Patent ID: 8651481

Claim:
A two dimensional banknote thickness detection assembly, for detecting the thickness of a banknote on a document transport path, the assembly comprising a plurality of banknote thickness detection apparatuses, each apparatus comprising: a first detector unit having a sheet document contact point adjacent the document transport path, the detector unit comprising a piezoelectric element, a first portion of the piezoelectric element being fixed relative to the document transport path, and the piezoelectric element being arranged such that contact between a banknote and the sheet document contact point as a banknote passes the detector unit along the document transport path causes flexing of a second portion of the piezoelectric element relative to its first portion; and a sensing circuit connected to the piezoelectric element for outputting an electric signal based on a charge generated by the piezoelectric element upon flexing, the outputted signal being related to the thickness of the banknote; wherein the respective sheet document contact points of each apparatus are spaced laterally from one another in a direction substantially perpendicular to the direction of passage of the banknote, such that the outputted signal from each respective sensing circuit relates to the thickness of corresponding laterally spaced regions of the banknote; the assembly further comprising a processor adapted to generate a two dimensional spatial map of the thickness of at least a portion of the banknote, based on at least some of the outputted signals, the relative positions of the corresponding detector units and knowledge of the speed at which the banknote passes between the reference surface and the detector unit.