The StUMP (Start-Up Metis Print Quality) was originally observed in the Poseidon printer during
early life printing of the Metis black pen. In cases of printing black and color (CMY) together, the
unutilized portion of the Metis die would develop the defect and affect the print swath after long
decap time. This issue worsens with pen age.
StUMP is believed to be the result of an interaction between chemicals that leach out from the
foam and pigment particles in the black ink. This interaction causes the pigment particles to
settle at an accelerated age, and this interaction worsens with time. Increased pigment settling
can impact decap performance and cause poor drop trajectory, resulting in puddling on the orifice
plate. It has since been shown that this defect is not unique to Mordor ink nor the Metis pen
An improved spitting algorithm was developed as part of adaptive startup to mitigate the StUMP
issue and replenish aged ink in the pen with fresh ink from the printer tank. The algorithm
involves burst spitting where the number of drops fired, spit frequency, and delay between each
burst are fine-tuned to clear settled pigment. The algorithm has been shown to improve the
print quality pass rate of Metis pens by 35%. Because the spitting algorithm is more effective
than the current default purge, oftentimes less ink is required to be purged as part of startup.
Newer pens may also experience a faster startup. This algorithm would be critical for traditional
IPH products that do not carry enough ink on-board to support a large ink purge as part of the
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INC, HP, "SPITTING ALGORITHM FOR PRINTER STATUP", Technical Disclosure Commons, (August 03, 2021)