JP3927757B2 - Image forming apparatus - Google Patents

Description

【００６６】
表１は、各記録モードでの定着装置の条件とＯＨＰの透過性との関係を示した表である。上記の条件での実験において、通常記録モードでは定着装置２１７の搬送速度を、加熱ローラ７１の１回転目は１１７ｍｍ／ｓ、２回転目も同じく１１７ｍｍ／ｓとした。また、特定記録モードでは定着装置２１７の搬送速度を、加熱ローラ７１の１回転目は１１７ｍｍ／ｓとし、２回転目は１０４ｍｍ／ｓとした。この場合、通常記録モードにおいても特定記録モードにおいても定着ローラの表面温度は、加熱ローラ７１の１回転目が１８０℃で、２回転目が１６４℃であった。
【００６７】
ＯＨＰシートにカラー画像を定着させた結果、通常記録モードでは、加熱ローラ７１の１回転目は良好であったが、２回転目では透過性は徐々に悪くなり、終端近傍では透過性は不良となった。
【００６８】
一方、特定記録モードにおいては、ＯＨＰシートの透過性は加熱ローラ７１の１回転目も２回転目も良好であった。
【００６９】
なお、実験に用いたレターサイズのＯＨＰシートは、短手方向の長さが２１６ｍｍであるため、定着装置２１７においては、加熱ローラ７１が２周すると定着は完了する。
【００７０】
以上のように、加熱ローラ７１の表面周囲温度は、加熱ローラ７１の１回転目に対して２回転目は１３℃低下する。しかし、図４に示したように第４の画像形成ステーションＰｄにおける転写部の転写ポイントと定着装置２１７の定着ポイントとの間の搬送距離間隔Ｌを設定するとともに、定着装置２７１の搬送速度を１１７ｍｍ／ｓから１０４ｍｍ／ｓに約１１％低下することにより、加熱ローラ７１の２回転目も１回転目と同様に良好な透過性を得ることができる。
【００７１】
なお、実験結果は、ＯＨＰシートについてのみ示したが、所定の厚みを有する厚紙においても、同様に良好な透過性を得ることができる。
【００７２】
次に、画像形成装置１における画像形成の手順を説明する。図５は、画像形成装置１の画像形成手順を示すためのフローチャートである。なお、画像形成装置１において、特定記録モードでＯＨＰシートまたは厚紙に画像形成を行なう場合、ＯＨＰシートまたは厚紙は手差しトレイ２０１にセットするものとする。また、画像形成装置１では、特定記録モードの他に、定着装置２１７の用紙搬送速度を途中で減速しない通常記録モードを実行可能である。
【００７３】
画像形成装置１で画像形成を行なう場合、まず、ユーザは、表示・入力部４１からＯＨＰシート及び厚紙に画像形成を行なう特定記録モードを行なうか、または通常記録モードかを選択する（ステップ３０１）。通常記録モードを行なう場合は、画像形成装置１の原稿台１１１または両面自動原稿送り装置１１２に原稿をセットし、図外のスタートボタンを押して通常の画像形成を行なう（ステップ３１６）。画像形成装置１の制御部３１は用紙が排出されたか否かを確認し（ステップ３１７）、定着装置２１７の用紙搬送速度を減速していないので、何も行わず（ステップ３１８）、そのまま画像形成を終了する。
【００７４】
一方、特定記録モードをユーザが選択した場合には、ユーザは、手差しトレイにＯＨＰシートまたは厚紙をセットする。制御部３１は、手差しトレイに用紙があるか否かをセンサＡ２０２によって検出する（ステップ３０２）。手差しトレイ２０１に用紙がセットされている場合は、用紙がＯＨＰシートか否かを種類検出手段であるセンサＢ２０３によって検出する（ステップ３０３）。手差しトレイ２０１にセットされた用紙がＯＨＰシートであった場合、次に、用紙の搬送方向にＯＨＰシートの短手方向がセットされたか否かを、長さ検出手段であるセンサＣ２０４によって検出する（ステップ３０４）。用紙の搬送方向にＯＨＰシートの長手方向がセットされた場合は、制御部３１は、画像形成を禁止するとともに、報知手段である表示・入力部４１に「ＯＨＰシートの向きを変えて下さい。」という警告文Ａを表示させる（ステップ３０５）。そして、再度ステップ３０２からの処理を行なう。
【００７５】
一方、用紙の搬送方向にＯＨＰシートの短手方向がセットされた場合、前記の警告文が表示されている場合は表示・入力部４１における警告文の表示を消す （ステップ３０６）。そして、制御部３１は、ユーザによってスタートボタンが押されたか否かを確認する（ステップ３０７）。表示・入力部４１からスタートボタンが押されたことが伝達されると、制御部３１は画像の形成を行なう（ステップ３０８）。そして、制御部３１は、画像の転写が完了したか否かを確認する（ステップ３０９）。
【００７６】
次に、定着装置２１７において加熱ローラが定着開始から１回転したか否かを制御部３１は確認する（ステップ３１０）。加熱ローラ７１が１回転すると、制御部３１は、定着モータ駆動回路６５に信号を送り、定着モータ８５の回転速度を減速して、定着装置２１７の用紙搬送速度を減速する（ステップ３１１）。そして、制御部３１は、用紙が画像形成装置１から排紙されたか否かを確認し（ステップ３１７）、定着装置２１７の用紙搬送速度を減速したので、元の速度に戻し（ステップ３１８）、画像形成を終了する。
【００７７】
一方、ステップ３０３において、センサＢ２０３で検出した用紙がＯＨＰシートでない場合は、センサＣ２０４によって用紙の搬送方向の長さがＯＨＰシートの短手方向の長さ以上あるか否かを検出する（ステップ３１２）。用紙の搬送方向の長さがＯＨＰシートの短手方向の長さ以下であった場合は、前述のステップ３０７以降の処理を行なう。
【００７８】
一方、用紙の搬送方向の長さがＯＨＰシートの短手方向以上の長さである場合は、制御部３１は特定記録モードでの画像形成を禁止するとともに、表示入力部４１に「通常記録モードでのコピーを行ないます。よければ、スタートボタンを押して下さい。」といった警告文Ｂを表示させる（ステップ３１３）。
【００７９】
ここで、ユーザがスタートボタンを押すと、用紙の搬送方向がＯＨＰシートの短手方向の長さより長い厚紙に画像形成を行うため、定着装置２１７の用紙搬送速度を途中で減速しない通常記録モードで画像形成が行われる。この場合、加熱ローラ７１の２回転目からは加熱ローラ７１の表面温度が低下し、トナーの溶融性が低下する。ＯＨＰシートの場合、トナーの溶融性が低下すると、トナーの境界面での反射が増加して、トナーの透明性を低下するため、光の透過性が悪くなる。そのため、ＯＨＰシートを使用すると、カラー画像が表示できなくなり、白黒画像として表示してしまう場合がある。しかしながら、記録媒体が厚紙の場合、トナーの溶融性が低下しても、厚紙上に形成した画像においては、画像ムラや色濁りがほとんど発生しない。よって、上記ステップ３１３では、確認のために警告文Ｂを表示するものである。
【００８０】
制御部３１は、スタートボタンが押されたか否かを確認し（ステップ３１４）、警告文Ｂの表示を消して（ステップ３１５）、通常の画像形成を行なう（ステップ３１６）。制御部３１は、用紙が排紙された否かを確認し（ステップ３１７）、定着装置２１７の用紙搬送速度は減速していないので、何も行なわずに（ステップ３１８）、そのまま画像形成を終了する。
【００８１】
なお、本発明は、ＯＨＰシートや厚紙などの特定の記録媒体に限らず、普通紙などの記録媒体にも、適用可能である。
【００８２】
【発明の効果】
本発明によれば、以下の効果が得られる。
【００８３】
(1) 定着部での記録媒体の搬送速度を減速する特定記録モードを有する画像形成装置では、感光体上に形成したトナー像を記録媒体に転写する転写部の転写ポイントと、記録媒体に転写されたトナー像を定着ローラによって記録媒体に定着する定着部の定着ポイントとの搬送距離間隔Ｌは、記録媒体の搬送方向の長さＬｐよりも小さく、記録媒体の搬送方向の長さＬｐと定着ローラの周長πＤとの差よりも大きく、前記記録媒体の搬送方向の長さＬｐは、特定記録モードで使用する標準サイズの記録媒体における短手方向の長さであり、定着ローラが少なくとも１回転すると、転写部の転写ポイントから記録媒体が離れるので、定着ローラの１回転後に定着速度を減速しても、記録媒体へのトナーの定着を転写ずれなしに良好に行なうことができる。また、定着部と転写部との距離を記録媒体における搬送方向の長さよりも短くできるので、搬送用の記録媒体搬送機構を設ける必要がなく、画像形成装置のサイズを小さくすることができるとともに、特定モード実行時における画像形成速度の低下を最小限にすることができる。さらに、特定記録モード実行時において、画像形成装置における記録媒体の搬送方向の長さＬｐが特定記録モードで使用する標準サイズの記録媒体における短手方向の長さ以上であることが、記録媒体の搬送方向の長さＬｐを検出する長さ検出手段で検出され、特定記録モードで使用する標準サイズの記録媒体が、記録媒体の種類を検出する種類検出手段で検出されると、装置の各手段を制御する制御部は、特定記録モードへの画像形成を禁止し、装置の状態を報知する報知手段は、特定記録モードで使用する標準サイズの記録媒体の搬送方向の長さＬｐがこの記録媒体の短手方向の長さ以上であるため、記録媒体の向きの変更指示を報知するため、誤って記録媒体をセットしたために、転写ずれの生じた粗悪な画像が形成されることを未然に防止できる。
【００８６】
(2) 特定記録モード実行時に、画像形成装置によって記録媒体の搬送方向の長さＬｐが、特定記録モードで使用する標準サイズの記録媒体における短手方向の長さ以上であることが長さ検出手段で検出され、種類検出手段によって特定記録モードで使用する標準サイズの記録媒体以外の記録媒体が検出されると、特定記録モードでの画像形成を禁止するとともに、他のモードでの画像形成の実行可否が入力されるまで制御部は待機し、他のモードでの画像形成実行可否の入力待機状態であることを報知手段は報知するので、特定記録モードで使用する標準サイズの記録媒体以外の記録媒体を使用する際には、その記録媒体のサイズに応じて、記録モードを選択することができる。
【図面の簡単な説明】
【図１】本発明の実施形態に係る画像形成装置であるデジタルカラー複写機１の概略の構成図である。
【図２】定着装置２１７の概略の構成を示す断面図である。
【図３】制御部３１と各部との関係を示すブロック図である。
【図４】定着装置と画像形成ステーションの転写部との関係を示す配置図である。
【図５】画像形成装置１の画像形成手順を示すためのフローチャートである。
【符号の説明】
１−画像形成装置
７１−加熱ローラ
２１７−定着装置
２２２ｄ−感光体[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic color image forming apparatus that forms a color image on a recording medium with a plurality of color toners, and more particularly to an image forming apparatus that forms a toner image on a transparent member for an overhead projector or thick paper.
[0002]
[Prior art]
In an electrophotographic color image forming apparatus that forms a color image on a recording medium with a plurality of color toners, it is a transparent member for an overhead projector (hereinafter referred to as an OHP sheet) or a thick paper. When forming images on cardboard, the toner of each color is sufficiently melted to reduce the reflection at the toner interface and increase the transparency of the toner. Can be obtained. In order to form such a good color image on an OHP sheet or cardboard, a technique related to an apparatus as described below has been conventionally disclosed.
[0003]
That is, Japanese Patent Application Laid-Open No. 49-73141 relates to a fixing device configured to satisfactorily fix a thin recording sheet to a thick recording sheet by controlling the running speed of the recording sheet in accordance with the thickness of the recording sheet. Technology is disclosed. This fixing device controls the traveling speed according to the thickness of the recording paper and feeds the recording paper at a constant speed.
[0004]
However, when the toner image is fixed on the recording paper, the fixing roller usually rotates on the recording paper a plurality of times. For this reason, the surface temperature of the fixing roller changes. Therefore, even if the toner image can be satisfactorily fixed in the first half of the conveyance direction of the recording paper, the fixing roller may be poorly fixed because the surface temperature of the fixing roller decreases in the second half of the conveyance direction of the recording paper. is there.
[0005]
In order to solve the above problem, Japanese Utility Model Publication No. 4-1564 discloses a technique relating to a fixing device of a copying machine that decelerates the rotation speed of a fixing roller with a preset shift pattern within one copying cycle.
[0006]
However, in the fixing device of this copying machine, the relationship between the rotation amount of the fixing roller and the temperature drop has not been considered. That is, when fixing the toner image onto the recording paper with the fixing roller, no consideration has been given to the significant temperature drop after the second rotation when the fixing roller rotates a plurality of times.
[0007]
Japanese Patent Application Laid-Open No. 8-95422 discloses an image forming apparatus that reduces the rotation speed of the fixing roller with the passage of the recording paper after one rotation of the fixing roller after the recording paper enters the fixing roller. Is disclosed. In this image forming apparatus, the recording paper with almost no decrease in the surface temperature of the fixing roller enters the fixing roller, and at the first rotation, the fixing roller is driven at a constant speed, and the conveyance of the recording paper is delayed more than necessary. There is no. Further, since the subsequent rotation speed is reduced as the recording paper passes, even if the temperature of the fixing roller surface decreases, the amount of heat necessary for fixing is given to the toner image over the entire surface, and good fixing is achieved. This is executed over the entire surface of the recording paper, and the gloss of the image becomes uniform over the entire surface.
[0008]
[Problems to be solved by the invention]
However, in the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 8-95422, a conveyance means such as a conveyance deck is required to convey the sheet between the transfer unit and the fixing unit, resulting in complexity of the apparatus and cost. There was a problem of up. Further, since the distance between the transfer portion and the fixing portion is not considered, the distance between the two portions is unclear. Further, it was unclear when an image was transferred to a special recording material such as an OHP sheet or cardboard.
[0009]
The present invention solves the above-mentioned problems, and its object is to improve the fixability of an image on an OHP sheet or cardboard, and to obtain a good fixed image without image unevenness or image shift and without color turbidity. The present invention provides an image forming apparatus capable of reducing the outer size of the apparatus.
[0010]
[Means for Solving the Problems]
The present invention has the following configuration as means for solving the above problems.
[0011]
  (1) A transfer unit that transfers a toner image formed on a photoreceptor to a recording medium, and a fixing unit that fixes the toner image transferred onto the recording medium onto a recording medium by a fixing roller. In an image forming apparatus having a specific recording mode for reducing the conveyance speed of the recording medium,
  The conveyance distance interval L between the transfer point of the transfer unit and the fixing point of the fixing unit, the length Lp in the conveyance direction of the recording medium, and the circumferential length πD of the fixing roller are:
                      Lp> L> (Lp−πD)
Has a relationship represented byThe length Lp in the transport direction of the recording medium is the length in the short direction of the standard size recording medium used in the specific recording mode,
  Length detecting means for detecting the length Lp in the transport direction of the recording medium, type detecting means for detecting the type of the recording medium, notification means for informing the state of the apparatus, and a control unit for controlling each means of the apparatus And,
When executing the specific recording mode, the length detection unit detects that the length Lp in the conveyance direction of the recording medium is equal to or longer than the length in the short direction of the standard size recording medium used in the specific recording mode, and When the type detection means detects a standard size recording medium used in the specific recording mode,
The control unit prohibits image formation in a specific recording mode, and the notification unit notifies an instruction to change the direction of the recording medium.It is characterized by doing.
[0012]
  In this configuration, in the image forming apparatus having the specific recording mode for reducing the conveyance speed of the recording medium in the fixing unit, the transfer point of the transfer unit that transfers the toner image formed on the photosensitive member to the recording medium, and the recording medium The distance L between the conveyance point and the fixing point of the fixing unit that fixes the toner image transferred onto the recording medium by the fixing roller is smaller than the length Lp in the conveyance direction of the recording medium, and the length Lp in the conveyance direction of the recording medium. And the difference between the peripheral length πD of the fixing roller.Further, the length Lp in the transport direction of the recording medium is the length in the short direction of a standard size recording medium used in the specific recording mode.Accordingly, when the fixing roller rotates at least once, the recording medium moves away from the transfer point of the transfer portion. Therefore, even if the fixing speed is decelerated after one rotation of the fixing roller, the toner can be fixed to the recording medium satisfactorily without transfer deviation. Can be done. In addition, since the distance between the fixing unit and the transfer unit can be shorter than the length in the conveyance direction of the recording medium, there is no need to provide a recording medium conveyance mechanism for conveyance, and the size of the image forming apparatus can be reduced. It is possible to minimize a decrease in the image forming speed when executing the specific mode.In this configuration, when the specific recording mode is executed, the length Lp in the conveyance direction of the recording medium in the image forming apparatus is equal to or longer than the length in the short direction of the standard size recording medium used in the specific recording mode. Is detected by the length detection unit that detects the length Lp in the conveyance direction of the recording medium, and the standard size recording medium used in the specific recording mode is detected by the type detection unit that detects the type of the recording medium. The control unit that controls each unit of the apparatus prohibits image formation in the specific recording mode, and the notification unit that notifies the state of the apparatus is the length in the conveyance direction of the standard size recording medium used in the specific recording mode. Since Lp is equal to or longer than the length of the recording medium in the short direction, an instruction to change the direction of the recording medium is notified. Accordingly, it is possible to prevent the formation of a poor image having a transfer deviation due to the erroneous setting of the recording medium.
[0017]
  (2) When executing the specific recording mode, the length detection means,Length Lp in the conveyance direction of the recording mediumButIt is detected that the length in the short direction of the standard size recording medium used in the specific recording mode is greater than or equal to that of the standard size recording medium, and the type detecting means uses the specific recording mode.RuWhen a recording medium other than the recording medium is detected,
  The controller isSaidProhibits image formation in the specific recording mode and whether to execute image formation in other modesEnteredWait until
  The informing means informs that it is in an input standby state as to whether or not image formation can be executed in another mode.
[0018]
  In this configuration, when the specific recording mode is executed, the length Lp in the conveyance direction of the recording medium is set by the image forming apparatus.,The length detection means detects that the recording medium is longer than the length of the standard size recording medium used in the specific recording mode, and is used in the specific recording mode by the type detection means.RuWhen a recording medium other than the recording medium is detected, image formation in the specific recording mode is prohibited and image formation in other modes is feasible.EnteredThe control unit waits until it is input, and the notifying unit notifies that it is in an input standby state indicating whether image formation can be performed in another mode. Therefore, when using a recording medium other than the standard size recording medium used in the specific recording mode, the recording mode can be selected according to the size of the recording medium.
[0019]
  (3) (1) Or (2)In the configuration, the standard size recording medium used in the specific recording mode can be an OHP sheet.
[0020]
In this configuration, the OHP sheet is a standard size recording medium used in the specific recording mode. Therefore, it is possible to reliably form an image on the OHP sheet. Further, since the OHP sheet does not normally have a size other than the standard size, use in a direction other than the designated conveyance direction can be prohibited.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic configuration diagram of a digital color copying machine 1 which is an image forming apparatus according to an embodiment of the present invention. A document table 111 and an operation panel are provided on the upper surface of the copying machine main body 1, and an image reading unit 110 and an image forming unit 210 are provided inside the copying machine main body 1. A double-sided automatic document feeder (RADF) 112 is supported on the upper surface of the document table 111 so as to be openable and closable with respect to the document table 111 and has a predetermined positional relationship with respect to the upper surface of the document table 111. It is installed.
[0022]
The double-sided automatic document feeder 112 first transports a document so that one side of the document faces the image reading unit 110 at a predetermined position on the document table 111. Then, after the image reading on the one surface is completed, the document is reversed and conveyed toward the document table 111 so that the other surface faces the image reading unit 110 at a predetermined position on the document table 111. ing. Then, the double-sided automatic document feeder 112 discharges the original after one-sided image reading for one original is completed, and executes a double-sided conveyance operation for the next original.
[0023]
The above document transport and front / back reversing operations are controlled in relation to the operation of the entire copying machine.
[0024]
The image reading unit 110 is disposed below the document table 111 in order to read an image of the document conveyed on the document table 111 by the double-sided automatic document feeder 112. The image reading unit 110 includes document scanning bodies 113 and 114 that reciprocate in parallel along the lower surface of the document table 111, an optical lens 115, and a CCD line sensor 116 that is a photoelectric conversion element.
[0025]
The document scanning bodies 113 and 114 are composed of a first scanning unit 113 and a second scanning unit 114. The first scanning unit 113 has an exposure lamp that exposes the surface of the document image and a first mirror that deflects the reflected light image from the document in a predetermined direction, and is constant with respect to the lower surface of the document table 111. While reciprocally moving in parallel at a predetermined scanning speed. The second scanning unit 114 includes second and third mirrors for deflecting the reflected light image from the original deflected by the first mirror of the first scanning unit 113 in a predetermined direction. The first scanning unit 113 reciprocates in parallel while maintaining a constant speed relationship.
[0026]
The optical lens 115 forms a reflected light image from the original deflected by the third mirror of the second scanning unit 114 at a predetermined position on the CCD line sensor 116.
[0027]
The CCD line sensor 116 sequentially photoelectrically converts the formed light image and outputs it as an electrical signal. The CCD line sensor 116 is a three-line color CCD that can read a black-and-white image or a color image and output line data that is color-separated into R (red), G (green), and B (blue) color components. . The document image information converted into an electrical signal by the CCD line sensor 116 is further transferred to an image processing unit (not shown) and subjected to predetermined image data processing.
[0028]
Next, the configuration of the image forming unit 210 and the configuration of each unit related to the image forming unit 210 will be described.
[0029]
Below the image forming unit 210, a paper feeding mechanism 211 that separates sheets (recording media) P stacked and accommodated in a paper tray one by one and supplies them to the image forming unit 210 is provided. . The sheets P separated and supplied one by one are transported to the image forming unit 210 with timing controlled by a pair of registration rollers 212 disposed in front of the image forming unit 210. Further, the paper P on which an image is formed on one side is re-supplied and conveyed to the image forming unit 210 in synchronization with the image formation of the image forming unit 210.
[0030]
Further, a manual feed tray 201 is provided on one side surface of the copying machine main body 1 with one end portion extending outside the apparatus so that the paper P can be manually fed. The paper placed on the manual feed tray 201 is conveyed to the image forming unit 210. The manual feed tray 201 is provided with a sensor A202 that detects the presence or absence of a loaded paper, a sensor B203 that detects the type of paper, and a sensor C204 that detects the orientation of the paper with respect to the transport direction.
[0031]
A transfer conveyance belt mechanism 213 is arranged below the image forming unit 210. The transfer conveyance belt mechanism 213 is configured to convey the paper P by electrostatically adsorbing the transfer conveyance belt 216 stretched between the driving roller 214 and the driven roller 215 so as to extend substantially in parallel.
[0032]
Further, a fixing device 217 for fixing the toner image transferred and formed on the paper P on the paper P is disposed on the downstream side of the transfer and transport belt mechanism 213 in the paper transport path. The sheet P that has passed through the nip portion between the pair of fixing rollers of the fixing device 217 passes through a conveyance direction switching gate 218 and is discharged onto a discharge tray 220 attached to the other side surface of the copier body 1 by a discharge roller 219. To be discharged.
[0033]
The switching gate 218 selectively switches the conveyance path of the paper P after fixing between a path for discharging the paper P to the copying machine main body 1 and a path for resupplying the paper P toward the image forming unit 210. Is. The paper P whose transport direction has been switched again toward the image forming unit 210 by the switching gate 218 is turned upside down via the switchback transport path 221 and then supplied again to the image forming unit 210.
[0034]
Further, above the transfer conveyance belt 216 in the image forming unit 210, in the vicinity of the transfer conveyance belt 216, the first image formation station Pa, the second image formation station Pb, the third image formation station Pc, and The fourth image forming stations Pd are arranged in order from the upstream side of the sheet conveyance path.
[0035]
The transfer conveyance belt 216 is frictionally driven in the direction indicated by the arrow Z in FIG. 1 by the driving roller 214, holds the paper P fed through the paper feed mechanism 211 as described above, and holds the paper P at the image forming stations Pa to. Convey sequentially to Pd.
[0036]
Each of the image forming stations Pa to Pd has substantially the same configuration. Each of the image forming stations Pa, Pb, Pc, and Pd includes photosensitive drums 222a, 222b, 222c, and 222d that are driven to rotate in the direction of arrow F shown in FIG.
[0037]
Around each of the photosensitive drums 222a to 222d, there are chargers 223a, 223b, 223c, and 223d for uniformly charging the photosensitive drums 222a to 222d, and electrostatic latent images formed on the photosensitive drums 222a to 222d. Developing devices 224a, 224b, 224c, and 224d that respectively develop the images, transfer dischargers 225a, 225b, 225c, and 225d that transfer the developed toner images on the photosensitive drums 222a to 222d onto the paper P, and photoconductors Cleaning devices 226a, 226b, 226c, and 226d that remove toner remaining on the drums 222a to 222d are sequentially arranged along the rotation direction of the photosensitive drums 222a to 222d.
[0038]
Further, laser beam scanner units 227a, 227b, 227c, and 227d are provided above the photosensitive drums 222a to 222d, respectively. The laser beam scanner units 227a to 227d are respectively a semiconductor laser element (not shown) that emits dot light modulated according to image data, and a polygon mirror (for deflecting the laser beam from the semiconductor laser element in the main scanning direction). Deflection devices) 240a to 240d, fθ lenses 241a to 241d and 242a to 242d for forming images of the laser beams deflected by the polygon mirrors 240a to 240d on the surfaces of the photosensitive drums 222a to 222d, and mirrors 243a to 243d. It is configured.
[0039]
The laser beam scanner 227a has a pixel signal corresponding to the black component image of the color original image, the laser beam scanner 227b has a pixel signal corresponding to the cyan component image of the color original image, and the laser beam scanner 227c has a color original image. The pixel signal corresponding to the magenta color component image is input to the laser beam scanner 227d, and the pixel signal corresponding to the yellow color component image of the color original image is input to the laser beam scanner 227d.
[0040]
As a result, electrostatic latent images corresponding to the color-converted document image information are formed on the photosensitive drums 222a to 222d. The developing device 227a contains black toner, the developing device 227b contains cyan toner, the developing device 227c contains magenta toner, and the developing device 227d contains yellow toner. . The electrostatic latent images on the photosensitive drums 222a to 222d are developed with the toners of these colors. As a result, the document image information color-converted by the image forming unit 210 is reproduced as a toner image of each color.
[0041]
Further, a paper suction (brush) charger 228 is provided between the first image forming station Pa and the paper feed mechanism 211. The adsorption charger 228 charges the surface of the transfer conveyance belt 216. The sheet P supplied from the sheet feeding mechanism 211 is securely adsorbed on the transfer / conveying belt 216 and is not shifted between the first image forming station Pa and the fourth image forming station Pd. Be transported.
[0042]
On the other hand, a static eliminator 229 is provided almost directly above the drive roller 214 between the fourth image forming station Pd and the fixing device 217. An AC current for separating the sheet P electrostatically attracted to the transport belt 216 from the transfer transport belt 216 is applied to the static eliminator.
[0043]
In the digital color copying machine 1 configured as described above, cut sheet-like paper stored in a paper feed cassette is used as the paper P. In addition, an OHP sheet or cardboard of a predetermined size can be used by being set on the manual feed tray 201. When the paper P is sent out from the paper feed cassette or the manual feed tray 201 and supplied into the guide of the paper feed / conveyance path of the paper feed mechanism 211, the leading end of the paper P is detected by a sensor (not shown). The pair of registration rollers 212 are temporarily stopped based on the detection signal output from the sensor.
[0044]
Then, the sheet P is sent onto the transfer conveyance belt 216 rotating in the direction of the arrow Z shown in FIG. 1 in time with each of the image forming stations Pa to Pd. At this time, since the transfer conveyance belt 216 is charged by the adsorption charger 228 as described above, the sheet P is stably conveyed and supplied while passing through the image forming stations Pa to Pd. Is done.
[0045]
In each of the image forming stations Pa to Pd, each color toner image is formed and superimposed on the support surface of the sheet P that is electrostatically attracted and conveyed by the transfer conveyance belt 216. When the transfer of the image by the fourth image forming station Pd is completed, the sheet P is sequentially peeled off from the transfer conveyance belt 216 by the charge eliminator 229 from the leading end portion thereof and guided to the fixing device 217. The paper P on which the toner image is fixed by the fixing device 217 is discharged from a paper discharge port (not shown) onto the paper discharge tray 220.
[0046]
In the above description, the laser beam scanner units 227a to 227d perform optical writing on the photosensitive member by scanning and exposing a laser beam. However, a writing optical system (LED head) including a light emitting diode array and an imaging lens array may be used instead of the laser beam scanner units 227a to 227d. The LED head is smaller in size than the laser beam scanner unit and operates silently because there are no moving parts. Therefore, an LED head can be suitably used in an image forming apparatus such as a tandem digital color copying machine that requires a plurality of optical writing units.
[0047]
Next, the configuration of the fixing device 217 in the image forming apparatus 1 will be described. FIG. 2 is a cross-sectional view illustrating a schematic configuration of the fixing device 217. The fixing device 217 includes a heating roller 71 and a pressure roller 72 that are a pair of rollers that are in pressure contact with each other with a predetermined nip pressure. The heating roller 71 and the pressure roller 72 rotate in opposite directions as indicated by arrows in the drawing, and heat and press the recording material P that is a recording medium passing between the two. The heating roller 71 located on the upper side has a hollow cylindrical shape and includes an upper heater lamp 73 therein. Similarly, the pressure roller 72 has a hollow cylindrical shape and includes a lower heater lamp 74 therein.
[0048]
A pre-fixing guide 70 guides the conveyance of the recording material P conveyed from the image forming station Pd to the nip portion of the heating roller 71 and the pressure roller 72 on the upstream side of the fixing device 217 in the conveyance direction of the recording material P. Is provided.
[0049]
Around the heating roller 71, there is an upper peeling claw 81, an upper cleaning roller 79, an upper thermistor 75, and an upper oil application roller 77 from the upstream side to the downstream side with the pressure contact portion with the pressure roller 72 as the upstream side. These are provided in contact with the surface of the heating roller 71, respectively. Further, around the pressure roller 72, the lower peeling claw 82, the lower cleaning roller 80, and the lower thermistor 76 are pressed from the upstream side to the downstream side, with the pressure contact portion with the heating roller 71 being the upstream side. It is provided in contact with the surface of the roller 72.
[0050]
The upper peeling claw 81 is provided with an acute-angled tip portion in contact with the surface of the heating roller 71, and the lower peeling claw 82 is provided with an acute-angled tip portion in contact with the surface of the heating roller 71. The upper peeling claw 81 and the lower peeling claw 82 are for peeling the recording material P when the recording material P that has been fixed adheres to the surface of the heating roller 71 or the pressure roller 72.
[0051]
The upper cleaning roller 79 and the lower cleaning roller 80 clean the surfaces of the heating roller 71 and the pressure roller 72, respectively.
[0052]
The upper thermistor 75 and the lower thermistor 76 are for measuring the surface temperatures of the heating roller 71 and the pressure roller 72, respectively.
[0053]
The oil application roller 77 is for applying oil to the surface of the heating roller 71 and prevents the toner on the recording material from adhering to the surface of the heating roller 71.
[0054]
Next, control of each unit in the image forming apparatus 1 will be described. FIG. 3 is a block diagram illustrating the relationship between the control unit 31 and each unit. Each unit described below is connected to the control unit 31, and each unit is controlled by exchanging signals. That is, image reading unit 110, display / input unit 41, sensor A 202, sensor B 203, sensor C 204, image processing unit 51, image memory 52, main motor drive circuit 66, fixing motor drive circuit 65, lower heater lamp power supply 64, lower part The thermistor 76, the upper heater lamp power source 63, and the upper thermistor 75 are connected to the control unit 31, respectively.
[0055]
The image processing unit 51 includes an image forming unit 210, the main motor driving circuit 66 includes a main motor 86, the fixing motor driving circuit 65 includes a fixing motor 85, and the lower heater lamp power source 64 includes a lower heater lamp 74. The upper heater lamp 73 is connected to the upper heater lamp power source 63.
[0056]
Next, the distance relationship between the fixing device and the transfer unit of the image forming station in the image forming apparatus 1 of the present invention will be described. FIG. 4 is a layout diagram showing the relationship between the fixing device and the transfer unit of the image forming station.
[0057]
When the toner image is fixed on the recording material P in the fixing device 217, the surface temperature of the heating roller 71 is substantially constant at the first rotation. However, when the heating roller 71 makes one rotation, the surface temperature is lowered after the second rotation of the heating roller 71 because the heat is lost due to contact with the recording material P. Therefore, after the second rotation of the heating roller 71, the toner image is reliably fixed on the recording material P by reducing the feeding speed of the recording material P in the fixing device 217, that is, the rotation speed of the heating roller 71.
[0058]
In the present invention, as a specific recording mode, in order to reliably fix a color image on an OHP sheet or cardboard, in addition to the above method, a fixing device 217 and a transfer unit of the image forming station Pd are shown in FIG. Arrange as follows. That is, the contact portion between the photosensitive drum 222d and the transfer discharger 225d, which is the transfer point of the transfer portion in the fourth image forming station Pd on the most downstream side of the image forming portion in the image forming apparatus 1, and the fixing device 217. Let L be the conveyance distance interval that is the distance between the contact portion between the heating roller 71 and the pressure roller 72 that is the fixing point. Further, when the length of the recording material P as a recording medium in the conveyance direction is Lp, and the circumferential length of the heating roller 71 is πD,
Lp> L> (Lp−πD)
Arrange to maintain the relationship shown in. When the toner image is fixed, if the heating roller 71 rotates once, the sheet conveyance speed of the fixing device 217 is reduced to a predetermined speed.
[0059]
Since the transport distance interval L between the transfer point of the transfer section and the fixing point of the fixing device 217 in the fourth image forming station Pd is smaller than the length Lp in the transport direction of the recording material P, it can be moved between the two. There is no need to provide a transfer device, and only a guide or the like may be provided.
[0060]
Further, the conveyance distance interval L between the transfer point of the transfer unit and the fixing point of the fixing device 217 in the fourth image forming station Pd is the length Lp in the conveyance direction of the recording material P and the circumferential length πD of the heating roller 71. Therefore, when the heating roller 71 rotates once, the recording material P is not sandwiched between the photosensitive drum 220d and the transfer discharger 225d. For this reason, even if the rotational speeds of the heating roller 71 and the pressure roller 72 are reduced, there is no recording material P sandwiched in addition to the fixing device 217, so that image unevenness and image displacement do not occur.
[0061]
Note that the length Lp in the conveyance direction of the recording material P is the short direction of the recording material P, so that the conveyance between the transfer point of the transfer unit and the fixing point of the fixing device 217 in the fourth image forming station Pd is performed. The distance L can be further reduced.
[0062]
The effect of the configuration shown in FIG. 4 was confirmed by conducting an experiment with the following configuration. An OHP sheet was used as a standard size recording medium used in the specific recording mode. There are two types of OHP sheets that are generally commercially available, letter size (8.5 inch × 11 inch) and A4 size (210 mm × 297 mm).
[0063]
The temperature of the heating roller 71 of the fixing device 217 is determined by the upper heater lamp power source 63 and the lower heater lamp power source 64 based on the detected temperature of the upper thermistor 75 provided in contact with the heating roller 71. Control was performed by energizing the heater lamp 74. Further, at the time of waiting for the fixing operation, the upper heater lamp 73 was turned on / off at 650 W and the lower heater lamp 74 was turned on at 450 W, and the surface temperature of the heating roller 71 was controlled to 180 ° C. Further, during the fixing operation, the upper heater lamp 73 was turned on / off at 850 to 950 W, and the energization to the lower heater lamp 74 was stopped. The surface temperature of the heating roller was controlled to be 180 ° C., the same as that during standby.
[0064]
The diameters of the heating roller 71 and the pressure roller 72 were 40 mm. Accordingly, the circumference is 40π (125.7 mm). The distance L between the transfer point of the image forming station Pd and the fixing point of the fixing device 271 is 120 mm. This is because the difference between the 8.5-inch (216 mm) length in the short direction of the letter-sized OHP sheet and the circumferential length πD (125.7 mm) of the heating roller 71 is 90.3 mm, so that it is 216 mm and 90.3 mm. It was set to 120 mm.
[0065]
[Table 1]

[0066]
Table 1 is a table showing the relationship between fixing device conditions and OHP transparency in each recording mode. In the experiment under the above conditions, in the normal recording mode, the conveyance speed of the fixing device 217 was 117 mm / s for the first rotation of the heating roller 71 and 117 mm / s for the second rotation. In the specific recording mode, the conveyance speed of the fixing device 217 is 117 mm / s for the first rotation of the heating roller 71 and 104 mm / s for the second rotation. In this case, in both the normal recording mode and the specific recording mode, the surface temperature of the fixing roller was 180 ° C. for the first rotation of the heating roller 71 and 164 ° C. for the second rotation.
[0067]
As a result of fixing the color image on the OHP sheet, in the normal recording mode, the first rotation of the heating roller 71 was good, but the transparency gradually deteriorated in the second rotation, and the permeability was poor near the end. became.
[0068]
On the other hand, in the specific recording mode, the transparency of the OHP sheet was good in both the first and second rotations of the heating roller 71.
[0069]
Note that the letter-size OHP sheet used in the experiment has a length in the short side direction of 216 mm. Therefore, in the fixing device 217, the fixing is completed when the heating roller 71 makes two turns.
[0070]
As described above, the surface ambient temperature of the heating roller 71 is reduced by 13 ° C. in the second rotation with respect to the first rotation of the heating roller 71. However, as shown in FIG. 4, the conveyance distance interval L between the transfer point of the transfer unit and the fixing point of the fixing device 217 in the fourth image forming station Pd is set, and the conveyance speed of the fixing device 271 is 117 mm. By reducing about 11% from / s to 104 mm / s, the second rotation of the heating roller 71 can obtain good transparency as in the first rotation.
[0071]
In addition, although the experimental result was shown only about the OHP sheet, favorable permeability | transmittance can be obtained similarly also in the cardboard which has predetermined | prescribed thickness.
[0072]
Next, an image forming procedure in the image forming apparatus 1 will be described. FIG. 5 is a flowchart for illustrating an image forming procedure of the image forming apparatus 1. When the image forming apparatus 1 forms an image on an OHP sheet or cardboard in the specific recording mode, the OHP sheet or cardboard is set on the manual feed tray 201. In addition to the specific recording mode, the image forming apparatus 1 can execute a normal recording mode in which the sheet conveyance speed of the fixing device 217 is not decelerated halfway.
[0073]
When the image forming apparatus 1 forms an image, the user first selects from the display / input unit 41 whether to perform a specific recording mode for forming an image on an OHP sheet and cardboard or a normal recording mode (step 301). . When the normal recording mode is performed, a document is set on the document table 111 or the double-sided automatic document feeder 112 of the image forming apparatus 1, and a start button (not shown) is pressed to perform normal image formation (step 316). The control unit 31 of the image forming apparatus 1 confirms whether or not the sheet has been discharged (step 317), and does not decelerate the sheet conveyance speed of the fixing device 217. Exit.
[0074]
On the other hand, when the user selects the specific recording mode, the user sets an OHP sheet or cardboard on the manual feed tray. The control unit 31 detects whether or not there is a sheet in the manual feed tray by the sensor A 202 (step 302). If a sheet is set on the manual feed tray 201, it is detected by the sensor B203 which is a type detecting means whether or not the sheet is an OHP sheet (step 303). When the paper set on the manual feed tray 201 is an OHP sheet, next, a sensor C204 which is a length detection unit detects whether or not the transversal direction of the OHP sheet is set in the paper transport direction ( Step 304). When the longitudinal direction of the OHP sheet is set in the paper transport direction, the control unit 31 prohibits image formation and “change the direction of the OHP sheet” on the display / input unit 41 serving as notification means. Is displayed (step 305). Then, the processing from step 302 is performed again.
[0075]
  On the other hand, when the transversal direction of the OHP sheet is set in the paper transport direction, the warning message is displayedIs displayedDisplay warning text on the input unit 41Erase  (Step 306). And the control part 31 confirms whether the start button was pushed by the user (step 307). When it is transmitted from the display / input unit 41 that the start button has been pressed, the control unit 31 forms an image (step 308). Then, the control unit 31 confirms whether or not the image transfer is completed (step 309).
[0076]
Next, in the fixing device 217, the control unit 31 checks whether or not the heating roller has made one rotation from the start of fixing (step 310). When the heating roller 71 rotates once, the control unit 31 sends a signal to the fixing motor driving circuit 65 to reduce the rotation speed of the fixing motor 85 and to reduce the sheet conveyance speed of the fixing device 217 (step 311). Then, the control unit 31 confirms whether or not the sheet is discharged from the image forming apparatus 1 (step 317), and since the sheet conveyance speed of the fixing device 217 is reduced, the control unit 31 returns to the original speed (step 318). End image formation.
[0077]
On the other hand, if the sheet detected by the sensor B203 is not an OHP sheet in step 303, the sensor C204 detects whether the length of the sheet in the conveyance direction is equal to or longer than the length of the OHP sheet in the short direction (step 312). ). If the length of the paper in the transport direction is less than or equal to the length of the OHP sheet in the short direction, the processing from step 307 onward is performed.
[0078]
On the other hand, when the length of the paper in the conveyance direction is equal to or longer than the short side direction of the OHP sheet, the control unit 31 prohibits image formation in the specific recording mode and displays “normal recording mode” on the display input unit 41. The warning text B is displayed (step 313).
[0079]
  Here, when the user presses the start button, an image is formed on a thick paper whose paper transport direction is longer than the length of the short side of the OHP sheet. Image formation is performed. In this case, from the second rotation of the heating roller 71, the surface temperature of the heating roller 71 decreases, and the meltability of the toner decreases. In the case of an OHP sheet, when the meltability of the toner is lowered, reflection at the boundary surface of the toner is increased and the transparency of the toner is lowered, so that the light transmittance is deteriorated. for that reason, OWhen the HP sheet is used, a color image cannot be displayed and may be displayed as a black and white image. However, when the recording medium is thick paper, even if the meltability of the toner is reduced, image unevenness and color turbidity hardly occur in an image formed on the thick paper. Therefore, in step 313, the warning text B is displayed for confirmation.
[0080]
The control unit 31 confirms whether or not the start button has been pressed (step 314), turns off the warning message B (step 315), and performs normal image formation (step 316). The control unit 31 confirms whether or not the sheet is discharged (step 317). Since the sheet conveying speed of the fixing device 217 is not decelerated, nothing is performed (step 318) and the image formation is finished as it is. To do.
[0081]
The present invention is not limited to a specific recording medium such as an OHP sheet or cardboard, but can also be applied to a recording medium such as plain paper.
[0082]
【The invention's effect】
According to the present invention, the following effects can be obtained.
[0083]
  (1) In an image forming apparatus having a specific recording mode that reduces the conveyance speed of the recording medium in the fixing unit, the transfer point of the transfer unit that transfers the toner image formed on the photosensitive member to the recording medium, and the transfer to the recording medium The conveyance distance interval L from the fixing point of the fixing unit that fixes the toner image to the recording medium by the fixing roller is smaller than the length Lp in the conveyance direction of the recording medium, and is fixed to the length Lp in the conveyance direction of the recording medium. Greater than the difference with the roller circumference πDFurther, the length Lp in the transport direction of the recording medium is the length in the short direction of the standard size recording medium used in the specific recording mode.When the fixing roller rotates at least once, the recording medium moves away from the transfer point of the transfer portion. Therefore, even if the fixing speed is reduced after one rotation of the fixing roller, the toner is well fixed on the recording medium without transfer deviation. be able to. In addition, since the distance between the fixing unit and the transfer unit can be shorter than the length in the conveyance direction of the recording medium, there is no need to provide a recording medium conveyance mechanism for conveyance, and the size of the image forming apparatus can be reduced. It is possible to minimize a decrease in the image forming speed when executing the specific mode.Further, when the specific recording mode is executed, the length Lp in the conveyance direction of the recording medium in the image forming apparatus is equal to or longer than the length in the short direction of the standard size recording medium used in the specific recording mode. When the standard size recording medium used in the specific recording mode is detected by the type detecting means for detecting the type of the recording medium, detected by the length detecting means for detecting the length Lp in the transport direction, each means of the apparatus The control unit for controlling the recording unit prohibits image formation in the specific recording mode, and the notifying means for informing the state of the apparatus has a length Lp in the transport direction of a standard size recording medium used in the specific recording mode. Since the recording medium is inadvertently set in order to notify the instruction to change the orientation of the recording medium, the recording medium is set inadvertently. It can be prevented.
[0086]
  (2) When executing the specific recording mode, the length Lp in the conveyance direction of the recording medium is set by the image forming apparatus.,A recording medium other than the standard size recording medium used in the specific recording mode is detected by the length detection means and is detected by the length detection means to be longer than the length in the short direction of the standard size recording medium used in the specific recording mode. Is detected, image formation in the specific recording mode is prohibited and image formation in other modes is feasibleEnteredThe control unit waits until it is input, and the notifying means notifies that the input standby state for whether or not image formation is possible in other modes is performed, so a recording medium other than the standard size recording medium used in the specific recording mode can be selected. When used, the recording mode can be selected according to the size of the recording medium.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a digital color copying machine 1 which is an image forming apparatus according to an embodiment of the present invention.
2 is a cross-sectional view illustrating a schematic configuration of a fixing device 217. FIG.
FIG. 3 is a block diagram illustrating a relationship between a control unit 31 and each unit.
FIG. 4 is a layout diagram illustrating a relationship between a fixing device and a transfer unit of an image forming station.
FIG. 5 is a flowchart for illustrating an image forming procedure of the image forming apparatus 1;
[Explanation of symbols]
1-Image forming apparatus
71-Heating roller
217-Fixing device
222d-Photoconductor

Claims (2)

A recording unit for transferring the toner image formed on the photosensitive member to the recording medium; and a fixing unit for fixing the toner image transferred to the recording medium on the recording medium by a fixing roller. In an image forming apparatus having a specific recording mode for reducing the conveyance speed of
The conveyance distance interval L between the transfer point of the transfer unit and the fixing point of the fixing unit, the length Lp in the conveyance direction of the recording medium, and the circumferential length πD of the fixing roller are:
Lp>L> (Lp−πD)
Have a in represented by the relationship, the length Lp of the transportation direction of the recording medium is the length in the lateral direction of the recording medium of a standard size used in a particular recording mode,
A length detecting means for detecting the length Lp in the conveyance direction of the recording medium, a type detecting means for detecting the type of the recording medium, a notifying means for informing the state of the apparatus, and a controller for controlling each means of the apparatus; With
When executing the specific recording mode, the length detection unit detects that the length Lp in the conveyance direction of the recording medium is equal to or longer than the length in the short direction of the standard size recording medium used in the specific recording mode, and When the type detection means detects the recording medium used in the specific recording mode,
The image forming apparatus according to claim 1, wherein the control unit prohibits image formation in a specific recording mode, and the notification unit notifies an instruction to change a direction of the recording medium . When a particular recording mode is executed, along with the length detection means detects that the length Lp of the transportation direction of the recording medium is equal to or greater than the length of the lateral direction of the recording medium of a standard size used in the specific recording mode , when the type detection means detects the recording medium other than the record medium that is used in the particular recording mode,
Wherein the control unit is configured to prohibit image formation in the particular recording mode, the propriety of execution of the image formation in the other mode waiting to be entered,
The image forming apparatus according to claim 1 , wherein the notifying unit notifies that an input standby state indicating whether or not to perform image formation in another mode is in an input standby state.

Images