1269947 (1) 九、發明說明 【發明所屬之技術領域】 本發明係關於紙張輸送控制裝置，特別關於用以控 制：在用來控制紙張的輸送時機之對準滾輪、及將圖像承 載體上的墨粉圖像轉印到紙張上之轉印裝置、以及用來將 轉印的墨粉圖像定影於紙張上之定影裝置之間被輸送的紙 張之輸送，之圖像形成裝置之紙張輸送控制裝置。 【先前技術】 人們希望延長複印機或印表機等之圖像形成裝置的使 用壽命。爲達到延長使用壽命之目的，需要解決低質紙張 給感光鼓帶來的損壞以及污染等技術課題。即，由於使用 含有大量重碳酸鈣或滑石粉等添加物的低質紙張時，這些 紙粉或墨粉會廣範圍地附著到感光鼓的表面上並形成薄 膜，或招致感光鼓表面之損傷，而其結果則引起圖像缺 Φ 陷。 引發如上述問題的主要原因，係可舉出與感光鼓直接 接觸之轉印滾輪。因此，爲了解決該問題點，在採用接觸 式轉印方式時，爲避免在轉印部將紙粉按壓粘貼到感光 鼓，可採用的有效方法爲：減低轉印滾輪之對於感光鼓的 按壓力或轉印滾輪採用硬度較柔軟之材質等。更有效的方 法爲：採用將轉印滾輪完全地從感光鼓分離之非接觸式轉 印方式。例如，藉由使轉印滾輪從感光鼓分離 0.2〜 0.3 mm程度，能夠抑制紙粉被按壓粘貼到感光鼓，從而遏 -4- (2) 1269947 止感光鼓之損傷。亦有實際例子，以接觸式轉印方式將低 貝紙張轉印3 0，0 0 0〜6 0，0 0 0張程度而達到感光鼓的壽命之 裝置，藉由採用如此之非接觸式轉印方式，可得到 200,000張以上之壽命。 但是’採用非接觸式轉印方式之圖像形成裝置，其問 題爲：因爲在轉印部紙張並未被牢牢地夾住而輸送，所以 其輸送狀態則不穩定會引起紙張輸送速度的些微變化，且 φ 該速度變化則導致轉印偏移。關於這一點，以下詳細說明 之。 將紙張在對準滾輪、轉印部及定影裝置之間輸送時， 主要藉由對準滾輪和定影裝置的紙張輸送速度之差，來使 輸送中之紙張處於彎曲狀態。在一般，爲了確保紙張能夠 穩定地進入定影裝置，即爲了使在定影裝置內的紙張上不 產生皺紋等，在轉印部和定影裝置之間，係大多使紙張彎 曲，而使沿著輸送導引構件來輸送。在這種狀態下，當紙 •張的後端一離開對準滾輪之鉗部時，控制紙張之輸送者會 從對準滾輪變換爲定影裝置之滾輪。此時，因在輸送過程 中發生的紙張之彎曲量，會引起在轉印部的紙張之輸送速 度變化，其結果最後得出的圖像中會出現轉印偏移。例 如，在轉印部和定影裝置之間紙張彎曲的情況下，由於當 因消停 ， 被於 。 送態處象 輸狀部現 來 曲印移 置彎轉偏 裝之於印 影51對轉 定紙相的 由的會緊 藉_則縮 僅 U 分像 係 — 部圖 張置一田目 紙π之所 ，景張生 時π紙發 輪和的會 滾部部而 準印印因 對轉轉， 地、3 ΊΕΙ 開到於態 離直位狀 張，，之 紙此除止 -5- (3) 1269947 另外，如果採用接觸式轉印方式，由於紙張係可藉由 轉印滾輪等來夾持輸送，因此可以盡可能減少上述之輸送 速度變化。 但是，不管採用接觸式轉印方式還是非接觸式轉印方 式，如果不極力減少紙張之彎曲，則在紙張後端離開對準 滾輪之際就會發生轉印偏移。 因此，作爲對策手段，係可以考慮一種作法，即在轉 φ 印部的紙張輸送方向上游側，形成一個足以能夠吸收紙張 的彎曲之空間，當紙張離開對準滾輪時，由該空間吸收紙 張之彎曲以消除在定影裝置和轉印裝置之間的紙張彎曲 量。但是，從機械的小型化之角度，難以在轉印部的紙張 輸送方向上游側確保足夠的空間。此外，亦被提案：設置 用以控制輸送速度之同時，在轉印部和定影裝置之間檢測 紙張的彎曲之程度之感測器，根據其檢測結果控制定影裝 置之輸送速度，且防止在轉印部和定影裝置之間相互爭拉 φ 紙張，或防止紙張的彎曲量超過一定値之技術（參照曰本 特開平1 0 - 9 7 1 5 4號公報）。 專利文獻1 :日本特開平1 0-97 1 54號公報 【發明內容】 [發明所欲解決之問題] 然而，在日本專利文獻特開平10-9 7 1 5 4公報所示之 裝置，必須特別地設置用以檢測紙張的彎曲之感測器，且 由於需要感測器以及用來支撐感測器之構件等，會妨礙裝 -6- (4) 1269947 置之小型化，並招致成本上升。 本發明鑒於以往技術中存在的問題，其目的在於提供 一種圖像形成裝置之紙張輸送控制裝置，以簡單的結構即 可遏制因輸送過程中的紙張之彎曲而引起的轉印偏移之現 象。 〔用以解決問題之手段〕 p 申請專利範圍第1項之圖像形成裝置之紙張輸送控制 裝置，係用以控制在用來控制紙張的輸送時機之對準滾 輪、及將圖像承載體上的墨粉圖像轉印到紙張上之轉印裝 置、以及用來將被轉印的墨粉圖像定影到紙張上之定影裝 置之間被輸送的紙張之輸送之裝置，而具備有：彎曲形成 機構、及輸送速度控制裝置。彎曲形成機構，係在轉印裝 置與定影裝置之間於紙張形成彎曲地將紙張輸送。輸送速 度控制裝置，係用於變換控制紙張的輸送速度，以使在紙 φ 張的後端離開對準滾輪之前，位於轉印裝置與定影裝置之 間的紙張之彎曲量小於以彎曲形成機構所形成的紙張之彎 曲量。 該裝置，在輸送紙張之際，係在轉印裝置與定影裝置 之間於紙張形成彎曲地輸送。接著，在紙張之後端離開上 述對準滾輪之前，控制變換紙張的輸送速度，使紙張的彎 曲量少於變換速度之前的彎曲量。 在本發明中，係在紙張之後端離開對準滾輪之前，變 換紙張之輸送速度。具體而言，對準滾輪之情況係將輸送 -7- (5) 1269947 速度變換成更慢之速度。又’定影裝置之情況係將輸送速 度變換成更快之速度。藉此，在轉印裝置與定影裝置之間 之前所形成的紙張之彎曲量則變少，其結果，因爲在紙張 之後端將要離開對準滾輪之前，紙張之彎曲係大致被消 除，所以在轉印部的紙張輸送速度之變化較以往裝置變 少。因此，可以遏制轉印偏移。 申請專利範圍第2項之圖像形成裝置之紙張輸送控制 % 裝置’係於申請專利範圍第1項中，更具備有用以檢測被 輸送的紙張之尺寸的尺寸檢測裝置。接著，輸送速度控制 裝置，係根據尺寸檢測裝置之檢測結果控制紙張輸送速度 之變換時機及/或輸送速度之變化率。 在本發明中，在轉印裝置與定影裝置之間所形成的紙 張之彎曲量，係因紙張尺寸大小不同而有所不同。又，根 據紙張尺寸之大小，紙張後端離開對準滾輪之時機也不 同。因此，將在輸送速度控制裝置的輸送速度之變換時機 # 及/或輸送速度之變化率，根據紙張尺寸大小來控制。於 此，可根據紙張尺寸大小進行適當之控制，且對所有的紙 張尺寸大小都可遏制產生轉印偏移。 申請專利範圍第3項之圖像形成裝置之紙張輸送控制 裝置，係於申請專利範圍第1項中，轉印裝置係具有與圖 像承載體不接觸而轉動之非接觸式轉印滾輪。在作爲轉印 裝置中採用非接觸式轉印滾輪之情況時，在圖像承載體與 轉印滾輪之間並無夾持紙張。因此，如上述之轉印偏移現 象會比接觸式轉印滾輪較顯著地顯現出。但是，根據本發 -8- (6) 1269947 明’由於在輸送過程中藉由變換紙張之輸送速度來減少紙 張之彎曲量，因此儘管採用非接觸式轉印方式，也可遏制 轉印偏移。 申請專利範圍第4項之圖像形成裝置之紙張輸送控制 裝置，係於申請專利範圍第1項中，在轉印裝置與定影裝 置之間，紙張係沿垂直方向輸送。將紙張沿水平方向輸送 之情況時，輸送過程中之紙張係藉由紙之自身重量容易沿 φ 著用以輸送之導引構件被輸送，但將紙張沿垂直方向輸送 之情況時，紙張則難以沿著導引構件被輸送。爲此，紙張 之輸送會變得不穩定，且如上述之因紙張輸送速度的變化 所引起的轉印偏移之問題則變得更顯著。因此，本發明係 適用於將紙張沿垂直方向輸送之裝置，而變得更有效。 申請專利範圍第5項之圖像形成裝置之紙張輸送控制 裝置，係於申請專利範圍第1、2、3或4項中，更具備有 將從紙張收容部取出的紙張輸送給對準滾輪之供紙滾輪。 # 接著，輸送速度控制裝置係在紙張後端離開供紙滾輪且到 離開對準滾輪前之間，將紙張輸送速度變換。 被收容在供紙盒等的紙張收容部之紙張，係藉由前饋 滾子從紙張收容部被取出，且藉由供紙滾輪被送往供紙輸 送路徑。其後，紙張係藉由對準滾輪待機，且在適當之時 機被輸送到轉印裝置。此時，根據紙張之尺寸以及供紙輸 送路徑之長度，紙張係可存在於被供紙滾輪和對準滾輪之 兩方夾持而輸送之狀態。在如此狀態中，在紙張被供紙滾 輪夾持時即使變換紙張的輸送速度，也有可能供紙滾輪之 -9- (7) 1269947 夾持變成負荷而無法得到如上述的申請專利範圍第1項之 結構所期待之效果。 因此’本申請專利範圍之發明，係作成在紙張後端離 開供紙滾輪且到離開對準滾輪之前，將紙張輸送速度變 換。藉由這種結構，能夠得到更顯著之作用效果。 申請專利範圍第6項之圖像形成裝置之紙張輸送控制 裝置，係於申請專利範圍第5項中，輸送速度控制裝置， φ 係在紙張後端離開供紙滾輪且到離開對準滾輪前之間，將 紙張輸送速度以兩階段或更多之階段變換。 在此’紙張後端被供紙滾輪和對準滾輪之兩方夾持之 狀態’係在對準滾輪側會受到因供紙滾輪之夾持而引起的 負荷。從如此狀態紙張離開供紙滾輪時，在其瞬間由於在 對準滾輪側的負荷突然變輕，因此紙張的輸送速度則上 升。因此’例如，首先作爲第1階段，在紙張離開供紙滾 輪之瞬間將紙張的輸送速度減低；再來作爲其次之第2階 # 段’在紙張離開對準滾輪之前，將紙張的輸送速度再次減 低，而將在轉印裝置與定影裝置之間的紙張之彎曲量變 少。藉由進行如上述之輸送控制，可更遏制因轉印偏移所 引起的畫質之劣化。再者，藉由將紙張輸送速度分兩階段 以上變換，因將輸送速度微妙地改變，故可防止圖像形成 倍率（所謂等倍度）之極端的變化。 申請專利範圍第7項之圖像形成裝置之紙張輸送控制 裝置，係於申請專利範圍第1項中，輸送速度控制裝置係 控制變換定影裝置之輸送速度。 -10- (8) 1269947 在變換紙張的輸送速度之際，若變換對準滾輪之旋轉 速度，則圖像形成倍率（所謂等倍度）會改變。因此，若有 必要進行正確倍率的圖像形成之情況時，係變換定影裝置 側之輸送速度爲較理想。 申請專利範圍第8項之圖像形成裝置之紙張輸送控制 裝置，係於申請專利範圍第1項中，輸送速度控制裝置係 控制變換對準滾輪之輸送速度。 如上所述，在紙張被供紙滾輪和對準滾輪之兩方夾持 之情況，以兩階段變換紙張輸送速度時，則只需變換對準 滾輪之旋轉速度即可對應，且控制變得容易。 申請專利範圍第9項之圖像形成裝置之紙張輸送控制 裝置，係於申請專利範圍第1項中，更具備有用以檢測被 輸送的紙張的厚度之厚度檢測裝置，且輸送速度控制裝置 係根據厚度檢測裝置之檢測結果來控制紙張輸送速度之變 化率。 因紙張的厚度不同，所謂紙張的硬度之強弱（紙張之 難彎曲度/易彎曲度）會有所不同。因此，藉由根據紙張之 厚度來控制紙張輸送速度之變化率，能夠根據各種之紙張 來進行適當的輸送速度之變換，且可遏制各種的紙張之轉 印偏移。 【實施方式】 [發明之實施形態] [裝置構造] -11 - 1269947 Ο) 第1圖係顯示採用本發明的一實施形態之紙張輸送控 制裝置的圖像形成裝置之槪略剖面圖。在第1圖中，係以 紙張之輸送系統爲中心，只顯示了圖像形成裝置之一部 分。該圖像形成裝置1，係於底部具有供紙部2，並且在 供紙部2的上方具有圖像形成部3，更且在圖像形成部3 的上方具有定影裝置4以及排紙部5。接著，形成一個從 供紙部2到排紙部5朝縱方向輸送紙張之縱向輸送路徑 φ 6。此外，在縱向輸送路徑6之更裝置側方，設有用以將 通過定影裝置4後之紙張再度返回到下方之返回輸送路徑 Ί 〇 供紙部2具有：將紙張收納於內部之供紙盒1 〇、及 配置於供紙盒1 〇的上方之用以將紙張送出之前饋滾子 1 1、及用以將來自供紙盒1 〇之紙張挾持而往上方輸送之 供紙滾輪1 2。此外，在供紙盒1 0之側方，設有可開閉自 如的手動供紙盤1 4，並且在手動供紙盤1 4和縱向輸送路 φ 徑6之間，設有用以將手動供紙盤14上的紙張輸送到縱 向輸送路徑6之導引構件1 5及手動供紙滾輪1 6。 圖像形成部3，係具有作爲圖像承載體之感光鼓2 0， 且在感光鼓2 0的周圍，配置有：用於使感光鼓2 0的表面 帶電之帶電器21、及用於將感光鼓20進行掃描曝光之曝 光單元22、及用於在感光鼓20上形成墨粉圖像之顯影裝 置23、及用於將形成在感光鼓20上的墨粉圖像轉印到紙 張上之轉印滾輪24、以及用於淸掃感光鼓20的表面之淸 潔裝置25。此外，轉印滾輪24係與感光鼓20的表面並 -12- (10) 1269947 不接觸’採用非接觸式轉印方式將形成在感光鼓2 0上的 墨粉圖像轉印到紙張上。此外，在感光鼓2 0與轉印滾輪 24處於最接近位置的轉印部之紙張輸送方向上游側（第1 圖中爲下方），配置有用以控制紙張之往轉印部的輸送時 機之對準滾輪26。 定影裝置4，係具有：於內部設有加熱器之加熱滾輪 3 〇、及按壓於加熱滾輪3 0而與加熱滾輪3 0 —起將紙張夾 φ 持而輸送之加壓滾輪3 1。藉由紙張通過該兩滾輪3 0、3 1 之間，紙張上之墨粉圖像則被加熱、加壓，而被定影於紙 張上。 縱向輸送路徑6，係藉由用來引導紙張的板狀之導引 構件所構成，並由：位於供紙滾輪1 2和對準滾輪2 6之間 的第1輸送路徑3 5、及位於對準滾輪2 6和轉印部之間的 第2輸送路徑3 6、及位於轉印部和定影裝置4之間的第3 輸送路徑3 7、及位於定影裝置4和排紙部5之間的第4 φ 輸送路徑3 8所構成。 [控制部] 如第2圖所示，該圖像形成裝置1係具有控制部 40。控制部40係具有CPU、ROM、RAM等之微電腦。接 著，在該控制部40連接有：用於驅動供紙滾輪1 2之供紙 滾輪驅動部4 1、及用於驅動對準滾輪2 6之對準滾輪驅動 部4 2、及用於驅動定影裝置4中的各滾輪3 0、3 1之定影 驅動部4 3、以及用於驅動圖像形成部3的各構成構件之 -13- (11) 1269947 圖像形成驅動部4 4。又，在該控制部4 0連接有：用於檢 測紙張尺寸之感測器45、及用於檢測紙張的輸送位置之 感測器46、以及用於檢測被輸送來的紙張是否屬於厚度 特別厚的特殊紙張之特殊紙檢測部4 7。特殊紙檢測部 4 7，係例如設置在裝置的操作面板（未圖示）上的「特殊紙 指定鍵」等。 接著，本裝置，雖然在紙張之輸送過程中可變換紙張 φ 的輸送速度，但變換速度的時機以及速度變化率，係因紙 張的尺寸以及紙張的厚度（硬度之強度）而不同。因此，在 控制部40之ROM中，將各紙張之尺寸或厚度之變換時機 以及速度變化率以表儲存著。 [紙張輸送動作] 其次，使用第3圖之流程圖來說明紙張的輸送動作。 又，關於朝感光鼓20的靜電顯影之形成、或墨粉圖像之 • 形成、更且轉印動作，係與以往裝置無異，在此省略這些 說明。 如上所述，根據紙張是否爲特殊紙，並且根據需要印 刷的紙張之尺寸，輸送速度之變換時機以及速度之變化率 會有不同，因此，首先最初在步驟S 1中，讀取按照紙張 的種類、尺寸而預先被設定在表的數據。在該數據中，除 了前述的數據之外，還包括各紙張的通常之輸送速度（變 換輸送速度前之速度）。 其次，在步驟S2中，等待印刷開始之指令。印刷開 -14- (12) 1269947 始之指令被發出之情況時，係由S 2移動到步驟S 3。在步 驟S 3中，係將紙張從供紙盒1 〇輸送到第1輸送路徑 3 5。該紙張之送出，係藉由前饋滾子1 1及供紙滾輪1 2來 進行。其次’在步驟S 4中’係判斷紙張是否已到達對準 滾輪2 6處，若紙張已到達對準滾輪2 6處，則移動到步驟 S 5，而使紙張之輸送暫時停止。 其次’在步驟S 6中，爲了使在圖像形成部3之圖像 φ 形成時機與紙張之輸送時機相配合，判斷是否爲可將紙張 輸送到轉印部之時機。若已到達可將紙張輸送給轉印部的 時機，則由步驟S 6移動到步驟S 7，而重新開放紙張之輸 送。即，開始再次供紙。 在此’藉由定影裝置4及對準滾輪2 6輸送紙張時的 紙張之輸送速度’係被設定爲：在定影裝置4與轉印滾輪 24之間的第3輸送路徑3 7中，於紙張形成彎曲的程度之 速度。因此，在紙張的後端離開對準滾輪26之前，在第 φ 3輸送路徑3 7中紙張係彎曲的。 其次’在步驟S 8中，判斷是否爲變換輸送速度之時 機。在此’變換輸送速度之時機及變換後之速度（速度變 化率），係如上所述，在步驟s 1中，已藉由紙張之種類、 尺寸預先被決定。具體上，從紙張後端剛離開供紙滾輪 1 2之後到離開對準滾輪26之時機，詳細後述之。 在到達變換輸送速度的時機之情況，則從步驟s 8移 動到步驟S 9，且變換成在步驟S 1所設定之輸送速度。藉 由如此之速度變更’紙張之輸送速度則變慢。因此，在變 -15- (13) 1269947 更紙張的輸送速度之前，在第3輸送路徑3 7中紙張爲彎 曲之狀態，但藉由對準滾輪26之輸送速度變慢之結果， 解除了紙張之彎曲狀態’且在紙張之後端離開對準滾輪 2 6時，位於第3輸送路徑3 7中的紙張之彎曲係變成大致 被解除之狀態。如上所述，在紙張之後端離開對準滾輪 2 6之際，由於在第3輸送路徑3 7中的紙張之彎曲則大致 被消除，因此在紙張之後端離開對準滾輪2 6之後，可遏 0 制紙張在轉印部停止或紙張之輸送速度發生變化之現象。 [改變紙張輸送速度之具體例] 作爲具體例子，設定以下之條件。又，在以下的說明 之各時機（時間），係從藉由對準滾輪26之重開紙張輸送 (開始第2次供紙）之時間。 又，在本實施例中，因第2輸送路徑的空間小，紙張 之彎曲會移動到第3輸送路徑，故轉印偏移量=紙張後端 φ 將要離開對準滾輪之前的第3輸送路徑中之紙張彎曲量。 首先，將所需的參數如下式（1 )〜（6 )所示： (1) 紙張長度：Lm(mm) = 420(最大通紙長度=A3尺寸） (2) 定影裝置〜轉印部間（第3輸送路徑）之距離： N 1 (m m ) = 9 0 (3 )轉印部〜對準滾輪間（第2輸送路徑）之距離： N2(mm) = 30 (4)對準滾輪〜供紙滾輪間（第丨輸送路徑）之距離： N3(mm) = 70 -16- (14) 1269947 (5 ) ^寸準檢輪之初始輸送速度：V r (m m / s e c) = 1 〇 〇 7 5 (6)疋影輸送速度：Vf(mm/sec)=100 在此’將紙張後端離開對準滾輪2 6之時機設爲 T s ( m s e c )時，則爲：1269947 (1) VENTION DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a paper conveyance control device, and more particularly to control: an alignment roller for controlling a conveyance timing of a sheet, and an image bearing member Paper transfer of the image forming apparatus by transfer of the transfer device of the toner image onto the paper and the conveyance of the conveyance device for fixing the transferred toner image on the paper Control device. [Prior Art] It is desirable to extend the life of an image forming apparatus such as a copying machine or a printer. In order to achieve a long service life, it is necessary to solve technical problems such as damage and contamination caused by low-quality paper to the photosensitive drum. That is, since low-quality paper containing a large amount of additives such as calcium bicarbonate or talc is used, these paper powders or toners may adhere to a wide range of the surface of the photosensitive drum and form a film, or cause damage to the surface of the photosensitive drum. As a result, the image is missing. The main cause of the above problems is a transfer roller which is in direct contact with the photosensitive drum. Therefore, in order to solve this problem, in the contact transfer mode, in order to avoid the paper powder being pressed and adhered to the photosensitive drum at the transfer portion, an effective method can be employed: reducing the pressing force of the transfer roller to the photosensitive drum Or the transfer roller is made of a softer material. A more efficient method is to use a non-contact transfer method in which the transfer roller is completely separated from the photosensitive drum. For example, by separating the transfer roller from the photosensitive drum by 0.2 to 0.3 mm, it is possible to suppress the paper powder from being pressed and adhered to the photosensitive drum, thereby suppressing the damage of the photosensitive drum by -4-(2) 1269947. There is also a practical example of a device that transfers the low-bay paper by a contact transfer method to a temperature of 3 0,0 0 0 to 60 0,0 0 to reach the life of the photosensitive drum, by adopting such a non-contact type Printing method, you can get more than 200,000 life. However, the image forming apparatus using the non-contact transfer method has a problem in that since the paper is not firmly held in the transfer portion, the conveyance state is unstable, which causes the paper conveying speed to be slightly small. Change, and φ this speed change causes a transfer offset. In this regard, the details are described below. When the paper is conveyed between the registration roller, the transfer portion, and the fixing device, the paper being conveyed is bent in the state mainly by the difference in the paper conveying speed of the registration roller and the fixing device. In general, in order to ensure that the paper can stably enter the fixing device, that is, in order to prevent wrinkles or the like from occurring on the paper in the fixing device, the paper is mostly bent between the transfer portion and the fixing device, so that the paper is guided along the conveyance guide. Lead the component to transport. In this state, when the rear end of the sheet is separated from the nip of the registration roller, the conveyer controlling the sheet is changed from the registration roller to the roller of the fixing device. At this time, due to the amount of bending of the paper which occurs during the conveyance, the conveyance speed of the paper at the transfer portion is changed, and as a result, a transfer offset occurs in the image finally obtained. For example, in the case where the paper is bent between the transfer portion and the fixing device, it is caused by the cessation of the paper. At the delivery state, the image of the output is now bent, and the deflection of the print is reversed. The shadow of the reversed image is reversed by the shadow 51. Then the U-image system is reduced. In the case of Jing Zhangsheng, the π paper hair wheel and the rolling part will be printed and turned, and the ground, 3 ΊΕΙ will open to the straight position, and the paper will be removed -5- (3) 1269947 In addition, if the contact transfer method is employed, since the paper can be conveyed by a transfer roller or the like, the above-described change in the conveying speed can be minimized. However, regardless of whether the contact transfer method or the non-contact transfer method is used, if the bending of the paper is not minimized, the transfer offset occurs when the trailing end of the paper leaves the registration roller. Therefore, as a countermeasure, it is possible to consider a method of forming a space sufficient to absorb the bending of the paper on the upstream side of the paper conveying direction of the φ printing portion, and absorbing the paper by the space when the paper leaves the alignment roller. Bending to eliminate the amount of paper bending between the fixing device and the transfer device. However, from the viewpoint of miniaturization of the machine, it is difficult to secure a sufficient space on the upstream side in the sheet conveying direction of the transfer portion. Further, it is proposed to provide a sensor for detecting the degree of bending of the paper between the transfer portion and the fixing device while controlling the conveying speed, and controlling the conveying speed of the fixing device according to the detection result thereof, and preventing the rotation. The technique of striking φ paper between the printing unit and the fixing device, or preventing the amount of bending of the paper from exceeding a certain amount (refer to Sakamoto Kaiping No. 1 0 - 9 7 1 5 4). [Problem to be Solved by the Invention] However, the device disclosed in Japanese Patent Laid-Open Publication No. Hei 10-9 7 1 5 4 must be specially A sensor for detecting the bending of the paper is provided, and the sensor and the member for supporting the sensor are required to hinder the miniaturization of the -6-(4) 1269947 and cause an increase in cost. The present invention has been made in view of the problems in the prior art, and an object thereof is to provide a paper conveying control device for an image forming apparatus which can suppress a transfer offset caused by bending of a sheet during conveyance with a simple structure. [Means for Solving the Problem] p The paper conveying control device of the image forming apparatus of claim 1 is for controlling the alignment roller for controlling the timing of conveying the paper, and the image bearing member a transfer device for transferring the toner image onto the paper, and a device for conveying the conveyed paper between the fixing device for fixing the transferred toner image onto the paper, and having: bending Forming mechanism and conveying speed control device. The bending forming mechanism conveys the sheet of paper between the transfer device and the fixing device in a curved manner. The conveying speed control device is configured to change the conveying speed of the paper so that the bending amount of the paper between the transfer device and the fixing device is smaller than that of the bending forming mechanism before the rear end of the paper φ sheet leaves the alignment roller The amount of bending of the formed paper. This apparatus transports the paper between the transfer device and the fixing device in a curved manner while conveying the paper. Next, before the trailing end of the sheet leaves the alignment roller, the conveying speed of the sheet is controlled so that the amount of bending of the sheet is smaller than the amount of bending before the shifting speed. In the present invention, the conveying speed of the paper is changed before the trailing end of the paper leaves the registration roller. Specifically, the alignment of the rollers converts the speed of the transport -7-(5) 1269947 to a slower speed. Further, in the case of the fixing device, the conveying speed is changed to a faster speed. Thereby, the amount of bending of the paper formed before the transfer device and the fixing device is reduced, and as a result, since the bending of the paper is substantially eliminated before the rear end of the paper is to be separated from the registration roller, The change in the paper conveying speed of the printing portion is smaller than that of the conventional device. Therefore, the transfer offset can be suppressed. The paper conveying control % device of the image forming apparatus of claim 2 is in the first item of the patent application, and further has a size detecting device for detecting the size of the conveyed paper. Next, the conveyance speed control means controls the change timing of the paper conveying speed and/or the rate of change of the conveying speed based on the detection result of the size detecting means. In the present invention, the amount of bending of the paper formed between the transfer device and the fixing device differs depending on the size of the paper. Also, depending on the size of the paper, the timing at which the trailing edge of the paper leaves the alignment roller is different. Therefore, the rate of change of the conveying speed of the conveying speed control device and/or the rate of change of the conveying speed are controlled in accordance with the paper size. Here, appropriate control can be performed according to the paper size, and transfer offset can be suppressed for all paper sizes. The paper conveying control device of the image forming apparatus of the third aspect of the patent application is the first aspect of the patent application, wherein the transfer device has a non-contact transfer roller that rotates without contact with the image bearing member. In the case where a non-contact transfer roller is used as the transfer device, no paper is sandwiched between the image carrier and the transfer roller. Therefore, the transfer offset phenomenon as described above can be more noticeably exhibited than the contact transfer roller. However, according to the present invention -8-(6) 1269947, the transfer deflection can be suppressed despite the use of the non-contact transfer method because the paper is reduced in the conveyance speed during the conveyance process. . The paper conveying control device of the image forming apparatus of claim 4 is in the first aspect of the patent application, in which the sheet is conveyed in the vertical direction between the transfer device and the fixing device. When the paper is conveyed in the horizontal direction, the paper in the conveyance process is easily conveyed by the guiding member for conveying by the weight of the paper itself, but when the paper is conveyed in the vertical direction, the paper is difficult. It is transported along the guiding member. For this reason, the conveyance of the paper becomes unstable, and the problem of the transfer offset caused by the change in the conveyance speed of the paper as described above becomes more remarkable. Therefore, the present invention is more applicable to a device for conveying paper in a vertical direction. The paper conveying control device of the image forming apparatus of claim 5 is in the first, second, third or fourth aspect of the patent application, and further comprises conveying the paper taken out from the paper receiving portion to the alignment roller. Paper feed roller. # Next, the conveying speed control device shifts the paper conveying speed between the paper feed roller and the front of the paper leaving the paper feed roller. The paper stored in the paper accommodating portion of the paper feed cassette or the like is taken out from the paper accommodating portion by the feedforward roller, and is fed to the paper feed transport path by the paper feed roller. Thereafter, the paper is held by the registration roller and is conveyed to the transfer device at an appropriate timing. At this time, depending on the size of the paper and the length of the paper feed path, the paper may be in a state of being conveyed by both the paper feed roller and the registration roller. In such a state, even if the paper conveyance speed is changed when the paper is nipped by the paper feed roller, there is a possibility that the paper feed roller -9-(7) 1269947 is loaded and the load cannot be obtained as in the above-mentioned patent application. The effect expected by the structure. Therefore, the invention of the scope of the present application is made to change the paper conveying speed before the paper feed end is separated from the paper feed roller and before leaving the registration roller. With this configuration, a more remarkable effect can be obtained. The paper conveying control device of the image forming apparatus of claim 6 is in the fifth item of the patent application, the conveying speed control device, φ is disposed before the paper end of the paper leaves the paper feeding roller and before leaving the alignment roller In between, the paper conveying speed is changed in two stages or more. Here, the state in which the trailing end of the sheet is nipped by both the paper feed roller and the registration roller is caused by the load on the side of the registration roller caused by the chucking of the paper feed roller. When the paper is separated from the paper feed roller in this state, the load speed of the paper rises at a moment when the load on the side of the registration roller suddenly becomes light. Therefore, for example, first, as the first stage, the paper conveying speed is reduced at the moment when the paper leaves the paper feed roller; secondly, as the second second step # segment, the paper conveying speed is again before the paper leaves the registration roller. The amount of bending of the paper between the transfer device and the fixing device is reduced. By performing the conveyance control as described above, the deterioration of the image quality due to the transfer offset can be further suppressed. Further, by changing the paper conveying speed in two or more stages, the conveying speed is subtly changed, so that extreme changes in the image forming magnification (so-called equal magnification) can be prevented. The paper conveying control device of the image forming apparatus of claim 7 is in the first item of the patent application, and the conveying speed control device controls the conveying speed of the converting fixing device. -10- (8) 1269947 When the paper feed speed is changed, if the rotation speed of the registration roller is changed, the image forming magnification (so-called equal magnification) changes. Therefore, if it is necessary to form an image of a correct magnification, it is preferable to change the conveying speed on the side of the fixing device. The paper conveying control device of the image forming apparatus of claim 8 is in the first aspect of the patent application, and the conveying speed control device controls the conveying speed of the shifting alignment roller. As described above, when the paper is nipped by both the paper feed roller and the registration roller, when the paper conveyance speed is changed in two stages, it is only necessary to change the rotation speed of the registration roller, and the control becomes easy. . The paper conveying control device of the image forming apparatus of claim 9 is in the first aspect of the patent application, and further has a thickness detecting device for detecting the thickness of the conveyed paper, and the conveying speed control device is The detection result of the thickness detecting device controls the rate of change of the paper conveying speed. The hardness of the paper (the difficulty of bending/bending of the paper) varies depending on the thickness of the paper. Therefore, by controlling the rate of change of the paper conveying speed in accordance with the thickness of the paper, it is possible to change the appropriate conveying speed in accordance with various paper sheets, and it is possible to suppress the transfer offset of various papers. [Embodiment] [Embodiment of the Invention] [Device Structure] -11 - 1269947 第) Fig. 1 is a schematic cross-sectional view showing an image forming apparatus using a sheet conveyance control device according to an embodiment of the present invention. In Fig. 1, only a part of the image forming apparatus is shown centering on the paper conveying system. The image forming apparatus 1 has a paper feed portion 2 at the bottom, an image forming portion 3 above the paper feed portion 2, and a fixing device 4 and a paper discharge portion 5 above the image forming portion 3. . Next, a longitudinal conveying path φ 6 for conveying the sheet in the longitudinal direction from the sheet feeding portion 2 to the sheet discharging portion 5 is formed. Further, on the side of the apparatus of the longitudinal transport path 6, a return transport path for returning the sheet that has passed through the fixing device 4 to the lower side is provided. The paper feed unit 2 has a paper feed cassette 1 for storing paper therein. And a paper feed roller 12 that is disposed above the paper feed cassette 1 to feed the paper before feeding the paper, and a paper feed roller 12 for transporting the paper from the paper feed cassette 1 to the upper side. Further, on the side of the paper feed cassette 10, a manual paper feed tray 14 that can be opened and closed is provided, and between the manual paper feed tray 14 and the longitudinal conveyance path φ diameter 6, a manual paper feed is provided. The paper on the tray 14 is conveyed to the guiding member 15 of the longitudinal conveying path 6 and the manual paper feed roller 16. The image forming unit 3 has a photosensitive drum 20 as an image bearing member, and a charging unit 21 for charging the surface of the photosensitive drum 20 is disposed around the photosensitive drum 20, and is used for The exposure unit 22 that performs the scanning exposure of the photosensitive drum 20, and the developing device 23 for forming a toner image on the photosensitive drum 20, and the toner image for forming the photosensitive drum 20 are transferred onto the paper. A transfer roller 24 and a cleaning device 25 for sweeping the surface of the photosensitive drum 20. Further, the transfer roller 24 is not in contact with the surface of the photosensitive drum 20 and -12-(10) 1269947. The toner image formed on the photosensitive drum 20 is transferred onto the paper by a non-contact transfer method. Further, on the upstream side (lower in FIG. 1) of the transfer portion of the transfer portion where the photosensitive drum 20 and the transfer roller 24 are closest to each other, a pair of transport timings for controlling the transfer of the paper to the transfer portion is disposed. Quasi-roller 26. The fixing device 4 includes a heating roller 3 that is internally provided with a heater, and a pressure roller 3 1 that is pressed against the heating roller 30 and that holds the paper sheet φ together with the heating roller 30. By passing the paper between the two rollers 30, 31, the toner image on the paper is heated and pressurized to be fixed on the paper. The longitudinal conveying path 6 is constituted by a plate-shaped guiding member for guiding the paper, and consists of: a first conveying path 35 between the paper feed roller 12 and the registration roller 26, and a pair The second transport path 36 between the quasi-roller 26 and the transfer portion, and the third transport path 37 between the transfer portion and the fixing device 4, and between the fixing device 4 and the paper discharge portion 5 The fourth φ transport path 38 is formed. [Control Unit] As shown in Fig. 2, the image forming apparatus 1 includes a control unit 40. The control unit 40 is a microcomputer having a CPU, a ROM, a RAM, and the like. Next, the control unit 40 is connected to a paper feed roller drive unit 41 for driving the paper feed roller 12, and an alignment roller drive unit 4 for driving the registration roller 206, and for driving the fixing. The fixing drive unit 43 of each of the rollers 30 and 31 in the apparatus 4, and the-13-(11) 1269947 image forming drive unit 44 for driving the constituent members of the image forming unit 3 are formed. Further, the control unit 40 is connected with a sensor 45 for detecting the paper size, a sensor 46 for detecting the conveyance position of the paper, and a sensor for detecting whether the conveyed paper is particularly thick. Special paper detection unit for special paper 47. The special paper detecting unit 47 is, for example, a "special paper designating key" provided on an operation panel (not shown) of the apparatus. Next, in the present apparatus, although the conveying speed of the paper φ can be changed during the conveyance of the paper, the timing of changing the speed and the rate of change in speed differ depending on the size of the paper and the thickness of the paper (the strength of the hardness). Therefore, in the ROM of the control unit 40, the timing of changing the size or thickness of each sheet and the rate of change in speed are stored in a table. [Paper conveying operation] Next, the paper conveying operation will be described using the flowchart of Fig. 3 . Further, the formation of the electrostatic development of the photosensitive drum 20, the formation of the toner image, and the transfer operation are the same as those of the conventional apparatus, and the description thereof is omitted here. As described above, depending on whether or not the paper is a special paper, and depending on the size of the paper to be printed, the timing of changing the conveying speed and the rate of change of the speed may be different. Therefore, first, in step S1, the type according to the paper is read first. The size and the data set in the table in advance. In this data, in addition to the aforementioned data, the normal conveying speed of each sheet (the speed before the conveying speed is changed) is included. Next, in step S2, an instruction to start printing is awaited. When the command from the beginning of printing -14- (12) 1269947 is issued, the process moves from S 2 to step S 3 . In step S3, the paper is conveyed from the paper feed cassette 1 to the first transport path 35. The paper is fed by the feedforward roller 1 1 and the paper feed roller 1 2 . Next, 'in step S4', it is judged whether or not the sheet has reached the registration roller 26, and if the sheet has reached the registration roller 26, the process moves to step S5 to temporarily stop the conveyance of the sheet. Next, in step S6, in order to match the timing of formation of the image φ at the image forming unit 3 with the timing of conveyance of the paper, it is determined whether or not the paper is conveyed to the transfer unit. If the timing at which the paper can be fed to the transfer portion has been reached, the process proceeds from step S6 to step S7 to reopen the paper feed. That is, the paper feed starts again. Here, the conveyance speed of the sheet when the sheet is conveyed by the fixing device 4 and the registration roller 26 is set to be in the third conveyance path 37 between the fixing device 4 and the transfer roller 24, on the sheet. The rate at which the degree of bending is formed. Therefore, the sheet is bent in the φ 3 transport path 37 before the trailing end of the sheet leaves the registration roller 26. Next, in step S8, it is judged whether or not it is the timing for changing the conveyance speed. Here, the timing of changing the transport speed and the speed after the conversion (speed change rate) are determined in advance in step s1 by the type and size of the paper. Specifically, the timing from the end of the paper just after leaving the paper feed roller 12 to the timing of leaving the registration roller 26 will be described in detail later. In the case where the timing of changing the conveying speed is reached, the process proceeds from step s 8 to step S9, and is converted to the conveying speed set in step S1. By this speed change, the paper conveying speed is slower. Therefore, before the conveyance speed of the paper is changed to -15-(13) 1269947, the paper is in a state of being bent in the third conveyance path 37, but the conveyance speed of the registration roller 26 is slowed, and the paper is released. In the bent state 'and when the trailing end of the sheet leaves the registration roller 26, the bending of the sheet in the third transport path 37 becomes substantially released. As described above, when the trailing end of the sheet leaves the registration roller 26, the bending of the sheet in the third transport path 37 is substantially eliminated, so that after the trailing end of the sheet leaves the alignment roller 26, it can be suppressed. 0 The paper stops at the transfer unit or the paper conveying speed changes. [Specific Example of Changing Paper Feeding Speed] As a specific example, the following conditions are set. Further, the timing (time) of the following description is the time from the re-opening of the sheet feeding by the registration roller 26 (the second paper feed is started). Further, in the present embodiment, since the space of the second transport path is small, the bending of the paper moves to the third transport path, so the transfer offset = the trailing edge of the paper φ, the third transport path before leaving the alignment roller The amount of paper bending in the middle. First, the required parameters are as shown in the following equations (1) to (6): (1) Paper length: Lm (mm) = 420 (maximum paper length = A3 size) (2) Fixing device to transfer unit Distance of (third transport path): N 1 (mm) = 9 0 (3) Distance between transfer portion to alignment roller (second transport path): N2 (mm) = 30 (4) Alignment roller ~ Distance between the paper feed roller (the second conveying path): N3 (mm) = 70 -16- (14) 1269947 (5) The initial conveying speed of the inch inspection wheel: V r (mm / sec) = 1 〇〇 7 5 (6) Shadow transport speed: Vf (mm/sec) = 100 Here, when the timing of the paper rear end leaving the alignment roller 26 is T s ( msec ), it is:
Ts= 1 000 Lm/Vr (7)； 又’從2次供紙開始起，到紙張後端離開供紙滾輪 1 2之時間T c (m s e c)爲：Ts = 1 000 Lm/Vr (7); Again, the time T c (m s e c) from the start of the second paper feed to the trailing edge of the paper leaving the paper feed roller 1 2 is:
Tc=l 000 (Lm-N3)/Vr (8)。 因此’將（1)、（4)、（5)中的參數分別代入到式（7)、式 (8)時，則Tc = l 000 (Lm - N3) / Vr (8). Therefore, when the parameters in (1), (4), and (5) are substituted into the equations (7) and (8), respectively,
Tc= 1 000 (420-70)/1 〇〇.75 = 3 474(msec)Tc = 1 000 (420-70) / 1 〇〇.75 = 3 474 (msec)
Ts=1000 420/100.75=4169(msec)。 在此’封準浪輪速度變換的時機T m (m s e c)，係應設 定在當使用最大紙張尺寸（A3)時紙張後端離開供紙滾輪後 〜離開對準滾輪後之範圍內。即爲：Ts = 1000 420 / 100.75 = 4169 (msec). Here, the timing T m (m s e c) of the seal wheel speed change should be set within a range from when the paper end is separated from the paper feed roller when the maximum paper size (A3) is used, and after the alignment roller is left. That is:
Tc<Tm<Ts (9) 〇 在此，對準滾輪速度變換的時機Tm(mseC)，係在上 述式（9)之範圍內，且盡可能接近Tc値爲佳（因該値越 大，等倍率越趨於惡化之傾向），因此，T m設定爲： •••Tm = 3500(msec) (10)。 其次，計算變換速度前的紙張彎曲量δ’（mm)。 首先，將紙張的前端進入定影裝置4之後到進行變換 速度的時間作爲Th(msec)時，則：Tc<Tm<Ts (9) Here, the timing Tm (mseC) of the alignment of the roller speed is within the range of the above formula (9), and it is preferable to be as close as possible to Tc (because the larger the 値, The tendency of the equal magnification tends to deteriorate. Therefore, T m is set to: •••Tm = 3500 (msec) (10). Next, the amount of paper bending δ' (mm) before the conversion speed is calculated. First, when the leading end of the paper enters the fixing device 4 and the time at which the conversion speed is performed is Th (msec), then:
Th = Tm-Tf (11) -17- (15) 1269947 2 6開始2次輸送紙張到紙張 Ο ’可用以下之式（12)表示。 (12)。 在此，Tf係從對準滾輪 進入定影裝置4的時間（m s e <Th = Tm-Tf (11) -17- (15) 1269947 2 6 Start feeding paper to paper twice Ο ' can be expressed by the following formula (12). (12). Here, the Tf is the time from the alignment roller to the fixing device 4 (m s e <
Tf= 1000 (Nl+N2)/Vr 因此’變換速度前的紙張之彎曲囊s，，係由定影裝置 4所控制的輸送速度Vf和由對準滾輪26所控制的輸送速 度Vr之間的相對速度乘以上述之輸送時間T h的値，則： 5, = (Vr-Vf) Th/1 〇〇〇 (13)。 φ 在這種狀態下，在對準滾輪變換速度時機Tm，例如 將對準滾輪26之輸送速度相對於初始速度放慢a(%)時， 則變換速度後的對準滾輪26之輸送速度Vr，（mm/sec)爲： Vr，= (100-a) Vr/1 00 (14)。 因此，變換速度之前，通過對準滾輪26之距離 Lc(mm)爲：Tf = 1000 (Nl + N2) / Vr Therefore, the curved sac of the paper before the 'speed change' is the relative between the conveying speed Vf controlled by the fixing device 4 and the conveying speed Vr controlled by the aligning roller 26. The speed multiplied by the above-mentioned transport time T h is: 5, = (Vr-Vf) Th/1 〇〇〇 (13). φ In this state, when the alignment speed Tm is aligned, for example, when the conveying speed of the registration roller 26 is slowed by a (%) with respect to the initial speed, the conveying speed of the registration roller 26 after the speed is changed. , (mm/sec) is: Vr, = (100-a) Vr/1 00 (14). Therefore, before the speed is changed, the distance Lc (mm) through the alignment roller 26 is:
Lc = Vr Tm/ 1 000 ( 1 5 )； 而變換速度後之剩餘的輸送距離Lr(mm)，係根據式 • (15)爲：Lc = Vr Tm / 1 000 ( 1 5 ); and the remaining transport distance Lr (mm) after the speed is changed according to the formula: (15):
Lr = Lm-Lc = Lm-Vr T m /1 0 0 〇 (16)。 接著，變換速度後之由對準滾輪26控制輸送速度的 輸送時間（從變換速度時機Tm到紙張後端離開對準滾輪 26爲止所需的時間）Tr(mSec)爲： 丁 r= 1 〇〇〇 Lr/Vr ’ （17)。 因此，當紙張後端離開對準滾輪26時的彎曲量 5r(mm)，係可根據式（13)、式（14)、式（16)、式（17)得出： -18- (16) 1269947 6r = 6, + (Vr,-Vf) · Tr/1 000 = (Vr-Vf) · Th/1 000 + {(l 00-a) · Vr/100-Vf} · Tr/1 000 = (Vr-Vf) · (Tm-Tf)/1 000+{(100-a) · Vr/100-Vf} · Lr/Vr， = (Vr-Vf) · (Tm-Tf)/1000+{(100-a) · Vr/100-Vf} · (Lm-Vr · Tm/1 000) · 1 00/(1 00-a)/Vr (18) 現在，將速度變化率：a = 3%時，則根據式（12)以及將 (1)〜（3)、（5)、（6)、（10)的値代入式（18)，則得出： ...δ r = 0.1 6 5 (mm) (19) 〇 另外，若在輸送過程中沒有變換輸送速度之情況時， 紙張後端離開對準滾輪26之前的紙張彎曲量（=轉印偏移 量）δ (m m )，係由定影裝置4所控制的輸送速度V f和由對 準滾輪26所控制的輸送速度Vr之間的相對速度乘以從對 準滾輪26到定影裝置4的輸送時間Tr(mseC)的値，即 爲·· S = (Vr-Vf) (Ts-Tf)/1 000 = 2.233(mm) (20)。 在此，作爲轉印偏移量的目標値，因只要作爲0.5 mm 以下，則成爲標準圖像規格內，故本實施例之結果，係根 據式（1 9 )，可確認屬於正常範圍。 此外，本發明之效果（=轉印偏移減少量），爲： 5-5r = 2.068(mm) 〇 [根據紙張的尺寸設定變換時機之想法] 於第4圖’顯不根據紙張尺寸的變換時機之想法。在 -19- (17) 1269947 該第4圖中，直線L 1係表示從2次供紙開始的紙張彎曲 量變化之計算値。又，複數條虛線L2係表示在縱向輸送 A 3紙張時，將對準滾輪2 6之輸送速度變換後時的紙張彎 曲量之計算値。此外，彎曲量爲負値係表示紙張處於拉伸 狀態被輸送，因此實際之彎曲量可視爲零。從該第4圖明 顯得知，各紙張長度之由對準滾輪2 6的輸送速度變換時 機，係作爲：與第4圖所示之三角形a B C相似形狀地將 • 頂點A作爲基準，將頂點C配合紙張長度而成之三角形 的頂點B之位置即可。又’在紙張輸送過程中，因各紙張 的尺寸不同’紙張的彎曲量也會不同，但若最大長度之紙 張（ = A3)彎曲量爲0.5mm以下的話，則其他之紙張尺寸之 情況也必定會成爲〇 · 5 mm以下之彎曲量。 [其他實施形態] (a)上述實施形態中，輸送速度之變換係只一次，但 鲁從紙張之後端離開供紙浪輪1 2起到紙張之後端離開對準 滾輪2 6的期間內，亦可使變化兩階段以上。 在此，將兩階段的情況之流程圖顯示於第5屬。該實 施例，係與第1實施形態同樣地，在步驟S 7重開紙張之 輸送之後，然後在步驟S 8判斷是否爲速度之變換時機， 若尙非變換時機之情況，則從步驟S8移動到步驟S8a。 該步驟S 8 a，係判斷紙張之後端是否已離開供紙滾輪1 2。 接著，在紙張之後端離開供紙滾輪1 2之前，一直重復判 斷步驟S 8及步驟S 8 a。在尙未到達輸送速度之變換時機 •20- (18) 1269947 之前，若紙張之後端已離開供紙滾輪1 2之情況時，則從 步驟S8a移動到步驟S8b，且將輸送速度變換成第1速 度。該第1速度，係比在第1實施形態中的變換後之輸送 速度（本實施形態爲第2速度）較快，且比至今爲止的輸送 速度較慢之速度。 其次，若已到達輸送速度的變換時機之情況時，則從 步驟S 8移動到步驟S 9，而將輸送速度變換爲與上述實施 p 形態同樣之輸送速度（第2速度）。 在紙張輸送時，在紙張被供紙滾輪1 2和對準滾輪26 之兩方夾持之狀態，在對準滾輪2 6 —側會受到因供紙滾 輪1 2之夾持而引起的負荷。因此，在紙張後端離開供紙 滾輪1 2之瞬間，對準滾輪2 6 —側之負荷會變輕，且有可 能瞬間地紙張之輸送速度會上升而產生轉印偏移。 但是，在本實施形態中，會進行：在紙張後端離開供 紙滾輪1 2之瞬間將輸送速度降低到第1速度，更且在紙 φ 張離開對準滾輪2 6之前再將紙張之輸送速度降低到第2 速度而減少紙張之彎曲，之輸送控制。因此，與第1實施 形態相比，更減少因轉印偏移所引起的圖像畫質之劣化。 (b) 上述實施形態中，在變換紙張的輸送速度之情況 時，係以變換對準滾輪2 6的輸送速度之方式來作的，但 亦可以變換定影裝置4的輸送速度之方式來作。此種情 況，係可抑制倍率誤差使其減少。 (c) 上述實施形態中，將本發明適用於採用非接觸式 轉印方式之圖像形成裝置，但本發明當然亦可適用於採用 -21 - (19) 1269947 接觸式轉印方式之圖像形成裝置。即，在以往的接觸式轉 印方式中，作爲感光鼓破損對策，亦可例如減低轉印滾輪 之對於感光鼓的按壓力，或將轉印滾輪之材質改變爲硬度 較柔軟者。由於如此之情況係容易發生轉印偏移，因此適 用本發明可有效地遏制轉印偏移之發生。 [發明之效果] • 如上所述，在本發明中，僅藉由變換紙張的輸送速 度，即可輕易地遏制紙張輸送過程中因紙張的彎曲所引起 的轉印偏移現象。 根據以上本發明，以簡單的結構即可遏制因輸送過程 中的紙張之彎曲而發生的轉印偏移現象。 以上所述僅爲本發明之較佳實施例而已，並不用於限 制本發明，對於本領域的技術人員來說，本發明可以有各 種更改和變化。凡在本發明的精神和原則之內，所作的任 φ 何修改，等同替換，改進等，均應包含在本發明的申請專 利範圍之內。 【圖式簡單說明】 第1圖係採用本發明之一實施形態的圖像形成裝置之 一部分槪略剖面圖。 第2圖係上述圖像形成裝置之控制方塊圖。 第3圖係紙張輸送控制處理之流程圖。 第4圖係說明用以決定不同紙張之輸送速度變換時機 -22- (20) 1269947 的基本構想之圖面。 第5圖係其他實施形態的紙張輸送控制處理之流程 圖。 【主要元件符號說明】 1 :圖像形成裝置 2 :供紙部 φ 3 :圖像形成部 4 :定影裝置 5 :排紙部 6 :縱向輸送路徑 7 :返回輸送路徑 1 〇 :供紙盒 η :前饋滾子 1 2 :供紙滾輪 φ 1 4 :手動供紙盤 15 :導引構件 1 6 :手動供紙滾輪 2 0 :感光鼓 21 :帶電器 2 2 :曝光單元 2 3 :顯影裝置 2 4 :轉印滾輪 2 5 :淸潔裝置 -23- 1269947 (21) 26 :對準滾輪 3 0 :加熱滾輪 3 1 :加壓滾輪 3 5 :第1輸送路徑 3 6 :第2輸送路徑 3 7 :第3輸送路徑 3 8 :第4輸送路徑 φ 4 0 :控制部 4 1 :供紙滾輪驅動部 42 :對準滾輪驅動部 4 3 :定影驅動部 4 4 ·圖像形成驅動部 4 5 :紙張尺寸感測器 46 :紙張位置感測器 47 :特殊紙檢測部 -24Lr = Lm-Lc = Lm-Vr T m /1 0 0 〇 (16). Next, the conveyance time of the conveyance speed (the time from the conversion speed timing Tm to the time when the trailing end of the paper leaves the registration roller 26) Tr(mSec) after the speed is changed is: D = 1 〇〇 〇Lr/Vr ' (17). Therefore, the amount of bending 5r (mm) when the trailing end of the paper leaves the alignment roller 26 can be obtained according to the formula (13), the formula (14), the formula (16), and the formula (17): -18- (16) 1269947 6r = 6, + (Vr, -Vf) · Tr/1 000 = (Vr-Vf) · Th/1 000 + {(l 00-a) · Vr/100-Vf} · Tr/1 000 = (Vr-Vf) · (Tm-Tf)/1 000+{(100-a) · Vr/100-Vf} · Lr/Vr, = (Vr-Vf) · (Tm-Tf)/1000+{( 100-a) · Vr/100-Vf} · (Lm-Vr · Tm/1 000) · 1 00/(1 00-a)/Vr (18) Now, when the rate of change of speed is: a = 3%, Then, according to equation (12) and substituting (1) to (3), (5), (6), and (10), we obtain: δ r = 0.1 6 5 (mm) (19) In addition, if there is no change in conveying speed during conveyance, the amount of paper bending (= transfer offset) δ (mm) before the trailing edge of the paper leaves the registration roller 26 is determined by the fixing device. The relative speed between the conveyance speed Vf controlled by 4 and the conveyance speed Vr controlled by the registration roller 26 is multiplied by the conveyance time Tr(mseC) from the registration roller 26 to the fixing device 4, that is, S = (Vr-Vf) (Ts-Tf) / 1 000 = 2.233 (mm) (20). Here, the target 转印 of the transfer offset amount is within the standard image specification as long as it is 0.5 mm or less. Therefore, the results of the present example can be confirmed to be within the normal range according to the formula (1 9 ). Further, the effect of the present invention (= transfer offset reduction amount) is: 5-5r = 2.068 (mm) 〇 [Improvement of the timing of the change according to the size of the paper] In Fig. 4, the display is not changed according to the paper size. The idea of timing. In -19-(17) 1269947, in Fig. 4, the straight line L 1 indicates the calculation of the change in the amount of bending of the paper from the second paper feed. Further, a plurality of broken lines L2 indicate the calculation of the amount of bending of the paper when the conveying speed of the registration roller 26 is changed when the A 3 paper is conveyed in the longitudinal direction. Further, the amount of bending is negative, which means that the paper is conveyed in a stretched state, so the actual amount of bending can be regarded as zero. As is apparent from Fig. 4, the timing of changing the conveying speed of each sheet length by the registration roller 26 is as follows: the vertex A is used as a reference and the vertex is similarly shaped as the triangle a BC shown in Fig. 4 C can match the position of the vertex B of the triangle formed by the length of the paper. Also, 'in the paper conveying process, the amount of bending of the paper varies depending on the size of each paper. However, if the maximum length of paper (= A3) is less than 0.5 mm, the other paper sizes must be It will become a bending amount of 〇·5 mm or less. [Other Embodiments] (a) In the above embodiment, the transfer speed is changed only once, but the time from the rear end of the paper leaving the paper feed wheel 12 to the end of the paper leaving the registration roller 26 is also Can change more than two stages. Here, a flow chart of the two-stage situation is shown in the fifth genus. In this embodiment, similarly to the first embodiment, after the conveyance of the paper is resumed in step S7, it is determined in step S8 whether or not the speed is changed, and if it is not the case of the change timing, the movement is performed from step S8. Go to step S8a. In the step S 8 a, it is judged whether or not the rear end of the paper has left the paper feed roller 12. Next, the step S 8 and the step S 8 a are repeated until the trailing end of the sheet leaves the paper feed roller 12. If the rear end of the paper has left the paper feed roller 12 before the change speed of the conveyance speed is reached, 20-(18) 1269947, the process moves from step S8a to step S8b, and the conveyance speed is changed to the first. speed. The first speed is faster than the conveyance speed after the conversion in the first embodiment (the second speed in the present embodiment), and is slower than the conveyance speed to date. Next, when the transfer timing of the conveyance speed has been reached, the process proceeds from step S8 to step S9, and the conveyance speed is converted to the conveyance speed (second speed) similar to the above-described p-type. At the time of paper conveyance, when the paper is nipped by both the paper feed roller 12 and the registration roller 26, the load on the side of the registration roller 26 is caught by the paper feed roller 12. Therefore, at the moment when the trailing end of the paper leaves the paper feed roller 12, the load on the side of the registration roller 26 becomes lighter, and there is a possibility that the conveyance speed of the paper may rise instantaneously to cause a transfer offset. However, in the present embodiment, the conveyance speed is lowered to the first speed at the moment when the trailing end of the paper leaves the paper feed roller 12, and the conveyance of the paper is again before the paper φ leaves the alignment roller 26. The speed is reduced to the second speed to reduce the bending of the paper, and the conveyance control. Therefore, deterioration of image quality due to transfer offset is further reduced as compared with the first embodiment. (b) In the above embodiment, when the conveyance speed of the sheet is changed, the conveyance speed of the registration roller 26 is changed. However, the conveyance speed of the fixing device 4 may be changed. In this case, the magnification error can be suppressed and reduced. (c) In the above embodiment, the present invention is applied to an image forming apparatus using a non-contact transfer method, but the present invention can of course be applied to an image using a -21 (19) 1269947 contact transfer method. Form the device. In other words, in the conventional contact type transfer method, as a countermeasure against damage of the photosensitive drum, for example, the pressing force of the transfer roller to the photosensitive drum can be reduced, or the material of the transfer roller can be changed to a softer hardness. Since the transfer offset is liable to occur in such a case, the present invention can effectively suppress the occurrence of transfer offset. [Effects of the Invention] As described above, in the present invention, the transfer offset phenomenon caused by the bending of the paper during the conveyance of the paper can be easily suppressed only by changing the conveying speed of the paper. According to the above invention, the transfer offset phenomenon which occurs due to the bending of the paper during conveyance can be suppressed with a simple structure. The above description is only the preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes can be made to the present invention. All modifications, equivalent substitutions, improvements, etc., which are within the spirit and scope of the invention, are intended to be included within the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic cross-sectional view showing a part of an image forming apparatus according to an embodiment of the present invention. Fig. 2 is a control block diagram of the above image forming apparatus. Figure 3 is a flow chart of paper conveying control processing. Figure 4 is a diagram showing the basic concept of the timing of changing the conveying speed of different papers -22- (20) 1269947. Fig. 5 is a flow chart showing the paper conveyance control process of another embodiment. [Description of main component symbols] 1 : Image forming apparatus 2 : Paper feed section φ 3 : Image forming section 4 : Fixing device 5 : Paper discharge section 6 : Vertical conveyance path 7 : Return conveyance path 1 〇 : Paper feed cassette η : Feedforward roller 1 2 : Paper feed roller φ 1 4 : Manual paper feed tray 15 : Guide member 1 6 : Manual paper feed roller 2 0 : Photosensitive drum 21 : Charger 2 2 : Exposure unit 2 3 : Developing device 2 4 : Transfer roller 2 5 : Cleaning device -23- 1269947 (21) 26 : Aligning roller 3 0 : Heating roller 3 1 : Pressing roller 3 5 : First conveying path 3 6 : 2nd conveying path 3 7 : 3rd transport path 3 8 : 4th transport path φ 4 0 : Control unit 4 1 : Paper feed roller drive unit 42 : Alignment roller drive unit 4 3 : Fixing drive unit 4 4 · Image forming drive unit 4 5 : Paper Size Sensor 46 : Paper Position Sensor 47 : Special Paper Detection Section - 24