Method for monitoring a fountain solution layer in an image forming device
Examples of the preferred embodiments use an ink quantity metric (e.g., lightness L*, darkness, image density, line width) of printed content to determine thickness of fountain solution applied by a fountain solution applicator on an imaging member surface and/or determine image forming device real-time image forming modifications for subsequent printings. For example, in real-time during the printing of a print job, a sensor (e.g., spectrometer) may measure the ink quantity metric of the current printing on print substrate. Based on this measurement of printed content output from the image forming device, the image forming device may adjust image forming (e.g., fountain solution deposition flow rate) to reach or maintain a preferred fountain solution thickness on the imaging member surface for subsequent (e.g., next) printings of the print job.
1. A method of measuring fountain solution thickness on an imaging member surface during a printing operation of an image by a digital image forming device, comprising:
a) measuring an ink quantity metric of an image printed at a region of a print substrate with a sensor of the digital image forming device, the image having at least one printed line at the region; and
b) determining, with a controller of the digital image forming device, the thickness of fountain solution on the imaging member surface during the printing operation of the image based on the measured ink quantity metric.
2. The method of claim 1 , the step a) including measuring the ink quantity metric of the image with the sensor being a spectrometer downstream of an image transfer station of the digital image forming device in an image processing direction.
3. The method of claim 2 , further comprising comparing the measured ink quantity metric to a predefined target ink quantity metric, and modifying the fountain solution dispense rate based on the comparison for a subsequent printing of a subsequent image by the digital image forming device using the modified fountain solution dispense rate.
4. The method of claim 1 , the step b) further comprising estimating the thickness of fountain solution on the imaging member surface via a lookup table stored in a storage device of the digital image forming device.
5. The method of claim 1 , wherein the ink quantity metric is one of an image density of the ink across the region and a width of a line of the printed image at the region.
6. The method of claim 1 , wherein the ink quantity metric of the current image printed at the region is a measure of lightness at the region.
7. A method of controlling fountain solution thickness on an imaging member surface of a rotating imaging member in a digital image forming device, the digital image forming device configured to print a current image having an ink quantity metric level at a region of a printed substrate, the method comprising:
a) measuring an ink quantity metric of the current image printed at the region of the printed substrate;
b) comparing the measured ink quantity metric to a predefined target ink quantity metric; and
c) modifying a fountain solution dispense rate based on the comparison for a subsequent printing of a subsequent image by the digital image forming device using the modified fountain solution dispense rate.
8. The method of claim 7 , the step a) including measuring the ink quantity metric of the printed region with a spectrometer downstream of an image transfer station of the digital image forming device in an image processing direction.
9. The method of claim 7 , wherein the ink quantity metric is one of an image density of the ink across the region and a width of a line of the printed image at the region.
10. The method of claim 7 , wherein the thickness of fountain solution is estimated based on calibration curve data stored in a data storage device.
11. The method of claim 7 , further comprising before step a), printing the current image at the region of the printed substrate, the printing including applying a fountain solution layer at fountain solution dispense rate onto the imaging member surface, vaporizing in an image wise fashion a portion of the fountain solution layer to form a latent image, applying ink onto the latent image over the imaging member surface, and transferring the applied ink from the imaging member surface to the printed substrate at the region.
12. The method of claim 11 , further comprising after step c), printing the subsequent image using the modified fountain solution dispense rate.
13. The method of claim 7 , wherein the ink quantity metric of the current image printed at the region is a measure of lightness at the region.
14. The method of claim 7 , the step a) including measuring a line width of a line of the printed image at the region of the printed substrate as correlating to the ink quantity metric, the step b) including comparing the measured line width to a predefined target line width.
15. The method of claim 14 , the step c) including decreasing the fountain solution dispense rate when the measured line width is less than the target line width, and increasing the fountain solution dispense rate when the measured line width exceeds the target line width.
16. A method of controlling laser output on an imaging member surface of a rotating imaging member in a digital image forming device, the digital image forming device configured to print a current image having an ink quantity metric level at a region of a print substrate, the printing including applying a fountain solution layer at a dispense rate onto the imaging member surface, vaporizing in an image wise fashion a portion of the fountain solution layer with a laser to form a latent image, applying ink onto the latent image over the imaging member surface, and transferring the applied ink from the imaging member surface to the print substrate, the method comprising:
a) measuring ink quantity metric of the current image printed at the region of the print substrate;
b) comparing the measured ink quantity metric to a predefined target ink quantity metric; and
c) modifying the laser power based on the comparison for a subsequent printing of a subsequent image by the digital image forming device using the modified laser power.
17. The method of claim 16 , the step a) including measuring the ink quantity metric of the printed region with a spectrometer downstream of an image transfer station of the digital image forming device in an image processing direction.
18. The method of claim 16 , wherein the ink quantity metric is one of an image density of the ink across the region and a width of a line of the printed image at the region.
19. The method of claim 16 , the step a) including measuring line width of a line of the printed image at the region of the print substrate as correlating to the ink quantity metric, the step b) including comparing the measured line width to a predefined target line width.
20. The method of claim 19 , and the step c) including increasing the laser power when the measured line width is less than the target line width, and decreasing the laser power when the measured line width exceeds the target line width.