Today I tested out to print something with the new design, but it did not really work as expected.

The good things are:

- The pumps can pump the ink up to the printhead and can eject ink out of the nozzles.

- If the pumps have enough power (when using two piezo discs) there is no problem with making bubbles.

- It's reliable. As long as there is no air in the lines it works without problems even after days of being not in use.

The only bad, but unfortunately essential thing is:

- It works good for streams of ink but not good for drops unlike the last design which, however did not work reliable.

So I have to find a way to get it more suitable for ejecting drops, somehow...

My first idea would be using DC again instead of AC.

I think the relatively slow rise of the voltage in the 50Hz mains sine wave could be the problem. With a DC square wave the voltage rise and therefore the piezo movement and ink pressure change would happen almost instantaneously what should be better for creating droplets.

The problem with using DC would be, that the piezo needs AC to move in both directions to perform not only a change in ink pressure, but a pumping action.

So the best should be a high voltage AC square wave.

At the moment I only have the parts to switch high voltage (up to 500V) DC.

I will try that out later, but it will likely not work and so I have to find or build something that can create a high voltage AC square wave....

I just figured out that the DC SSRs are really bad for switching the piezo disc compared to the IRFP460, so I will rather use these.

I built another printhead that has a drain directly underneath the nozzles to suck up the excess ink drops. It is mounted at an angle, so that ink drops do not form at the tip of the nozzle - what would block the nozzle -  but instead form on the side of the nozzle until they drip into the drain.

For this printhead I used 0.1mm nozzles. With two piezos in the pump the amount of ink per drop is a bit high what I think leads to the drops that are forming on the nozzle, but using only one piezo in turn is too less ink what leads to no droplets at all.

I think the new printhead in combination with a PCB with four IRFP460 and a rectifier should make the design ready for first printing tests.

New electronics for the piezos.

A transformer, rectifier, 12VDC power supply for the optocouplers and a board with four IRFP460 and 47k 1W resistors for switching and discharging the piezos.

Placed the electronics in two boxes for a cleaner look.