1. Field of the Invention
The present invention relates to a sheet processing apparatus which performs a process of, for example, double folding a sheet bundle made of a plurality of sheets, and discharging the same so as to be stacked, and an image forming apparatus including this sheet processing apparatus.
2. Description of the Related Art
Conventionally, an image forming apparatus for forming an image on a sheet, such as a copying machine, and a laser beam printer, may be provided with a sheet processing apparatus for bringing a sheet, on which an image has been formed, into a bundle state, performing a binding process at the substantially central portion, and performing a folding process, etc., so as to perform a saddle stitch bookbinding. In a sheet processing apparatus illustrated in FIGS. 21 to 23, sheets, on which images have been formed, are stored in a storage portion 803 so as to be bundled, and a binding process is performed at a substantially central portion of the sheet bundle. Moreover, the sheet bundle is jabbed at its substantially central portion by a jabbing member 830 so as to be put into a nip portion of a pair of folding rollers 810. A double folding process is performed to the sheet bundle while being conveyed by the pair of folding rollers 810. Then, a folded end portion processing is performed in order to further strengthen the folded end portion of the sheet bundle (which is called “folded bundle” hereinafter) to which a double folding processing has been performed. After that, the folded bundle is discharged to a folded bundle tray 840 so as to be stacked (refer to Japanese Patent Laid-Open No. 2008-184311).
FIG. 20 illustrates a flow chart when a folding process is performed to a second copy or succeeding copies in the conventional apparatus mentioned above. When a saddle stitch bookbinding mode is selected, a sheet is stored in a storage portion 803, and aligning and stapling processes are performed (S101). After that, a sheet bundle, to which the stapling process has been performed, is jabbed by the jabbing member 830 at its substantially central portion where the stapling process has been performed so as to be pushed into the nip portion of the pair of folding rollers 810. A double folding process is performed to the sheet bundle while being conveyed by the pair of folding rollers 810 (S102). The folded bundle to which the folding process has been performed is stopped at a position where its folded end portion is subjected to a folded end portion processing by a press unit 860 (S103).
Then, the folded end portion processing is performed (S104), but, during this folded end potion processing, the folded bundle P1, which has already been discharged and stacked on the folded bundle tray 840, is positioned outside the moving region of the press unit 860 (FIG. 21). Then, after finishing the folded end portion processing of the succeeding folded bundle P2, conveyer belts 844, 845 are reversely rotated so that the folded bundle P1 positioned outside the moving region is moved back to a bundle receiving position adjacent to a pair of second folding conveying rollers 812 (S105, FIG. 22).
Note that the moving back amount L of this folded bundle is determined according to the kind of sheet to be used, such that, when the succeeding folded bundle P2 is discharged, the leading edge (the downstream edge in the conveying direction) of the succeeding folded bundle P2 is positioned downstream in the conveying direction of the trailing edge (the upstream edge in the conveying direction) of the preceding folded bundle P1 which has already been stacked.
After that, the folded bundle P2 is discharged to the folded bundle tray 840 (S106), and the conveyer belts 844, 845 are forwardly rotated so that the folded bundles are stacked in imbricate state, thereby preventing a sheet jam or a sheet bending (S107).
At this time, when the length of the folded bundle P2, to which the folded end portion processing is to be performed, in the conveying direction is included within bundle conveying guides 813, 814, the trailing edge of the folded bundle is located outside the storage region (stacking region) of the storage portion 803. Therefore, during the folded end portion processing of the folded bundle, a sheet of the succeeding sheet bundle can be conveyed to the storage portion 803.
However, when the length of the folded bundle P2, to which the folded end portion processing is to be performed, in the conveying direction is not included within the bundle conveying guides 813, 814, the trailing edge of the folded bundle remains in the storage region of the storage portion 803 (FIG. 23). In this case, after finishing the folded end portion processing, this succeeding folded bundle P2 cannot be discharged until the trailing edge of the preceding folded bundle P1, which has already been discharged and stacked on the folded bundle tray 840, is finally moved back to the position adjacent to the pair of second folding conveying rollers 812. Accordingly, the start of conveying the succeeding sheet bundle to the sheet storage portion is delayed, thereby causing a problem that the productivity is deteriorated in the conventional control method.
Moreover, if the conveying length of the bundle conveying guides 813, 814 is increased so as to correspond to the length of the folded bundle P2, to which the folded end portion processing is performed, in the conveying direction, such that the folded bundle P2 is included within the bundle conveying guides 813, 814, although the deterioration of productivity can be prevented, there is a problem that the size of apparatus is caused to be increased.