Devices for sorting and stacking sheets of paper are not new, but it can be generally stated that all other sorters need enough velocity for the sheet to be thrown in to the tray. As the rollers that drive the paper are not in the tray stacking area, the only way for the paper to get fully into the tray is to be thrown. Upward sloping trays are the result, and it is important to have the tail edge of the sheets in the tray near the entry point of the next sheet to avoid head-to-tail crashes of the paper.
Thus it is the common practice to have the new sheet thrown into a tray which is sloped up at about 40 degrees. The paper entering the tray normally goes several inches beyond where it must come to rest, but slides back because of the tray slope.
There have been "Chain delivery stackers" on printing presses made by companies such as Addressagraph Multigraph, Ditty Glasser, and others for many years. These pull the sheet into the stacking area for reliable stacking.
Other sorters feed the new sheet about one inch or more over the lower surface of the tray area, even when the capacity is only a quarter of an inch stack of paper. This is done because the trailing edge, or corner, of the top sheets in the tray often curl up. If the leading edge of the new sheet coming into the tray hits the tail edge of a sheet already in the tray, there is a paper jam, a mis-sort, or a sheet is pushed out of the stacking area. Feeding the paper well above where the sheets in the tray should lie is the conventional way to solve this problem, but very curled paper still causes problems. Also, it adds size to the sorter and/or the need to open the tray spacing to receive a sheet. Examples of sorters that open the tray spacing so that the new sheet can come into the tray well above the sheets in the tray, then closing the stack to reduce the size of the sorter are shown in U.S. Pat. Nos.:
______________________________________ U.S. Pat. No. 2,589676 Crissy U.S. Pat. No. 4,328,962 DuBois U.S. Pat. No. 4,332,377 DuBois U.S. Pat. No. 4,397,461 DuBois U.S. Pat. No. 4,433,837 Romanowski ______________________________________
The present invention uses fixed trays that can be fully loaded with paper as the curl problem is eliminated.