Sheet storage device and image forming unit therewith

Abstract

A sheet storage device includes a housing, a sheet stacking tray, a shaft, a first pulley, a second pulley, a plurality of wires, and a driving device. The driving device includes a drive portion and a drive transfer portion. The sheet stacking tray ascends as a driving-side coupling rotates in a forward direction, and descends as the driving-side coupling rotates in a reverse direction. When a driven-side coupling stops rotating in the reverse direction, the driving-side coupling rotates idly relative to the driven-side coupling.

What is claimed is: 
     
         1 . A sheet storage device comprising:
 a housing;   a sheet stacking tray that is supported inside the housing so as to be ascendable and descendable and on which a sheet is stacked;   a shaft that extends in a width direction of the housing and that is supported so as to be rotatable in forward and reverse directions;   a first pulley that is fixed to one end of the shaft;   a second pulley that is fixed to another end part of the shaft;
 a plurality of wires suspending the sheet stacking tray; the plurality of wires wound around the first and second pulleys as the shaft rotates in a forward direction, and unwound from the first and second pulleys as the shaft rotates in a reverse direction; and 
   a driving device including:
 a drive portion that generates a rotational driving force; and 
 a drive transfer portion that transmits the rotational driving force in a forward direction to the first pulley and that shuts off the rotational driving force in a reverse-direction, 
   wherein   the drive transfer portion includes:
 a driving-side coupling that is provided on a drive shaft of the drive portion so as to rotate together with the drive shaft, the driving-side coupling rotating together with the drive shaft; and 
 a driven-side coupling that is provided on the first pulley so as to rotate together with the first pulley, the driven-side coupling being coupled to the driving-side coupling, 
   when with the rotational driving force in a forward direction the driving-side coupling rotates in the forward direction, the driving-side coupling and the driven-side coupling couple to each other to transmit the rotational driving force in the forward-direction from the drive portion, so that the first and second pulley rotates in the forward direction with the shaft, so that the plurality of wires are wound around the first and second pulleys to lift up the sheet stacking tray,   when with the rotational driving force in the reverse direction the driving-side coupling rotates in the reverse direction, the driven-side coupling with uncoupled state, by following rotation of the driving-side coupling in the reverse direction, rotate in the reverse direction, due to a weight of the sheet stacking tray the plurality of wires are unwound from the first pulley and the sheet stacking tray descends, and   when the sheet stacking tray stops descending and the driven-side coupling stops rotating in the reverse direction while the driving-side coupling is rotating in the reverse direction, the driving-side coupling rotates idly relative to the driven-side coupling that has stopped.   
     
     
         2 . The sheet storage device according to  claim 1 , wherein
 the driving-side coupling is disposed to face the driven-side coupling on an axis of the drive shaft so as to be slidable in the direction along the axis of the drive shaft,   the drive transfer portion includes an urging member that urges the driving-side coupling toward the driven-side coupling,   the driving-side coupling makes contact with the driven-side coupling and rotates in the forward direction to engage with the driven-side coupling so as to transmit the rotational driving force in the forward direction of the drive portion to the first pulley.   
     
     
         3 . The sheet storage device according to  claim 1 , wherein
 The first and second pulleys each have a plurality of cylindrical winding portions around which the plurality of wires are wound, and   the plurality of winding portions are arranged side by side in an axis direction of the drive shaft and have a tapered outer diameter that increases toward one side in the axial direction.   
     
     
         4 . The sheet storage device according to  claim 3 , wherein
 the plurality of wires includes:
 a first wire and a second wire of which one ends are fixed respectively to the plurality of winding portions of the first pulley; and 
 a third wire and a fourth wire of which one ends are fixed respectively to the plurality of winding portions of the second pulley. 
   
     
     
         5 . The sheet storage device according to  claim 1 , wherein
 the driven-side coupling faces the driving-side coupling with respect to the direction along an axis of the drive shaft, and is formed integrally with the first pulley on an end surface of the first pulley facing the driven-side coupling.   
     
     
         6 . An image forming unit comprising:
 an image forming apparatus including an image forming portion that forms an image on the sheet; and   the sheet storage device according to  claim 1  including a sheet feed mechanism that is connected to the image forming apparatus and that feeds the sheet to the image forming portion.