Sheet conveying device and image forming apparatus including same

Abstract

A sheet conveying device includes a conveying roller pair, a correction unit, and a control unit. The correction unit includes a correction roller pair and a roller holder. The control unit moves the roller holder from a reference position, and returns the roller holder to the reference position after the sheet is nipped by the correction roller pair, and after this sheet correction operation, the control unit releases the nip of the conveying roller pair. At least either a swing speed vh when returning the roller holder to the reference position, or a deflection amount of the sheet before the roller holder is returned to the reference position, is adjusted so that tension is not applied to the sheet between the conveying roller pair and the correction roller pair.

What is claimed is: 
     
         1 . A sheet conveying device comprising:
 a conveying roller pair for conveying a sheet at a first speed v1;   an edge detection sensor disposed on a downstream side of the conveying roller pair in a conveying direction so as to detect an edge position of the sheet in a width direction perpendicular to the conveying direction;   a skew detection sensor disposed on the downstream side of the conveying roller pair in the conveying direction so as to detect skew of the sheet;   a correction unit disposed on the downstream side of the edge detection sensor and the skew detection sensor in the conveying direction, the correction unit including a correction roller pair that nips the sheet conveyed by the conveying roller pair so as to convey the sheet at a second speed v2 slower than the first speed v1 and is capable releasing the nip,   a roller holder that supports the correction roller pair in a swingable manner in the conveying direction about a swing fulcrum on one end side in the sheet width direction, and in a reciprocatable manner in the width direction, a skew correction motor that drives the roller holder to swing in the conveying direction,   a shift correction motor that drives the roller holder to move in the sheet width direction, and   a control unit controls the conveying roller pair and the correction unit basis on the detection results by the edge detection sensor and the skew detection sensor, wherein   the control unit performs a sheet correction operation which inclines the roller holder from a reference position by a predetermined angle on the basis of a detection result by the skew detection sensor before the front end of the sheet reaches the correction unit, returns the roller holder to the reference position after the sheet is nipped by the correction roller pair, and moves the roller holder in the sheet width direction basis on the detection result by the edge detection sensor, and after this sheet correction operation, the control unit releases the nip of the conveying roller pair, and   at least either a swing speed vh when returning the roller holder to the reference position, or a deflection amount of the sheet before the roller holder is returned to the reference position, is adjusted so that tension is not applied to the sheet between the conveying roller pair and the correction roller pair.   
     
     
         2 . The sheet conveying device according to  claim 1 , wherein the swing speed vh satisfies vh≤v1−v2. 
     
     
         3 . The sheet conveying device according to  claim 1 , wherein the deflection amount is larger than or equal to a maximum movement amount of the roller holder in the conveying direction. 
     
     
         4 . The sheet conveying device according to  claim 1 , further comprising a registration sensor disposed on the downstream side of the correction unit in the conveying direction so as to detect passing of the sheet, wherein
 the control unit returns the roller holder to the reference position at timing when the registration sensor detects the front end of the sheet.   
     
     
         5 . The sheet conveying device according to  claim 1 , wherein the skew correction motor and the shift correction motor are stepping motors capable of controlling rotation direction and rotation amount by pulse control. 
     
     
         6 . An image forming apparatus comprising:
 the sheet conveying device according to  claim 1 ; and   an image forming unit arranged to form an image on the sheet conveyed by the sheet conveying device.