Automatic document feeder capable of feeding a document in the form of a computer form

Claim 1

An automatic document feeder (ADF) for an image recorder having a top open platen, comprising: document transporting means located to face the platen for transporting a continuous document constituted by a sequence of continuous pages and having a plurality of equally spaced feed holes; holes sensor means located upstream of the platen with respect to an intended direction of transport of the continuous document for generating feed pulses by sensing the feed holes of said continuous document; counter means for counting said generated feed pulses; document sensor means for sensing presence of the continuous document at a sensing position where the feed holes are sensed by said holes sensor means; calculating means for subtracting, when said document sensor means stops sensing the presence of the continuous document while transport for setting a last page of said document on the platen is under way, said calculating means subtracting a number of feed holes having been counted by said holes sensor during an interval between a start of said transport and a time when said document sensor means stops sensing presence of said continuous document from a number corresponding to a number of feed holes of one page of said document; document displacement sensor means for sensing a displacement of the continuous document from the time when said document sensor means stops sensing presence of the continuous document; and control means for controlling said document transporting means such that the transport of the continuous document is stopped when, while said document sensor means is sensing presence of said document, the number of said feed holes having been sensed by said holes sensor means coincides with a number of feed holes corresponding to one page, and such that said transport of said document is interrupted when, after said document sensor means has stopped sensing presence of said document, a displacement of said document having been sensed by said document displacement sensor means coincides with a displacement associated with a result of calculation produced by said calculating means; wherein said calculating means further includes means for multiplying a result of said subtracting by said calculating means by a predetermined constant, and wherein a product thus obtained is provided to said control means, said control means controlling a motor drive downstream of said holes sensor and said document sensor, wherein said control means controls said motor drive based upon said product, and wherein said document displacement sensor means includes an encoder associated with said motor drive.