Software suggestions and requests

[CescoAiel]

The amount of 'drawback' is IMHO negligible, as it will be an extremely tiny amount compared to how much is needed to raise the fluid level...

[DoulosDS]

The amount of 'drawback' is IMHO negligible, as it will be an extremely tiny amount compared to how much is needed to raise the fluid level...

You are probably right, however, any periodic irregularity becomes glaringly obvious when viewing the surface quality of a smooth print; e.g. the rocket. Let me crunch some numbers before I conjecture further...

Assume the pump tube has an inner diameter of 0.25" which has an area of 0.049 in2. If the pump roller pinches a section of tube 0.5" long, beginning and ending at 100% open and pinched entirely closed in the middle, we could estimate the displaced volume of the pinch as half the volume normally enclosed by the unpinched tube, or 0.25" x 0.049 in2 = 0.0123 in3. Converting to Canadian units: 201.56 mm3. If the print tank is approximately 3" in diameter or 75 mm, the area is 4418 mm2, and the pinch results in a Z error of 0.0456 mm. A fine human hair is approximately 0.04 mm to 0.06 mm in diameter.

Yeah, that might be negligible, especially in a larger print tank. One way to avoid any error is to force the model slicer to use an integer number of motor turns, divided by the number of lobes in the pump (assuming direct drive by a stepper motor) per slice. The pump should be started and stopped about halfway between pinches. That would eliminate the drip counting system, and the pump could speed up the printing process. If the surface tension and viscosity of the resin is a limiting factor, the pump could transfer sufficient extra brine to ensure all the areas printed previously are covered with fresh liquid resin, then remove the excess brine leaving only the amount required by the slice Z increment. A pause before printing the next layer would allow any resin flow to cease.

I hope the pump and motor can be implemented for less than half the cost of the printer... anybody know where to get an inexpensive peristaltic pump?

[DoulosDS]

Peristaltic Pump Amazon.JPG Found this pump on Amazon for $12, free shipping. I was thinking I would need to replace the motor with a stepper, but I don't think that's necessary. I can add an optical sensor to detect the rotor arms as they pass (looks like there are 3). The software can count them and run the motor forward and reverse as needed to adjust the resin level. If the flow rate and RPM specs are accurate, it should transfer 0.2 ml per 1/3 revolution. Conveniently, that is the same volume I calculated for Z-axis error due to tube pinch displacement in my previous post. So, if the print tank is approximately 3" in diameter or 75 mm, the area is 4418 mm2, and 1/3 rotation of the pump results in a Z-axis increment of 0.0456 mm. That's not great resolution, but it means the maximum resin level adjustment rate is only 13.5 mm/min or 0.228 mm/sec. I think that a second pump could run in parallel with this one, maybe with a higher flow rate. Both pumps could pump extra brine to overcome resin surface tension and viscosity issues, ensuring all the previous layer is covered with fresh, liquid resin. Then remove all but the increase for the current slice, within a few seconds.

[DoulosDS]

Peristaltic Pump Ebay.JPG Here is the best inexpensive peristaltic pump I could find with a relatively high flow rate: 500 ml/min for $30 and free shipping. It doesn't provide much info on specs, like rotor RPM, number of rollers (3? 4?), and tubing inner diameter. It does say the in/out hose barbs are for 1/4" tubing, so I expect the pump tube is 1/4" ID also. It may be possible to soup it up with thinner wall tubing, or speeding up the rotor. Regardless, at 500 ml/minute, it could speed up printing.

[CescoAiel]

So, if the print tank is approximately 3" in diameter or 75 mm, the area is 4418 mm2, and 1/3 rotation of the pump results in a Z-axis increment of 0.0456 mm. That's not great resolution, but it means the maximum resin level adjustment rate is only 13.5 mm/min or 0.228 mm/sec.

0.045mm is a good enough resolution for most prints (0.05 is considered typical layer thickness for laser based printing), and can be doubled (ie rise halved) to 0.0225mm by increasing the tank diameter to 8,5 cm, and almost tripled (approx 0.015mm) by going to 10cm.
Of course that also decreased the max rise speed, but then again, how many filament 3D printers complete a 0.2mm (standard thickness for those printers) layer in 1 sec?
Also faster pumps usually also mean less accuracy...