Peachy Printer drip system alternatives/fixes
October 01, 2013 12:02PM
I'm putting this in the general section because there isn't a peachy section yet, the rest of the related threads are in polar bot & robot arm section http://forums.reprap.org/list.php?185

Some of the concerns for the drip system / water metering: (maybe some are irrelevant, maybe there's more)

-water resevior level decreasing slows the drip
-are drips consistent enough?
-want faster / controllable flow
-corrosion of metal wires in saltwater

What I suggested was to use a water wheel and count the rotations.
http://en.wikipedia.org/wiki/Water_wheel#Overshot_wheel
-can make a simple braking system to have some control and stop the flow
-as long as flow isn't so fast that it can go through unmetered, you have a precise volume per rotation
-can be made entirely of plastic; no metal touching saltwater
-cheap, and keeping it stupidly simple.
-could look cool

To make sure water doesn't overflow the water wheel you could make a housing that is tight to the wheel on the side that the water flows on. diagram

Maybe someone has other ideas that will work, I know rylan and the team want suggestions made here on reprap.
Maybe this is somewhere to start with other water flow ideas: http://en.wikipedia.org/wiki/Flow_measurement

Some background on my experience with peachy and 3d printers:
I'm a member of saskatoon techworks that rylan and some of the team are part of, and I talked with most of the team there yesterday.
I've used techwork's solidoodle a bit but I'm by no means an expert.
I'd call myself an entrepreneur that appreciates simplicity in designs, and advocate of open source, so I love the direction rylan is taking the 3d printer industry.

-erik

Edited 2 time(s). Last edit at 10/01/2013 12:39PM by ert485.
Re: Peachy Printer drip system alternatives/fixes
October 01, 2013 01:52PM
-water resevior level decreasing slows the drip

I see no reason why. gravity is the force that applies and it will work equally on any level of liquid

-are drips consistent enough?



Drip bags are used in hospitals every day but if you want absolute precision check out:

http://en.wikipedia.org/wiki/Infusion_pump

-want faster / controllable flow

see above, or regulate flow with same method as drip bags

-corrosion of metal wires in saltwater

if you are talking about the counter construction: use gold plated ( won´t even cost 1/100 cent at these dimensions)


Blog:

[3dptb.blogspot.de]

Books on 3D patents:
[goo.gl] (english)
[www.amazon.de] (deutsch)
Re: Peachy Printer drip system alternatives/fixes
October 01, 2013 02:40PM
now i want to take one of those infusion pumps apart..lol

i was thinking a peristaltic pump might give a person the controle they wanted, if you could get by the sight pulsing they have.


[mike-mack.blogspot.com]
Re: Peachy Printer drip system alternatives/fixes
October 01, 2013 03:57PM
maboo Wrote:
-------------------------------------------------------
> -water resevior level decreasing slows the drip
>
> I see no reason why. gravity is the force that
> applies and it will work equally on any level of
> liquid

The taller container of liquid the more pressure there is at the bottom. the top of a fluid has zero pressure, the bottom has pressure proportional to the depth. more pressure at the tube source, faster flow. I'm sure its not significant for small prints, worst case you keep filling the reservoir as you print big objects. Don't know if that applies to drip bags, I'd assume they want consistent drips too. That was one thing the team mentioned yesterday. Can drip bags flow enough to do large prints? and would it be hard to control the rate electrically? (I'm assuming simple drip bags only have manual control)
Re: Peachy Printer drip system alternatives/fixes
October 01, 2013 09:37PM
re-thought the water level - pressure problem
actually the effective depth is the top of the water in the reservoir to the lowest point in the tube when the tube is full of water (ie. it siphons down the tube as well)

so that means if the drip point is much lower that the reservoir it will have more consistent flow from full to empty.
Re: Peachy Printer drip system alternatives/fixes
October 01, 2013 11:30PM
you can have a constant flow by having the drip reservoir being constantly over flowed, with excess dripping over the top. look up how they made some clocks using water drips a long time ago.
Re: Peachy Printer drip system alternatives/fixes
October 02, 2013 01:11AM
How about using steam pressure in the sealed bag (Water vapor pressure rise with temperature), either as a metering system for keeping the internal pressure the same, or pushing up the layer of polymer predictable (as if on an inflating ballon)
Re: Peachy Printer drip system alternatives/fixes
October 02, 2013 03:56AM
ert485 Wrote:

> The taller container of liquid the more pressure
> there is at the bottom. the top of a fluid has
> zero pressure,

Surely not zero, or the water on top would float in the air. It has 9.81m/s² accelaration from gravity

>the bottom has pressure
> proportional to the depth. more pressure at the
> tube source, faster flow. I'm sure its not
> significant for small prints, worst case you keep
> filling the reservoir as you print big objects.
> Don't know if that applies to drip bags, I'd
> assume they want consistent drips too. That was
> one thing the team mentioned yesterday. Can drip
> bags flow enough to do large prints? and would it
> be hard to control the rate electrically? (I'm
> assuming simple drip bags only have manual
> control)

We should not exaggerate the effect of the pressure that is applied from teh water it is minimal. See the pressure in deap sea:
pressure in the ocean increases by about 1 atmosphere for every 10 meters of depth,
Source: http://en.wikipedia.org/wiki/Deep_sea

I am about to build my conatainers for my pechy and I was planning to use a pump to supply a small amount of liquid to the upper container. Whenever it reaches a cercain level, the pump will resupply the upper container. That way the peechy does not have to carry all that water (and weight) on top of the device. I rather leave it in a conatiner underneath the resin containern and resupply when needed. This w y you could overcome your concerns with constant pressure conditions.


Blog:

[3dptb.blogspot.de]

Books on 3D patents:
[goo.gl] (english)
[www.amazon.de] (deutsch)
Re: Peachy Printer drip system alternatives/fixes
October 02, 2013 11:17AM
maboo Wrote:
-------------------------------------------------------
> ert485 Wrote:
>
> > The taller container of liquid the more
> pressure
> > there is at the bottom. the top of a fluid has
> > zero pressure,
>
> Surely not zero, or the water on top would float
> in the air. It has 9.81m/s² accelaration from
> gravity

The pressure is from the weight on top of it. If there isn't anything on top of it, no pressure. For what is relevant (you mention 10m per atmosphere ie 100kPa) I think there would be a difference in drip rate from 0.5kPa to 3kPa (~5cm vs 30cm)

I like the idea of filling it with a constant overflow, I had thought of that for things other than keeping a constant pressure. Its just like any garden waterfall/birdbath kinda thing I'm sure they'd be cheap, they don't need to do much or be precise.

Maybe you could control the pressure manually (the operator not the computer) by changing the height that the water starts leaving the reservoir. (high exit point higher dripping pressure)
Re: Peachy Printer drip system alternatives/fixes
October 02, 2013 11:51AM
Hmm ... piezoelectric droplet generator controlled by DC offset in stereo signal.
Re: Peachy Printer drip system alternatives/fixes
October 02, 2013 04:48PM
wow i just told you a perefect way to do it. Get 2 liter, put in a tiny adjustable drip valve at the bottom of it, and a tube that goes from it to the resin resevoir. put the bottle in a larger tub. fill the bottle and tub with water. Place the tub above the resin floating tub run a small water pump into the water holding tub, have the output go into the 2 liter bottle. leave the cap off, the overflow will go into the tub, and the 2 liter will have a constant amount of water in it, and output a steady amount of drips.
Re: Peachy Printer drip system alternatives/fixes
October 06, 2013 08:48AM
Medical drip systems are reasonably constant but also have semi-skilled human monitoring.

Maintaining a fixed level is easy enough without having to invent anything.
[www.bastish.net]

There is a limit to how simple one wants to make something if it will make the operation more complicated.

The amount of corrosion in selected stainless steel or platinum wire will be low.
There exist optical beam break (think end stop) devices that monitor drops in medical infusion lines.
Use a microphone to listen for the drop falling from 200 mm into a tube, the small wave it generates may assist with surface tension when the level is supposed to rise.

The rate of drops is irrelevant, the software uses it to determine the next slicing layers height dynamically in this design.

Using the water to float the resin is cool but while using drops serves the minimalism approach it is a bit primitive just to save on a control interface and does not raise the level in discreet steps as would preferred.

While I have not any finished ideas I think some kind of tank raising system with a connecting pipe would be better suited to transferring a fixed volume of water in and out of a build chamber. A simple motor and screw could raise a tank and a interrupter disk on the motor could send signals back if it had to be managed with the microphone interface.


Kalle
--
Lahti, Finland
The only stable form of government is Open Source Government. - Kalle Pihlajasaari 2013
Re: Peachy Printer drip system alternatives/fixes
October 13, 2013 12:51PM
I always liked the Darwin paste extruder concept which used ideal gas equation to guarentee the nozzle pressure never deviated by more than 10%.

IIRCC it involved a bladder which was approx 100ml in capacity, and then it was inserted into a soft drinks bottle which was approx 1L capacity and then the gas inside the bottle was charged to about 1bar gauge.

As the gas was never expanded to more than 1L from its start point of 900ml it never dropped in pressure more than 11%.

I loved that idea, whose ever it was.

I wonder if that principle could be used with Peachy to control the rate of saline solution into the Peachy chamber?


AS
Re: Peachy Printer drip system alternatives/fixes
October 15, 2013 05:30PM
Just some quick thoughts...

The drip rate isn't constant and it doesn't need to be unless you want to print from the web or a device that doesn't or can't read the drip rate. My idea to keep the drip rate constant (if needed) is the same as a pet water dispenser. Basically, the water is up top in a closed system such as a 2 liter bottle. It is placed upside down in a reservoir and will maintain a constant height in the reservoir. That reservoir would feed the drip system.

a small example
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