Recording sheet stacking apparatus in image recording system

Claim 1

A sheet stacking apparatus for use in an image recording system in which a feeding means feeds recording sheets to an image forming means to record a first image on a first side of said sheets, a conveying means conveys the recording sheets with the first image recorded thereon to a sheet stacking apparatus, and said feeding means delivers said recording sheets from said sheet stacking apparatus to said image forming means to form a second image on a second side of said sheets, said sheet stacking apparatus comprising; a sheet stacking means having a tray for receiving said recording sheets thereon; a stopper provided on said tray to stop said recording sheets and align the leading edges of said recording sheets; a bumper roller which is capable of retractably shifting to a downward position to be in pressure contact with said recording sheets and transport said recording sheets by rotary motion of said roller so that the leading edges thereof reaches said stopper and, an upward position to detach from said recording sheets when said leading edges reach said stopper; a sensor located upstream from said roller for detecting the passage of said recording sheets through said conveying means and; a control means for controlling the position of said roller in response to a signal from said sensor so that said roller is shifted downward onto the recording sheets to be aligned when said sheets enter said tray.