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• CK Fittings, PE Tube, new Printhead and other Improvements

  Dominik Meffert • 10/08/2024 at 04:54 • 0 comments

  Latest Video of the Printer:

  New Tubes and Fittings
  

  For the past months while working on the test stand and code for the ESP32, I did not use the printer prototype, and while it was standing there, some of the fittings got leaky.

  Until now, it wasn't that big of a deal that the fitting's NBR seals got dissolved by the ethanol over time, because I changed the prototype's design over and over again, and with it the fittings, but after a lot of testing I thought that most parts of the current design were working reliable enough to keep them this way so that it was finally worth it to replace the push-in fittings with a more suitable type of fitting.

  A better option than the pneumatic push-in fittings are CK fittings (sometimes also called rapid screw fittings), which don't have a seal that can get leaky but instead use the tube itself as the seal by clamping it between the two halves of the fitting.

  Since I had to replace every fitting connection on the printer, I also wanted to replace the currently used PU tubes with PE tubes, which in contrast to the PU tubes, are suitable for long-time exposure to ethanol because of their better chemical resistance.

  No more Watercooling
  

  While I was replacing the fittings and tubes, I also thought about replacing the water cooler with an air cooler, so I could get rid of the water cooling pump, radiator, reservoir bottle, and tubes to end up with more space for other parts and less cost and complexity.

  Until now, the water cooler was used to get rid of the heat of the Peltier module when it's used for cooling the ink. 

  The Peltier module can be used for heating or cooling the ink depending on the room temperature to always keep the ink on a reference temperature of around 25⁰C for viscosity measurement.

  The ink's viscosity changes with temperature even if the ink mixture stays the same, so it's necessary to always measure the viscosity at the same temperature to be certain that changes in the viscosity reading also represent changes in the ink mixture.

  To keep the viscosity constant during printing, the printer can add more ethanol to the mix to compensate for the evaporation of ethanol, which would otherwise lead to an increase in the ink's viscosity.

  As long as the room temperature doesn't exceed 25⁰C by a lot there wouldn't be much heat to dissipate, so I think the cooling can be handled by an air cooler as well for the most time of the year.

  So, I replaced the water cooler with an air cooler.

  New Flushing Concept

  A while ago I added a flush valve and flush line to the printhead that could be used for flushing the nozzle and gutter line with ink for cleaning.

  It turned out that this wasn't the best idea because the ink would harden inside the tubes when the printer is not used for some time and when I recently ended up with clogged lines that I had to replace, I decided to change the printer design in a way that makes it possible to draw all ink from the nozzle and gutter line via vacuum and then flush these lines with ethanol without adding unwanted ethanol to the ink tank.

  To do so, I added two valves to the output of the return pump, which are both switched with the same relay. The valve that leads to the ink tank is connected to the normally closed pin and the valve that leads to the flush bottle is connected to the normally open pin so that the ink flows into the ink tank until the flush line function is activated which switches the relay so that the ink tank valve closes and the flush bottle valve opens.

  With this change, it's possible to flush the gutter and nozzle line into the flush bottle to prevent clogged lines and too diluted ink in the future.
  

  Some Footage

  Here are some photos I took while replacing...

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• Visualizing Drop Breakup

  Dominik Meffert • 09/11/2024 at 00:49 • 0 comments

  After taking a look at the charging and charge sensing, I also wanted to take a look at the drop formation. Both processes are crucial for building a working CIJ printer.

  On many CIJ printers, a stack of 2 piezo rings is mounted on the nozzle to let it vibrate at a fixed frequency. Normally all parts are designed to work together within certain constraints:

  The piezo frequency, stream/nozzle diameter, pressure, and viscosity need to fit well enough together to make a controlled breakup of the stream into equal-sized drops possible.

  So much for the theory...

  In reality, this seems to be a big challenge, and I'm constantly working to get it right at some point.

  To learn more about the drop breakup, I was looking for a way to record it on camera.

  Changes to the previous Test Stand
  

  For recording the stream on camera, I replaced the 1 1/4 pipe tank with a pump to be able to record a continuous stream breaking into drops instead of drops dripping from a nozzle.

  The next step was to let the stream vibrate at a certain frequency to get an even, non-random breakup. To make recording easier, I wanted to use a larger stream so that no magnifying glass or microscope would be needed. Because of that, breaking the stream into droplets now requires a more powerful source of vibration.

  For this, I replaced the piezo with a vibration speaker, like the type of speaker that can play music via vibration when attached to the surface of a desk or wall.

  I got an 8R 20W vibration speaker and used a TDA2030 amplifier for driving it which I powered by 12V DC.

  After verifying that the speaker could be used well for playing music through my desk, I attached it, together with the amplifier, to the test stand on which I also attached a 9mm hose fitting for using it as a nozzle, a silicone hose that was connected to the pump and some more fittings to hold everything in place.

  Now, I had two options for recording a slow-motion effect of the drop breakup:

  - Using a strobe light matched with the speaker frequency.

  - Matching the speaker frequency with the camera's shutter setting.

  At first, I tried using the strobe light, so I got a 50W LED mounted on a heat sink and did a quick test run. 

  Then later, while waiting on the parts for building a strobe circuit, I also tested out using the other method and it worked well enough that I actually never tried using the strobe for recording.

  Maybe later, when a higher frequency is used again, the "camera shutter effect" will likely no longer work that well, and so a strobe light will be needed to make the breakup visible.

  When I tested it at 50khz last year, I placed the stream in front of a 5mm LED which was also driven at 50khz. 

  So, it also was a strobe light - but just a small one.

  Testing with Water

  First, I did a quick test where I set the speaker frequency just below 60Hz and the camera to 60fps, which made it look like the water would flow in reverse. The pipe with the cap in which the stream flows is used to reduce splatter.

  Link to the video:

  While there clearly was some effect visible it was not close to what I wanted.

  So, I tried using a container with an overflow hole to reduce possible vibration that the pump could transfer to the stream.

  This is how the test stand looked after the change:

  In addition to that, I also tried using a smaller nozzle (4mm OD / 2mm ID tube)

  With these changes, it started looking more like individual drops, but there was also a lot of splatter, and it seemed like there was a lot of water breaking out of the stream and falling not straight down.

  Link to the video:

  Testing with Glycerin

  To get rid of the splattering, I wanted to try using a fluid with a higher...

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• Test Stand and Charge Testing

  Dominik Meffert • 09/08/2024 at 20:10 • 0 comments

  Proof of Concept:
  

  Over the past months, I worked on a few things, and I just found the time to write about them.
  

  The first thing I worked on was a stand for charging drops and testing if I could sense the charge somehow to start the work on the charging system from scratch.

  I started by building a pipe with a valve and a 1mm nozzle that I could fill with water, which I could let drop out slowly by slightly opening the valve. 

  Then I built a test stand out of two 1m 3030 profiles and a few shorter pieces for attaching the pipe on it with 3D printed mounting brackets.

  For charging the drops I soldered a 1.5mm² wire onto a 1/4 inch brass fitting and mounted the fitting on another 3D printed bracket.

  I used 56V DC for charging the drop while it passed through the fitting without touching it.

  The drops get charged at the moment they break loose from the stream, so I placed the brass fitting closer to the nozzle.
  

  At first, I tried to sense the charge on the drop with a piece of copper mesh in a funnel connected to an oscilloscope probe which was connected to an amplifier, but because I could sense nothing but the 50Hz mains frequency with it, I tried using just the tip of the oscilloscope probe for sensing the drop.

  I guess the mesh acted as an antenna and picked up noise from the environment.

  With the probe connected to the amplifier and oscilloscope, it was possible to sense the charged drops when they hit the probe's tip.

  It was also possible to sense the frequency at which the drops hit the probe.

  Here is a picture of the setup.

  I used the AD620 instrumental amplifier module for testing. It was needed to connect the S- input to GND to get a reading out of it.
  

  The power supply's ground was connected to the ground clip of the oscilloscope probe, the 1 1/4 pipe, the drip tray, and the frame of the stand.

  Based on the test result, it seemed like it would work to sense charged water drops with it, and to prove that it wasn't just luck, I tested 5 of the same amplifiers in the same configuration.
  

  I also tried turning the power supply off and reducing the charging voltage, which was visible on the oscilloscope. Without a voltage, there was nothing sensed when the drop hit the probe, and a lower charging voltage resulted in a lower amplitude of the sensed signal.

  When the tip of the probe was connected to the ground of the probe by water, there was also no reading visible on the oscilloscope.

  The result was the same on all 5 AD620 amplifiers I tested.

  A picture of the whole setup

  After finding out that it was possible to sense charged water drops, I wanted to try building a proper sense electrode to replace the oscilloscope probe.

  Building a Sense Electrode:

  What I want to build here is the gutter sensor of a CIJ Printer.

  Many CIJ Printers have such a sensor, and while some models also have a senseless phase detection sensor (sometimes in addition to the gutter sensor), I want to focus on the type of sensor that is located in the gutter for now.

  On the printhead of an older CIJ printer model, the gutter sensor looks like this from the top:

  The metal on the upper part is connected to the printhead ground and covers the plastic block from the top and sides.

  From the bottom, it looks like this:

  A small metal pipe with a wire connected is attached to the plastic block.

  Further down the tube, there is a small metal pipe which also has...

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• Monitoring Sensor Data with MYSQL and Grafana on a Raspberry Pi

  Dominik Meffert • 07/01/2024 at 22:00 • 0 comments

  For the last month, I tried out different ways to log and monitor the data that the sensors on the machine collect to get a graphical way to watch the operation of the machine over time.

  This way it is possible to verify that everything is working as expected and to find problems that would be otherwise hard to detect.

  It's also just nice to see your machine's sensor readings on a dashboard :)

  I tried out:

  - saving the data on my router's FTP server

  - saving the data on Google Sheets

  - saving the data on InfluxDB

  Finally, I ended up saving the data on a MYSQL database that I set up on a Raspberry Pi, which appeared to me as the most independent/universal solution.

  In addition to that I installed Grafana on the Raspberry Pi to get a nice way to display the sensor data.

  In the current picture, all values besides the pressure are as expected, so I still have to find a way to get a stable pressure.

  The readings I currently get from the machine are:

  - The room temperature

  - The nozzle temperature

  - The viscosimeter temperature

  - The conductivity

  - The fall time (the time an 8mm steel ball needs to drop around 100mm in a 10mm PC tube at 25⁰C - equal to the current dynamic viscosity)

  - The pressure

  Update:

  Today, I installed a new pressure regulator which finally outputs a stable pressure.

  It's also visible in the readings:

  Now, that all sensor readings are stable the work on the fluid management system is finished until new problems appear and I can finally continue working on the printhead design.

  Update:

  I just found out what caused the pressure regulator to fail:

  The pin inside the pressure regulator got stuck, because the used PVB/Ethanol mix is quite sticky. Maybe in the future I can find a pressure regulator with a different design that also works for adhesives or sticky fluids. At least it's no general problem of the system. Until then it's needed to clean and "unstick" the pin of the pressure regulator before running the system.

  Another Update:

  I switched to using another type of pressure regulator which also has a spring at the bottom for closing the seal so that doesn't get stuck open that easily.

  The next thing I want to do is learn more about things like electrostatic induction and conduction and how to measure the charge on droplets.

  For this, I'm planning to build a test stand for charging single water drops with variable voltage, detecting when the drops hit a copper mesh, and measuring their charge to learn how to do these things and which factors are important for a successful charge induction and measurement.

  Thank you for your interest in my project :)

• Noise Reduction and new Pump Design

  Dominik Meffert • 05/14/2024 at 20:10 • 0 comments

  Problems with the large Pressure Pump

  When I started working on the new design around Christmas last year the first part I bought was a portafilter coffee machine pump with a high flow and pressure rating.

  My initial idea was to use only one single pump for moving all fluid in the system and use a venturi nozzle to generate the needed vacuum for the return line and makeup/solvent loading.

  While it worked well with water and pure ethanol, more and more problems arose as the viscosity increased.

  With the high-viscosity ethanol + PVB mixture that I want to use for printing, the venturi valve injected a lot of small bubbles at a high rate into the mixture creating a layer of foam on top of it which kept on rising until the ink tank started foaming over. At the same time, the small bubbles got sucked into the pump causing it to run unstable which would damage the pump over time while creating a loud unhealthy sounding noise.

  Over the last weeks, I tried a few things to reduce the foaming problem, but nothing of it could solve it completely...

  Another problem with this design was that while the venturi nozzle could still generate a high-flow suction when powered by a high-viscosity fluid, the vacuum level got reduced so much that it could no longer draw in the fluid through the return line...

  While this wasn't already bad enough the pump also generated a lot of heat which makes it hard to keep the temperature inside the system constant...

  With these problems and the fact that these kinds of pumps are pretty noisy and also quite expensive when bought new, it was time to start working on a better and cheaper solution.

  Brushless DC Pump for Ink Circulation

  A few weeks ago I already added two small 24V brushless pumps to the printer for ink circulation inside the viscosimeter and for water cooling.

  While thinking about the changes needed for replacing the large pump I realized that the viscosimeter circulation pump can also be used for circulating all the ink inside the printer and not only the ink inside the viscosimeter. Because of that I could remove the valves needed for the "viscosimeter sample refresh" function and just keep the pump circulating the ink all the time.

  For lifting the steel ball inside the viscosimeter a solenoid valve connected parallel to the pump outlet can be opened from time to time.

  The ink flows from the ink tank to the circulation pump and gets pumped to the viscosimeter.
  

  From there it flows into a T fitting which is connected to the outlet of the relief valve that regulates the pressure of the pressurized part of the system.
  

  From there the ink flows into the heat exchanger that keeps the ink at 25⁰C by heating and cooling it.

  Finally, the ink enters the ink tank again to complete the cycle that keeps the ink well-mixed and at a steady temperature.

  Brushless DC Pump for Water Cooling
  

  The water cooling system is used for cooling a TEC 12706 Peltier module for heating up or cooling down the ink so that it can be kept always at 25⁰C independent from the room temperature.

  The water flows from the water reservoir tank to the circulation pump and gets pumped into the heat exchanger.

  The Peltier module is driven by a BTS7960 H-Bridge module so that it can be used for cooling and heating as well.

  The H-Bridge is powered by an XL4016 step-down converter module which outputs 12V.

  From the heat exchanger, the water flows into the radiator and from there it flows into the water reservoir tank to complete the water cooling cycle.

  Peristaltic Pump for Solvent/MakeUp

  For adding solvent/makeup (ethanol) to the mix I switched to using a peristaltic...

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• Touch Screen and more Pictures

  Dominik Meffert • 04/23/2024 at 04:01 • 0 comments

  Here are some pictures of the 7-inch ESP32 powered control touchscreen and the latest changes to the prototype:

  The squares on the left are touch buttons for the printer functions and on the right, you can see the sensor data on the top and the current time, date, day, and room temperature on the bottom.

  Since the display has no IO pins, I reassigned the 4 pins that were used for the micro SD card to use 2 of them for I2C (SCL and SDA) and the other two for PWM.

  To access the pins I soldered wires to a micro SD extension flat-band cable.

  Connected via I2C are a DS3231 real-time clock, an ADS1115 ADC, and an MCP23017 IO extension.

  - The MCP23017 is used for switching the relays and valves and reading the inductive sensors of the viscosimeter.

  - The ADS1115 is used for reading the analog voltage of the pressure, conductivity, and temperature sensors.

  - The DS3231 is used to keep track of the time and measure the room temperature.

  The touchscreen is powered by an AMS1117 3.3V regulator.

  While the ESP32 is running well on 3.3V the LCD seems to need a higher voltage since it's flickering a bit when powered by 3.3V which doesn't happen when powered by its USB-C connection.

  To get rid of the heat from the Peltier module I added a dual-fan radiator, with the fans pointing toward the grid frame of the machine.

  Currently, I'm using two XL4016 step-down converters for converting 24V from the power supply to 5V and 12V.

  While the 5V is used for powering the I2C devices and sensors, the 12V is used for the Peltier module and viscosimeter valve.

  A single relay module is used to open the valve for lifting the 8mm steel ball inside the viscosimeter. The falling steel ball gets detected by 2 inductive sensors.

  For the viscosimeter, I used a clear polycarbonate pipe with a 10x8mm diameter and 150mm length. The distance between the two sensors is 60mm.

  I used a dual MOSFET module for switching the 12706 Peltier module with a 1kHz PWM signal.

  The Peltier model draws around 50W during testing and the MOSFET module gets very hot without cooling so I will likely place the MOSFET modules for both Peltier modules next to each other and add a small silent 40mm fan for cooling.
  

  Together with the pump that pumps the ink around inside the viscosimeter and also heats it up, a thermistor in the cross-fitting, and some PID code, the temperature of the ink inside the viscosimeter can be kept constant without oscillation.

  In the future, I will add some code to flush the viscosimeter from time to time with fresh ink to check if the viscosity has changed and automatically add solvent if the viscosity has risen too high because of solvent evaporation. 

  For flushing, the viscosimeter is connected to the main ink cycle by two valves that can be opened to let fresh ink flow through the viscosimeter while the pump is running and the measuring pipe's valve is opened to flush all the old ink out.
  

  For the next update I'm planning to add a data logging feature to write all sensor readings and machine function states together with a timestamp to a file on an FTP server to make it possible to analyze every test run and see what changes in the sensor readings follow the performed action.

  I think this will add a lot of value to the machine since it makes the testing results more comparable and will provide a way to share the collected data besides recording videos and taking pictures. In the best case, it would be possible to display the sensor readings as graph lines...

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• Quick Update - Touch Panel and Viscosimeter Cooler

  Dominik Meffert • 04/16/2024 at 16:17 • 1 comment

  Hi,

  sorry for posting no updates in a while.

  I'm still working on the project and over the last months I added an ESP32 powered 7-inch touch panel to the machine and changed the code so that a PC is no longer needed for running the machine.

  I also built a new viscosimeter that features a thermistor, Peltier cooler, and circulation pump for keeping the temperature, always the same while measuring, even if the room temperature changes.

  Before, I couldn't get a reliable reading of the ink's viscosity since it changed from day to day depending on the room temperature. On some days when the sun was heating the room all day long the ball drop time reduced by it's half just by the rising of the temperature during the day.

  When the ink gets pumped around it also heats up, so that without cooling the viscosity would continuously drop until the temperature reaches its highest point which is also dependent on the room temperature.

  The good thing about ink heating is, that with it the ink in the viscosimeter and the rest of the printer heats up on its own so that only cooling is necessary to keep the ink temperature stable.

  Currently, I only finished the Peltier cooler of the viscosimeter, but I will also add a cooler to the printhead to keep the ink that exits the nozzle at the same temperature as the ink sample in the viscosimeter so that the measured viscosity equals the viscosity of the ink stream.

  While I haven't seen a cooling system on any CIJ printer so far, I have seen designs that feature a temperature sensor on the viscosimeter and on the nozzle.

  In contrast to commercial manufacturers who put a lot of work into designing the best ink for their products, I don't know the temperature-viscosity curve of the ink mixtures I'm using and I think it is nice to have a way to keep the ink's temperature constant at the nozzle and the viscosimeter.

• Hydraulic-Powered Printer

  Dominik Meffert • 01/02/2024 at 23:13 • 0 comments

  The current printer is powered by pressurized air from an air compressor and vacuum from a vacuum pump. Both the pressurized air and vacuum are used to move the ink around.
  

  The pressurized air pushes the ink from the ink tank to the printhead and through the nozzle forming the ink stream that hits the opening of the gutter. From there the ink gets drawn into the reservoir tank by vacuum. It gets collected there until the ink tank needs to be refilled. Then the ink gets drawn from the reservoir tank into the pump tank by vacuum. When the pump tank is filled, pressurized air with a higher pressure than that of the ink tank is applied to the pump tank to pump the ink from the pump tank into the ink tank.
  

  Compared to that, the new hydraulic-powered printer is much simpler since it uses ink as a hydraulic fluid. This way the pressurized ink can be taken from the hydraulic system which can also generate the vacuum that is needed for drawing the ink back into the system by the use of a hydraulic-powered venturi pump.

  Because of that, there is no need for a separate vacuum pump or air compressor which will make the printer cheaper, less complex, and more compact.

  All it needs is a powerful ink pump and a low-pressure air pump to power the hydraulic-powered printer.

  For that, I used a Fluid-O-Tech rotating vane pump (200l/h) and an AquaForte v30 pond air pump.

  Until lately, I didn't know anything about hydraulic systems and so I thought the pump's output would have to go directly to the nozzle, which would have made finding a suitable pump very hard, but just a few weeks ago I read an article about RC hydraulic systems where they used a relief valve for limiting the hydraulic pressure by feeding some of the pump's output back to the tank.

  This makes everything easier because, by the use of such a relief valve, a pump running at a constant speed and a much higher flow rate than that what is used by the ink stream can be used for powering the system.
  

  The same can also be done by the use of fixed restrictions and a PWM-controlled pump, but since the constant flow pump + relief valve were cheaper, I used this method.

  After reading about the relief valve I looked for such a valve, but since hydraulic system relief valves are usually designed to work at high pressures e.g. from 10 to 200 bar I had to look for a relief valve that is designed to work at low pressures and so I bought a water relief valve that is designed to work from 2 to 8 bar.

  The valve I got works by opening up just enough to keep the pressure before the valve at the set level. When now some valve opens up to supply e.g. the venturi pump, printhead, or viscosimeter with ink, the relief valve restricts the flow out of it to keep the pressure of the system at the set level. It has a "screw" at the top that compresses a spring for setting the pressure.

  The valve was the first element of the new printer design and after confirming that it worked the way I thought it would, I ordered a venturi pump for testing both together to see if I could get the set system pressure and the needed vacuum for the printer from those two parts.
  

  The venturi pump can generate a vacuum by the use of a gas or fluid that "draws" the air with it when it is ejected from a small nozzle into a narrowing and then expanding tube.

  I was a bit worried if it would work at all since the type of venturi pump I used is intended to be used with pressurized air, but it turned out to work pretty well with water when I tested it out.
  

  With that, I could confirm that just a supply of fluid at the right pressure and flow rate can be used to power the printer.

  After testing out the relief valve and venturi pump, next up was finding the right ink pump.

  This was not that easy, because the pump has to provide some capabilities to be...

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• PVB Ink from PVB Filament

  Dominik Meffert • 12/13/2023 at 22:09 • 0 comments

  For the project, I'm currently using an ink made out of ethanol and polyvinyl butyral (PVB) with an additive for increasing its conductivity (sodium acetate).

  Until now, I used PVB powder for it and while it can be used for ink without problems, I'm still a bit concerned about using it, because it is not a commonly used item, so it can be a little hard to find a shop that sells it.

  Because of that, I tried to find something else and saw that there is PVB-based 3D printing filament available almost everywhere you can buy filament.

  So, I ordered a spool of PVB filament to test out if it dissolves in ethanol while increasing its viscosity.

  For the test, I wrapped some filament around my hand and cut the windings together to get a few equal-sized pieces that could stand upright inside the cup like spaghetti noodles.

  This way the filament dissolved better than when it was cut into shorter pieces or when PVB in powder form was used.

  The shorter pieces stuck to the wall or bottom of the cup, and the powder formed clumps that only came in contact with the ethanol on the surface and stayed dry inside so it took a long time until they dissolved whitout constantly breaking them apart with a spoon.

  At the same time, the longer pieces came in contact with the ethanol over the whole length and dissolved in about an hour without further ado.

  By heating the ethanol before adding the filament the time it takes to dissolve can be reduced even further.

  After the filament was completely dissolved, I checked the viscosity of the mix with the Zahn 1 cup and saw that its viscosity had increased from around 26s of pure ethanol to over 30s with the filament mixed in.
  

  It also gave the mix a nice color so that no separate color pigments were needed to add color to the mix. It could still be, that on paper it would appear rather white than blue since the color is not as intense as the color of ink pigments.

  One disadvantage of the filament compared to the powder could be its purity. While the powder is only made out of PVB, the filament may also contain other substances that could clog the nozzle or the filter, so it's important to keep an eye on that.

  Overall, I think the PVB filament can be used to mix PVB ink and if it's easier to get than PVB powder it should be an suitable alternative.

• Falling Ball Viscosimeter

  Dominik Meffert • 12/03/2023 at 07:35 • 0 comments

  Great thanks to Robert and @Paulo Campos for helping me with this :)

  To measure the viscosity of the ink more reliably I replaced the drain time counter with a falling ball viscosimeter, another viscosity measuring method that is also used by many commercial CIJ printers.

  The falling ball viscosimeter works by counting the time a (steel) ball takes to fall a certain distance inside a tube that is filled with the fluid of which the viscosity should be measured.

  The size and weight of the ball and the distance never change, but the time reading will change with viscosity. The fall time increases when the viscosity gets higher and decreases when the viscosity gets lower.

  I did a lot of testing with it and as long as the fluid inside the tube doesn't move, the time readings are quite stable.

  Here is my progress on it in chronological order:

  First test of the Viscosimeter

  Test of the Stepper Motor Lifter

  Test of the Pump Lifter

  Test of the optical Sensors and Pump

  In commercial CIJ printers, the viscosimeter is calibrated by selecting the ink type that is used and doing some test readings with it. Based on the test readings the printers can calculate the relation between measured time and viscosity. This is possible because the exact viscosity of the used commercial ink type is known and always the same. Over time, some of the solvent in the ink bottle can evaporate which increases viscosity, so it's recommended to always use a fresh ink bottle for calibration. With the right calibration, the printers can show the actual kinematic viscosity reading in cPs.
  

  In theory, it would be possible to use this method for this DIY CIJ printer - ordering some ethanol based CIJ printer ink and using it for calibrating the viscosimeter. The problem with it, besides the high price of CIJ printer ink, is that the ink's viscosity is not shared with the public so there would be no reliable values for calculation. It's stated that the ink's viscosity is usually around 5 cPs, but for calculating a precise conversation value it would be no bad idea to get the exact viscosity from the ink's manufacturer. With some luck, it could still be possible to find one ink that has a datasheet that mentions its viscosity. In this case, this ink could easily be used for calibrating the viscosimeter and also for printing if the price tag doesn't make it unattractive compared to self mixed ink.

  Another way would be buying some calibration oil (oil with known viscosity) which probably could provide reliable values for calculation. The problem with it would be that for the calibration all lines would have to be cleaned from ink, then filled with oil for calibration, then cleaned again, and then filled with ink again to prevent mixing of both fluids and contamination of the ink. So, with some effort, this could also be a way to get readings in cPs from the viscosimeter.

  If no ink or oil is used for calibration it should also be possible to find out the optimal viscosity by keeping the ink pressure steady and looking at the feedback signal while increasing...

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