Software suggestions and requests

[DoulosDS]

0.045mm is a good enough resolution for most prints (0.5 is considered typical layer thickness for laser based printing)...

I was searching the whole forum for this info; then I found in on my own thread! I'm glad to hear my $12 PS pump can meter out one slice per 1/n revs in the smallest print tank I expect to use, and could slice it a lot thinner in the largest tank I envision. And, how much faster can the pump move a slice volume of brine than the drip system? This could speed things up a lot.

As for accuracy, the peristaltic pump hose degrades gradually over time, but that change should be negligible during a print. If the pump is run at high speed, the rate of relaxation of the pinched tube may cause an error relative to running at slower speed. If the tube is unable to resume the full, unpinched volume before the next roller pinches it off, the volume between pinches will vary with pump speed. If two pumps are used: one low flow rate for slice volume, and one high flow rate for displacing the resin to cover the previous slice, I think there's no problem. The slicer pump can run slowly, and the displacement pump can run at a uniformly high speed in both forward and reverse. If there is any reduction in pinched volume due the speed of the pump, it should be cancelled out. Of course, the displacement pump would run an equal number of revolutions in both directions and stop between pinches.

!!! Whoa !!! I just enlarged the image of the motor label for the high displacement PS pump on eBay... it says the flow rate at 24 VDC is 4500 ml/min! (editing: WRONG! That's a typo on the label.) That's 75 ml/sec or 7,500 mm3/sec. In the previous example of a 7.5 cm diameter print tank, that is a Z rate of 1.7 mm/sec. That should be plenty fast for displacement, even in a larger tank, or the pump can be run at a slower, but uniform speed. I have sent the seller a question whether the pump listed is the same as pictured, and can it run on 12 VDC at 1/5 the flow rate.

[CescoAiel]

Note there was a typo in that quote... There was a 0 missing:

0.045mm is a good enough resolution for most prints (0.05 is considered typical layer thickness for laser based printing)

[DoulosDS]

I have sent the seller a question whether the pump listed is the same as pictured, and can it run on 12 VDC at 1/5 the flow rate.

No, the pump is NOT as pictured. It is a 12 VDC pump with 500 ml/min max flow rate. It has 3 rollers on the rotor. I have asked the seller if he has any more of the 24 VDC pumps left... I will let you know what he says.

[DoulosDS]

..... I have asked the seller if he has any more of the 24 VDC pumps left... I will let you know what he says.

He says the 24 VDC pump does NOT pump 4500 ml/min but only 450 ml/min... the label was misprinted (then why use it to illustrate the 12 VDC pump?) and he didn't say whether he still had them for sale (if anyone is wanting one.).

[DoulosDS]

Another comment on peristaltic pump accuracy: those driven by DC motors, rather than stepper motors, have gear trains to provide the necessary torque. The $12 pump I found on Amazon has a maximum rotor speed of 100 RPM, but the motor is rated at 5000 RPM (probably no-load speed), so I am guessing there's a planetary gear system between the motor and the pump. If there can be a sensor on the motor shaft, the precision of the pump output can be multiplied by the gear ratio. Assuming a gear ratio of 36:1, that would make the slice thickness accuracy much better. Given the torque load of the pump rotor, I expect the motor doesn't coast very long after the power is shut off, maybe one revolution or less. Instead of a sensor on the shaft, it may be possible to detect the motor armature transitions in the motor current or voltage. Depending on the number of segments in the armature, that would provide even greater precision.

[CescoAiel]

Another comment on peristaltic pump accuracy: those driven by DC motors, rather than stepper motors, have gear trains to provide the necessary torque. The $12 pump I found on Amazon has a maximum rotor speed of 100 RPM, but the motor is rated at 5000 RPM (probably no-load speed), so I am guessing there's a planetary gear system between the motor and the pump. If there can be a sensor on the motor shaft, the precision of the pump output can be multiplied by the gear ratio. Assuming a gear ratio of 36:1, that would make the slice thickness accuracy much better. Given the torque load of the pump rotor, I expect the motor doesn't coast very long after the power is shut off, maybe one revolution or less. Instead of a sensor on the shaft, it may be possible to detect the motor armature transitions in the motor current or voltage. Depending on the number of segments in the armature, that would provide even greater precision.

True, but you'd still need to keep in mind the number of rollers squeezing the pump-tube and their relative position to the end of the housing (ie where it stops pinching and allows the tube to return to normal diameter)

[DoulosDS]

True, but you'd still need to keep in mind the number of rollers squeezing the pump-tube and their relative position to the end of the housing (ie where it stops pinching and allows the tube to return to normal diameter)

Right; the motor controller would just keep the pump stopping point from drifting or dithering. The pump would always turn an integer multiple of 1/n for n lobes. My idea of sensing the pump lobe position optically would allow too much slice-to-slice variation. If the armature modulation counter goes over the number of armature bars, the controller could report an error or even correct an error if somehow the motor revolution counter lost count.