HP Designjet H35000 HP Designjet H35000 and H45000 Printer Series - Headstrike - Page 2

Definition A headstrike is any event that causes the printheads or other parts of the carriage to come in contact with the media while printing. Causes Headstrikes usually happen when one or two conditions arise on the printer and/or the media. The first condition is a head height that is too low. Head height is the distance from the media surface to the lowest point of the carriage. On the UV-cure printers, the standard head height is 0.070". The printheads are recessed within the carriage an additional 0.015", creating a total distance between media and printheads of 0.085". Head height should be set by proper adjustment of the carriage using the supplied gauge and wrenches. Consult the printer User Manual for detailed steps on setting head height. The second condition that can lead to headstrikes is unexpected deformation of the media, such that the media surface becomes higher than it was when the head height was set. This can occur when a roll-fed media bunches up on the platen, when a rigid media is not flat initially, or when an originally flat media deforms while printing, usually because of heat, and bows upward. All of these situations can lead to a headstrike by the carriage onto the media. Not all headstrikes are obvious. When the otherwise flat media deforms during printing, it may be only slightly enough to graze the carriage. Printing may continue uninterrupted and the headstrike may even go undetected without close inspection of the output. Other headstrikes are more severe and lead to immediate cancellation of the print by the printer software, or shortly thereafter by the operator when the print defect caused by the headstrike is observed. Potential Long-Term Effects In all cases it is very important to take action promptly after the headstrike not only to correct the conditions that caused the strike, but to clean the printheads from any possible ink and media contact that could have occurred. The UV-cure printers have hardware features intended to protect the printheads from contact in the event of a headstrike, but there is no reliable method to know whether printhead contact has occurred. Therefore it is imperative that the printheads by cleaned immediately following any headstrike or suspected headstrike. The illustration on page 2 of this document shows the possible consequences of a headstrike that is not addressed. Recovery Cleaning the printheads after a headstrike is no different from the normal, routine cleaning that should be done daily. Consult Tech Note 2736, DisplayMaker UVR & UVX: Daily Cleaning Procedures, for these procedures. See also Tech Note 2739, Recovering Jets on UV-Cure Printers, and Tech Note 2738, Maintaining Jetting & Evaluating Jetting Performance on UV-Cure Printers, for related topics on printhead maintenance. Anatomy of a Headstrike These illustrations show the possible series of events that can be caused by a headstrike. The ultimate result can be a permanent loss of jetting capacity on the affected printhead(s). 2