Unlike YMC color printing, which is required only to deliver realistic portraits and pleasing graphics, the K panel serves a more quantifiable purpose, namely machine readability. In practically all instances of K panel usage, there is a requirement both for bar codes and well defined text - and sometimes for signatures, which can be ìspideryî in appearance unless compensated for. Unfortunately, these requirements are in opposite corners.
The P640i provides three controls for K panel printing: these are:
1.Black panel compensation (Adjustment screen, this page TN4 - x) If a line of black dots is printed along the card motion axis, the heating element (pixel) in question doesn’t cool down completely between adjacent dots. Without compensation, the steadily increasing residual heat would cause the printed dot to increase noticeably in size (“bloom”), below left. Properly compensated, the dot size is reasonably constant, below right.
Without compensation | With compensation |
2.Black panel density (Color Calibration screen, page TN4 - x) This control the amount of heat energy applied to any pixel required to be “black”. A higher value gives darker printing, but can cause undesirable blooming (indefinite edges).
3.Black panel preheat (Color Calibration screen, page TN4 - x) Think of this as a temperature offset applied across the entire head, specifically for K panel printing. A higher value results in better resin transfer on the leading edge of graphics and text than you would get with a “cold start”, but it may lead to undesirable blooming (indefinite edges) overall.
The following default values deliver a good compromise between barcode readability and the appearance of text and signatures: Compensation 55, Density 117, Preheat 15
Overlay - Panel Speed: Speed at which the “OP” overlay panel, if any, is printed (rarely used in printers with laminating capability). If a Uv ribbon is selected, the text changes to say “Uv Panel Speed”.
Overlay Panel - Compensation: Mainly used with Uv ribbon to optimize the appearance of ultraviolet
Ribbon - Position (mm): This has to do with positioning the color ribbon relative to the print head such that when the head descends it lands solidly within the panel, not too early, not too late. Keep in mind the following:
•While the head is down and printing, ribbon motion is controlled by the card itself, not by the ribbon takeup (which at this time serves only to peel the ribbon cleanly off the card).
•The color panels are about ½" (12 mm) longer than the image printed on the card. This means that between one color printing pass and the next, when the head briefly lifts, the takeup drive has to shift the ribbon rapidly to bring the next color panel under the head.
Ribbon sensor | Motion sensor |
SupplyTakeup
arborarbor
•The transition from one panel to the next in the color ribbon is marked by a black stripe which activates the ribbon sensor below the supply roll. It is used, together with a count of pulses from the motion sensor, to determine ribbon position.
P640i Card Printer User Guide | 47 |