Taking Care of the Printbar and managing Print Quality

Before reading this article you should be familure with the different components such as BNB and Printbar explained here:

While thermal inkjet has had a lot of advances over the past decade, the technology still does have some fragile components that need to be looked after to ensure longevity of the BNB and the Printbar.

The most important thing to keep in mind when operating an 1170 printer is how far the substrate is away from the printbar. This is something that takes practice and time to dial in for each application.

The printbar can be permanently damaged if the height of the printbar is not closely watched and set correctly. Printbars that are physcially damaged due to something crashing into them or them crashing into something else are not covered under warranty.

The SA1170 (used on AP1170, CP1170, NF1170, and TK1170) has two height adjustment mechanisms that can adjust the printhead height. The first is the global adjustment available from the home screen. This adjustment moves the entire lower portion of the printer up and down between 0 and 30mm (0 - 1.18”).

The second adjustment is the Pen to Paper Adjustment from the Settings tab. The Pen to Paper Adjustment controls how far the actual printbar comes down when the printer uncaps and goes into printing mode. When the Pen to Paper Adjustment (also known as PPS) is set to 0, the printbar move down as far as possible. By increasing the Pen to Paper Adjustment you can have the print bar not come down as far.

Note: The LP1170 only has the Pen to Paper Adjustment as there is not an electronic height adjustment on that model.

Both of these adjustments can be used in tandem to ensure that print quality is acceptable and that the printhead is protected from media.

When we are trying to understand print issues, Postmark always recommends sending a test print (available from the help tab) as this helps us determine a lot of different items such as how far the media is away from the printhead, if there are any nozzle issues, and if the encoder is working as intended.

Below is a picture of a nozzle pattern that we include with each printer that is shipped:

Here is a picture of a nozzle pattern where the printhead is too far away from the substrate.

Note that we see blurry areas of the print as well as prominent lines between each die. If you test print looks like this, it means that the printhead is most likely too far away from the substrate. This can be due to the global height adjustment setting or the Pen to Paper adjustment setting.

When you have print quality issues related to the printhead height, we recommend watching the substrate as it passes under the printhead and inspect how far the nozzles are away from the substrate. In most cases, anything above 2-3mm you will start to see drop offs in print quality as the ink droplets can move in the time they leave the nozzles and make it on to the substrate.

If the bottom of portion of the printer is very close to the substrate, but the print bar doesn’t appear to come down low enough, it usually means that the Pen to Paper adjustment needs to be adjusted. Even if this adjustment is set to 0, sometimes it can help to move the slider to the right and then back to 0 to resend the value to the printer firmware.

Protect the Printhead

While print quality is a very important aspect of setting the printhead height correctly, protecting the printhead is even more critical and is an item that needs to be closely watched.

When anything touches the printhead it is an opportunity to not only block nozzles on the printhead, but it can also lead to permanent damage to the print bar which will require the BNB to be replaced.

As explained above, when setting the printhead height we recommend watching the substrate as it goes under the print bar. When watching the substrate you should be watching that the substrate does not rub on the print bar as well as ensure that the print bar is not hitting anything else (such as the transport belt).

We have seen two different types of failures that can occur when the print bar is damaged. In both of these failures we have done failure analysis to the BNB and found physical damage to the print bar that causes these failures. These failures are usually not recoverable and require the BNB to be replaced.

1. Printbar is damaged near the nozzles. This will cause a color channel’s dies (in sets of two) to slowly cut out as air gets into the printbar assembly. When this occurs, usually the printer will not display any error codes.

After these issues have occurred, we looked at the print bar under a microscope and we could see where the print bar had been damaged:

The second error that occurs is when the print bar is damaged and the electrical connections short out. This will usually display the error “Failed Printhead” or “Electrical Failure” and the detailed status will be 62.XX.01 to 62.XX.15

Details on Error Codes

The two digits (shown as “XX”) can help identify which die has the failure.
For example, if the error code is 62.05.01, it indicates the error is on Die 05

When this occurs, usually there is more physical damage to the print bar. Below are some pictures we have taken of BNB’s that have been damaged and could not be recovered. A digital microscope can be very helpful in identifying cracked printhead dies.

Note, cracked dies are not covered under warranty - this is why it is important to make sure that the printbar is always protected.