JP2007139915A

JP2007139915A - Image forming device

Info

Publication number: JP2007139915A
Application number: JP2005330880A
Authority: JP
Inventors: Tatsuhiko Oikawa; 達彦及川
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2005-11-15
Filing date: 2005-11-15
Publication date: 2007-06-07

Abstract

<P>PROBLEM TO BE SOLVED: To prevent deterioration in image quality due to "color shift" or "displacement" by reducing a rapid load fluctuation occurring when a leading tip of recording paper is transported to a secondary transfer facing roller and a secondary transfer roller and when an end tip of the recording paper passes through them. <P>SOLUTION: The image forming device is provided with the secondary transfer roller 15 bringing an intermediate transfer belt 9 into a press-contact to the recording paper 18 in order to transfer an image transferred to an intermediate transfer belt 9 to the recording paper again; and a registration roller 16 to supply the recording paper 18 to a secondary transfer part. Furthermore, recording paper thickness detecting mechanisms 19, 20, 21, 22, 23, 24 and 29 for detecting the thickness of the recording paper are provided in a transporting path of the recording paper 18. The secondary transfer roller 15 is opened or closed according to the thickness of the detected recording paper 18. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、画像形成工程において画像の「色ずれ」や「位置ずれ」を調整する機能を備えたタンデム型のカラー画像形成装置等の画像形成装置に関するものである。 The present invention relates to an image forming apparatus such as a tandem color image forming apparatus having a function of adjusting “color shift” and “position shift” of an image in an image forming process.

図１１は一般的なタンデム型カラー画像形成装置の構成例を示す概略図である。図１１の構成は一般的なカラー色Ｙ（イエロー）、Ｍ（マゼンタ）、Ｃ（シアン）の４色を搭載した例である。
図１１には、感光体ドラムＹ１、この感光体ドラムＹ１用の現像ユニットＹ５、感光体ドラムＭ２、この感光体ドラムＭ２用の現像ユニットＭ６、感光体ドラムＣ３、この感光体ドラムＣ３用の現像ユニットＣ７、感光体ドラムＢＫ４、及びこの感光体ドラムＢＫ４用の現像ユニットＢＫ８が示されている。
図１１には、さらに、中間転写ベルト９、この中間転写ベルト９の駆動ローラ１０、減速ギヤ１１、駆動モータ１２、中間転写ベルト９の従動ローラ１３、２次転写対向ローラ１４、この２次転写対向ローラ１４に対向する２次転写ローラ１５、レジストローラ１６、記録紙挿入検出センサ１７、及び記録紙１８が示されている。
図示していない４色の光学書き込みユニットＹ、光学書き込みユニットＭ、光学書き込みユニットＣ、光学書き込みユニットＢＫにて、これも図示していない駆動モータで回転する４色の独立した感光体ドラムＹ１、感光体ドラムＭ２、感光体ドラムＣ３、感光体ドラムＢＫ４上に潜像画像を書き込む。
次にこのように各４色の現像ユニットＹ５、現像ユニットＭ６、現像ユニットＣ７、現像ユニットＢＫ８によって、各感光体ドラムに光学書き込みで書き込まれた潜像画像に各色のトナーを静電吸着にて吸着させる。さらに、このように個々の感光体ドラムに吸着させた４色のトナーを中間転写ベルト９に４色の各感光体ドラムから所定の位置に４色の画像を転写させる。すなわちこの動作で各色を重ねた画像を形成する。
この中間転写ベルト９は駆動ローラ１０と従動ローラ１３、２次転写対向ローラ１４に懸架され、駆動モータ１２と減速ギヤ１１を介して一定速度で駆動されている。次に、このように中間転写ベルト９に形成された画像は記録紙１８に転写される。記録紙１８は記録紙挿入検出センサ１７を通ってレジストローラ１６にて記録紙１８の先端を揃えられる。 FIG. 11 is a schematic diagram illustrating a configuration example of a general tandem type color image forming apparatus. The configuration of FIG. 11 is an example in which four colors of general color colors Y (yellow), M (magenta), and C (cyan) are mounted.
FIG. 11 shows the photosensitive drum Y1, the developing unit Y5 for the photosensitive drum Y1, the photosensitive drum M2, the developing unit M6 for the photosensitive drum M2, the photosensitive drum C3, and the developing for the photosensitive drum C3. A unit C7, a photosensitive drum BK4, and a developing unit BK8 for the photosensitive drum BK4 are shown.
FIG. 11 further shows an intermediate transfer belt 9, a driving roller 10 for this intermediate transfer belt 9, a reduction gear 11, a drive motor 12, a driven roller 13 for the intermediate transfer belt 9, a secondary transfer counter roller 14, and this secondary transfer. A secondary transfer roller 15, a registration roller 16, a recording paper insertion detection sensor 17, and a recording paper 18 that face the opposing roller 14 are shown.
In four-color optical writing unit Y, optical writing unit M, optical writing unit C, and optical writing unit BK (not shown), four-color independent photosensitive drums Y1 that are rotated by a driving motor (not shown), A latent image is written on the photosensitive drum M2, the photosensitive drum C3, and the photosensitive drum BK4.
Next, toner of each color is electrostatically attracted to the latent image written by optical writing on each photosensitive drum by the development unit Y5, development unit M6, development unit C7, and development unit BK8 in this manner. Adsorb. Further, the four color toners adsorbed on the individual photosensitive drums in this way are transferred onto the intermediate transfer belt 9 from the four color photosensitive drums to the predetermined positions. That is, an image in which each color is superimposed is formed by this operation.
The intermediate transfer belt 9 is suspended by a drive roller 10, a driven roller 13, and a secondary transfer counter roller 14, and is driven at a constant speed via a drive motor 12 and a reduction gear 11. Next, the image thus formed on the intermediate transfer belt 9 is transferred to the recording paper 18. The recording paper 18 passes through the recording paper insertion detection sensor 17, and the leading edge of the recording paper 18 is aligned by the registration roller 16.

次に記録紙１８を２次転写ローラ１５の位置まで搬送し、２次転写対向ローラ１４と２次転写ローラ１５の間を通過させる。この２次転写対向ローラ１４と２次転写ローラ１５との間を通過する時に中間転写ベルト９に形成されていた重ね画像は記録紙１８に転写される。
この後、画像形成された記録紙１８は図示しない定着ユニットに搬送され、４色のトナーは記録紙１８に熱溶着されて固定される。このような画像形成装置においては画像の「色ずれ」又は「位置ずれ」が問題となる場合がある。この原因の１つに、中間転写ベルト９の速度変動がある。
中間転写ベルト９上の各色の画像を「色ずれ」又は「位置ずれ」が無いように形成するためには各感光体ドラム（１〜４）間の距離と各感光体ドラム（１〜４）の速度及び中間転写ベルト９の速度からタイミングを計算し、４色の転写位置を制御したり、各感光体ドラム（１〜４）の回転速度及び中間転写ベルト９の回転速度を一定速度で回転する必要がある。
中間転写ベルト９が回転している時に各色の感光体ドラムＹ１、感光体ドラムＭ２、感光体ドラムＣ３、感光体ドラムＢＫ４からは、夫々中間転写ベルト９上の同一の１次転写領域上に各トナー像が順次転写されて重ねトナー画像を形成する。各感光体ドラム間は所定間隔ずつ搬送方向にずれているために、各感光体ドラムから中間転写ベルト上の１次転写領域上に転写される各トナー像の転写タイミングにはズレがある。
この時に中間転写ベルト９の速度変動が発生した場合、その瞬間に転写されていた画像は、他の３色の画像転写されていた場所から、速度変動に起因してずれた場所に転写されることになる。
このような速度変動の結果、各トナー像は「色ずれ」又は「位置ずれ」を含んだ重ねトナー像として中間転写ベルト９上に現れ、さらに記録紙１８に画像（トナー）が転写されたときには品質の劣化した最終画像となる。 Next, the recording paper 18 is conveyed to the position of the secondary transfer roller 15 and passed between the secondary transfer counter roller 14 and the secondary transfer roller 15. The superimposed image formed on the intermediate transfer belt 9 when it passes between the secondary transfer counter roller 14 and the secondary transfer roller 15 is transferred to the recording paper 18.
Thereafter, the recording paper 18 on which an image is formed is conveyed to a fixing unit (not shown), and the four color toners are thermally welded to the recording paper 18 and fixed. In such an image forming apparatus, there may be a problem of “color shift” or “position shift” of an image. One of the causes is a fluctuation in the speed of the intermediate transfer belt 9.
In order to form an image of each color on the intermediate transfer belt 9 so that there is no “color shift” or “position shift”, the distance between the photosensitive drums (1 to 4) and the photosensitive drums (1 to 4). The timing is calculated from the speed of the intermediate transfer belt 9 and the speed of the intermediate transfer belt 9 to control the transfer positions of the four colors, and the rotation speed of each photosensitive drum (1 to 4) and the rotation speed of the intermediate transfer belt 9 are rotated at a constant speed. There is a need to.
When the intermediate transfer belt 9 is rotating, each color of the photosensitive drum Y1, the photosensitive drum M2, the photosensitive drum C3, and the photosensitive drum BK4 is placed on the same primary transfer region on the intermediate transfer belt 9. The toner images are sequentially transferred to form a superimposed toner image. Since the photosensitive drums are deviated in the transport direction by a predetermined interval, there is a deviation in the transfer timing of each toner image transferred from each photosensitive drum onto the primary transfer area on the intermediate transfer belt.
At this time, when the speed fluctuation of the intermediate transfer belt 9 occurs, the image transferred at that moment is transferred from the place where the image of the other three colors was transferred to a place shifted due to the speed fluctuation. It will be.
As a result of such speed fluctuation, each toner image appears on the intermediate transfer belt 9 as a superimposed toner image including “color shift” or “position shift”, and when the image (toner) is further transferred to the recording paper 18. The final image is degraded in quality.

図１２は「色ずれ」又は「位置ずれ」の原因である中間転写ベルトの速度変動例を示す概略図である。図１３は記録紙の先端挿入時を示す概略図である。図１２の例は、横軸で時間を、そして縦軸で中間転写ベルト９の速度Ｖｐを表している。
最初の速度Ｖｐが遅くなっている時点は、図１３に示すように、記録紙１８の先端が２次転写対向ローラ１４と２次転写ローラ１５のニップ部に搬送された瞬間である。ここでは記録紙１８によって２次転写対向ローラ１４と２次転写ローラ１５を押しのける力が発生し、中間転写ベルト９に大きな負荷トルクが瞬時に発生することになる。
この時に駆動モータ１２（図１１）には大きな力が瞬時に必要になり、この負荷トルクより駆動モータ１２の発生トルクが小さいと中間転写ベルト９の速度は低下することになる。記録紙１８の厚さがより厚くなれば、中間転写ベルト９に瞬時に大きな負荷トルクが発生することになる。
図１４は記録紙の後端排出時を示す概略図である。図１１、図１２及び図１４では、同一部分に同一符号を付して、とくに必要な部分以外の各図での説明は省略する。
図１４に示すごとく、記録紙１８の後端が２次転写対向ローラ１４と２次転写ローラ１５を抜ける時は図１３の場合とは反対に中間転写ベルト９の負荷トルクが急激に減少するために駆動モータ１２に同様に掛かっている負荷が急激に軽減することになる。
このために図１２の後半においては記録紙１８の先端がニップ部に進入する場合とは逆に中間転写ベルト９は速度が増加することになる。駆動モータ１２は通常は緩やかな負荷変動に対し、速度制御で対応するが、上記のような大きく、かつ急激な負荷変動に対して瞬時に速度制御はできない。
このために記録紙１８の先端が２次転写対向ローラ１４と２次転写ローラ１５に搬送される瞬間及び記録紙１８の後端が２次転写対向ローラ１４と２次転写ローラ１５を抜ける時のような負荷変動が発生した場合には速度制御ができない。
このため、中間転写ベルト９の速度Ｖｐが変動する原因となり、画像の各感光体ドラムからの転写時に転写位置ずれを起こすために「色ずれ」又は「位置ずれ」が発生していた。 FIG. 12 is a schematic diagram illustrating an example of the speed variation of the intermediate transfer belt that causes “color misregistration” or “position misregistration”. FIG. 13 is a schematic view showing the time when the leading end of the recording paper is inserted. In the example of FIG. 12, the horizontal axis represents time, and the vertical axis represents the speed Vp of the intermediate transfer belt 9.
As shown in FIG. 13, the time point at which the initial speed Vp is slow is the moment when the leading edge of the recording paper 18 is conveyed to the nip portion between the secondary transfer counter roller 14 and the secondary transfer roller 15. Here, a force that pushes the secondary transfer counter roller 14 and the secondary transfer roller 15 is generated by the recording paper 18, and a large load torque is instantaneously generated in the intermediate transfer belt 9.
At this time, a large force is instantaneously required for the drive motor 12 (FIG. 11), and if the generated torque of the drive motor 12 is smaller than this load torque, the speed of the intermediate transfer belt 9 is lowered. If the thickness of the recording paper 18 becomes thicker, a large load torque is instantaneously generated in the intermediate transfer belt 9.
FIG. 14 is a schematic view showing the time when the trailing edge of the recording paper is discharged. In FIG. 11, FIG. 12 and FIG. 14, the same reference numerals are given to the same parts, and the description in each figure other than the necessary parts is omitted.
As shown in FIG. 14, when the trailing edge of the recording paper 18 passes through the secondary transfer counter roller 14 and the secondary transfer roller 15, the load torque of the intermediate transfer belt 9 decreases rapidly, contrary to the case of FIG. In addition, the load applied to the drive motor 12 is abruptly reduced.
For this reason, in the latter half of FIG. 12, the speed of the intermediate transfer belt 9 increases in contrast to the case where the leading edge of the recording paper 18 enters the nip portion. The drive motor 12 normally responds to moderate load fluctuations by speed control. However, the drive motor 12 cannot instantaneously control speeds in response to such large and sudden load fluctuations.
Therefore, when the leading edge of the recording paper 18 is conveyed to the secondary transfer counter roller 14 and the secondary transfer roller 15 and when the trailing edge of the recording paper 18 passes through the secondary transfer counter roller 14 and the secondary transfer roller 15. When such load fluctuation occurs, speed control cannot be performed.
For this reason, the speed Vp of the intermediate transfer belt 9 fluctuates, and “color misregistration” or “position misregistration” occurs in order to cause a transfer misregistration when images are transferred from the respective photosensitive drums.

上記の如き中間転写ベルトの速度変動に起因した「色ずれ」又は「位置ずれ」が解消されなければ、記録紙上への画像（トナー）転写に不都合が生じ、画像品質の劣化は免れず、この対策が望まれている。
そこで、本発明の目的は、記録紙の先端が２次転写対抗ローラと２次転写ローラとのニップ部に搬送される瞬間及び記録紙の後端がニップ部から抜けるときのような急激な負荷変動を軽減し、「色ずれ」又は「位置ずれ」による画像品質の劣化を防止する画像形成装置を提供することにある。 If the “color shift” or “position shift” due to the speed fluctuation of the intermediate transfer belt as described above is not eliminated, the image (toner) transfer onto the recording paper is inconvenient, and the deterioration of the image quality cannot be avoided. Countermeasures are desired.
Accordingly, an object of the present invention is to apply a sudden load such as when the leading edge of the recording paper is conveyed to the nip portion between the secondary transfer counter roller and the secondary transfer roller and when the trailing edge of the recording paper comes out of the nip portion. An object of the present invention is to provide an image forming apparatus that reduces fluctuations and prevents deterioration of image quality due to “color shift” or “position shift”.

上記の課題を解決するために、請求項１に記載の発明は、像担持体と、該像担持体上から１次転写された画像を受ける中間転写ベルトと、該中間転写ベルト上の１次転写画像を記録紙に２次転写させるために前記中間転写ベルトに前記記録紙を圧接させるための２次転写ローラと、前記記録紙を前記２次転写ローラに供給するレジストローラ対と、備えた画像形成装置において、前記記録紙の搬送経路中に設けた前記記録紙の厚さを検出する記録紙厚さ検出機構と、前記２次転写ローラを開閉動作させて前記中間転写ベルト面との間隔を増減変更させる駆動源と、これらを制御する制御手段と、を備え、前記制御手段は、前記記録紙厚さ検出機構により検出された前記記録紙の厚さの変化に応じて前記駆動源を制御して前記２次転写ローラを開閉動作させて前記中間転写ベルト面との間隔を増減変更することを特徴とする。
請求項２の発明は、請求項１において、前記記録紙厚さ検出機構は、ニップ部を通過する前記記録紙の厚さに応じて動作する可動レジストローラを備えた前記レジストローラ対と、該可動レジストローラの動作に連動して作動する記録紙厚さ検出センサと、前記中間転写ベルトと２次転写ローラとのニップ部を通過する前記記録紙の厚さに応じて２次転写ローラを開閉動作するための駆動源と、制御手段と、を備え、前記制御手段は、前記記録紙の厚みに応じて２次転写ローラを開閉するように前記駆動源を動作させることを特徴とする。
請求項３の発明は、請求項１、又は２に記載の前記記録紙の有無を検出する記録紙検出センサを設け、前記制御手段はこの記録紙の検出結果によって前記２次転写ローラの開閉タイミングを制御することを特徴とする。 In order to solve the above-described problems, the invention described in claim 1 includes an image carrier, an intermediate transfer belt that receives an image primarily transferred from the image carrier, and a primary on the intermediate transfer belt. A secondary transfer roller for pressing the recording paper against the intermediate transfer belt for secondary transfer of the transfer image onto the recording paper; and a registration roller pair for supplying the recording paper to the secondary transfer roller. In the image forming apparatus, a gap between the recording sheet thickness detection mechanism that detects the thickness of the recording sheet provided in the recording sheet conveyance path and the intermediate transfer belt surface by opening and closing the secondary transfer roller. And a control means for controlling the drive source, and the control means controls the drive source according to a change in the thickness of the recording paper detected by the recording paper thickness detection mechanism. Control the secondary transfer roller Is closing operation, characterized in that increasing or decreasing change the interval between the intermediate transfer belt surface.
According to a second aspect of the present invention, in the first aspect, the recording paper thickness detection mechanism includes the registration roller pair including a movable registration roller that operates according to the thickness of the recording paper that passes through the nip portion, A recording sheet thickness detection sensor that operates in conjunction with the operation of the movable registration roller, and opens and closes the secondary transfer roller according to the thickness of the recording sheet that passes through the nip portion between the intermediate transfer belt and the secondary transfer roller. A drive source for operation and a control unit are provided, and the control unit operates the drive source to open and close the secondary transfer roller according to the thickness of the recording paper.
According to a third aspect of the present invention, there is provided a recording paper detection sensor for detecting the presence or absence of the recording paper according to the first or second aspect, and the control means determines the opening / closing timing of the secondary transfer roller based on the detection result of the recording paper. It is characterized by controlling.

請求項４の発明は、請求項３において、前記制御手段は、前記記録紙検出センサが前記記録紙の先端を検出した時から、該記録紙先端が前記記録紙検出センサと２次転写ローラとの間を通過するのに要する時間の経過を待って前記２次転写ローラの開閉を行うことを特徴とする。
請求項５の発明は、請求項３において、前記制御手段は、前記記録紙検出センサが前記記録紙の後端を検出した時から、該記録紙後端が前記記録紙検出センサと前記２次転写ローラとの間を通過するのに要する時間の経過を待って次の２次転写ローラの開閉を行うことを特徴とする。
請求項６の発明は、請求項１、又は２において、前記レジストローラと前記２次転写ローラ間に、記録紙厚さ検出ローラと、この記録紙厚さ検出ローラに同期して動く記録紙厚さ検出センサを設け、さらに、前記２次転写ローラには開閉のための駆動源を設け、前記制御手段は、記録紙の厚みに応じて前記駆動源を制御することにより前記２次転写ローラを開閉することを特徴とする。
請求項７の発明は、請求項６において、前記記録紙の有無を検出する記録紙検出センサを設け、前記制御手段は、この記録紙の検出結果によって前記２次転写ローラの開閉タイミングを制御することを特徴とする。
請求項８の発明は、請求項７において、前記制御手段は、前記記録紙検出センサが前記記録紙の先端を検出した時から、該記録紙先端が前記記録紙検出センサと２次転写ローラとの間を通過するのに要する時間の経過を待って前記２次転写ローラの開閉動作を行うことを特徴とする。
請求項９の発明は、請求項７において、前記制御手段は、前記記録紙検出センサ位置が前記記録紙の後端を検出した時から、該記録紙後端が前記記録紙検出センサと前記２次転写ローラとの間を通過するのに要する時間の経過をまって、次の２次転写ローラの開閉を行うことを特徴とする。
請求項１０の発明は、請求項６において、前記記録紙厚さ検出ローラは開閉可能な駆動源を備えていることを特徴とする。
請求項１１の発明は、請求項１乃至１０において、前記記録紙厚さ検出センサは前記駆動源である２次転写ローラ開閉モータのホームポジション位置を兼ねることを特徴とする。 According to a fourth aspect of the present invention, in the third aspect of the present invention, since the recording means detects the leading edge of the recording paper from the time when the recording paper detection sensor detects the leading edge of the recording paper, the control sheet detects that the recording paper detection sensor, the secondary transfer roller, The secondary transfer roller is opened and closed after a lapse of time required to pass between the two.
According to a fifth aspect of the present invention, in the third aspect, the control means is configured such that the recording paper detection sensor detects the trailing edge of the recording paper from the time when the recording paper detection sensor detects the trailing edge of the recording paper. The secondary transfer roller is opened / closed after waiting for the time required to pass between the transfer rollers.
According to a sixth aspect of the present invention, there is provided a recording paper thickness detection roller between the registration roller and the secondary transfer roller, and a recording paper thickness that moves in synchronization with the recording paper thickness detection roller. And a drive source for opening and closing the secondary transfer roller, and the control means controls the drive source according to the thickness of the recording paper to control the secondary transfer roller. It is characterized by opening and closing.
According to a seventh aspect of the present invention, in the sixth aspect, a recording paper detection sensor for detecting the presence or absence of the recording paper is provided, and the control means controls the opening / closing timing of the secondary transfer roller based on the detection result of the recording paper. It is characterized by that.
According to an eighth aspect of the present invention, in the seventh aspect of the invention, the controller is configured such that when the recording paper detection sensor detects the leading edge of the recording paper, the leading edge of the recording paper is the recording paper detection sensor, the secondary transfer roller, and the like. The secondary transfer roller is opened / closed after a lapse of time required to pass between the two.
According to a ninth aspect of the present invention, in the seventh aspect of the invention, the control means detects the recording paper detection sensor and the 2 after the recording paper detection sensor position has detected the trailing edge of the recording paper. The secondary transfer roller is opened and closed after a lapse of time required to pass between the secondary transfer roller and the secondary transfer roller.
According to a tenth aspect of the present invention, in the sixth aspect, the recording paper thickness detecting roller includes a drive source that can be opened and closed.
According to an eleventh aspect of the present invention, in the first to tenth aspects, the recording paper thickness detection sensor also serves as a home position of a secondary transfer roller opening / closing motor as the driving source.

本発明によれば、２次転写ローラを記録紙の厚さ応じて移動させることにより記録紙厚さによる中間転写ベルトの負荷トルクを軽減させることができ、これによって「色ずれ」又は「位置ずれ」の原因である中間転写ベルトの速度変動を押さえることが可能となり、「色ずれ」又は「位置ずれ」の無い高品質の画像を提供する。 According to the present invention, the load torque of the intermediate transfer belt due to the thickness of the recording paper can be reduced by moving the secondary transfer roller according to the thickness of the recording paper. It is possible to suppress fluctuations in the speed of the intermediate transfer belt, which is a cause of “,” and provide a high-quality image free from “color shift” or “position shift”.

以下、図面を参照して、本発明の実施形態を詳細に説明する。図１は本発明による記録紙厚さ検出機構の第１の実施の形態を示す概略図である。図２は図１の記録紙厚さ検出機構を作動状態において示す概略図である。なお、図１１を併せて参照しつつ説明する。
本発明は、図１１に示した像担持体（感光体１〜４）と、各像担持体上から順次１次転写された画像を受ける中間転写ベルト９と、中間転写ベルト上の１次転写画像を記録紙に２次転写させるために中間転写ベルトに前記記録紙を圧接させるための２次転写ローラ１５と、記録紙を２次転写ローラ１５に供給するレジストローラ対１６と、備えた画像形成装置に適用される記録紙厚さ検出機構に関するものである。
本発明の特徴的な構成は、記録紙の搬送経路中に設けた記録紙の厚さを検出する記録紙厚さ検出機構１９〜２５ａ、２５ｂと、２次転写ローラ１５を開閉動作させて中間転写ベルト面との間隔を増減変更させる駆動源２９と、これらを制御する制御手段２７と、を備え、制御手段が、記録紙厚さ検出機構により検出された記録紙の厚さの変化に応じて駆動源２９を制御して２次転写ローラ１５を開閉動作させて中間転写ベルト面との間隔を増減変更するようにした点にある。
記録紙１８は、図示しない給紙部から延びる搬送経路を介して、図の右方から左方へ搬送される。記録紙１８の先端は可動レジストローラ１６ａと固定レジストローラ１６ｂを含むレジストローラ１６対の間（ニップ部）に搬送される。この時、可動レジストローラ１６ａは記録紙１８の厚さに応じて図の点線のように上下方向（図２の位置）に移動する。
上下方向へ移動可能な可動レジストローラ１６ａの適所（回転中心部）には記録紙厚さ検出レバー１９の一端（Ｑ点）が連結され、検出レバー１９はその中央部の支点Ｐで回動可能に構成されている。この記録紙厚さ検出レバー１９の他端（Ｒ点）には透過型光センサを使用した記録紙厚さ検出センサ２０が図示しない取り付け方法によって取り付けられており、記録紙厚さ検出レバー１９と一緒に支点Ｐを中心として上下方向へ回転可能となっている。
フォトインタラプタから成る記録紙厚さ検出センサ２０は、上面、或いは側面に設けた凹所の２つの内壁に夫々図示しない発光部、及び受光部を対向して備えており、後述する記録紙厚さ検出センサシャッタ２２がこの凹所内に出入りすることによってセンサ２０はＯＮ、ＯＦＦする。搬送された記録紙１８が可動レジストローラ１６ａを上方へ押し上げるに従って、点線で示す２次転写ローラ１５と同様に、下方に下がり、後述する「明」の状態となる。
これにより記録紙厚さ検出センサシャッタ２２は記録紙厚さ検出センサ２０の上面に設けた凹所の内壁に対向配置された発光部及び受光部から退避し、記録紙厚さ検出センサ２０は記録紙１８の進入、すなわち、その厚さを検出する。
このために、記録紙１８が可動レジストローラ１６ａと固定レジストローラ１６ｂとのニップ部に搬送されて可動レジストローラ１６ａが上昇すると、記録紙厚さ検出センサ２０は記録紙１８の厚さに応じて下方に移動できる。 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view showing a first embodiment of a recording paper thickness detection mechanism according to the present invention. FIG. 2 is a schematic view showing the recording paper thickness detection mechanism of FIG. 1 in an operating state. The description will be made with reference to FIG.
The present invention includes an image carrier (photosensitive members 1 to 4) shown in FIG. 11, an intermediate transfer belt 9 that receives images sequentially transferred from the respective image carriers, and a primary transfer on the intermediate transfer belt. An image provided with a secondary transfer roller 15 for pressing the recording paper against an intermediate transfer belt for secondary transfer of the image onto the recording paper, and a registration roller pair 16 for supplying the recording paper to the secondary transfer roller 15 The present invention relates to a recording sheet thickness detection mechanism applied to a forming apparatus.
A characteristic configuration of the present invention is that the recording sheet thickness detection mechanisms 19 to 25a and 25b for detecting the thickness of the recording sheet provided in the recording sheet conveyance path and the secondary transfer roller 15 are opened and closed to perform an intermediate operation. A drive source 29 that increases or decreases the distance from the transfer belt surface and a control unit 27 that controls the drive source 29 are provided. The control unit responds to a change in the thickness of the recording paper detected by the recording paper thickness detection mechanism. Thus, the drive source 29 is controlled to open and close the secondary transfer roller 15 to increase or decrease the distance from the intermediate transfer belt surface.
The recording paper 18 is conveyed from the right side to the left side of the drawing via a conveyance path extending from a paper feeding unit (not shown). The leading edge of the recording paper 18 is conveyed between a pair of registration rollers 16 (a nip portion) including a movable registration roller 16a and a fixed registration roller 16b. At this time, the movable registration roller 16a moves in the vertical direction (position in FIG. 2) as indicated by a dotted line in accordance with the thickness of the recording paper 18.
One end (point Q) of the recording paper thickness detection lever 19 is connected to an appropriate position (rotation center) of the movable registration roller 16a movable in the vertical direction, and the detection lever 19 can be rotated at a fulcrum P at the center thereof. It is configured. A recording paper thickness detection sensor 20 using a transmissive optical sensor is attached to the other end (point R) of the recording paper thickness detection lever 19 by an attachment method (not shown). Together, it can rotate up and down around the fulcrum P.
The recording paper thickness detection sensor 20 made of a photo interrupter has a light emitting portion and a light receiving portion (not shown) facing each other on two inner walls of a recess provided on the upper surface or the side surface. The sensor 20 is turned on and off when the detection sensor shutter 22 enters and exits the recess. As the conveyed recording paper 18 pushes up the movable registration roller 16a upward, the recording paper 18 descends downward as in the case of the secondary transfer roller 15 indicated by the dotted line, and enters a “bright” state described later.
As a result, the recording paper thickness detection sensor shutter 22 is retracted from the light emitting portion and the light receiving portion disposed opposite to the inner wall of the recess provided on the upper surface of the recording paper thickness detection sensor 20, and the recording paper thickness detection sensor 20 performs recording. The entrance of the paper 18, that is, its thickness is detected.
Therefore, when the recording sheet 18 is conveyed to the nip portion between the movable registration roller 16a and the fixed registration roller 16b and the movable registration roller 16a is raised, the recording sheet thickness detection sensor 20 corresponds to the thickness of the recording sheet 18. Can move downward.

また、支点Ｐ点と可動レジスローラ１６ａのＱ点と反対側の記録紙厚さ検出センサ２０のＲ点までの距離は、
ＰＱ＝ＰＲ、又はＰＱ＞ＰＲ
の関係で構成される。
このように構成することによって、記録紙１８のニップ部通過時には、記録紙１８の厚さと同等の距離か、それ以下の距離だけ記録紙厚さ検出センサ２０が下方に移動することになる。さらに、支点Ｐ点には２次転写ローラレバー２１の一端を固定してあり、この２次転写ローラレバー２１は、記録紙厚さ検出レバー１９とは独立別個に、支点Ｐを中心として上下方向へ回動できるように構成されている。
この場合、記録紙厚さ検出センサ２０は搬送されている記録紙１８の厚さに応じて上昇する可動レジスローラ１６ａに対応する記録紙厚さ検出レバー１９の動きに応じて下方に移動する。この際、２次転写ローラレバー２１は、詳しい説明はしないが、例えば、引張りばねで図１の位置を維持しているので、偏心カム２３が作動しない限り図１の位置を維持する。
２次転写ローラレバー２１の適所には光センサである記録紙厚さ検出センサ２０のシャッタの役割を果たす記録紙厚さ検出センサシャッタ２２が接続され、かつ、２次転写ローラレバー２１は図示していない適宜な連結方法によって２次転写ローラ１５と連結されており、２次転写ローラレバー２１の上下動作に連動して２次転写ローラ１５は図１の実線位置と点線との間を上下に移動できる（図２の位置）。
記録紙厚さ検出センサ２０は例えば透過型光センサにより構成し、２次転写ローラレバー２１に取り付けられた記録紙厚さ検出センサシャッタ２２によって記録紙厚さ検出センサ２０からの検出光のオン（明）、オフ（暗）を行う。
上述したように、フォトインタラプタからなる記録紙厚さ検出センサ２０は図１及び図２に示してないが、上面側、或いは側面側に凹所を有したコの字状に配置されたベースの対向する内壁上に夫々発光部と受光部を配置した構成を有し、発光部と受光部間に記録紙厚さ検出センサシャッタ２２が出入することによって発光部からの光を透過又は遮断する。すなわち、記録紙厚さ検出センサシャッタ２２は記録紙厚さ検出センサ２０のシャッタの役割を果たす。
２次転写ローラレバー２１の、さらに左方向に延びる端部は、支点Ｍで回転する偏芯カム２３の外周面と当接可能な位置に設けてあり、結果として、２次転写ローラレバー２１は偏芯カム２３の回転に応じて上下に駆動される。この偏芯カム２３は図示していないがステッピングモータやＤＣモータ等により駆動される。 Further, the distance from the fulcrum point P to the point R of the recording paper thickness detection sensor 20 on the side opposite to the point Q of the movable resist roller 16a is:
PQ = PR or PQ> PR
It consists of the relationship.
With this configuration, when the recording paper 18 passes through the nip portion, the recording paper thickness detection sensor 20 moves downward by a distance equal to or less than the thickness of the recording paper 18. Further, one end of the secondary transfer roller lever 21 is fixed to the fulcrum P point, and this secondary transfer roller lever 21 is vertically separated from the recording paper thickness detection lever 19 in the vertical direction. It is comprised so that it can rotate to.
In this case, the recording sheet thickness detection sensor 20 moves downward according to the movement of the recording sheet thickness detection lever 19 corresponding to the movable resist roller 16a that rises according to the thickness of the recording sheet 18 being conveyed. At this time, although not described in detail, the secondary transfer roller lever 21 maintains the position of FIG. 1 as long as the eccentric cam 23 does not operate because the position of FIG.
A recording paper thickness detection sensor shutter 22 serving as a shutter of the recording paper thickness detection sensor 20 which is an optical sensor is connected to an appropriate position of the secondary transfer roller lever 21, and the secondary transfer roller lever 21 is illustrated. The secondary transfer roller 15 is connected to the secondary transfer roller 15 by an appropriate connection method that is not connected. The secondary transfer roller 15 moves vertically between the solid line position and the dotted line in FIG. It can move (position in FIG. 2).
The recording paper thickness detection sensor 20 is constituted by, for example, a transmission type optical sensor, and the detection light from the recording paper thickness detection sensor 20 is turned on by the recording paper thickness detection sensor shutter 22 attached to the secondary transfer roller lever 21 ( (Light), Off (dark).
As described above, the recording paper thickness detection sensor 20 made of a photo interrupter is not shown in FIGS. 1 and 2, but the base of the base disposed in a U shape having a recess on the upper surface side or the side surface side. It has a configuration in which a light emitting part and a light receiving part are arranged on the opposing inner walls, respectively, and the light from the light emitting part is transmitted or blocked by the recording paper thickness detection sensor shutter 22 entering and exiting between the light emitting part and the light receiving part. That is, the recording paper thickness detection sensor shutter 22 serves as a shutter for the recording paper thickness detection sensor 20.
The end of the secondary transfer roller lever 21 that extends further to the left is provided at a position where it can contact the outer peripheral surface of the eccentric cam 23 that rotates at the fulcrum M. As a result, the secondary transfer roller lever 21 It is driven up and down according to the rotation of the eccentric cam 23. Although not shown, the eccentric cam 23 is driven by a stepping motor, a DC motor or the like.

図３は本発明の画像形成装置における制御ブロック図である。図３の制御ブロック図では、演算装置（制御手段）２７にモータ駆動制御装置２８を介して２次転写ローラ開閉モータ２９が接続される。この２次転写ローラ開閉モータ２９は図１及び図２の偏芯カム２３を通して２次転写ローラレバー２１を駆動する。
さらに、演算装置２７には記録紙１８の厚さに応じて移動する記録紙厚さ検出センサ２０と記録紙１８の有無を検出する記録紙検出センサ２４が接続されている。
本発明の第１の実施の形態に係る記録紙厚さ検出機構は、記録紙厚さ検出レバー１９、記録紙厚さ検出センサ２０、２次転写ローラレバー２１、記録紙厚さ検出センサシャッタ２２、偏心カム２３、記録紙厚さ検出センサ２４、２次転写ローラ開閉モータ２９などから構成されている。 FIG. 3 is a control block diagram in the image forming apparatus of the present invention. In the control block diagram of FIG. 3, a secondary transfer roller opening / closing motor 29 is connected to an arithmetic device (control means) 27 via a motor drive control device 28. The secondary transfer roller opening / closing motor 29 drives the secondary transfer roller lever 21 through the eccentric cam 23 shown in FIGS.
Further, a recording paper thickness detection sensor 20 that moves according to the thickness of the recording paper 18 and a recording paper detection sensor 24 that detects the presence or absence of the recording paper 18 are connected to the arithmetic unit 27.
The recording sheet thickness detection mechanism according to the first embodiment of the present invention includes a recording sheet thickness detection lever 19, a recording sheet thickness detection sensor 20, a secondary transfer roller lever 21, and a recording sheet thickness detection sensor shutter 22. , An eccentric cam 23, a recording paper thickness detection sensor 24, a secondary transfer roller opening / closing motor 29, and the like.

図４は図１及び図２の本発明の第１の実施の形態の動作を説明する制御タイミングチャートである。図５は本発明の第１の実施の形態の動作を説明するフローチャートである。図６は図５の丸付きの２に続くフローチャートである。
図１及び図２の第１の実施の形態の動作と図４の制御タイミングチャートを図５及び図６のフローチャートを用いて説明する。記録紙１８が搬送を開始される（Ｓ１）と、レジストローラ１６対の可動レジストローラ１６ａと固定レジストローラ１６ｂのニップ部に導かれる。
記録紙１８の先端が可動レジストローラ１６ａと固定レジストローラ１６ｂとのニップ部に挿入されレジストコントローラにより記録紙ありと判定されると（Ｓ２）、可動レジストローラ１６ａは記録紙１８の厚さに応じて上方に移動する。
この時、Ｑ点で可動レジストローラ１６ａに結合された記録紙厚さ検出レバー１９も記録紙１８の厚さに応じて上方に移動するため、支点Ｐを中心として記録紙厚さ検出レバー１９が全体として反時計方向に回転する。このため、記録紙厚さ検出レバー１９の反対方向に取り付けられたＲ点に設けられた記録紙厚さ検出センサ２０は下方に移動する（Ｓ３）。
次に、レジストローラ対６のニップ部の下流側に配置した記録紙検出センサ２４にて記録紙１８の進入の有無を検出し（Ｓ４）、記録紙１８の先端有りを検出すると（Ｓ５）、演算装置２７（図３）は、記録紙検出センサ２４（図３）の位置Ｔ点（図１）と２次転写対向ローラ１４の中心位置であるＳ点（図１）間距離と記録紙１８の搬送速度から２次転写対向ローラ１４のＳ点に記録紙１８の先端が到達するまでの時間ｔ（ｔｓ）を計算する。この時間から２次転写ローラ開閉モータ２９を駆動開始する時間ｔ（ｒｏ）（動作フローチャートではＣ＝ｎ）を設定する（Ｓ６）。
時間カウントを開始し（Ｓ７）、このｔ（ｒｏ）時間が経過（Ｃ＝０）すると（Ｓ８）、２次転写ローラ開閉モータ２９を駆動する。この時、２次転写ローラ開閉モータ２９の回転方向は記録紙厚さ検出センサ２０の状態を見て決定する（Ｓ９）。 FIG. 4 is a control timing chart for explaining the operation of the first embodiment of the present invention shown in FIGS. FIG. 5 is a flowchart for explaining the operation of the first embodiment of the present invention. FIG. 6 is a flowchart following the circled 2 in FIG.
The operation of the first embodiment of FIGS. 1 and 2 and the control timing chart of FIG. 4 will be described with reference to the flowcharts of FIGS. When conveyance of the recording paper 18 is started (S1), the recording paper 18 is guided to a nip portion between the movable registration roller 16a of the registration roller 16 pair and the fixed registration roller 16b.
When the leading edge of the recording paper 18 is inserted into the nip portion between the movable registration roller 16a and the fixed registration roller 16b and the registration controller determines that there is recording paper (S2), the movable registration roller 16a corresponds to the thickness of the recording paper 18. Move up.
At this time, since the recording paper thickness detection lever 19 coupled to the movable registration roller 16a at the point Q also moves upward according to the thickness of the recording paper 18, the recording paper thickness detection lever 19 is centered on the fulcrum P. As a whole, it rotates counterclockwise. For this reason, the recording paper thickness detection sensor 20 provided at the point R attached in the opposite direction of the recording paper thickness detection lever 19 moves downward (S3).
Next, the recording paper detection sensor 24 disposed downstream of the nip portion of the registration roller pair 6 detects the presence or absence of the recording paper 18 (S4). When the presence of the leading edge of the recording paper 18 is detected (S5), The computing device 27 (FIG. 3) determines the distance between the position T (FIG. 1) of the recording paper detection sensor 24 (FIG. 3) and the point S (FIG. 1) which is the center position of the secondary transfer counter roller 14 and the recording paper 18. The time t (ts) until the leading edge of the recording paper 18 reaches the point S of the secondary transfer counter roller 14 from the transport speed of 2 is calculated. From this time, a time t (ro) for starting driving the secondary transfer roller opening / closing motor 29 (C = n in the operation flowchart) is set (S6).
Time counting is started (S7), and when this t (ro) time has elapsed (C = 0) (S8), the secondary transfer roller opening / closing motor 29 is driven. At this time, the rotation direction of the secondary transfer roller opening / closing motor 29 is determined by looking at the state of the recording paper thickness detection sensor 20 (S9).

記録紙厚さ検出センサ２０が「明」であるかどうか判断し（Ｓ１０）、「明」の時は２次転写ローラ開閉モータ２９を反時計方向に駆動（オン）する（Ｓ１１）。このため、図１の状態にある偏心カム２３は反時計方向に回転し、図２のように２次転写ローラレバー２１を下方へ移動して２次転写ローラ１５を下方へ移動する。さらに、記録紙厚さ検出センサシャッタ２２が下方へ移動し（Ｓ１２）、記録紙厚さ検出センサ２０の発光部と受光部との間に入り、記録紙厚さ検出センサ２０は「暗」となる。
次に、記録紙厚さ検出センサ２０が「暗」であるかどうか判断し（Ｓ１３）、「暗」であるならば、２次転写ローラ開閉モータ２９の駆動を停止（オフ）する（Ｓ１４）。
ステップ（Ｓ１０）において記録紙厚さ検出センサ２０が「暗」の時は一度「明」するために２次転写ローラ開閉モータ２９を反時計方向（ＣＣＷ方向）に駆動する（Ｓ１５）。
次いで、図２の状態にあるときに、２次転写ローラ開閉モータ２９が時計方向に回動して偏心カム２３を時計方向に回転し、２次転写ローラレバー２１を上方へ移動し、２次転写ローラ１５を上方へ移動する。さらに、２次転写ローラレバー２１と一体の記録紙厚さ検出センサシャッタ２２も上方へ移動する（Ｓ１６）。
次に、記録紙厚さ検出センサ２０が「明」であるかどうか判断し（Ｓ１７）、「明」であるならば、２次転写ローラ開閉モータ２９の駆動を停止（オフ）する（Ｓ１８）。
これ以降は上記に記載した通り、記録紙厚さ検出センサ２０が「暗」の時の動作と同じ動作となる。すなわち、ステップＳ１０で「暗」の時は２次転写ローラ開閉モータ２９を時計方向（ＣＷ方向）に駆動し、記録紙厚さ検出センサ２０を「明」にして（Ｓ１３）、２次転写ローラ開閉モータ２９の駆動を停止する。次いで、記録紙先端が２次転写ローラ１５に到達したかどうかを判断する（Ｓ１９）。 It is determined whether or not the recording paper thickness detection sensor 20 is “bright” (S10). If it is “bright”, the secondary transfer roller opening / closing motor 29 is driven (turned on) counterclockwise (S11). For this reason, the eccentric cam 23 in the state of FIG. 1 rotates counterclockwise, and the secondary transfer roller lever 21 is moved downward and the secondary transfer roller 15 is moved downward as shown in FIG. Further, the recording paper thickness detection sensor shutter 22 moves downward (S12), enters between the light emitting portion and the light receiving portion of the recording paper thickness detection sensor 20, and the recording paper thickness detection sensor 20 is “dark”. Become.
Next, it is determined whether or not the recording paper thickness detection sensor 20 is “dark” (S13). If it is “dark”, the drive of the secondary transfer roller opening / closing motor 29 is stopped (off) (S14). .
In step (S10), when the recording paper thickness detection sensor 20 is "dark", the secondary transfer roller opening / closing motor 29 is driven counterclockwise (CCW direction) to "light" once (S15).
Next, when in the state of FIG. 2, the secondary transfer roller opening / closing motor 29 rotates clockwise to rotate the eccentric cam 23 clockwise, and the secondary transfer roller lever 21 moves upward, The transfer roller 15 is moved upward. Further, the recording paper thickness detection sensor shutter 22 integrated with the secondary transfer roller lever 21 also moves upward (S16).
Next, it is determined whether or not the recording sheet thickness detection sensor 20 is “bright” (S17). If it is “bright”, the drive of the secondary transfer roller opening / closing motor 29 is stopped (off) (S18). .
Thereafter, as described above, the operation is the same as the operation when the recording paper thickness detection sensor 20 is “dark”. That is, when “dark” in step S10, the secondary transfer roller opening / closing motor 29 is driven clockwise (CW direction), and the recording paper thickness detection sensor 20 is set to “bright” (S13). The drive of the opening / closing motor 29 is stopped. Next, it is determined whether the leading edge of the recording paper has reached the secondary transfer roller 15 (S19).

記録紙先端が２次転写ローラ１５に到達したならば、記録紙１８に画像の転写を開始する（Ｓ２０）。２次転写ローラ１５と中間転写ベルト９の間で記録紙１８に画像が転写される（Ｓ２１）。
次いで、レジストローラ１６対を記録紙１８の後端が通過したかどうかを確認し（Ｓ２２）、通過したならば、可動レジストローラ１６ａを下方へ移動し、これと共に記録紙厚さ検出レバー１９を下方へ移動し（Ｑ点）、さらに、記録紙厚さ検出レバー１９の他端（Ｒ点）にある記録紙厚さ検出センサ２０を上方へ移動する（Ｓ２３）。
また、２次転写ローラ開閉モータ２９は、常に、記録紙厚さ検出センサ２０が「暗」から「明」になった時に停止する。この状態では、図２に示すごとく、２次転写対向ローラ１４と２次転写ローラ１５の間は記録紙１８の厚さ分に近い隙間が開くことになる。
１）ＰＱ＝ＰＲの時、記録紙１８の厚さ＝２次転写対向ローラ２４と２次転写ローラ１５の間隙
２）ＰＱ＞ＰＲの時、記録紙１８の厚さ＞２次転写対向ローラ２４と２次転写ローラ１５の間隙
となる。
このように記録紙１８の厚さに応じて２次転写対向ローラ２４と２次転写ローラ１５との間に間隙ができる。このため、記録紙１８にて２次転写対向ローラ１４と２次転写ローラ１５を押しのける量が少なくなくなる。
従って、中間転写ベルト９にかかる負荷が小さくなり、駆動モータ１２の必要トルクが少なくてすむことになる。また、本発明は記録紙１８の厚さが変わっても自動的に２次転写対向ローラ１４と２次転写ローラ１５の間隔を最適に制御することができる。
この間隔は支点Ｐ点と可動レジストローラ１６ａのＱ点と反対側の記録紙厚さ検出センサ２０のＲ点までの距離との比で決定され、記録紙１８が無い状態で２次転写対向ローラ１４と２次転写ローラ１５の間に隙間を生じさせないようにするために、
ＰＱ＝ＰＲ、又はＰＱ＞ＰＲ
が望ましい。 When the leading edge of the recording paper reaches the secondary transfer roller 15, image transfer to the recording paper 18 is started (S20). An image is transferred to the recording paper 18 between the secondary transfer roller 15 and the intermediate transfer belt 9 (S21).
Next, it is confirmed whether or not the trailing edge of the recording paper 18 has passed through the pair of registration rollers 16 (S22). If the recording paper 18 has passed, the movable registration roller 16a is moved downward, and the recording paper thickness detection lever 19 is moved along with this. The recording sheet thickness detection sensor 20 at the other end (point R) of the recording sheet thickness detection lever 19 is moved upward (S23).
The secondary transfer roller opening / closing motor 29 always stops when the recording paper thickness detection sensor 20 changes from “dark” to “light”. In this state, as shown in FIG. 2, a gap close to the thickness of the recording paper 18 is opened between the secondary transfer counter roller 14 and the secondary transfer roller 15.
1) When PQ = PR, the thickness of the recording paper 18 = the gap between the secondary transfer counter roller 24 and the secondary transfer roller 15 2) When PQ> PR, the thickness of the recording paper 18> the secondary transfer counter roller 24 And the secondary transfer roller 15.
In this way, a gap is formed between the secondary transfer counter roller 24 and the secondary transfer roller 15 according to the thickness of the recording paper 18. For this reason, the amount by which the secondary transfer counter roller 14 and the secondary transfer roller 15 are pushed by the recording paper 18 is not small.
Therefore, the load applied to the intermediate transfer belt 9 is reduced, and the required torque of the drive motor 12 can be reduced. Further, the present invention can automatically control the interval between the secondary transfer counter roller 14 and the secondary transfer roller 15 automatically even if the thickness of the recording paper 18 changes.
This interval is determined by the ratio between the fulcrum point P and the distance to the point R of the recording paper thickness detection sensor 20 opposite to the point Q of the movable registration roller 16a. The secondary transfer counter roller without the recording paper 18 is present. 14 and the secondary transfer roller 15 in order not to generate a gap.
PQ = PR or PQ> PR
Is desirable.

次に、記録紙検出センサ２４で記録紙１８の後端を検出すると（Ｓ２４）、先端検出の時と同じように演算装置２７で記録紙検出センサ２４のＴ点から２次転写対向ローラ１４までの距離と記録紙１８の速度からｔ（ｔｓ）時間を保証できるｔ（ｔｓ）以上の時間Ｃ＝ｍをセットし（Ｓ２５）、この時間をカウントする（Ｓ２６）。
セットした時間が経過する（Ｓ２７）まで２次転写ローラ開閉モータ２９をそのまま固定することにより２次転写対向ローラ１４と２次転写ローラ１５の間は記録紙１８の厚さ分に近い隙間に保たれ、記録紙１８の後端まで正常に転写されることになる。次に、２次転写ローラ１５を記録紙後端が通過したかどうかを判断し（Ｓ２８）、通過したならば、記録紙１８への画像の転写は完了する。
次の記録紙１８が挿入されると、同様に上記の動作が繰り返されることにより記録紙１８の厚さが変化しても２次転写対向ローラ１４と２次転写ローラ１５の間の隙間は最適な間隔に制御できる。
このように、記録紙１８が２次転写対向ローラ１４と２次転写ローラ１５の間を通る時に、記録紙の厚さに違いがあっても、各ローラ１４、１５を押しのける時の負荷トルクが軽減されるために中間転写ベルト９を駆動している駆動モータ１２の必要トルクが小さくて済み、低コストの駆動モータで高品質の画像形成が可能になる。
上述のごとく、第１の実施の形態では、通常の構成品であるレジストローラ対１６に記録紙１８の厚さを検知する構成品を設け、２次転写ローラ１５の上下動で記録紙１８の厚さを判断することにより、低コストで記録紙１８の厚さを割り出すことができるようになる。
また、記録紙１８の有無検出手段２４をレジストローラ１６対と２次転写ローラ１５間に配置することによって、記録紙１８の先端又は後端又は記録紙の長さを識別できるようになり、２次転写ローラ１５の移動タイミングをきめ細かに制御することが可能になり、記録紙１８の長さに対し適切な画像転写を行うことが可能になるので、「色ずれ」又は「位置ずれ」の無い高品質の画像を提供できる。 Next, when the trailing edge of the recording paper 18 is detected by the recording paper detection sensor 24 (S24), the arithmetic unit 27 performs the operation from the point T of the recording paper detection sensor 24 to the secondary transfer counter roller 14 in the same manner as when detecting the leading edge. Is set to a time C = m that is equal to or longer than t (ts) that can guarantee the time t (ts) based on the distance and the speed of the recording paper 18 (S25), and this time is counted (S26).
By fixing the secondary transfer roller opening / closing motor 29 as it is until the set time elapses (S27), the gap between the secondary transfer counter roller 14 and the secondary transfer roller 15 is kept close to the thickness of the recording paper 18. As a result, the image is normally transferred up to the rear end of the recording paper 18. Next, it is determined whether the trailing edge of the recording paper has passed through the secondary transfer roller 15 (S28). If it has passed, the transfer of the image onto the recording paper 18 is completed.
When the next recording sheet 18 is inserted, the gap between the secondary transfer counter roller 14 and the secondary transfer roller 15 is optimal even if the thickness of the recording sheet 18 is changed by repeating the above operation. It is possible to control the interval.
As described above, when the recording paper 18 passes between the secondary transfer counter roller 14 and the secondary transfer roller 15, even if there is a difference in the thickness of the recording paper, the load torque when pushing the rollers 14, 15 is increased. In order to be reduced, the required torque of the drive motor 12 driving the intermediate transfer belt 9 can be reduced, and high-quality image formation can be achieved with a low-cost drive motor.
As described above, in the first embodiment, a component for detecting the thickness of the recording paper 18 is provided on the registration roller pair 16 which is a normal component, and the recording paper 18 is moved by the vertical movement of the secondary transfer roller 15. By determining the thickness, the thickness of the recording paper 18 can be determined at a low cost.
Further, by arranging the recording sheet 18 presence / absence detecting means 24 between the pair of registration rollers 16 and the secondary transfer roller 15, the leading end or the trailing end of the recording sheet 18 or the length of the recording sheet can be identified. The timing of movement of the next transfer roller 15 can be finely controlled, and an appropriate image transfer can be performed with respect to the length of the recording paper 18. Therefore, there is no “color shift” or “position shift”. High quality images can be provided.

図７は本発明による記録紙厚さ検出機構の第２の実施の形態を示す概略図である。図８は図７の記録紙厚さ検出機構を作動状態において示す概略図である。
図７及び図８の第２の実施の形態と第１の実施の形態との相違点は記録紙厚さ検出のためのローラを、レジストローラ１６と別個に、記録紙厚さ検出ローラ２５ａ、検出固定ローラ２５ｂとして新たに適宜な方法で設けたことである。
図４の動作タイミングチャート、図５及び図６の動作フローについては、レジストローラ１６という記載を記録紙厚さ検出ローラ２５に読み換えることで説明ができる。
また、記録紙厚さ検出ローラ２５対を新たに設けたことによりレジストローラ１６対と２次転写ローラ１５との距離を自由に選択できることにより記録紙厚さ検出レバー１９の配置や２次転写ローラレバー２１のレイアウトが容易になるメリットが得られる。
図９は本発明による記録紙厚さ検出機構の第２の実施の形態の変形例を示す概略図である。第２の実施の形態において、記録紙厚さ検出ローラ２５ａにプランジャマグネット２６を設けている。
記録紙厚さ検出ローラ２５ａは、記録紙１８が記録紙厚さ検出ローラ２５ａに搬送される前はプランジャマグネット２６によって上方に引っ張られて開いており、かつ記録紙１８の感知により下降して閉じるようになっている。記録紙厚さ検出ローラ２５ａは記録紙１８の通過中も閉じている。
記録紙厚さ検出ローラ２５ａは、第２レジストローラとでも言うべき役割を担っており、記録紙１８の感知までは搬送路を維持するようにプランジャマグネット２６の作用で搬送路を開き、記録紙１８の感知、すなわち、記録紙厚さ検出ローラ２５ａを通過中及び通過直後は閉じている。
記録紙厚さ検出ローラ２５ａはレジストローラ１６対のように記録紙全幅に渡って設ける必要はなく、記録紙厚さ検出レバー１９の一端の固定部材としての役割も担っている。
上述したように、記録紙厚さ検出ローラ２５ａはレジストローラの役割を有するから、通常はプランジャマグネット２６の作用で搬送路を維持するように開いており、レジストローラ１６対と同様に記録紙１８に接するように閉じる。 FIG. 7 is a schematic view showing a second embodiment of a recording paper thickness detection mechanism according to the present invention. FIG. 8 is a schematic view showing the recording paper thickness detection mechanism of FIG. 7 in an operating state.
The difference between the second embodiment of FIGS. 7 and 8 and the first embodiment is that a recording sheet thickness detection roller is provided separately from the registration roller 16, and a recording sheet thickness detection roller 25a, The detection fixing roller 25b is newly provided by an appropriate method.
The operation timing chart of FIG. 4 and the operation flows of FIGS. 5 and 6 can be explained by replacing the description of the registration roller 16 with the recording paper thickness detection roller 25.
Further, since the recording paper thickness detection roller 25 pair is newly provided, the distance between the registration roller 16 pair and the secondary transfer roller 15 can be freely selected, so that the arrangement of the recording paper thickness detection lever 19 and the secondary transfer roller can be selected. There is an advantage that the layout of the lever 21 becomes easy.
FIG. 9 is a schematic view showing a modification of the second embodiment of the recording paper thickness detection mechanism according to the present invention. In the second embodiment, a plunger magnet 26 is provided on the recording paper thickness detection roller 25a.
The recording paper thickness detection roller 25 a is opened by being pulled upward by the plunger magnet 26 before the recording paper 18 is conveyed to the recording paper thickness detection roller 25 a, and is lowered and closed by sensing the recording paper 18. It is like that. The recording paper thickness detection roller 25a is closed even while the recording paper 18 passes.
The recording paper thickness detection roller 25a plays a role to be called a second registration roller, and opens the conveyance path by the action of the plunger magnet 26 so as to maintain the conveyance path until the recording paper 18 is detected. 18 is closed, that is, during and immediately after passing the recording paper thickness detection roller 25a.
The recording sheet thickness detection roller 25a does not need to be provided over the entire width of the recording sheet like the registration roller 16 pair, and also serves as a fixing member at one end of the recording sheet thickness detection lever 19.
As described above, since the recording paper thickness detection roller 25a functions as a registration roller, it is normally opened to maintain the conveyance path by the action of the plunger magnet 26, and the recording paper 18 is the same as the registration roller 16 pair. Close to touch.

また、上述したように、記録紙厚さ検出ローラ２５ａは記録紙幅全体をカバーしていない。従って、記録紙検出センサ２４により記録紙１８の後端が記録紙厚さ検出ローラ２５ａを通過したことを検出した後はプランジャマグネット２６を駆動し、記録紙厚さ検出ローラ２５ａを開いて記録紙１８の搬送を容易にすることにより記録紙１８ヘの損傷を防止することが可能になる。
記録紙厚さ検出ローラ２５ａをプランジャマグネット２６により開閉することによって、記録紙１８が挿入される前に記録紙厚さ検出ローラ２５ａは上方向に退避することができ、記録紙１８の記録紙厚さ検出ローラ２５ａへの衝突による先端損傷を防止することができ、搬送を容易にすることが可能となる。
さらに、第１及び第２の実施の形態において２次転写ローラ開閉モータ２９はステッピングモータやＤＣモータが使用されるが、記録紙１８が搬送経路に無い時は２次転写対向ローラ１４と２次転写ローラ１５の間隔を“０”にしておく必要があり、この動作を２次転写ローラ開閉モータ２９のホームポジション動作といい、装置の電源オン時及び制御上必要な時期に行う必要がある。
２次転写対向ローラ１４と２次転写ローラ１５の間隔が“０”の状態は記録紙厚さ検出センサ２０の発光部と受光部との間に記録紙厚さ検出センサ２２が入った「暗」の状態なので、上記のホームポジション動作を、記録紙厚さ検出センサ２０を使用して行なうことにより、新たなホームポジション用のセンサを設けることなく安価に行うことができる。 As described above, the recording paper thickness detection roller 25a does not cover the entire recording paper width. Accordingly, after the recording paper detection sensor 24 detects that the trailing edge of the recording paper 18 has passed through the recording paper thickness detection roller 25a, the plunger magnet 26 is driven to open the recording paper thickness detection roller 25a and open the recording paper. It becomes possible to prevent the recording paper 18 from being damaged by facilitating the conveyance of 18.
By opening and closing the recording paper thickness detection roller 25a by the plunger magnet 26, the recording paper thickness detection roller 25a can be retreated upward before the recording paper 18 is inserted, and the recording paper thickness of the recording paper 18 is increased. It is possible to prevent damage to the tip due to collision with the height detection roller 25a, and to facilitate conveyance.
Further, in the first and second embodiments, a stepping motor or a DC motor is used as the secondary transfer roller opening / closing motor 29. However, when the recording paper 18 is not in the transport path, the secondary transfer counter roller 14 and the secondary transfer roller opening / closing motor 29 are secondary. The interval between the transfer rollers 15 needs to be set to “0”, and this operation is referred to as a home position operation of the secondary transfer roller opening / closing motor 29 and needs to be performed when the apparatus is turned on and at a time required for control.
When the distance between the secondary transfer counter roller 14 and the secondary transfer roller 15 is “0”, the recording paper thickness detection sensor 22 is inserted between the light emitting portion and the light receiving portion of the recording paper thickness detection sensor 20. Therefore, by performing the above-described home position operation using the recording paper thickness detection sensor 20, it can be performed at low cost without providing a new home position sensor.

図１０は２次転写駆動モータのホームポジション動作を説明するフローチャートである。図７乃至図１０を参照して、先ず、レジストローラ対１６（第１の実施の形態の場合）に記録紙が有るかどうか、又は、記録紙厚さ検出ローラ２５ａ、２５ｂ（第２の実施の形態の場合）に記録紙が有るかどうかを記録紙検出センサ２４で判断する（Ｓ３０）。
次に、最初に搬送経路、すなわち第１の実施の形態のレジストローラ対１６又は第２の実施の形態の記録紙厚さ検出ローラ２５ａの下に記録紙１８が無い状態で記録紙厚さ検出センサ２０が「明」かどうかを判断する（Ｓ３１）。「明」の時は２次転写ローラ駆動（開閉）モータ２９をＣＣＷ方向に回転させる（Ｓ３２）。
記録紙厚さ検出センサ２０の状態を判断し（Ｓ３３）、「暗」である場合には、２次転写ローラ開閉モータ２９を一旦停止させ（Ｓ３４）、次に２次転写ローラ開閉モータ２９をＣＷ方向に回転させる（Ｓ３５）。
この状態で記録紙厚さ検出センサ２０が「明」かどうか判断し（Ｓ３６）、「明」になるまで駆動し、「明」で２次転写ローラ開閉モータ２９を停止し（Ｓ３７）、ホームポジション動作を完了する。
スタート時に記録紙厚さ検出センサ２０が「暗」の場合は２次転写ローラ開閉モータ２９をＣＷ方向に駆動し、用紙厚センサ２０が「明」になった時に２次転写ローラ開閉モータ２９を停止し、ホームポジション動作を完了する。
記録紙厚さ検出ローラをプランジャマグネットで開閉することにより、記録紙が挿入される前に記録紙厚さ検出ローラは上方向に退避することができ、記録紙１８の記録紙厚さ検出ローラへの衝突による先端損傷を防止することができ搬送を容易にすることが可能となる。 FIG. 10 is a flowchart for explaining the home position operation of the secondary transfer drive motor. Referring to FIGS. 7 to 10, first, the registration roller pair 16 (in the case of the first embodiment) has a recording paper, or the recording paper thickness detection rollers 25a and 25b (second implementation). The recording paper detection sensor 24 determines whether or not there is recording paper (S30).
Next, the recording paper thickness is first detected in the absence of the recording paper 18 under the transport path, that is, the registration roller pair 16 of the first embodiment or the recording paper thickness detection roller 25a of the second embodiment. It is determined whether or not the sensor 20 is “bright” (S31). When “bright”, the secondary transfer roller drive (open / close) motor 29 is rotated in the CCW direction (S32).
The state of the recording paper thickness detection sensor 20 is judged (S33). If it is “dark”, the secondary transfer roller opening / closing motor 29 is temporarily stopped (S34), and then the secondary transfer roller opening / closing motor 29 is turned off. Rotate in the CW direction (S35).
In this state, it is determined whether or not the recording paper thickness detection sensor 20 is “bright” (S 36), and it is driven until it becomes “bright”, and the secondary transfer roller opening / closing motor 29 is stopped at “bright” (S 37). Complete position movement.
When the recording paper thickness detection sensor 20 is “dark” at the start, the secondary transfer roller opening / closing motor 29 is driven in the CW direction, and when the sheet thickness sensor 20 becomes “bright”, the secondary transfer roller opening / closing motor 29 is driven. Stop and complete home position movement.
By opening and closing the recording paper thickness detection roller with the plunger magnet, the recording paper thickness detection roller can be retracted upward before the recording paper is inserted, and the recording paper thickness detection roller of the recording paper 18 is moved to the recording paper thickness detection roller. It is possible to prevent the tip from being damaged due to the collision, and to facilitate the conveyance.

本発明による記録紙厚さ検出機構の第１の実施の形態を示す概略図である。1 is a schematic diagram showing a first embodiment of a recording paper thickness detection mechanism according to the present invention. 図１の記録紙厚さ検出機構を作動状態において示す概略図である。It is the schematic which shows the recording paper thickness detection mechanism of FIG. 1 in an operation state. 本発明の画像形成装置における制御ブロック図である。3 is a control block diagram in the image forming apparatus of the present invention. FIG. 図１及び図２の本発明の第１の実施の形態の動作を説明する制御タイミングチャートである。3 is a control timing chart for explaining the operation of the first exemplary embodiment of the present invention of FIGS. 1 and 2. 本発明の第１の実施の形態の動作を説明するフローチャートである。It is a flowchart explaining the operation | movement of the 1st Embodiment of this invention. 図５の丸付きの２に続くフローチャートである。6 is a flowchart following circled 2 in FIG. 5. 本発明による記録紙厚さ検出機構の第２の実施の形態を示す概略図である。It is the schematic which shows 2nd Embodiment of the recording paper thickness detection mechanism by this invention. 図７の記録紙厚さ検出機構を作動状態において示す概略図である。It is the schematic which shows the recording paper thickness detection mechanism of FIG. 7 in an operation state. 本発明による記録紙厚さ検出機構の第２の実施の形態の変形例を示す概略図である。It is the schematic which shows the modification of 2nd Embodiment of the recording paper thickness detection mechanism by this invention. ２次転写駆動モータのホームポジション動作を説明するフローチャートである。6 is a flowchart for explaining a home position operation of a secondary transfer drive motor. 一般的なタンデム型カラー画像形成装置の構成例を示す概略図である。1 is a schematic diagram illustrating a configuration example of a general tandem color image forming apparatus. 「色ずれ」又は「位置ずれ」の原因である中間転写ベルトの速度変動例を示す概略図である。FIG. 6 is a schematic diagram illustrating an example of a speed variation of an intermediate transfer belt that is a cause of “color shift” or “position shift”. 記録紙の先端挿入時を示す概略図である。It is the schematic which shows the time of leading edge insertion of a recording paper. 記録紙の後端排出時を示す概略図である。FIG. 6 is a schematic diagram illustrating when the trailing edge of a recording sheet is discharged.

符号の説明Explanation of symbols

９中間転写ベルト
１５２次転写ローラ
１６レジストローラ対
１６ａ可動レジストローラ
１６ｂ固定レジストローラ
１８記録紙
１９記録紙厚さ検出機構（記録紙厚さ検出レバー）
２０記録紙厚さ検出機構（記録紙厚さ検出センサ）
２１記録紙厚さ検出機構（２次転写ローラレバー）
２２記録紙厚さ検出機構（記録紙厚さ検出センサシャッタ）
２３記録紙厚さ検出機構（偏心カム）
２４記録紙厚さ検出機構（記録紙厚さ検出センサ）
２５ａ記録紙厚さ検出機構（記録紙厚さ検出ローラ）
２５ｂ記録紙厚さ検出機構（記録紙厚さ検出固定ローラ）
２６駆動源（プランジャマグネット）
２７演算装置（制御手段）、
２９駆動源（２次転写ローラ開閉モータ） 9 Intermediate transfer belt
15 Secondary transfer roller 16 Registration roller pair 16a Movable registration roller 16b Fixed registration roller 18 Recording paper 19 Recording paper thickness detection mechanism (recording paper thickness detection lever)
20 Recording paper thickness detection mechanism (recording paper thickness detection sensor)
21 Recording paper thickness detection mechanism (secondary transfer roller lever)
22 Recording paper thickness detection mechanism (recording paper thickness detection sensor shutter)
23 Recording paper thickness detection mechanism (eccentric cam)
24 Recording paper thickness detection mechanism (recording paper thickness detection sensor)
25a Recording paper thickness detection mechanism (recording paper thickness detection roller)
25b Recording paper thickness detection mechanism (recording paper thickness detection fixed roller)
26 Drive source (plunger magnet)
27 arithmetic unit (control means),
29 Drive source (secondary transfer roller opening / closing motor)

Claims

像担持体と、該像担持体上から１次転写された画像を受ける中間転写ベルトと、該中間転写ベルト上の１次転写画像を記録紙に２次転写させるために前記中間転写ベルトに前記記録紙を圧接させるための２次転写ローラと、前記記録紙を前記２次転写ローラに供給するレジストローラ対と、備えた画像形成装置において、前記記録紙の搬送経路中に設けた前記記録紙の厚さを検出する記録紙厚さ検出機構と、前記２次転写ローラを開閉動作させて前記中間転写ベルト面との間隔を増減変更させる駆動源と、これらを制御する制御手段と、を備え、
前記制御手段は、前記記録紙厚さ検出機構により検出された前記記録紙の厚さの変化に応じて前記駆動源を制御して前記２次転写ローラを開閉動作させて前記中間転写ベルト面との間隔を増減変更することを特徴とする画像形成装置。 An image carrier, an intermediate transfer belt that receives an image primarily transferred from the image carrier, and the intermediate transfer belt to transfer the primary transfer image on the intermediate transfer belt onto a recording sheet. In the image forming apparatus comprising a secondary transfer roller for pressing the recording paper and a pair of registration rollers for supplying the recording paper to the secondary transfer roller, the recording paper provided in the conveyance path of the recording paper A recording paper thickness detection mechanism for detecting the thickness of the recording paper, a drive source for opening / closing the secondary transfer roller to increase / decrease the distance from the intermediate transfer belt surface, and a control means for controlling them. ,
The control means controls the drive source in accordance with a change in the thickness of the recording paper detected by the recording paper thickness detection mechanism to open and close the secondary transfer roller to An image forming apparatus characterized by increasing or decreasing the interval.

前記記録紙厚さ検出機構は、ニップ部を通過する前記記録紙の厚さに応じて動作する可動レジストローラを備えた前記レジストローラ対と、該可動レジストローラの動作に連動して作動する記録紙厚さ検出センサと、前記駆動源と、前記制御手段と、を備え、
前記制御手段は、前記記録紙の厚みに応じて２次転写ローラを開閉するように前記駆動源を動作させることを特徴とする請求項１記載の画像形成装置。 The recording paper thickness detection mechanism includes a registration roller pair including a movable registration roller that operates according to the thickness of the recording paper that passes through the nip portion, and a recording that operates in conjunction with the operation of the movable registration roller. A paper thickness detection sensor, the drive source, and the control means,
The image forming apparatus according to claim 1, wherein the control unit operates the drive source so as to open and close a secondary transfer roller according to the thickness of the recording paper.

前記記録紙の有無を検出する記録紙検出センサを設け、前記制御手段はこの記録紙の検出結果によって前記２次転写ローラの開閉タイミングを制御することを特徴とする請求項１、又は２記載の画像形成装置。 The recording paper detection sensor for detecting the presence or absence of the recording paper is provided, and the control unit controls the opening and closing timing of the secondary transfer roller according to the detection result of the recording paper. Image forming apparatus.

前記制御手段は、前記記録紙検出センサが前記記録紙の先端を検出した時から、該記録紙先端が前記記録紙検出センサと２次転写ローラとの間を通過するのに要する時間の経過を待って前記２次転写ローラの開閉を行うことを特徴とする請求項３記載の画像形成装置。 The control means determines whether the time required for the leading end of the recording sheet to pass between the recording sheet detecting sensor and the secondary transfer roller from when the recording sheet detecting sensor detects the leading end of the recording sheet. 4. The image forming apparatus according to claim 3, wherein the secondary transfer roller is opened and closed after waiting.

前記制御手段は、前記記録紙検出センサが前記記録紙の後端を検出した時から、該記録紙後端が前記記録紙検出センサと前記２次転写ローラとの間を通過するのに要する時間の経過を待って次の２次転写ローラの開閉を行うことを特徴とする請求項３記載の画像形成装置。 The control means includes a time required for the trailing edge of the recording sheet to pass between the recording sheet detection sensor and the secondary transfer roller after the recording sheet detection sensor detects the trailing edge of the recording sheet. 4. The image forming apparatus according to claim 3, wherein the next secondary transfer roller is opened / closed after the elapse of time.

前記レジストローラと前記２次転写ローラ間に、記録紙厚さ検出ローラと、この記録紙厚さ検出ローラに同期して動く記録紙厚さ検出センサを設け、さらに、前記２次転写ローラには開閉のための駆動源を設け、前記制御手段は、記録紙の厚みに応じて前記駆動源を制御することにより前記２次転写ローラを開閉することを特徴とする請求項１、又は２記載の画像形成装置。 A recording sheet thickness detection roller and a recording sheet thickness detection sensor that moves in synchronization with the recording sheet thickness detection roller are provided between the registration roller and the secondary transfer roller. The drive source for opening and closing is provided, and the control means opens and closes the secondary transfer roller by controlling the drive source according to the thickness of the recording paper. Image forming apparatus.

前記記録紙の有無を検出する記録紙検出センサを設け、前記制御手段は、この記録紙の検出結果によって前記２次転写ローラの開閉タイミングを制御することを特徴とする請求項６記載の画像形成装置。 7. The image forming apparatus according to claim 6, wherein a recording sheet detection sensor for detecting the presence or absence of the recording sheet is provided, and the control unit controls the opening / closing timing of the secondary transfer roller based on a detection result of the recording sheet. apparatus.

前記制御手段は、前記記録紙検出センサが前記記録紙の先端を検出した時から、該記録紙先端が前記記録紙検出センサと２次転写ローラとの間を通過するのに要する時間の経過を待って前記２次転写ローラの開閉動作を行うことを特徴とする請求項７記載の画像形成装置。 The control means determines whether the time required for the leading end of the recording sheet to pass between the recording sheet detecting sensor and the secondary transfer roller from when the recording sheet detecting sensor detects the leading end of the recording sheet. 8. The image forming apparatus according to claim 7, wherein the image forming apparatus opens and closes the secondary transfer roller.

前記制御手段は、前記記録紙検出センサ位置が前記記録紙の後端を検出した時から、該記録紙後端が前記記録紙検出センサと前記２次転写ローラとの間を通過するのに要する時間の経過をまって、次の２次転写ローラの開閉を行うことを特徴とする請求項７記載の画像形成装置。 The control means is required for the trailing edge of the recording paper to pass between the recording paper detection sensor and the secondary transfer roller from when the recording paper detection sensor position detects the trailing edge of the recording paper. 8. The image forming apparatus according to claim 7, wherein the next secondary transfer roller is opened and closed over time.

前記記録紙厚さ検出ローラは開閉可能な駆動源を備えていることを特徴とする請求項６記載の画像形成装置。 The image forming apparatus according to claim 6, wherein the recording sheet thickness detection roller includes a drive source that can be opened and closed.

前記記録紙厚さ検出機構は前記駆動源である２次転写ローラ開閉モータのホームポジション位置を兼ねることを特徴とする請求項１乃至１０の何れか一項に記載の画像形成装置。 The image forming apparatus according to claim 1, wherein the recording sheet thickness detection mechanism also serves as a home position of a secondary transfer roller opening / closing motor serving as the driving source.