US 6,409,294 B1 · Digital postage franking with coherent light velocimetry

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.

Claims20

Dependent claims

A postage meter comprising a digital print head and a velocity sensor having an output, said postage meter having a bed defining a paper path with a direction, said digital print head and said velocity sensor positioned along said paper path;

said velocity sensor comprising a light source and a light sensor, said light source comprising first and second monochromatic collimated beams, said first beam impinging upon said paper path at a first angle leading said direction and defining a sensing area, said second beam impinging upon said sensing area at said first angle lagging said direction, said first and second beams yielding a diffraction pattern within said sensing area;
said light sensor sensing light intensity at a region within said sensing area, said velocity sensor further comprising a frequency detector responsive to said sensed light intensity yielding a signal indicative of the measured frequency, said signal comprising the output of the velocity sensor;
said print head operatively coupled with said velocity sensor output.

Dependencies are inferred from the claim text.

Digital postage franking with coherent light velocimetry

Life of this patent

Digital postage franking with coherent light velocimetry

Life of this patent

Abstract

Claims20