HP LaserJet Enterprise, HP LaserJet Managed, HP PageWide Enterprise, HP PageWide Managed - Configuration Guide using the Embedded Web Server (EWS)

Background – Explanation of Calibration and Cleaning
The purpose of a print alignment calibration is to adjust one or more elements of the print system such that print
and image quality is returned to an optimal state. These calibrations carefully measure each CMYK print result to
ensure that the colors are properly aligned in the resulting image.
●
Color Plane Registration
●
Maximum Density (Dmax) Calibration
●
Halftone Density (Dhalf) Calibration
Color Plane Registration
CPR Calibration sets several printer parameters; top of page (vertical scanning start position), start of line
(horizontal scanning start position), and scale in the scan direction (horizontal scanning magnication). We refer
to registration errors as being in the Process Direction (PD) or the Scan Direction (SD). Process Direction is in the
direction of motion of the paper through the printer; Scan Direction is perpendicular to the Process Direction.
● Top of page calibration sets the delay, or oset, between each of the colors, CMYK, so that the color planes
are lined up in the process direction.
● Start of line calibration aligns each of the colors in the scan direction.
As with Halftone Adjustment, CPR calibration is done by writing patterns on the image transfer belt and then
using sensors to read the patterns. Variations in the timing of the patterns tell the printer how to compensate for
top of page, start of line, and scale in the scan direction.
There are several sources of CPR error in the print system. While cartridge and ITB variation are large
contributors, there are other factors which may contribute to CPR error. These include the laser scanner
assembly and heat dissipation during printing. Therefore, following long periods of print operation, the printer
may require a calibration to be performed.
Maximum Density (Dmax) Calibration
The purpose of Maximum Density calibration is to set the maximum density (100% exposure) of each of the
primary print colors (cyan, magenta, yellow, and black). During Dmax calibration, patches are generated and
developed onto the image transfer belt (ITB). The developed patches pass by two internal sensors that “read”
the patches and the data is used by the printer to adjust the print parameters so that the printer generates the
desired “nominal” maximum density.
Halftone Density (Dhalf) Calibration
The purpose of the Halftone Density (Dhalf) calibration is to adjust the density between zero and 100%. As with
CPR calibration, patches are developed onto the image transfer belt (ITB) and read by the sensors. The data is
then used to calculate the halftone mapping that will generate the desired nominal performance. The result of
this calibration is a halftone which is adjusted to compensate for the non-linearity of the laser printing system.
The halftones (which are also called an “ordered dither” halftone set) that are adjusted are used for normal print
operations (not the scan/copy path).
In the case of a measurement failure, the printer is designed to use an average calibration which is an average of
several printers measured over life in dierent environments. While not optimal, this average should give most
customers a reasonably well calibrated printer. Errors will be written to the event log in this case.
Calibration Controls
Calibration execution controls are found under the Calibration/Cleaning menu structure (Device Maintenance,
Calibration/Cleaning).
76 Chapter 6 Congure printer features using the EWS ENWW