Printhead health in industrial inkjet printing, in-line and off-line detection of poor drop formation

For most inkjet applications, it is very important that exactly one drop is generated with the desired speed, volume, shape, and direction as a result of a single actuation action of a printhead. The printheads are the heart of every printer and their condition is crucial for the printing performance. Rayleigh-Taylor instability occurs when inertial forces overcome the restoring surface tension forces, which occurs above a certain critical acceleration of the meniscus. There are several mechanisms that result in satellite drops or misting. A built-in measurement method of the meniscus position, which also allows measurements in the jetting situation, is offered by a sensing nozzle plate with a capacitive layer inside the nozzle. In most cases, the term control is associated with feedback control. Feedback control aims primarily at stabilization and disturbance rejection. Given the highly repetitive character of the jetting process, iterative learning control (ILC) is a logical choice as control strategy.