Re: [DIYbio] open source syringe pump

On 09/23/2014 01:56 PM, Nathan McCorkle wrote:
> Why do you say they'd only be good for continuous flow? I'd assume
> they're good for any flow that can deal with the small amount of
> pulsing the steppers would impose.

Dispensing with syringes is a mature business with suppliers like Nordsen EFD
selling machines that carefully apply solder paste, adhesive, etc with little or no
oozing and quantifiable dot volumes. They do it with forward pressure, then pull back, a
and it's non-linear real-world stuff with recipes that work and not so much theory.

This one's just a crude thing, so getting an equilibrium after non-repeatable start up effects
is all you can hope for. That's because it has so little control, no sensors, and rough edges
on parts made by filament extruders in stretchy plastic.

Even some low cost practical adhesive dispenser for $100 from China on ebay
uses solenoid valves, pressure and vacuum also to get less oozing of the syringe contents.

To me, this seems like another good app for lab gear based on micro python so the
"recipe programming" is easier than the usual microcontroller development cycle,
and scientists might even customize the timing of it for an oddball soup of live
critters to be dispensed in a quantifiable way even though it loves to ooooze out
every time the syringe pump stops. Adding a sensor for pressure could be done
in a non-invasive way -- not touching the syringe contents -- so no contamination or clean up.
Pulling on the syringe plunger would be possible with
some kind of latch grabber same as or similar to the one in the open hardware docs we're talking about:

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0107216

What pulling gets you is a way to counter all the low tolerance fit of parts,
and parts that store some spring energy and have friction by pulling back on
the syringe plunger to stop oozing. Instead of sensing pressure, a force sensor
could be mounted in the syringe handle gripper and capable of reading force
pushing and another one for force pulling. If your parts fit and slide well and
you know your syringe plunger diameter, one could calculate recipes for various syringe
diameters, then empirically improve each size's recipe.

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