Sheet stacker and finisher furnished with the same

A sheet stacking device comprising:

• a sheet discharging port through which sheets are sequentially carried out;
• a sheet discharging path connected to said sheet discharging port, for feeding sheets therefrom;
• tray means disposed downstream of said sheet discharging path;
• a sheet-end regulating member provided on the tray means;
• conveying means for transporting toward said sheet-end regulating member sheets carried out onto the tray means through the sheet discharging port, said conveying means configured so as, in conveying toward said sheet-end regulating member a sheet having been carried in onto said tray means, to impart conveyance force to the sheet for a running time predetermined according to the nature of the sheet's surface material to keep the sheets orderly stacked on said tray means;
• conveyance control means for controlling said conveying means to impart the conveyance force to the sheet for the predetermined running time;
• and
• sensor means provided in said sheet discharging path and comprising sensors for detecting a sheet moving over a predetermined distance spanning an interval, said sensor means therein for detecting pass time of a sheet being conveyed on said sheet discharging path, and outputting a pass-time determining output signal to said conveyance control means;
• wherein
• said conveyance control means comprises comparing means for comparing the sheet-pass time as determined by the output signal from said sensor means with a preset reference sheet-pass time, and
• said conveyance control means predetermines said running time based on the comparison result from said comparing means.