CNC Painter Development Update

[svenakela]

Printers use Cyan, Yellow, Magenta and optionally black and the color you see is...

Well, that is very up to your printer manufacturer. My HP printer uses CMYK (new Hp's uses 8 colours), my Epson runs on eight different pigments (CMY, red, blue, gloss pigment and two blacks) and my old HP runs on RGB. And for sure, the plotter I use has RGB and black.
This is pretty off topic, but putting ink into a paper as a printer or adding a layer of paint with a spraygun is not the same thing. First of all a printer is putting very small drops of colour into the paper. Small enough to not interfer with its neighbouring colour drop and it's hot enough to dry so fast that it doesn't mix with next drop out.
The spraypaint layer is covering the surface and if it's thin it will let the light be filtered in the same way as the inked paper. Maybe an extrem example, but adding a blue layer on top of a silver surface will not give te same result as mixing silver and blue as a single layer, right?..
I agree that printing on a black paper isn't the best way to get good colours. But I spraypaint my almost black motorcycle parts in any colour, and you cannot tell were I put the yellow scratch filler.

The colour problem, if a green area is supposed to meet a red area and the colours are sprayed at the same time and the spraygun doesn't change colour fast enough there will be a zone between the areas that will have a third colour, brownish. If the paint layer is thick enough and the colours can dry between the layups the mixed zone should be smaller, as long as the gantry is spraying and not "laying" or dotting the paint out there will be a zone but hopefully smaller and the colours should fade into each other instead of making a blended third not-so-wanted alternative. That is really happening when a printer cartridge is worn out.

Sorry Vacpress for the off topic, back to your gantry.

Cheers,
Sven

[tachus42]

Yes I guess the trick is how thick you put the ink on.
I'm taking a guess but I imagine most light colored paint has a white pigment in it (titianium dioxide?). The trick is probably to get the paint shop to mix you some process color paint without any white pigment in it, then it should be nice and transparent.

Vac you might want to allow for the posibility of a spare rail to run a counter weight on in your next machine. You would have a wire running from each end of the print head around a pulley to the counter weight. I have seen some quite small motors stop and start big heavy print heads suprisingly fast inducing wobbles in big heavy printers which is not a problem if your media is attached to frame but if it is not... .

As for the gantry axis not moving can't you just print on a downhill slope or something?

[tachus42]

Idea for a print head.
Have you seen those pumps they use for blood, food, corrosive chemicals where rotating wheels squeaze the liquid though a flexable tube?
If you made one powered by a stepper each time you moved the stepper you would get a small amount of ink disspenced to the end of the tube where a air jet can blow it onto the page. The tube could be removed and replaced or cleaned after each run. If you used a pump with a circumferance of 5cm and a tube with a internal diameter of 3mm each 1.8 degree step would pump out about 5 microlitres.

[Zagroseckt]

I Realy dont have the right to talk here but may i sugest you look into the print heads that bakery shops use.

I'm not saying USE one just look at how there doing it.
The proses can be moded to your use verry easly.

[tachus42]

Are you talking about air brushes used for cake decoration? Or some sort of pump to dispence dough or icing?
The idea of the Peristaltic Pump (found out the correct name) was as a alternative to the wire in the wire jet. The wire probably can meter out smaller amounts of paint but the pump should be easy to build, is pontentially less messy and clog free. - I'm just throwing it out as a Idea.

5 microlitres times a paint coverage of 7.5m^2 per litre (300 square feet per galon) is 37.5 mm^2 or a dot about 7mm diameter. About 3 or 4 dpi thats, a little low but it's damm close to what is required gearing down the stepper, using smaller tube or diluting the paint or similar techniques would make it feasible.

One possible advantage would be you might be able use the same jet for all four colors with 4 tubes going into one venturi.

[sdfine]

The cartridges used for printing on cakes is the same as any other inkjet ink cartridge. The manuafcturers use clean cartridges and fill them with extremely fine food colorings. Even though the food colorings are very fine the cartridges are still prone to clogging.

[sdfine]

I wonder if the Peristaltic Pump can be used for pumping precise amounts of air (like the Wirejet) instead of using it to pump the ink.

[vacpress]

i just got home with 8' of 1x1x1/16 CRS steel square tube... hopefully this adds the stability this thing needs.

sven- those comments are totally on topic. in another thread, tachus & I discussed a similar idea- that we are not really mixing ink or paint, we are using halftone patterns and "pixels", i think, to create the color density, gradation, etc. the trick is going to be "tuning" the thing, once we get a basic software figured out. if the software knows how to at least do an off\on for each pixel, or pixel area, we can figure a way to make the colors right... i hope.. and if not - then it will jsut be a big quirky plotter.

tachus- the venturi and peristaltic pump is a good idea- and one i thought of also, but i am sorta leaning towards some sort of blade\wire\hoop\disc\etc that is run in a circle through the trough of paint - much like pixation.. i bet "wire metering" or whatever it would be called is used for other uses than the wirejet.

sdfine- i dont think the peristaltic pump can pump precise amounts of air, i dont know why though heres a link: http://www.animatedsoftware.com/pumpglos/peristal.htm
one good posibble thing about the peristaltic, it looks like it could move pretty viscous fluids...

cake painting machine are an interesting thing to bring up - it reminds me of the industrialized inkjet heads i was looking at before i really decided to build this thing. there are problems with inkjets though that the pixation machine overcomes... the inkjet heads seem to need a very accurate delivery

i am gonna spend 5 or 6 hours on the machine today. ill post some pics!

[teilhardo]

Good luck with the steel Vac
At your rate it looks like you might be able to finish the mechanics of it today. Then onto designing the print head...

[vacpress]

teil- yeah. the printhead in my 3d drawings is not a final design at all.. for 1, i only have 1 paint gun..

i think i want to spend a day with the thing doing vector stuff using standard CNC software and a Pen or marker. I can get the thing "dialed-in" that way.

i need new wheels though... my wheels are too light, and too large. i need 6", hard rubber wheels, with heavy metal hubs...

[publitime]

vacpress




I think i will be simple to convert a photo to G CODE.
I tryes something last night.
The program i used is simular with a program for laserwork.
All you have to do is import a photo into the program.
The program will translate the photo to g code.
Thene the laserbeam will burn the photo into wood are an other material.
With the laser you will get a black and white picture .
So to make a black and white picture it will be easy.
I have just to put a spraygun in place of the laser and ready.
To do the same with multiple colors it can not be that hard.

[tachus42]

re Peristaltic pump - i see great minds think alike ha ha
The problem comes down to how to meter out very small amounts of a viscous fluid continuously with a large variation in flow rate without sticking it though any sort of small hole - there aren't two many options other than the 'fluid film' option which is probably the best i can't really think of any others apart from the pump.
I didn't read the pixelation patents but i did notice on one of the pictures of the wire jet the was a area to the side of the print with bands of paint where "the excess paint is cleaned off" does this mean the wire is rewound? air pressure is increased and the wire cycled to remove "cling ons" or perhaps another air jet to clean paint off that is dripping down off something?

Getting the color output right was the reason that i thought ghostscript was a good idea, it has all the mechanisims built in. If you get paints that are close to cmyk the biggest issue will be getting the transfer curve for each color right but there are some simple ways to do this with special test prints.