Sheet transporting device

Abstract

A roller shaft extends between a pair of frame walls. A feed roller is mounted on the roller shaft for feeding a stack of sheets placed on a feeding tray one by one from an uppermost sheet. A transmission gear is concentrically coupled to one end portion of the roller shaft to be rotated by driving of a driving motor. A boss extends axially inwardly from a center position of the transmission gear. The roller shaft has a flat key portion at the one end portion thereof. The flat key portion has a substantially D-shape in cross section. The flat key portion is coupled to the boss by being received in a non-circular hole of the boss. With this arrangement, an eccentric displacement of the roller shaft relative to the transmission gear is suppressed, and the feed roller is easily detachable from the roller shaft with a simplified operation.

What is claimed is:  
     
         1 . A sheet transporting device for use in an image forming apparatus comprising: 
 a pair of frame walls opposed to each other;    a roller shaft extending between the frame walls, opposite end portions of the roller shaft being received in insertion holes formed in the frame walls, respectively;    a feed roller which is mounted on the roller shaft and is rotatable about an axis of the roller shaft, the feed roller for feeding sheets stacked on a sheet stacking portion of the image forming apparatus one by one from an uppermost sheet;    a transmission gear which is provided at an outer side of one of the frame walls, the transmission gear having a center position opposed to the insertion hole of the frame wall; and    an attachment structure which is so configured as to mount the roller shaft between the frame walls so as to transmit a driving force of the transmission gear to the roller shaft, the attachment structure including: 
 a boss which is formed co-axially with the transmission gear and projects in the axial direction of the roller shaft to be received in the insertion hole of the frame wall, the boss being formed with a non-circular hole extending in the axial direction of the roller shaft; and  
 an engaging end portion which is formed in an end portion of the roller shaft and has such a configuration as to be received in the non-circular hole of the boss in a non-rotatable state relative to the transmission gear.  
   
     
     
         2 . The sheet transporting device according to  claim 1 , wherein the other end portion of the roller shaft has a stopper structure which is so configured as to keep the roller shaft from coming off the frame wall through the insertion hole formed in the frame wall unless an external force is applied, the stopper structure being detachably attachable to the sheet transporting device.  
     
     
         3 . The sheet transporting device according to  claim 2 , wherein the stopper structure includes a cutaway groove which is formed in a surface of the other end portion of the roller shaft, and a stopper ring which is detachably mounted in the cutaway groove.