Image forming apparatus

Abstract

An image forming apparatus includes an apparatus main body that carries out an image forming processing with respect to a sheet. A sheet supplying unit is mounted detachably into the apparatus main body and adapted to supply a sheet from a stack of sheets stored therein toward an inside of the apparatus main body. The sheet supplying unit includes a position keeper for keeping the sheet stack in a determined position by contacting sides of the stack. The keeping position is changeable in accordance with the size of a sheet. A lock mechanism locks the position keeper in a keeping position. The locking mechanism releases the locking of the position keeper when the sheet supplying unit is detached from the apparatus main body and placed on a surface. However, the locking mechanism locks the position keeper when the sheet supplying unit is lifted from the surface.

1 . An image forming apparatus comprising:
 an apparatus main body operable to carry out an image forming processing with respect to a sheet; and   a sheet supplying unit detachably mounted into the apparatus main body and adapted to supply a sheet from a stack of sheets stored therein toward an inside of the apparatus main body, wherein:   the sheet supplying unit includes:   a position keeper for keeping the sheet stack in a determined position by contacting with sides of the sheet stack, and the keeping position being changeable in accordance with the size of a sheet; and,   a lock mechanism for locking the position keeper in a keeping position,   the lock mechanism releases the locking of the position keeper when the sheet supplying unit is detached from the apparatus main body and placed on an operative surface and sets the locking of the position keeper when the sheet supplying unit is lifted up from the operative surface.   
   
   
       2 . An image forming apparatus according to  claim 1 , wherein:
 the position keeper includes a recess and projection portion having a plurality of recesses and projections alternately formed at a predetermined pitch in a moving direction thereof,   the lock mechanism includes:
 a lock plate having a locking teeth engageable with the recess and projection portion of the position keeper to keep the position keeper in the keeping position; and, 
 an operating member operable to move the lock plate in a direction of disengaging the locking teeth from the recess and projection portion of the position keeper by receiving a pushing force from the operative surface when the sheet supplying unit is placed on the operative surface. 
   
   
   
       3 . An image forming apparatus according to  claim 2 , wherein:
 one or both of the lock plate and the operating member have an inclined surface in a contact portion where the lock plate and the operating member contact each other,   the inclined surface has an inclination such that the operating member moves the lock plate to release the locking of the position keeper when the operating member receives the pushing force.   
   
   
       4 . An image forming apparatus according to  claim 1 , wherein the position keeper includes a pair of cursors arranged in a sheet widthwise direction and operatively connected with each other, and the pair of cursors are operable to hold the sheet stack on the opposite sides of the sheet stack. 
   
   
       5 . An image forming apparatus according to  claim 4 , wherein
 the position keeper further includes:
 a rack and pinion mechanism which includes
 two racks extending from respective bottoms of the pair of cursors and formed with driving teeth in their respective inner side surfaces, and 
 a pinion engaged with the respective driving teeth of the two racks; and 
 
 a recess and projection portion formed in an outer side surface of at least one of the racks, and having a plurality of recesses and projections alternately formed at a predetermined pitch in a moving direction thereof, 
 the lock mechanism includes a lock plate having a locking teeth engageable with the recess and projection portion of the position keeper to keep the position keeper in the keeping position. 
   
   
   
       6 . An image forming apparatus according to  claim 5 , wherein:
 the projections of the recess and projection portion each have a round shape, and   the locking teeth are saw teeth each having a sharp leading edge.