build a 3d printer with a pneumatic dispenser, help?

I like to build a 3d printer with a pneumatic dispenser to print silicone. The dispenser has a constant air pressure, trigger by a 5-24V signal. It is like replacing the extruder of an FDM printer with a pneumatic dispenser. The 3d printer needs to send an 'on' signal (5V-24V) to the dispenser. I was wondering how to wire the dispenser and make appropriate changes to G-code. I am using Arduino Mega, Ramps 1.4, and Marlin firmware.

For wiring, I now wire the dispenser to the fan pin, like many people do to turn 3d printers to laser engravers. M106 g-code turns on the dispenser, but I only want the dispenser on while drawing the pattern (within a G1 command), and 'off' for the rest of time. G1 can specify the extrusion (G1 Exx). But in my case my dispenser is not driven by a stepper motor, and not connected to an extruder port.

I have researched a lot but still get nowhere. Any ideas would be appreciated!

I'm not sure that the Arduibo/RAMPS is the best solution for this.

I do think that you're on the right track for the wiring the same way as the laser, but there is also the question of duty cycle.

Your dispenser is going to accelerate and decelerate as it changes direction, and you most likely do not want to maintain the same rate of dispensing when the nozzle is moving slowly as you will want when it moves quickly. I know that this is also an issue with the lasers, where they must control the duty cycle of the laser in order to maintain an even etching or cutting when the print head moves. The other option is to overshoot the end of a line and just turn the laser off, so that it is only on while the print head is moving at speed. This will not work for your dispenser, as I doubt that it will be able to stop silicone from oozing out suddenly. We can't even do this well with FDM printers, and we can retract filament there. There seems to be no method to do that with your solution.

There are problems with pneumatic dispensers stopping quickly, because air compresses easily, a sudden cessation of pressure is only possible if you vent pressure. You are going to need another valve to release pressure.

Both of these problems are sort of solveable if the silicone flows VERY slowly when extruding, in which case you make print moves very slow, and non-print moves very quick. You'll still get a bit of stringing between print moves, but I doubt that this is 100% avoidable given the nature of what you're trying to do.

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MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

The standard firmware builds of RepRapFirmware on Duets (and maybe some other boards) can do this, see [duet3d.dozuki.com]. The outputs are 3.3V so you may need to add a level shifter.

Edited 2 time(s). Last edit at 09/18/2019 01:29PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

... I'm normally using "pulsed" dispensers and control them with the "STEP" signal of an extruder port, so no problems in the edges

For "continuous" controlling I'm either using an output pin and add the G-code for setting and releasing this pin before and after every "G1..." line, or use the STEP pulse too with a "retriggered monoflop" circuit, which elongates the single pulses, so continuous pulsing will result in a constant ON signal with a slightly "overshoot" in the size of the monoflop duration.

The users with the "constant" pneumatic extruders moves so slow, that there isn't literally any acceleration, so constant moving speeds and homogenuous dispensed lines in the edges too ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Thank you SupraGuy, dc42, and Viktor for the very useful replies.

SupraGuy: You have brought several important points that I had overlooked. As you and Viktor mentioned, the move is expected to be very slow. The dispenser does have an add-on to retract/retain fluid by vacuum.
dc42: I am getting an Arduino Due, not sure how different it is from Duet.
Vitktor: I had thought about turn on/off fan for each G1. How quickly does G code execute, from turning on a fan to move the nozzle? Would I expect to see some extra material at the beginning / end of line? And does this bump up the printing time? Would you please recommend a 'pulsed' dispenser, and a 'retriggered monoflop' circuit?

Thank you guys again! Very helpful! Now I have a better idea what to do.

Edited 1 time(s). Last edit at 09/18/2019 08:52PM by yahoo.

... my "pulsed" dispensers were from Vermes (could be a bit "pricey"): [www.vermes.com]

A typical "monoflop" circuit ist built with a NE555 or a 74121 IC ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Many thanks Viktor. It does look like an expensive dispenser. Will ask them for a quote.

Quote
yahoo

dc42: I am getting an Arduino Due, not sure how different it is from Duet.

Very, the processor it uses (SAM3X8E) is more or less obsolete, and the Arduino Due is crippled by not making the networking functionality of the SAM3X8E available. A few years ago a user of Arduino Due/RADDS ported RepRapFirmware to that combination, but changed to a Duet shortly afterwards. I used to release builds of RepRapFirmware for Due/RADDS, but stopped because AFAIK nobody is using it now - the users I know about all upgraded to Duets.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

... I'm using the Due with my dispensers and US-cleaners, but mostly for "compatibility" (we have some shields and BOB's for them) and without network - so not this bad.

But could be too changing to the Duet, if finding the time to change/upgrade the hardware bases ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]