Masterclass on Waveform Development

PROGRAM

The focus of the course is to train participants in assessing, developing and improving waveforms for drop on demand inkjet printheads. Participants will also be familiarized with measures for reliable printhead operation. Hands-on practical lab work is complemented by short theoretical lessons. The covered topics are proper inkjet system setup and analysis, inkjet acoustics, single and multi-pulse waveform design, grayscale waveform design, generation of small drops, idle pulse design and jet recovery. Lab work is done in small groups on drop watching platforms, each of them equipped with a Ricoh MH5421F print head jetting water-based or UV-based inks.

BACKGROUND

In piezo drop on demand (DoD) inkjet print heads, ink droplets are generated due to pressure waves introduced by the motion of piezoelectric actuators which are in turn controlled by an electrical signal called the waveform. As the propagation time (which is the speed of sound of the jetted fluid in relation to the channel length) of the pressure waves in an inkjet channel is significantly larger than the time needed for the piezoelectric actuator to reach its full amplitude, acoustic interference effects dominate the jetting process.

A piezo inkjet channel can be seen as an acoustic resonator where pressure waves are reflected with the same polarity on closed ends or with inverse polarity at open ends. Each movement of the piezoelectric actuator creates a new pressure wave, which resonates in the inkjet channel (with a certain attenuation per cycle) and can constructively (pressure amplification) or destructively (pressure attenuation) interfere with previously created pressure waves.

One of the major factors affecting the quality and reliability of piezo drop on demand (DoD) inkjet printing machines is the design of the waveform. While there are limitations on possible jetting performance due to the rheological properties of the ink, to achieve highest jetting quality or print speed, the waveform has to be properly adjusted.

ADVANCED WAVEFORM

After attending the training, you should:

• Be able to find common error sources in the printhead and in the ink supply system
• Be familiar with test equipment and methodologies
• Understand inkjet acoustics and pulse timing to amplify or dampen pressure waves for waveform design
• Know the key differences when optimizing different ink types (aqueous and solvent, UV, Hot-Melt)
• Define maintenance intervals as well as print start sequences based on open nozzle time measurements
• Predict same drop speed waveform scaling for printheads of the same series with a different voltage rating
• Know waveform design features and limitations with major print head drive concepts
• Know basic techniques on improving jetting performance with single and multi-drop waveforms