초록 ▼

A method and apparatus for determining the distance between transitions from a first logical state to a second logical state stored on a medium (i.e., a document). This determination is used to precisely characterize the information pattern in order to authenticate the information and the medium on

A method and apparatus for determining the distance between transitions from a first logical state to a second logical state stored on a medium (i.e., a document). This determination is used to precisely characterize the information pattern in order to authenticate the information and the medium on which the information is stored. The invention uses a reader having a leading and trailing read apparatus which allow information to be read simultaneously from two or more locations spaced a known distance apart. The distance between the centerlines of each read apparatus is preferably an odd integer multiple of one half the distance between logical clock transitions. The distance between a first transition at the leading read apparatus and a next transition at the trailing read apparatus is used as a reference (i.e., the "Reference Value"). The Reference Value is compared with the distance between the first transition and the next transition on the medium (i.e., the "Jitter Value"). Detection of an deviations in spacing between transitions is unaffected by variations in the velocity of the medium with respect to the reader.

대표청구항 ▼

[ What is claimed is:] [1.] A method for determining the distance between a first point and a second point on a storage medium, the first and second points being detectable by a leading and trailing read apparatus as the first and second points move past the leading and trailing read apparatus, the

[ What is claimed is:] [1.] A method for determining the distance between a first point and a second point on a storage medium, the first and second points being detectable by a leading and trailing read apparatus as the first and second points move past the leading and trailing read apparatus, the leading and trailing read apparatus being spaced apart a known distance, the method comprising the steps of:(a) detecting the first point as the first point moves past the leading read apparatus;(b) detecting the second point as the second point moves past the leading read apparatus;(c) detecting the first point as the first point moves past the trailing read apparatus;(d) measuring a jitter Value starting from the detection of the first point at the leading read apparatus and ending upon detection of the second point at the leading read apparatus; and(e) measuring, a Reference Value starting from the detection of the first point at the leading read apparatus and ending upon detection of the first point at the trailing read apparatus.