The present invention relates to a sheet trimming apparatus which trims plural sheets, a sheet post-processing apparatus equipped with the sheet-trimming apparatus and an image-forming system equipped with the sheet-trimming apparatus.
With a high-speed image-forming apparatus such as an electrophotograghic type image-forming apparatus connected with a sheet post-processing apparatus which carries out various kinds of post-processes, there have been popularized versatile image-forming systems which make it possible that various kinds of processes are conducted by one apparatus, such as a perforating process, a stitching process, a folding process on sheets which have been image-formed.
The various kinds of post-processing apparatuses include a sheet-trimming apparatus which evens the edge of a bundle of plural sheets and, for example, an image-forming system including a trimming apparatus which trims an edge of sheets after a center-folding process and a saddle-stitching process are carried out has been disclosed in Patent Document 1. The sheet-trimming apparatus described in Patent Document 1 is called a guillotine type one, the trimming blade of which is pressed on sheets in the direction perpendicular to the surface of sheets to trim them.
A sheet-trimming apparatus the trimming blade of which is pressed on sheets in an oblique direction has been disclosed in Patent Document 2.    Patent Document 1 Japanese Patent Application Publication No. 2003-228205    Patent Document 2 Japanese Patent Application Publication No. 2003-191196
The guillotine type trimming apparatus described in Patent Document 1 needs large force for driving the trimming blade, and besides, it needs a high power motor because the power of driving means needs to be set at the maximum value in the working range, and thus, there are caused problems that it needs a large-sized apparatus and high power consumption. Especially it is difficult to incorporate the trimming apparatus into a post-processing apparatus composing an image-forming system.
Regarding the trimming apparatus described in Patent Document 2, though a table which sustains sheets also functions as a blade-receiving member which receives the trimming blade, a part of the table is chopped off by the trimming blade during trimming operations repeated many times and a notch is formed on the table, resulting in some problems such as incomplete cut of sheets and unevenness of the trimmed edge surface caused by the notch.
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