Four Methods to Test Inkjet Jetting Sustainability Over Time

Testing whether a printhead keeps jetting cleanly over hours or days is an important production-readiness test, and there is no single right way to do it. We’ve come across four methods to conducting long-duration jetting tests — dropwatching, basin printing with periodic nozzle checks, rotating-drum printing, and true roll-to-roll printing — and each one trades insight against realism and material cost. This post lays out what each method can and cannot see, so you can choose the right one for your project needs.

Jetting sustainability is the question of whether every nozzle keeps firing the way it should over a long run. The failure modes are missing jets and drift in the jets that survive: changes in velocity, drop volume, satellite count, or trajectory that accumulate over time. A head that looks flawless in a quick dropwatch can clog, ingest air, wet out, or otherwise drift outside spec once it has been running for an extended period of time.

The four common methods differ along a few axes: how many nozzles they watch at once, whether the feedback is continuous or sampled, how faithfully they reproduce production airflow and substrate effects, and how much material they consume. Those tradeoffs are what make one method right for early screening and another right for final validation.

Method 1: Dropwatching

In a dropwatcher test, the camera views one row of nozzles at a time while the printhead pans back and forth in front of it. Field of view is a deliberate tradeoff: around five nozzles gives the most accurate drop volume measurement, while 50 or more nozzles lets you cover ground quickly when you only need to confirm that a drop is present.

Strengths

• Far more insight into drop volume, velocity, formation, and satellites — and into deviations in any of those over time
• Works with any ink at any jetting speed
• No wasted material beyond the fluid itself

Limitations

• It only watches a subset of nozzles at any instant. Even at hundreds of nozzles per minute, it cannot see the entire head at all times, so brief intermittent dropouts can slip past between scans.
• It does not reproduce the airflow or substrate-under-printhead effects of real printing, so it will not catch every failure mechanism that production conditions create.

Method 2: Basin printing with periodic nozzle checks

This method prints continuously into a basin to keep the head firing, then periodically scans the head over a substrate to lay down a nozzle check pattern before returning to the basin. The check pattern is a full-head snapshot taken at intervals.

Strengths

• Gives feedback on all nozzles at once, at a single moment in time
• Can catch intermittent issues that appear over the length of the nozzle check pattern — typically around 300mm, but it can be longer or shorter
• The check pattern is easy to archive and analyze further
• Works with all inks at any jetting speed
• Limited wasted material beyond the fluid

Limitations

• Feedback is sampled, not continuous — you only learn about jetting health at the moments you print a check pattern
• There is some airflow and substrate interaction as the head moves over the substrate, but it is not the same as running continuously under the heads
• It reveals little about drop volume, velocity, or satellite deviations unless they are pronounced enough to show up in the printout, and reading those out of a print quickly and correctly is hard without dedicated print quality analysis

Method 3: Continuous printing onto a rotating drum

Here the head prints continuously onto a rotating drum that is wiped clean on each revolution. You inspect the printed band — with a camera or by eye — to spot missing jets as they happen.

Strengths

• Continuous feedback on missing jets across the whole head
• Catches intermittent issues
• No wasted material beyond the ink

Limitations

• Performance depends on the combination of ink, wiper, and drum surface. Inks that wet too much blur adjacent lines together and defeat camera analysis, and some inks leave residue the wiper cannot fully remove, which builds up over time.
• It is speed-limited. Above roughly 1 m/s, fluid can start flying off the drum surface.
• The airflow is not necessarily representative of production. A spinning drum generates its own air currents that are probably unique to that setup.

Method 4: True roll-to-roll printing

A true roll-to-roll (R2R) setup prints continuously onto moving substrate and analyzes the printed result on the far side. It is the closest of the four to real production.

 

Strengths

• Continuous feedback on missing jets across the entire head
• A true representation of production airflow and substrate effects
• Works with any ink at any jetting speed
• Catches intermittent issues

Limitations

• Like the basin and drum methods, it reveals little about drop volume, velocity, or satellite deviations unless they are large enough to print visibly, and pulling that information out of a print is slow and error-prone without dedicated analysis tools
• It consumes a lot of expensive substrate over a long test
• Without an inspection camera doing continuous analysis, you are left unwinding printed rolls and checking them by eye, which is extremely time consuming

Choosing a method — or a sequence

The four methods are not really competitors; they sit at different points in a test program. Much of the early work can be done with little or no waste: dropwatching for deep drop-level insight, and basin or drum testing for full-head coverage. Those first-pass scans tell you most of what you need before you commit expensive material.

True roll-to-roll printing is best reserved for final validation, when you need a faithful picture of how the head behaves under real airflow and substrate conditions and can justify the substrate cost. Sequencing the methods this way — cheap, insight-rich screening first, production-realistic confirmation last — gets you the most reliable answer for the least material.

Good news – ImageXpert has worked with all four methods and can provide guidance and the right tools for your project. Contact Us to discuss in more detail.