4 ms·

It's a good project. If you print a lot, here's my project using which you can create tons of cheap filament: https://medium.com/endless-filament/make-your-fi

• regularfry 6y ago
  Is it the control algorithm you're after, or an output diameter measurement technique? You don't mention how you're measuring the width at the extruder die or after the freeze bath.
  • econcon 6y ago
    Hello! I've dual axis laser micrometer which has a sampling rate of 100 of times per second. I can use microcontroller to read the measurements and want to dynamically change the puller roller speed. (It's a geared down stepper motor) Pinch roller (puller) is very simple, it uses steel rollers which have sandpaper pasted (with epoxy) on it for gripping fimament - it can pull with force of 10kg before it slips. I want to achieve tolerance range of +/-0.02mm in diameter
    • regularfry 6y ago
      Where is that micrometer mounted? The problem you're going to have (which I'm sure you're aware of) is that if it's after the freeze bath, you're miles away from where the thickness is actually determined. If the speed of the rollers makes the filament go through the bath at 1m/s (say) and the bath is 2m long, you can't react to any deviation in the temperature of the plastic as it leaves the nozzle (for instance) any sooner than 2 seconds later, and any drift has had that long to cause a problem. That way lies an oscillating system, unless you're quite careful. The way you've posed the system, my gut feeling is that your problems are going to come down to reaction time. Once a problem manifests in the system, how quickly can you a) detect it; b) react; and c) have that reaction take effect? There are three things I'd look at. The first is to make sure the entire path of the plastic until it has set is tightly temperature-controlled. You can't have breezes varying the temperature of the plastic before it enters the bath, so you want a PID-controlled warming tube to control its descent into the bath. Similarly you need to control the temperature, depth, and turbidity of the bath so that the length of time the plastic is less-than-fully-solid is tightly controlled. If you do that, you've got a chance that you've controlled the physics of the filament well enough that quick deviations will be damped out, and slow drifts get picked up by the micrometer. The second is mounting the micrometer as close to where the filament enters the bath as you can get it. That's the point that's as close as you can get to where the plastic's frozen and the thickness is determined, so there's as little lag as possible between where you're measuring and where you're having an effect. That will let the system react to much faster deviations than it would be able to otherwise. Third, I'd make that bath as short as possible. The length of filament hanging in the bath will act like a spring, so when the rollers speed up to try to thin the filament out, that acceleration will be blunted as the filament lifts up into a shallower catenary. You can compensate for this in the control system, but it's better not to have to. In fact, if you could get rid of the need for a bath by instead rolling the filament immediately onto a chilled metal roller close to the extruder die, that might open up other possibilities, but that ends up baking stresses into the filament which you might not want to deal with.