Gallery, Projects and General > The Design Shop
Automatic paint mixing.
Joules:
You’re getting into the territory of the 3D printer using retraction. Do you still plan on having 5 nozzles ?
How about using a wide section of wiper blade on a servo to squeegee the syringe ends. The wiper sweeps the same colour area each time so no cross contamination. Maybe stagger the syringes in a line if you drive each one individually. I was trying to think up a way of using one stepper and cycling the syringes as mentioned earlier, the wiper would also move and use the same section per colour.
Interesting project, can see 3D printing being very helpful here. Look up gattling guns for rotating your syringe prior to extrusion of paint, or Geneva mechanisms. Now you’re at two steppers and a servo.
In fact with two Geneva mechanisms, one could rotate the paint and the other do the wipe per colour, now we do away with one servo as well.
Joules:
I particularly like the above mechanism as it can do the index and wipe in one action. The indexing lever for the wipe ring could raise the wiper a fraction so all the other wipers miss the other syringes.
S. Heslop:
I had also thought about a carousel. More than anything I figure it'd be slow as each of the 5 colours is indexed and the stepper resets it's position for each plunger. And you'd miss out on the ability to draw paint back.
It would look very cool though, and having one stepper motor would make it easy to make it a fairly chunky one. I also wonder if you could come up with some sort of mechanism so at the end of the stepper motor screw's travel it engages the indexing mechanism, meaning you'd only need one motor. Plus it'd make the dispensing tips easier to access and reduce the need for any kinds of pipes routing the syringes to the tips.
Wipers could be an option. But I think disposable dispensing tips might be better way to deal with dry paint building up on the nozzles. I'm thinking though that instead of a shutter, borrowing more ideas from 3d printing, some kind of silicone rubber condom that sits over the nozzles that can serve as both a seal to stop them drying out when the device is placed on its stand as well as be easy to clean off if dry paint builds up on it. I guess my biggest concern with strings of paint is that they might affect the dispensing accuracy if you've got a considerable amount of paint sometimes dangling and sometimes falling off.
It's fun thinking up goofy mechanisms. What if there's a carousel and the stepper motor's connection to the syringe plungers is a kind of comb shape that fits around the plunger, or something connected to the plunger, so it doesn't need to move as much to line up with each syringe and can do the retract at the end of the stroke. What if it can push all the syringes at once but 5 sorts of clutches or pawls disconnects each syringe from the stepper as it reaches the correct amount. What if compressed air pushes the plungers like in solder paste dispensers, but there's some kind of encoder to read the position of the plunger rather than trying to measure the flow... But by the end of the day I think a £10 stepper on each syringe would probably be the easiest to get working, and still somewhat affordable. I just wonder if they'd have enough power to really jet the paint out through a small restriction.
Joules:
I think the question becomes, how much is the minimum paint to mix per batch. The larger the amount, the smaller the error in paint at the nozzle. The Arduino should track syringe position so it can line up on each one and know when one will need replacing. I estimate a complete set of five colours extruded and indexed in under 30 seconds, depending on volume extruded. Perhaps lift the carousel off and seal the ends in one go when not in use. Certainly mix a few colours each session, than just one or two. Nema 17 steppers would be man enough for the job, they manage to force plastic through fine nozzles. Using the carousel you can deposit paint into a small screw top tube for mixing and storage prior to use.
Another problem with retraction would be, drawing air into the nozzle would promote quicker drying. Look at inkjet printers and how they purge prior to printing. All that expensive ink wasted, as printers didn’t used to purge like they do now.
PK:
There was recently a thread on solder paste dispensing in which micro-pumping using either a solenoid or piezo element was used to pump tiny qtys.
I wonder if that approach could have any application here...
Back to syringes, but still on the solder paste theme.... http://www.applecture.com/electronic-dispenser-for-manual-solder-paste-application-to-pcb-for-reflow-soldering-or-hot-air-soldering-technics-53341
PK
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