport direction and opposed to the transfer surface of the sheet, and that is capable of removing charge from the sheet;
a second charge removing member that is disposed upstream of the transfer position in a sheet conveying direction and opposed to a non-transfer surface of the sheet, and that is capable of removing electric charge from the sheet;
a switching means for switching at least one of the first and second charge removing members between an electrically grounded state and a floating state;
A moisture detection means for detecting the moisture state of the sheet;
Equipped with
The transfer device, wherein the switching means switches the first charge removing member and the second charge removing member between the grounded state and the floating state based on a detection result of the moisture detection means.

A transfer device that transfers a toner image carried on a surface of an image carrier onto a transfer surface of a sheet that is transported to a transfer position,
a first charge removing member that is disposed upstream of the transfer position in a sheet transport direction and opposed to the transfer surface of the sheet, and that is capable of removing charge from the sheet;
a second charge removing member that is disposed upstream of the transfer position in a sheet conveying direction and opposed to a non-transfer surface of the sheet, and that is capable of removing electric charge from the sheet;
a switching means for switching at least one of the first and second charge removing members between an electrically grounded state and a floating state;
A resistance detection means for detecting an electrical resistance value of a surface of the sheet;
Equipped with
The transfer device, wherein the switching means switches each of the first charge removing member and the second charge removing member between the grounded state and the floating state based on a detection result of the resistance detection means.

A transfer device that transfers a toner image carried on a surface of an image carrier onto a transfer surface of a sheet that is transported to a transfer position,
a first charge removing member that is disposed upstream of the transfer position in a sheet transport direction and opposed to the transfer surface of the sheet, and that is capable of removing charge from the sheet;
a second charge removing member that is disposed upstream of the transfer position in a sheet conveying direction and opposed to a non-transfer surface of the sheet, and that is capable of removing electric charge from the sheet;
a switching means for switching at least one of the first and second charge removing members between an electrically grounded state and a floating state;
Equipped with
The transfer device, wherein the switching means switches the first charge removing member and the second charge removing member between the grounded state and the floating state, respectively, based on the material or type of the sheet.

A transfer device that transfers a toner image carried on a surface of an image carrier onto a transfer surface of a sheet that is transported to a transfer position,
a first charge removing member that is disposed upstream of the transfer position in a sheet transport direction and opposed to the transfer surface of the sheet, and that is capable of removing charge from the sheet;
a second charge removing member that is disposed upstream of the transfer position in a sheet conveying direction and opposed to a non-transfer surface of the sheet, and that is capable of removing electric charge from the sheet;
a switching means for switching at least one of the first and second charge removing members between an electrically grounded state and a floating state;
A temperature and humidity detection means for detecting the temperature and humidity of the surroundings;
Equipped with
The transfer device, wherein the switching means switches the first charge removing member and the second charge removing member between the grounded state and the floating state based on a detection result of the temperature and humidity detection means.

A transfer device that transfers a toner image carried on a surface of an image carrier onto a transfer surface of a sheet that is transported to a transfer position,
a first charge removing member that is disposed upstream of the transfer position in a sheet transport direction and opposed to the transfer surface of the sheet, and that is capable of removing charge from the sheet;
a second charge removing member that is disposed upstream of the transfer position in a sheet conveying direction and opposed to a non-transfer surface of the sheet, and that is capable of removing electric charge from the sheet;
a switching means for switching at least one of the first and second charge removing members between an electrically grounded state and a floating state;
Equipped with
The switching means is
When a toner image is transferred at the transfer position with the front surface of the sheet as the transfer surface, the first charge removing member and the second charge removing member are each in the floating state,
A transfer device characterized in that when a toner image is transferred at the transfer position using the back surface of the sheet on which a toner image has been transferred to the front surface as the transfer surface, the first charge-removing member and the second charge-removing member are each grounded.

A transfer device that transfers a toner image carried on a surface of an image carrier onto a transfer surface of a sheet that is transported to a transfer position,
a first charge removing member that is disposed upstream of the transfer position in a sheet transport direction and opposed to the transfer surface of the sheet, and that is capable of removing charge from the sheet;
a second charge removing member that is disposed upstream of the transfer position in a sheet conveying direction and opposed to a non-transfer surface of the sheet, and that is capable of removing electric charge from the sheet;
a switching means for switching at least one of the first and second charge removing members between an electrically grounded state and a floating state;
Equipped with
The transfer device is characterized in that when a sheet having different materials on its front and back sides is transported, the switching means switches the first and second charge-eliminating members to either the grounded state or the floating state based on the respective materials.

A transfer device that transfers a toner image carried on a surface of an image carrier onto a transfer surface of a sheet that is transported to a transfer position,
a first charge removing member that is disposed upstream of the transfer position in a sheet transport direction and opposed to the transfer surface of the sheet, and that is capable of removing charge from the sheet;
a second charge removing member that is disposed upstream of the transfer position in a sheet conveying direction and opposed to a non-transfer surface of the sheet, and that is capable of removing electric charge from the sheet;
a switching means for switching at least one of the first and second charge removing members between an electrically grounded state and a floating state;
Equipped with
a transfer device, wherein one of the first charge removing member and the second charge removing member is fixed to one of the grounded state and the floating state;

A transfer device as described in any one of claims 1 to 9, characterized in that the switching means is configured to be able to switch at least one of the first charge-eliminating member and the second charge-eliminating member between an electrically grounded state and a floating state based on either the state of the sheet transported to the transfer position or the surrounding environment.

The transfer device according to any one of claims 1 to 10, characterized in that the sheet that has been de-electrified by the first de-electrification member and the second de-electrification member does not come into contact with other members until it reaches the transfer position.

The transfer device according to any one of claims 1 to 11, characterized in that the first charge removing member and the second charge removing member are arranged to face each other across the sheet transport path.

The transfer device according to any one of claims 1 to 11, characterized in that the first charge removing member and the second charge removing member are arranged at positions offset in the sheet conveying direction on the sheet conveying path.

The transfer device according to any one of claims 1 to 11, characterized in that the first charge removing member and the second charge removing member are made of the same material.

An image forming apparatus comprising the transfer device according to any one of claims 1 to 14.

16. The image forming apparatus according to claim 15, wherein the first charge removing member and the second charge removing member are detachably installed in the main body of the image forming apparatus.