Digital postage franking with coherent light velocimetry

US6409294B1 · kind B1 · utility

Assignee

• Ascom Hasler Mailing Systems Inc · US

Inventors

• Eric Zimmermann · New York, US
• Christian Moy · Grossaffoltern, CH

Key dates

• Filing date: May 18, 2000
• Grant date: Jun 25, 2002
• Expiry date: May 18, 2020

Classification

• Technology area (CPC G): Physics
• CPC primary: G07B2017/00693
• WIPO field: Control
• WIPO sector: Instruments

Abstract

A postage meter (franking machine) uses a digital print head such as an ink-jet or thermal transfer or dot-matrix print head, for which it is necessary to know the velocity of the mail piece passing by the print head. Two collimated monochromatic beams strike the mail piece, one at an angle leading the mail piece velocity and the other at an angle lagging the mail piece velocity. The beams converge yielding a sensing region filled with a diffraction pattern. The mail piece, assumed to be rough at a scale that is appropriate for the velocity measurement, moves at some velocity. A detector detects light intensity (photon flux) at a small region within the sensing region, and the intensity signal has a frequency that is proportional to the mail piece velocity. The frequency is detected or measured, the instantaneous velocity is derived therefrom, and the velocity is used to control the print head. In this way a two-dimensional print image (postage indicium) is faithfully printed on the mail piece with minimal distortion even in the event of non-constant velocity of the mail piece.