A team at [Vanderbilt University] have been hacking together their own peristaltic pumps. Peristaltic pumps are used to deliver precise volumes of fluid for research, medical and industrial applications. They’re even occasionally used to dose fish tanks.
They work by squeezing the fluid in a flexible tube with a series of rollers (check out the awesome gif from Wikipedia to the right). We’ve seen 3D printed peristaltic pumps before, and cheap pumps have been appearing on eBay. But this build is designed to be lab grade, and while the cheap eBay devices can deliver ~20ml/min this one can deliver flow rates in the microliter/min range. It also has a significant cost advantage over commercial research grade pumps which typically cost thousands of dollars, each of these pumps costs only fifty bucks.
The pump has a clear hacker heritage, using an Arduino Uno, Adafruit Motor shield, and 3D printed mechanical parts. So it’s particularly awesome that they’ve also made their design files and Arduino code freely available!
[Via the Pelling Lab on Twitter]
Nice build, but i do not get, where the precision comes from. Is the deformation of the tubing predictable that precisely?
Also, VVS….
“Flow rate is dependent upon both tubing diameter and step rate. We found flow rates to range between ~50-250 μl/min for 1/16” tubing and ~500-1500 μl/min for 1/4″ tubing.”
I’m sure the step rate could be greater if a stepdown gearbox was used, but even then the limiting factor is the tubing.
Yes.
The rollers are at fixed distances along an arc, the diameter of the tubing is known, so you have a cylinder of known volume. Now it’s just a matter of how fast you turn the stepper.
Since the tubing is a small diameter the liquid will cling to the tube and effectively act as a solid piston. As the previous reply pointed out, accuracy is limited by the resolution of the stepper, or speed controller for continuous operation.
Accuracy is greatly influenced by the elasticity of the tubing. Peristaltic tubing degrades over time and flattens out, pumping less fluid. This is the single biggest component. Anyone doing microliters/minute and expecting accurate flows would use a syringe pump.
Long term, sure. I’m betting the lifespan of the tubing could be worked out easily enough to overcome wear and tear. For certain applications it still probably holds the edge over a syringe pump.
Harmonic drive anyone? No backlash and fantastic precision on angular velocity
No “outer” tube guide at the 3 rollers? Interesting.
The gif, and a related video show a version with an outer wall. Wall thickness/material probably controls the necessity of this.
The gif is from Wikipedia, not their project though and the video doesn’t seem to have any kind of outer wall?
You don’t need one. It’s common on peristaltic pumps to squeeze the tube against the wall of an outer housing, but if you can hold the tube steady, you can also use the roller pull on the tube so that it pinches the tube wall.
Precision comes from the distance between the pinch points on the tube. Once the tube is filled each (1/number of corners) rotation will deposit the volume of fluid between the two pinch points. There is some variability due to bubbles, squeezing of liquid through the pinch points, etc. But I believe that is the principle.
This is what the Peachy Printer needs instead of that uncontrolled drip system they use now. I even mentioned that to them. Then you can load and unload the tank in a known manner.
+1
This can be an incredibly cheap way to deliver a precise amount of fluid to the vat. I saw the drip technique and I was basically saying to myself how dumb of an idea it was to expect the drip to fall at exactly the same rate, plus measure it as it strikes a poorly designed fluid detection circuit (two pieces of wire).
Just a general observation: What is “hacker heritage”?
I don’t think it’s a good term. You can define it in two ways:
Either, you go down the route of following the term “hacker”. A hacker, to me, is someone who is very interested in the details of operation of any system, and took his time getting intimate with that systems reaction or applicability to non-standard use cases.
Well, the authors are “Shannon Faley, Bradly Baer, Matthew Richardson, Taylor Larsen, and Leon M. Bellan,
Vanderbilt University, Department of Mechanical Engineering”; um… so they’re educated engineers, using standard tools to implement a standard device. That’s what engineers do, as long as they are *not* hacking anything.
You can also go, and that’s what I’d like to prefer here, by concentrating on the “heritage” aspect of the term: It’s been built using tools that are typical to hackers.
In that way, there’s nothing hacker-related about that pump. It’s a well-known principle, solidly designed from start to finish. “Arduino Uno, Adafruit Motor shield, and 3D printed mechanical parts.” is pretty much the description of an easy-to-use, dedicated system to driving a motor and building a pump with that. Not hackish the least.
tl;dr
wish you had chosen tl;dc instead ;p
Hmmmm – what’s tl;dc? Never heard of that before and can’t find any explanation online
I’m guessing “too long; didn’t comment” as it didn’t add anything to the discussion.
I’ve seen a lot of peristaltic pumps in action and they tend to be 3 – 5 rollers and made as compact as possible to fit into machinery or on a medical device side mount. Since you can build it any way you’d like, is there any advantage to going the other way? Would a larger roller assembly of, say, 10 (or 25?) rollers have an advantage of accuracy/stability/tubing life?
Doubtful. However you use it, at at least one point the tube is crimped to seal it off. This crimp migrates w/ the rollers pushing the fluid along with it. Unless the pump is stationary for long periods, wear should be pretty uniform across the tubing inside the mechanism.
Assuming each roller makes a complete crimp, more rollers would increase wear on the tubing, though precision may get better as well if your motor driver has poor resolution. That is more rollers could be a sort of partial step between rotations.of the motor. The increased wear may not be a good trade off though, if only in terms of down time.
The real (IMO, not touching the medium is great too though) beauty of peristaltic pumps comes when you pair different diameter tubing around the same roller mount. Then you get a constant ratio of reagents all being delivered at the same time.
Can attest to accuracy this mechanism is used on ICP-OES machines. Tubing is replaced almost weekly when ran 4 hours a day. So accuracy will degrade about every 24 hours of use.
they use these pumps when i’ve donated platelets. The tubing is part of the package they use for each doner so the tubing is replaced every donation. Using this method means they can set up a machine to pump blood in minutes, and maintain a clean sterile environment very efficiently for multiple uses.
https://www.youtube.com/watch?v=QQzscW94VFA also quite suitable for mixing drinks…
Wow that’s a super cool design. Look how few parts there are, and it looks incredibly resistant to manufacturing tolerances. The only issue I see is this:
The tubes must be tight on the rollers to crimp completely, but how can you ensure when replacing the tube, you get the tension right?
If you make it tighter than it was, then the inner diameter of the tube, and therefore the volume didpensed, will be reduced. Perhaps it needs to be calibrated each time?
You would use the same length before stretching it, which would make it tension the same every time
Keep a bookmark on this one.
Does anyone know the proper term for the white grommet that keeps the tube in place?