Hacking the HP45

Powder and inkjet printing
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dragonator
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Hacking the HP45

Post by dragonator » Mon Nov 09, 2015 5:14 pm

(TL;DR: I am going to attempt to hack the HP45 for use on the next 3DP printer. I know some stuff, and need to figure out some more. Anyone is welcome to join this valiant quest.)

I have been putting this off for far too long, getting distracted with props, and clocks, and games. I want to continue with powder printing, and I cannot design a new printer with the C6602. It is too coarse. What I need is a better printhead. Main contender: The HP45 (HP51645A). What can it do, what does the internet know about it, what do I know about it, and what do I still need to figure out about it.

The HP45 is a fairly old printhead, but it is still in use and it boasts a decent list of features, even for today. 600DPI, 300 Nozzles capable of firing at 12kHz (20kHz max). It costs roughly €30 for an original, and €15 for an aftermarket. It does have a ciss compatible system, though they are hard to get. 52 contacts on the back provide connection with the printhead. They can be refilled without too much trouble by drilling a hole and filling it. It has a hollow reservoir without sponge, held at a slight vacuum with a spring. It can be emptied using a centrifuge.

Lucky for us, HP, when making the patents for their new, fancy inkjet thingamabob couldn't decide on what to make. A datasheet or a Patent. They decided both? I provided links to 2 patents, where the second one is the most interesting. It has EVERYTHING. Pin-outs, timing diagrams, even nozzle locations. I cannot guarantee that this is exactly the HP45, but this is huge. Even ink viscosity and surface tension is mentioned.

There are 52 contacts on the back of the printhead. It has 22 Addresses (connected to the gates) and 14 Primitives (12V source). It cascades through the 22 adresses, triggering the primitives where a nozzle needs to be fired. Closing the gates while the primitives are still high will break the printhead. There are also 14 common pins on the there, but it is not known if these can be used to sink (I have been told no). The remaining 2 contacts are a so called 10X resistor and a Thermal sense (temperature sensor). How exactly these work is not really known to me.

http://www.google.com/patents/US5635968
http://www.google.com/patents/US5946012
http://spritesmods.com/?art=inker&page=2

There are also a few things that I know myself. I have someone I know, who has worked a lot with the HP45, and he has shared a lot of incredibly useful information here. The printhead, as shown in the patents, has a multiplexed array of heating resistors. The ground is common. The source and the gate make the grid for multiplexing. The voltage is 12V, both for the source and the gate. The gate requires roughly 300mA.
There is 2 parts to timing. First the gate is opened. Then there is a 2us pulse on the source to trigger the nozzle. The nozzles need to heat up and stay warm, so the nozzles need to be triggered every now and then to keep it warm. It takes 3 pulses of 2us to trigger a nozzle. Simply triggering the printhead for 6us will break the nozzle. The once every now and then pulse can also be replaced with a 200ns pulse every cycle. Theoretical max speed is 33" per second, but even at 100us per cascade and 3 cascades per trigger, it gives a respectable 5.5" per second.

I made a full detail CAD of the HP45 for future use. I hope everything is properly positioned, but a few things were incredibly hard to measure by hand. You can download the cad model for personal use here.

http://ytec3d.com/wp-content/uploads/2015/11/HP45.zip

All above is theoretical. I first need a good way to make contact with the printhead. For this I will design a set of breakout boards and a 3D printed holder. If people want to join the hacking, I can also send you a set once I have it.

With a way of connecting the printhead, I need to start tests. First I need to be able to trigger a single nozzle. The fact that both the gate and the primitive are sourced does not help, but I have a few things I can try. Once I can trigger single nozzles, I need to:

-Trigger a full address
-Trigger a full cascade
-Trigger everything in the right order
-be able to test the condition of the nozzles (measurement is explained later)
-Make the temperature sensor work
-Figure out what the 10x resistor does
-Design a controller for it (Help is really appreciated here)
-Design a shiny new printer around it
-Post everything on a set of comprehensible Ytec pages so others can benefit too

Lots to do as you see.

Now in all honesty, I will still probably not do this in one go, considering that Fallout 4 is about to happen, and I like Fallout and making props, but I at the very least wanted to make a start. More posts once stuff happens.

ezrec
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Re: Hacking the HP45

Post by ezrec » Mon Nov 09, 2015 9:03 pm

I'm in for working on the controller - I have FPGA and SoC experience.

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Re: Hacking the HP45

Post by dragonator » Fri Nov 13, 2015 10:29 am

Additional information time.

Right now, among other things (*cough Fallout 4 :roll: *cough), I am working on the HP45 carrier with contacts. It is incredibly difficult to make a circuit that can contact all pads, but I am busy trying. I have 2 double layer PCB's that make contact. I tried 1 double sided PCB, but it wont fit. The pad spacing is simply too tight.

I compiled a list of information in excel for later use. A lot of the information was stored in images, so I reckoned I'd make this list now and get it over with. This is the patent information. For all I know, this is a different printhead, but I will see if it is right in my initial testing. The list is downloadable below.
HP45 contacts 5.JPG
HP45 contacts 5.JPG (192.95 KiB) Viewed 28545 times
HP45 contacts 3.JPG
HP45 contacts 3.JPG (335.35 KiB) Viewed 28545 times
One thing I saved for later in the previous post was how to test the nozzles. With 300 nozzles, you need to check the printhead to make sure everything is working. If single nozzles fail (and they will) the printer either needs to know, and maybe even compensate for it. Testing is fairly simple. You have a capacitor that is charged at a low voltage (<12V). Then a nozzle is opened. If the heater works, it should drain in a certain time. If the nozzle is broken, the drain time will be different. How exactly to patch this sensing module to every nozzle is again something I have not really thought off yet, but everything at the right time. I know it is possible, it was done before.
HP45 nozzle information 20151113.zip
(76.96 KiB) Downloaded 1417 times

ezrec
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Re: Hacking the HP45

Post by ezrec » Mon Nov 16, 2015 7:36 pm

Wouldn't you only need to patch the capacitor to the ground? That would give you a common testing point regardless of which element you selected.

aimran
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Re: Hacking the HP45

Post by aimran » Tue Nov 17, 2015 6:22 am

I know this is a bit late in the game but why the need to hack an print head? Can't we trick a normal printer into thinking it's printing on paper and move the print head in the y-axis using its paper feed roller mechanism? Each layer is sliced as a separate page to trick the printer and when print head hits y-axis limit button it retracts back to origin (or lifts upwards) and a powder roller slides for the new layer.

Obviously this assumes print head needs to be able to accept binder fluid.

Edit: related video - https://vimeo.com/94531800

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Re: Hacking the HP45

Post by dragonator » Tue Nov 17, 2015 7:49 am

Technically you are correct. It is possible to do so and for most people this will do just fine. I have a few reasons why I still want to completely hack a printhead though.

1. It is hard to replicate. You basically require that very printer to replicate the results. I like to make projects that others also can make. Also if I myself want to make another one 2 years later, chances are that the printer I initially used will no longer be available.

2a. I cannot precisely control the printhead. I am at the mercy of the printer driver. For printing color on wood, exact amounts of ink do not matter, but with 3DP, you want to be able to control exactly how much ink gets deposited. What if I need 150% of the ink the printer would normally deposit.

2b. Normal printers have chips on the printhead that start complaining when the printer is almost empty. These electronics can easily be bypassed if you have a hacked head. The HP45 does not have a way to check if it is empty, but it will tell the printer it cannot print if even a single nozzle has failed.

3. Hacking a full printhead does take considerably more energy once, but gives massive yield later on. More people benefit from it in the long run. Take the C6602, the printhead in Plan B. The only reason why I was able to make it was because of an open source project called Inkshield. If it was not for that development, Plan B (and quite a few other projects) would not exist.

@ezrec The capacitor on the ground seems like a better idea than on the source.

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Re: Hacking the HP45

Post by dragonator » Wed Nov 25, 2015 4:46 pm

Pogo pins are in, PCB is designed. Now all I have to do is design a decent holder and order the PCB's and I can start wiring things up. For the PCB it was absolutely impossible for me to do it on a single double sided PCB. The spacing is way too tight. I used 2 double sided pcb's and a 12 mil grid to make contact with all pads. The pogo pins are 0.7mm thick.

Next step, the carrier, then ordering parts.
2015-11-25 17.38.40.jpg
2015-11-25 17.38.40.jpg (361.88 KiB) Viewed 28183 times
HP45 breakout_pcb.jpg
HP45 breakout_pcb.jpg (306.01 KiB) Viewed 28183 times

aimran
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Re: Hacking the HP45

Post by aimran » Tue Dec 01, 2015 4:25 am

Got bored of FO4 already? ;)

I'd like to help but I really don't have any experience with 3DP nor electronics. I'm a mechanical engineer by trade and have only a Prusa i3 at home. Currently helping a guy localise the Prusa i3 in my country to cut a few hundred bucks. I'm doing that for free because it's interesting.

So not too sure how I'd fit in with your project. Although I'm more than convinced that powder bed printing (SLS or 3DP) is significantly better than FDM or SLA.

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Re: Hacking the HP45

Post by dragonator » Tue Dec 01, 2015 10:00 am

Not yet. Trust me, I have got something massive and awesome in the pipeline that is FO4. However I also try to do non-prop projects while doing prop work. Props are awesome, but I also try useful stuff.

3DP experience is mainly printhead related. This project becomes mechanical as soon as the printhead is hacked with the design of the next printer. At that point you are free to help. Multiple engineer produce a way better design than a single engineer. Having someone else say "why" every now and then helps to keep flaws and weaknesses out of the design.

While I will not go so far to say that powder bed printing is better than other techniques, it does pose some unique advantages (no support, cheap printing materials and varied printing powders for 3DP). The main reason I am in it is because I think it deserves more open source development than it has. DLP and FDM are massively over saturated. 3DP and in a lesser sense SLS are under-represented in open source world.

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Re: Hacking the HP45

Post by dragonator » Sun Dec 27, 2015 1:18 pm

sophisticated, refined, elegant...
2015-12-27 14.06.21.jpg
2015-12-27 14.06.21.jpg (469.43 KiB) Viewed 27972 times
2015-12-27 14.06.54.jpg
2015-12-27 14.06.54.jpg (432.07 KiB) Viewed 27972 times
These are all the properties I failed to include in the carrier design.

It's been a while since I did anything on the HP45 hacking. I have the attention span of a squirrel and I currently have way too much in progress, but I also have a week off for Christmas and New year, so I can start to catch up.

I finished the design of the PCB and I will be ordering it very soon. I designed and made a holder with a nice latch mechanism. When I started with the design I thought it would be a little less bulky, but it does seem to do it's job.

Anyone that wants to help with the hacking of the printhead itself, I can send you a PCB and if you do not have a 3D printer, a carrier. The spring contacts I have too little of but I can share an ebay link of the right type of pins. When I get the PCB's I will post a finished carrier and order the electrical components to source 12V. After that I will try to make single nozzles deposit ink. I cannot promise a time frame because I currently have 4 more projects running, but this project is moving again.

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