Factors Affecting Printhead Color Deviation: Droplet Size, Wear, and Manufacturing Tolerances
Printhead Ink Drop Size
Different printheads may produce varying ink drop sizes and ejection speeds due to differences in the printhead chip circuitry, piezoelectric crystal structure, and nozzle diameter.
These discrepancies may also arise from manufacturing tolerances or long-term wear of the printhead, and they cannot be fundamentally resolved.
If the differences between printheads are too large, another issue may occur:
Some printheads may produce two ink drops instead of one when printing a single ink drop. When this happens, the difference in ink drop size between the two drops becomes more inconsistent, and the printed image will show mismatched patterns between different printheads.
In such cases, we can first try adjusting the pressure so that the two ink drops from a printhead combine into one ink drop, then fine-tune the ink volume of other printheads to ensure consistent ink drop sizes across all printheads.
The calibration print pattern should appear as shown below:
This calibration pattern consists of four parts:
Overall Preview: Check the overall color condition. If the color blocks on both sides of the triangle in the middle show issues, it indicates that there is a problem with the printhead’s physical alignment (nozzle check) or the software (color registration). The example below shows the normal condition.
Left and Right Column Color Difference:
Indicates the color difference effect between the two nozzle rows of the printhead.
As shown in the figure below, if there is a color difference between the left and right nozzle rows of the printhead, you can adjust the half voltage of the printhead.
Vertical Nozzle Alignment Color Block:
Indicates the color difference caused by poor vertical nozzle alignment adjustment.
If the color blocks on the left and right sides of this section show a color difference, it means there is a vertical alignment problem with this printhead, and you need to return to the vertical calibration chart to re-calibrate the corresponding printhead’s vertical alignment.
Color Registration Calibration Color Difference:
Indicates the color difference caused by improper color registration calibration.
If the color blocks on the left and right sides of this section show a color difference, it means there is a color registration issue with this printhead, and you need to return to the color registration calibration chart to re-calibrate the printhead’s color registration.
For our printhead voltage adjustment, we only need to adjust the colors on both sides of the second section so that they match the colors of the other printheads.
If there are multiple groups of printheads, the color blocks between groups can be ignored; just ensure that the colors on both sides of the second section within each group are consistent, as shown below:
In the example of eight-head color calibration shown above, it is only necessary to calibrate both sides of each printhead within the two groups, as illustrated.
That is, printhead 3 needs to reduce voltage, and printhead 6 needs to increase voltage.