Sheet post-processing device and image forming apparatus

A sheet post-processing device comprising:

• placement means for placing sheets discharged from an image forming apparatus,
• restraining means situated adjacent to the placement means to be movable between a restraining position at which the restraining means restrains and aligns edges of the sheets discharged into the placement means and a retraction position to which the restraining means is retracted from the restraining position,
• urging means disposed adjacent to the placement means for urging the sheets discharged into the placement means toward the restraining means,
• sheet moving means situated adjacent to the placement means to be movable between a first position at which the sheet moving means nips the sheets on the placement means to move the sheets for a predetermined distance and a second position at which the sheet moving means is located away from the sheets on the placement means to allow the urging means to urge the sheets,
• post processing means including at least one of folding means for folding the sheets and saddle stitching means for stitching the sheets, and
• control means for controlling the restraining means, the urging means, and the sheet moving means to repeat steps in which the restraining means moves from the restraining position to the retraction position, the sheet moving means moves a first sheet on the placement means for the predetermined distance, the restraining means moves from the retraction position to the restraining position, the sheet moving means moves to the second position, and the urging means urges a next sheet toward the restraining means for alignment, until a stack of the sheets is formed on the placement means with edges of the sheets being successively offset, said control means controlling the post processing means for performing post processing to the stack of the sheets.

An image forming apparatus comprising:

• storage means for storing sheets,
• sheet feeder means for feeding the sheets from the storage means one by one,
• image forming means for forming an image on the sheets fed by the sheet feeder means,
• placement means for placing the sheets with the image formed thereon discharged from the image forming means,
• restraining means disposed adjacent to the placement means to be movable between a restraining position at which the restraining means restrains and aligns edges of the sheets discharged into the placement means and a retraction position to which the restraining means is retracted from the restraining position,
• urging means disposed adjacent to the placement means for urging the sheets discharged into the placement means toward the restraining means,
• sheet moving means situated adjacent to the placement means to be movable between a first position at which the sheet moving means nips the sheets on the placement means and moves the sheets by a predetermined distance and a second position at which the sheet moving means is located away from the sheets on the placement means and allows the urging means to urge the sheets,
• post processing means including at least one of folding means for folding the sheets and saddle stitching means for stitching the sheets, and
• control means for controlling the restraining means, the urging means, and the sheet moving means to repeat steps in which the restraining means moves from the restraining position to the retraction position, the sheet moving means moves a first sheet on the placement means for the predetermined distance, the restraining means moves from the retraction position to the restraining position, the sheet moving means moves to the second position, and the urging means urges a next sheet toward the restraining means for alignment, until a stack of the sheets is formed on the placement means with edges of the sheets being successively offset, said control means controlling the post processing means for performing post processing to the stack of the sheets.