CIJ Printer

To prove that the 312V charging voltage can be switched, I used an IRFP460 MOSFET for shorting the charge voltage to ground, which turns the charging off.

The charging voltage is already current-limited by a 100k ohm resistor on its output, so shorting it to ground is not a problem.

Now, I can try to apply some signal to the charge electrode and try to measure something on the phase detector next.

While with a single MOSFET, it's only possible to send a square wave to the charge electrode, I will ultimately need a sine wave that has the same frequency as the signal that is sent to the piezo.

Next, I will try to measure a signal with the square wave and if that doesn't work I will try to build a "sine wave driver circuit" and try again.

Update:

I figured out that the phase testing signal is not a sine wave, but a burst of 16 pulses which cover 0 to 360 degree in 22,5 degree steps of the piezo signal's sine wave...

More about it in the next build log.

While I spend the last day thinking about the USB charger noise, today I tested out ink stream charging with another voltage source:

A while ago I added a boost converter to the printer for creating 312V DC.

This voltage is already intended to be used as the voltage for ink droplet charging and so I used it for this.

In the video, you can see that by turning on the second switch - the first one from the left is for high voltage and the second one is for the charge voltage - the ink stream gets deflected towards the high voltage plate and by turning off the switch the ink stream returns to its straight alignment.

For this test I set the high voltage to 4.4kV so that the ink stream got more deflected, for not hitting the gutter in its deflected alignment.

This test proves that with the current setup ink stream charging and deflection works.

I think I will contiunue working on the phase detector and on the generation of testing signals next. For ultimately deflecting single droplets out of the ink stream.

Thank you for your interest in my project :)

I noticed something really interesting when I connected a cheap function generator to the charge electrode without connecting the ground (of the charge electrode).

By doing so I get a pretty high AC voltage reading on the charge electrode. The voltage is also not just a misreading, but actually present. I know that because it can influence the deflection of the ink stream when I turn on the high-voltage deflection plate. Turning the high voltage on while the unknown signal is present leads to an oscillating ink stream - the ink stream moves back and forth from the middle position at around 50Hz.

The function generator is powered by a common 5V USB smartphone charger.

While trying out a different USB charger the signal changed and by running the function generator from a power bank or my notebook the signal disappeared completely.

So, because of the 50Hz and because of the absence of the signal when the function generator is battery powered, I guess that the unknown signal is AC noise from mains that could somehow pass the USB charger and function generator to reach the charge electrode and also charge the ink stream.

I have to admit that I'm pretty happy about this noise because it is helpful to prove some things:

- It shows that the charging and deflection work in general with my current setup.

- It is reproducible. I had unwanted deflection before which was unfortunately not reproducible and so I couldn't dig deeper into it.

- It shows that AC charging leads to deflection in both directions, left and right from the middle position. This means it can charge the ink stream positive and negative. Before, when the high voltage cable was too close to the not connected charging cable, deflection happened only towards the high voltage plate which I think means only negative charging of the droplets caused by a positive voltage on the charge electrode. With the AC noise, it happens in both directions, tho.

- It visually confirms that there is no high voltage to ground leak, which had been a huge problem in the past.

While I was thinking about the source of the signal I decided to do a test to find out whether it comes from the printer, the function generator, the charger, or mains.

For that, I cut off the micro USB plug of an old USB cable to access the +5V and GND USB charger connections.

I then tried to prove my assumption by connecting the +5V USB Charger connection to the oscilloscope and the GND pin of the oscilloscope to mains PE.

By doing so, I could successfully prove that the noise came from the USB charger or mains, but not from the printer or function generator.

To be safe I also tried powering the oscilloscope via battery and could still measure the signal.

While I still don't know how exactly the signal gets generated - what I guess also doesn't really matter for the project - I think it's a pretty nice coincidence that I didn't connect the function generator's ground to the printer's ground and so could find this noise signal that was very useful for testing.

I just saw that I had even more luck because the other USB charger that I used for comparison creates much less noise and so it likely would have not caused any visible deflection of the ink stream so that the noise would have been overlooked.

I did the measurement without connecting the GND of the USB charger to anything and left it floating.

When I then connected the charger's GND to PE, the noise disappeared - it also worked when I swapped the charger's output lines.

My uneducated guess would be, that the noise is created by the switching of the USB charger which couples into the charger's output lines as well as in the mains' live and neutral. Because at some point in the building's electrical system, the neutral line is connected to earth the noise is also present on the PE line.

When now the charger's output, which is not connected to the oscilloscope, gets connected to PE where the oscilloscope's ground pin is also connected to, the oscilloscope receives the 5V DC from the charger's output which can provide much more current than the noise signal. With that the noise is no longer detectable.

While using the function generator and connecting the printhead's ground to it's output the noise was likely shorted so that it did no longer traveled across PE, but through the prindhead's ground to function generator's ground connection instead.

I also could be totally wrong with that...

Anyways... next up is creating a signal that can charge the ink stream as the noise does.

Over the last months, I did some testing with different printhead designs, self-mixed inks, and some new parts and features for improving the reliability of the printer, to prevent frustration while testing.

Great thanks again to @Paulo Campos for helping me with that.

There were two main problems I tried to solve with the improvements:

- Clogging of the nozzle

- Electrode output leaking to ground due to ink/dirt forming a conductive path to ground on the isolators.

Both errors prevent the printer from working, so it's best to prevent them or solve them quickly when they appear.

Maybe I will later add a feature to the printer to detect (and maybe even solve) them when they appear while the printer is printing.

I also improved another problem that caused a rise in ink pressure while reloading the timer chamber by adding a water pressure regulator to the ink line.

This rise led to a shifting of the ink stream break-up point and could shift the break-up point out of the charge electrode which would prevent the printer from working.

Adding a water pressure regulator reduced the reloading rise from about 10psi to 1psi which I think should be OK for now.

For getting more info about the ink in the system I added a temperature and a TDS sensor to the printer. It's important for the printer's operation to keep the ink at the right conductivity and viscosity.

With the TDS sensor and timer, it's possible to keep an eye on these values.

In the future, I want to mount the printhead on a moving carriage for labeling and 3D printing. While the printhead moves and the feed lines bend back and forth the ink pressure would float which could affect the operation and printing quality. To prevent this, I added a small spring-loaded puffer/damper to the ink line that should later act like a capacitor for keeping the ink pressure constant.

To make the observation of the ink stream break-up and droplet-formation easier, I replaced the white LED with a red LED.

The Output to Ground Leakage Problem:

In the past, I did a lot of testing with water-based inks, because water is safe to use and not flammable.

A major drawback of water is that it takes a long time to evaporate.

That leads to a lot of problems with it like:

- Corrosion on places where conductive water reaches in, but does not dry for a really long time like on the aluminum coated piezo ring or underside of aluminum profiles.

- Water puddles from ink stream alignment or dealing with a clogged nozzle. Because the water takes very long to dry, the ink can collect on the printhead, desktop, and floor even if only a small amount of ink misses the gutter or hits an electrode. With water, this leads really quickly to puddles that would otherwise just evaporate after a few seconds.

- Output to ground leakage caused by small amounts of conductive water settle in small scratches from cutting at the edges of the isolators, which renders the electrodes unusable for a long period of time after each splashing with test ink - what happens very often while testing.

This made testing in the past as good as impossible.

In the end, I came to the conclusion that the fire hazard of fast-drying liquids like ethanol is easier to handle with the right safety precautions than the problems caused by slow-drying water.

In the industry, most CIJ printers also use fast-drying ketone or alcohol-based inks.

And so I switched to ethanol-based ink.

Today, I received a bag of sodium propionate which contrary to sodium chloride and sodium carbonate (which I used before with water) dissolves well enough in ethanol to increase the conductivity to the needed level without the need to add water to the mix.

With ethanol, the situation really improved. When some ethanol got spilled on the printhead, table, or floor it could be wiped off and the residue on the surface evaporated completely after just a few seconds.

Some parts of the printer like the ink filter, piezo mount, and polystyrene parts were not compatible with ethanol, so I had to replace them.

On the printhead, I tried different materials for the isolators. While using the water ink I used polystyrene isolators and 3D printed isolators, but because the water settled in every small scratch and also soaked between the layers of 3D printed parts it did not work very well - the smooth polystyrene worked better for water than the 3D printed parts.

For ethanol, polystyrene is not suitable because it gets dissolved by it over time. 3D printed parts work better than with water but the ethanol also creeps between the layers and stays there longer.

In the end, I had the idea to use PTFE for the isolators which has a high chemical resistance and also a liquid and dirt-repelling surface which is very nice for keeping the isolators dirt free to prevent forming of conductive paths to ground on the isolator's surface.

I did some testing of the high-voltage electrode:

I measured the high voltage which I set to 3,33kV. Then I sprayed the isolator with ethanol which led to the measured voltage dropping to around 100V. Then I wiped the top and bottom of the isolator with a paper towel and blew some air on the isolator to let the residue evaporate. I measured the voltage again and measured 2,95kV which over the next seconds rose back to 3,33kV.

It seems like, from all tested materials PTFE worked the best so far.

I think that the ground leakage problem is solved for now and I can finally start testing with the electrodes. And in case of an isolator gets splashed with ink, the ink will dry off pretty quickly so that the testing can be continued after just a few seconds.

The Nozzle Clogging Problem:

Before the last change nozzle clogging was a serious problem. When some dirt or PTFE flake from sealing PTFE tape reached the nozzle, it obscured the ink stream which prevented drop break-up from happening, changed the break-up point position, or led to a non-straight ink stream that hit an electrode, missed the gutter or shoot across the room.

Sometimes it helped to wipe the nozzle tip with a finger to unclog the nozzle, but often it was needed to disassemble the nozzle assembly and clean or replace the nozzle.

So I added a nozzle cleaning feature to the printer, that connects the nozzle to the primary vacuum line if activated.

This way the nozzle can be flushed and dirt can be disposed of into the vacuum puffer chamber. While doing so any flushing solution can be used because unlike the normal ink, the dirt and flushing solution doesn't get recycled in the system and so they can not contaminate the ink in the system.

The cleaning function is turned on by the two valves on the back of the printer. The left one is used for the ink and the right one is used for the vacuum.

The "dirty ink" flows from the printhead through the main vacuum line to the vacuum puffer chamber and gets collected there. The vacuum puffer chamber has a float switch to shut the printer down or perform another action when it is full.

For draining the vacuum puffer chamber I added another chamber - a draining chamber to the printer.

The draining chamber has a valve for draining a valve for venting and a valve for vacuum.

For draining the vacuum puffer chamber, the vacuum of it is closed with the valve at the top. At the same time, the venting and drain valve of the draining chamber is closed and the vacuum valve of it is opened. By doing so the "dirty ink" is drawn through a check valve from the vacuum puffer chamber into the draining chamber.

When the vacuum puffer chamber is empty. The valve of it opens again while the vacuum valve of the draining chamber closes and the venting and drain valves of the draining chamber open.

The "dirty ink" that is now in the draining chamber can now exit the printer into a waste container.

With the newly added draining feature, it is possible to drain the vacuum puffer chamber which besides "dirty ink" also catches boiled-off ink and excess ink from the pump and reservoir chamber. The new feature makes it possible to drain the vacuum puffer chamber while the printer is printing. Otherwise, it would be required to shut off the vacuum first to drain the vacuum buffer chamber which would require a shutdown of the printer.

I think with the nozzle cleaning feature and draining feature nozzle clogging will be less of a problem.

Update:

It turned out that the new filter was not corrosion resistant - what should be no surprise, given that it was made out of aluminum and galvanized steel, two materials which are not compatible with the ink....

Because of that I'm now using a petrol filter again, like on the beginning of this project, but this time it is an steel free petrol filter.

There are many petrol filters out there which have galvanized steel parts in them which would start rusting and contaminating the ink. These are not suitable for the project and you have to use all plastic ones which are more corrosion resistant.

For now, this is the end of my report, and next up is the testing of the electrodes and trying to charge and deflect the ink stream.

I also want to test out mixing ink out of ethanol and PVB resin.

Thank you for your interest in my Project :)

Besides a couple of low voltages, the CIJ printer also needs high voltages for the charging circuit and deflection plate.

Here, you can see the power supply of an old CIJ printer that I bought for research:

It outputs 312V and 3 to 6 kilovolts. On this printer, the 312V is used for the charging circuit and the piezo driver, and the 3-6kv is used for the deflection plate.

On my printer, I'm currently using a 24V audio amplifier for driving the piezo, because they are available for sale and you don't have to build it by yourself which should make this part of the project easier.

I don't have the charging circuit ready so I can not fully test out if it works, but under the strobe led you can see droplet formation, so it looks promising.

However, if it turns out that the audio amplifier is not enough for driving the piezo I will have to build a proper piezo driver that uses the 312V for it.

Now I started looking for ways to generate 312V and 3-6kV.

312V Power Supply:

Here you can see my 312V power supply. I used a YH11068A boost converter powered by 12V. It turned out that the YH11068A needs some load to provide a stable output voltage and so I added three 100kOhm 5W resistors in parallel to the output. I also added another 100kOhm resistor in series with the output to limit the current for safety.

The YH11068A is protected by a 1A fuse on the input that will blow in case of an unintended current draw.

Finding out the thing with the needed load was a bit tricky, but because you can just buy the YH11068A, generating your 312V is not that complicated.

Adjustable 3-6kV power supply:

Here you can see my adjustable 3-6kV power supply. The output voltage can be adjusted by changing the switching frequency of the MOSFET.

Higher Frequency = Less Voltage

Lower Frequency = More Voltage

Because there was nothing out of the box available, I had to build it by myself.

First, I got myself a high-voltage probe, so that I could measure the high-voltage output without destroying my multimeter. The probe divides the voltage 1:1000 so that you can read like 4.20V for 4200V on the multimeter.

After that, I looked for a circuit that can generate adjustable 3-6kV while being easy to build.

I started with one of these 15kV modules that you can find on Amazon, eBay, and Aliexpress.

This module uses a transformer that gets switched at high frequency by a transistor for generating high voltage. Besides the transformer's primary winding, it also has a feedback winding for controlling the transistor which makes the circuit self-oscillating, so that it does not need any sort of frequency generator to run.

Unfortunately, in contrast to a TV's flyback transformer, it has no internal rectifier diodes, so its output is AC. It also has no way of controlling the output voltage, so it can not be used for the CIJ printer without modification.

Besides that, the transformer that comes with the module is very nice for generating high voltages and because these modules are available almost anywhere, it should be no problem to build the circuit with the same transformer anywhere else.

The modules usually come as DIY kits, so there was no need to first desolder the transformer from the PCB. 

Instead, it was only needed to remove the feedback winding from the primary side of the transformer to get it ready for further use. 

After removing the feedback winding I tried building a new transformer driver circuit, but this time driven by a function generator and an IRFP260 MOSFET. I also added multiple 1000V diodes in series to form a high-voltage diode that converted the output of the transformer to DC.

Here you can see my first high-voltage power supply testing setup

6060V @ 15500Hz

3000V @ 27400Hz

I tested out driving the MOSFET with PWM at different frequencies and noticed that the voltage at the output changed according to frequency as expected so I could continue with the work on the circuit.

The diodes at the output could not provide real DC, but only the positive AC half wave and so I decided to build a bridge rectifier and add a capacitor to get rectified and smooth DC.

For that, I used four 20kV 5mA diodes to build a bridge rectifier and a 20kV 1nF capacitor for smoothing.

I tested it out and realized that I now could get a higher voltage with the same frequency.

I also tested out drawing some arcs and shorting the circuit, to find out what happens.

Unfortunately, in contrast to the last test circuit, with the capacitor added the circuit could provide enough current to destroy not only the MOSFET but also the function generator :/

Now, I had to find a way to limit the current to a safe level to prevent damage to the electronics in case of a short circuit. It later turned out that short circuits happen from time to time if the high voltage deflection plate gets unintended hit by some droplets.

So, I got myself some 20mOhm 5W high voltage resistors to limit the current to a safe level for the electronics and also for the user.

I added the resistor between the negative high voltage output and GND. Now it's possible to short the high voltage to ground without causing damage to the electronics.

While waiting for a new function generator and a high-voltage cable to arrive, I tested out the nice XY-LPWM generator with integrated LCD, that I wanted to use for adjusting the switching frequency and with that the voltage of the high-voltage deflection plate.

The cable arrived and I could finally fix all parts with hot glue onto a hard paper that I mounted into an electronics box which I mounted on the printer frame.

Finally, I added a switch and a 1A fuse to the input of the high-voltage power supply and connected the high-voltage cable to the deflection plate.

With that, the work on the 3-6kV power supply was done.

Here you can see both power supplies running

And here you can see a test of the 3-6kV power supply.

With that, I finally have all needed voltages ready to drive my CIJ printer prototype.

Thanks for your interest in my Projects :)

The CIJ Printer needs a couple of different voltages for operation and here are the power supplies/converters that I use for generating these voltages:

- 24V Power Supply

The 24V 10A power supply is the main power supply of the printer. It generates 24V from mains for all other power supplies/converters. It also powers the solenoid valves and the audio amplifier/piezo driver.

- 12V Converter and 5V Converter

An XL4016 step-down converter powered by 24V is used for generating 12V for the plus/minus 12V converter and the high-voltage power supplies (more about them in the next build log).

Another XL4016 step-down converter powered by 24V is used for generating 5V for the Arduino and other logic-level electronics.

- Plus/Minus 12V Converter

A DD1912PA plus/minus 12V converter powered by 12V is used for generating plus/minus 12V for the charging circuit and phase detector in the future. This part of the project needs further research and at the moment it is not in use.

These are the low-voltage power supplies that I'm using at the moment.

In the next build log, I will give you a closer look at the high-voltage power supplies.

To prevent damaging my notebook in case something goes wrong and especially because of the high voltage circuit running at 3-6kV, I was looking for a way to control the CIJ printer prototype without an electrical connection to my notebook.

For doing so, I tried out sending the signal of the serial connection via lasers over optical cables (Toslink cables) and it worked just as well as a wire-based serial connection.

I built the connection like:

PC - USB Connection - Arduino Nano - Optical Connection - CIJ Printer's Arduino Mega

I connected my PC to an Arduino Nano via USB. The Arduino Nano uses hardware serial to communicate with the PC and uses software serial to communicate with the CIJ Printer's Arduino Mega. The software serial TX pin is connected to a laser and the software serial RX pin is connected to a laser receiver. The Arduino Nano just passes the serial connection from the PC to the CIJ Printer's Arduino which also uses software serial, a laser, and a receiver, so that the connection works as if the PC is directly connected to the CIJ Printer's Arduino.

I also thought about using a wireless connection, but I came to the conclusion that an optical cable connection would be more reliable and easier to build - so no wireless connection.

Here are the kind of lasers and receiver modules that I used for it:

I placed the laser and receiver in a 3D-printed part and fixed everything in place with hot glue. This is the part on the CIJ printer side:

And this is the part on the Arduino Nano side:

With that the PC should be safe :)

Over the last months, I added a lot of new stuff to the CIJ printer project, but I could not find the right moment to report about it.

Because of that I will rather show you the current state of the project and add more build logs about the new features after that.

Here are some pictures of the current CIJ printer prototype:

Here you can see the latest printhead prototype:

I added a cable guide, a new 24V audio amplifier for driving the piezo and a laser sender / receiver to isolate the PC from the printer prototype:

Here you can see the new power supplys for all needed voltages (24V, 12V, 5V, ±12V, 312V and adjustable 3000V to 6000V):

I finally took the vacuum pump from my desktop to the printer frame and secured it in place with 4 springs to prevent the vibration from entering the frame and causing a lot of noise:

More build logs with more details about the added parts coming soon...

For the last weeks, I was searching for a way to generate a sine wave signal for driving the piezo and a 0-5V square wave signal for driving the LED strobe with the same timing to prevent a "moving droplet effect". 

After trying out many things that didn't work I have to thank @Paulo Campos for the great help and for pointing me out that I can use a comparator to turn the sine wave signal into a square wave signal with the same timing. 

Since this project requires dealing with electrical circuits more intensively, I thought of using LTspice for drawing and simulating the circuits that I want to build.

While the electronics that I used for my former projects were mostly simple, based on Arduino projects or based on other open source projects, the CIJ printer project will be a bit more complicated, because there is not much information about the electronics of CIJ printers available and so I have to figure it out by myself.

So with the tip of using a comparator, I ordered some ICs, including the LM339 and LM393 comparators, and searched the internet for circuits that I can test out, modify and simulate in LTspice.

It took me a while, but I came up with a circuit that had the desired output in the simulation.

After simulating it, I tried to build it on a breadboard and measure the real circuit with an oscilloscope.

The spikes in the sine wave were caused by the notebook's power supply.

I got the desired output and so I drew the layout for a perf board and soldered it together.

After that, I connected everything for doing some testing with it.

The setup for testing looked a bit messy.

I tested out different piezos from ultrasonic cleaners. I heard that the optimal frequency for a 0.1mm nozzle at 40psi is around 48kHz to 50kHz and because of that, I bought ultrasonic cleaners that claimed to run at 50kHz. Unfortunately, there is no guarantee that the ultrasonic cleaners contain piezos that can run on the claimed frequency and so you have to be lucky to get a good one.

The piezo from the second ultrasonic cleaner that I tried contained a piezo that could run at 48kHz even though it was not its resonance frequency.

I tested the vibration of the piezo by sticking another smaller piezo on top of them and measuring its output with an oscilloscope. After sticking the smaller piezo on top and connecting the oscilloscope I tried out different frequencies from 40kHz to 50kHz to see at which frequency I can measure the highest voltage reading on the small piezo. This frequency should then be the piezo's resonance frequency. The first piezo that I tried worked best at 43kHz and the second one worked best at 47kHz, but it also worked not that bad at 48kHz, so I used it for further testing.

I carefully clamped it on top of the nozzle and looked at the ink stream under the LED strobe.

And it worked: Visible ink stream separation under the LED strobe at 48kHz.

Finally, I mounted the AD9833 + LM393 and also the LM386 amplifier on the printer frame next to the other electronics to keep everything relatively clean.

I still have to redesign the printhead to fit the flat piezo disc to the nozzle, but the next thing I want to work on is building a high-voltage power supply, like this one from an old CIJ printer, to power the charging/phasing and deflecting circuit.

Thanks for your interest in my project, until then.

I did some testing and tried some things out and decided to stay with the 40kHz for now.

I assume that the 40kHz 60W ultrasonic transducer is optimized for this frequency and so it's bad at moving at frequencies above and below 40kHz. There are also ultrasonic transducers available that are rated for other frequencies and I think the limited frequency range of the 40 kHz transducers is the reason why they exist.

While other transducers exist they are not quite common and so you have to buy them in china with long shipping times - and for this reason, I will not use them for now.

I will also live with the quite long distance that the stream needs before it splits into droplets. While it's wasting some space it's also no problem to move the ink return tube some more centimeters away from the nozzle.

And by doing so you get a nice line of droplets after a few centimeters even with 40kHz. Time will tell if they are suitable for charging and deflecting, but at the first glance, they look quite OK.

For driving the piezo rings I used a small LM386 amplifier. I also tried another more powerful amplifier and it worked well, too. It was even possible to drive the piezo and split the stream with the signal generator on its own and "tune" the stream by adjusting the output voltage.

I connected the amplifier to CH1 and an LED to CH2 and set both channels to 40kHz sine wave. While being a diode the LED should only turn on at one side of the curve and therefore blink with just 20kHz - I also tried a 40kHz non-zero crossing square wave and it worked, but it seems like the droplets look a bit different. Driving the piezo rings with the same square wave also worked, but I guess driving them with a sine wave will be better because by doing so they can flex back and forth instead of just flexing between the resting and bend positions.

Next, I want to drive the LED directly from an Arduino pin and use an AD9833 to generate the sine wave for the LM386 amplifier.