Patent ID: 8506036

Claim:
An imaging device comprising: a source of print media; a media transport system configured to transport the print media along a media path; a plurality of ink jets in a printhead associated with the media path, the plurality of ink jets being configured to eject drops of substantially clear ink onto the print media, the substantially clear ink having a fluorescent characteristic and the print media not having the fluorescent characteristic, the fluorescent characteristic enabling light to be emitted at an emission wavelength in response to light at an activating wavelength illuminating the fluorescent characteristic, the activating wavelength being different than the emission wavelength; a fluorescence sensor associated with the media path, the fluorescence sensor including (i) a light emitter for illuminating the print media and the drops of substantially clear ink on the print media with light of the activating wavelength, and (ii) a light detector for detecting an intensity of light at the emission wavelength received from positions on the print media where no drops of substantially clear ink were ejected and from positions on the print media where the drops of substantially clear ink were ejected onto the print media, the fluorescence sensor being configured to output signals indicative of the detected fluorescence intensities; and a controller operatively connected to the fluorescence sensor to receive the signals indicative of the fluorescence intensities at the positions where no substantially clear ink was ejected and the signals indicative of the fluorescence intensities at the positions where substantially clear ink was ejected, the controller being configured to identify a drop mass value for each drop of clear ink ejected onto the print media by the plurality of ink jets with reference to the fluorescence intensities indicated by the signals received from the fluorescence sensor, and to modify an operating parameter of the printhead to enable at least one ink jet in the ink jets of the printhead to eject ink drops having a predetermined mass.