Sheet conveying apparatus and image forming apparatus

Abstract

Provided is a sheet conveying apparatus which can improve rippling of a sheet. The sheet conveying apparatus which conveys the sheet includes an electromagnetic hysteresis brake 131 which is configured to apply a tension force in a conveying direction of the sheet and a controller 500 C which performs control on the electromagnetic hysteresis brake 131 to vary a load. The controller 500 C performs control on the load of the electromagnetic hysteresis brake 131 according to information relating to the sheet.

What is claimed is: 
     
         1 . A sheet conveying apparatus which conveys a sheet with an image formed thereon by an image forming portion, comprising:
 a load portion which is configured to apply a tension force in a conveying direction to the sheet; and   a load controller which performs control on the load portion to vary a load thereof,   wherein the load controller performs control on the load portion to vary the load thereof according to information relating to the sheet.   
     
     
         2 . The sheet conveying apparatus according to  claim 1 , further comprising:
 a first roller pair which includes a first roller A and a first roller B,   wherein the first roller B comes in press contact with the first roller A to form a nip portion, and nips and conveys the sheet; and   a second roller pair which includes a second roller A and a second roller B and is positioned on a downstream side in the conveying direction of the first roller pair,   wherein the second roller B comes in press contact with the second roller A to form a nip portion, and nips and conveys the sheet,   wherein an outer diameter of at least one of the first roller A, the first roller B, the second roller A, and the second roller B in a center area in the width direction perpendicular to the conveying direction of the sheet is larger than that in an end portion, and   wherein the load portion applies a load onto a rotation of the first roller pair.   
     
     
         3 . The sheet conveying apparatus according to  claim 1 ,
 wherein the load portion includes an electromagnetic brake of which the brake torque is changed by changing an exciting current, and   wherein the load controller performs control on the load portion to vary the load by changing a current value excited in the load portion.   
     
     
         4 . The sheet conveying apparatus according to  claim 1 ,
 wherein the load portion includes a plurality of torque limiters and a plurality of clutches which connects or disconnects the torque limiters, and   wherein the load controller performs control such that the clutches are selectively connected or disconnected to cause the torque limiters to vary the load.   
     
     
         5 . The sheet conveying apparatus according to  claim 1 ,
 wherein the information relating to the sheet is information relating to at least one of a basis weight, a type of the sheet, an environmental humidity, a humidity contained in the sheet, and an image density on the sheet.   
     
     
         6 . The sheet conveying apparatus according to  claim 1 ,
 wherein the information relating to the sheet is input by an operation portion which is provided in the image forming portion.   
     
     
         7 . The sheet conveying apparatus according to  claim 1 ,
 wherein when a basis weight of the sheet is a first basis weight, the load controller sets the load portion to be a first load, and   wherein when the basis weight of the sheet is a second basis weight larger than the first basis weight, the load controller sets the load portion to be a second load larger than the first load.   
     
     
         8 . The sheet conveying apparatus according to  claim 1 ,
 wherein when an image density on the sheet is a first density, the load controller sets the load portion to be a first load, and   wherein when the image density on the sheet is a second density larger than the first density, the load controller sets the load portion to be a second load larger than the first load.   
     
     
         9 . The sheet conveying apparatus according to  claim 1 , further comprising
 a humidity detection portion which detects an environmental humidity,   wherein when the environmental humidity detected by the humidity detection portion is a first humidity, the load controller sets the load portion to be a first load, and   wherein when the environmental humidity detected by the humidity detection portion is a second humidity lower than the first humidity, the load controller sets the load portion to be a second load larger than the first load.   
     
     
         10 . The sheet conveying apparatus according to  claim 1 , further comprising
 a moisture applying apparatus which applies moisture to the sheet on an upstream side in the conveying direction of the sheet from the load portion,   wherein the load controller sets the load portion to be a first load on the sheet of the first humidity, and   wherein the load controller sets the load portion to be a second load smaller than the first load on the sheet of which the humidity is a second humidity larger than the first humidity.   
     
     
         11 . An image forming apparatus comprising:
 an image forming portion which forms a toner image;   a fixing portion which heats and fixes the toner image formed on a sheet by the image forming portion;   a load portion which applies a tension force in a conveying direction to the sheet passed through the fixing portion; and   a load controller which performs control on the load portion to vary a load,   wherein the load controller performs control the load of the load portion according to information relating to the sheet.   
     
     
         12 . The image forming apparatus according to  claim 11 , further comprising:
 a first roller pair which includes a first roller A and a first roller B,   wherein the first roller B comes in press contact with the first roller A to form a nip portion, and nips and conveys the sheet; and   a second roller pair which includes a second roller A and a second roller B and is positioned on a downstream side in the conveying direction of the first roller pair,   wherein the second roller B comes in press contact with the second roller A to form a nip portion, and nips and conveys the sheet,   wherein an outer diameter of at least one of the first roller A, the first roller B, the second roller A, and the second roller B in a center area in the width direction perpendicular to the conveying direction of the sheet is larger than that in an end portion, and   wherein the load portion applies a load onto a rotation of the first roller pair.   
     
     
         13 . The image forming apparatus according to  claim 11 , wherein
 wherein the load portion includes an electromagnetic brake of which the brake torque is changed by changing an exciting current, and   wherein the load controller performs control on the load portion to vary the load by changing a current value excited in the load portion.   
     
     
         14 . The image forming apparatus according to  claim 11 , wherein
 wherein the load portion includes a plurality of torque limiters and a plurality of clutches which connects or disconnects the torque limiters, and   wherein the load controller performs control such that the clutches are selectively connected or disconnected to cause the torque limiters to vary the load.   
     
     
         15 . The image forming apparatus according to  claim 11 , wherein
 wherein the information relating to the sheet is information relating to at least one of a basis weight, a type of the sheet, an environmental humidity, a humidity contained in the sheet, and an image density on the sheet.   
     
     
         16 . The image forming apparatus according to  claim 15 , further comprising
 an operation portion,   wherein the information relating to the sheet is input by the operation portion.   
     
     
         17 . The image forming apparatus according to  claim 11 , wherein
 wherein when a basis weight of the sheet is a first basis weight, the load controller sets the load portion to be a first load, and   wherein when the basis weight of the sheet is a second basis weight larger than the first basis weight, the load controller sets the load portion to be a second load larger than the first load.   
     
     
         18 . The image forming apparatus according to  claim 11 , wherein
 wherein when an image density on the sheet is a first density, the load controller sets the load portion to be a first load, and   wherein when the image density on the sheet is a second density larger than the first density, the load controller sets the load portion to be a second load larger than the first load.   
     
     
         19 . The image forming apparatus according to  claim 11 , further comprising
 a humidity detection portion which detects an environmental humidity,   wherein when the environmental humidity detected by the humidity detection portion is a first humidity, the load controller sets the load portion to be a first load, and   wherein when the environmental humidity detected by the humidity detection portion is a second humidity lower than the first humidity, the load controller sets the load portion to be a second load larger than the first load.   
     
     
         20 . The image forming apparatus according to  claim 11 , further comprising
 a moisture applying apparatus which applies moisture to the sheet on an upstream side in the conveying direction of the sheet from the load portion,   wherein the load controller sets the load portion to be a first load on the sheet of the first humidity, and   wherein the load controller sets the load portion to be a second load smaller than the first load on the sheet of which the humidity is a second humidity larger than the first humidity.