Media-tracking system using thermal fluoresence quenching
A system is described for tracking a position of a receiver medium as it travels along a media path. A heat source provides heat to the receiver medium in a localized area sufficient to permanently alter a fluorescent agent in the receiver medium, thereby forming a reference mark characterized by a reduced level of fluorescence. A stimulating light source illuminates the receiver medium at a downstream position along the media path, the stimulating light source having a spectrum adapted to stimulate the fluorescent agent to fluoresce thereby producing emitted light. A sensor is used to sense the emitted light from the receiver medium thereby providing a sensed light level signal. The sensed light level signal is analyzed to determine a position of the receiver medium by detecting the reduced level of fluorescence associated with the reference mark.
1. A system for tracking a position of a receiver medium as it travels along a media path, comprising:
a heat source located at a first position along the media path adapted to provide heat to the receiver medium in a localized area, the receiver medium including a fluorescent agent that fluoresces to produce emitted light with an emission spectrum when illuminated by a light source having an appropriate excitation spectrum, wherein the provided heat is sufficient to permanently alter the fluorescent agent thereby forming a reference mark characterized by a reduced level of fluorescence;
a stimulating light source that illuminates the receiver medium when it has traveled to a second position along the media path, the stimulating light source having a spectrum adapted to stimulate the fluorescent agent to fluoresce thereby producing emitted light;
a sensor adapted to sense the emitted light from the receiver medium at the second position along the media path and provide a sensed light level signal; and
a data processor adapted to analyze the sensed light level signal to determine a position of the receiver medium as the receiver medium passes through the second position along the media path by detecting the reduced level of fluorescence associated with the reference mark.
2. The system of claim 1 wherein stimulating light source is an ultraviolet radiation source and the sensor senses emitted light having a visible emission spectrum.
3. The system of claim 1 wherein the heat source provides heat to the receiver medium by bringing a resistive heater into contact with a surface of the receiver medium.
4. The system of claim 3 wherein the media path includes a roller around which the receiver medium is wrapped or over which the receiver medium travels, and wherein the resistive heater is incorporated into a surface of the roller.
5. The system of claim 1 wherein the heat source provides heat to the receiver medium by illuminating it with a laser beam.
6. The system of claim 1 wherein the receiver medium moves along the media path in an in-track direction, and wherein the detected position of the reference mark is used to determine an in-track position of the receiver medium or a cross-track position of the receiver medium, the in-track position being a position in the in-track direction, and the cross-track position being a position in a cross-track direction that is perpendicular to the in-track direction.
7. The system of claim 1 wherein the heat source is used to form a plurality of reference marks at different predefined positions on the reference medium.
8. The system of claim 7 wherein the detected positions of the plurality of reference marks are used to determine an amount of skew of the reference medium, or a change in a size of the reference medium.
9. The system of claim 7 wherein the receiver medium moves along the media path in an in-track direction, and wherein at least two of the reference marks are formed at different cross-track positions on the reference medium, the cross-track positions being positions in a cross-track direction that is perpendicular to the in-track direction, the different cross-track positions being separated by predefined spacings.
10. The system of claim 7 wherein the receiver medium moves along the media path in an in-track direction, and wherein at least some of the reference marks are spaced apart at different in-track positions on the reference medium, the different in-track positions being separated by predefined spacings.
11. The system of claim 10 further including an encoding system that is used to determine a distance that the receiver medium has moved along the media path, and wherein the encoding system is used to determine the in-track position of the receiver medium intermediate to the detection of the reference marks.
12. The system of claim 11 wherein the encoding system determines the distance that the receiver medium has moved along the media path responsive to a detected roller position, a motor drive control signal, or a signal from an optical motion detection system.
13. The system of claim 1 wherein the receiver medium is a continuous web of receiver medium or the receiver medium is an individual sheet of receiver medium.
14. The system of claim 1 wherein the position of the reference mark is determined by computing a centroid of the sensed signal as a function of position.
15. The system of claim 1 wherein the position of the reference mark is determined by detecting a leading edge and a trailing edge of the reference mark and determining a midpoint between the leading edge and the trailing edge.
16. The system of claim 1 further including one or more additional sensors located at one or more additional positions along the media path adapted to sense the reference mark as the receiver medium passes through the one or more additional positions along the media path.
17. The system of claim 1 further including:
a printing system adapted to print image data onto the receiver medium; and
a control system that controls the printing system responsive to the detected position of the receiver medium in order to properly align the printed image data with the receiver medium.
18. The system of claim 1 further including:
a finishing system adapted to perform one or more media finishing operations on the receiver medium; and
a control system that controls the finishing system responsive to the detected position of the receiver medium in order to properly align the one or more media finishing operations with the receiver medium.
19. The system of claim 1 wherein the receiver medium moves along the media path in an in-track direction and the sensor provides a sensed signal at a particular cross-track sensor position, the cross-track sensor position being a position in a cross-track direction that is perpendicular to the in-track direction, and wherein the reference mark has a tapered shape thereby enabling a cross-track position of the receiver medium to be determined responsive to a sensed width of the reference mark at the particular cross-track sensor position.
20. The system of claim 1 wherein the sensor is a one-dimensional image sensor that forms a two-dimensional image of a portion of the receiver medium including the reference mark by capturing one-dimensional images at a series of times separated by predefined time intervals as the receiver medium is moved past the sensor.
21. The system of claim 1 wherein the sensor is a two-dimensional image sensor that captures a two-dimensional image of a portion of the receiver medium including the reference mark.