Upgrading a CO2 Laser with the Think3DPrint3D Duet controller
Posted by Radian
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Upgrading a CO2 Laser with the Think3DPrint3D Duet controller June 13, 2015 06:38PM |
I've been posting in the Ormerod forums about the conversion I'm doing on a cheapo Chinese Ebay Laser engraver. The Duet controller used in the Ormerod 3D printer is what got me started but it seems more appropriate to post details of the build in here. The reason I wanted a Duet controlling the Laser is that, thanks to the hard work of guys like dc42 and zombiepantslol, it has become a dream to use for 3D printing. The web control interface and improvements to just about every aspect of the firmware over the last year or so made the control system I had installed in the Laser pale in comparison (and that was after I ditched the Chinese junk that it came with fro some Pololu stepper drivers and LinuxCNC).
Hardware
The XY motors and endstop detectors were OK(ish) so I began by simply re-plugging them into the Duet XY connectors. The Y endstop was an opto-interrupter originally powered from 5V but it checked out OK at 3.3V making it compatible. The cable carrying both X motor and XY endstop connections is a flat flexible type and it works quite well as its own drag-chain so I de-soldered the socket from the original control PCB and wired it off to some 0.1" header sockets to plug into Duet. The X motor already had a 0.1" header so that plugged straight on.
The real key to getting it all working with the 3D printing hardware/firmware proved to be the M571 G-code command that enables Fan 0 on extruder moves (thanks to dc42 for pointing this out). Wiring this output to the Laser Enable input on the Laser PSU therefore neatly transforms the laying of filament into Laser path cutting. The only wrinkle (hardware wise) is that, while the Fan 0 Mosfet output is open-drain, there's a pull-up to the 12V~24V supply via a LED hanging on it. To block this I just soldered a series diode in the wire with the cathode to Fan 0 O/P.
The Laser tube PSU is often different in each version of the laser (generic naming K40 I, II ,III etx,) and mine looks like this:
I've seen lots of different suggestions for how these are interfaced, some of which contradicted the way mine was originally wired, so I did a bit of circuit tracing (great care is needed inside these things as they have very high voltages on capacitors which must be discharged before venturing in). I found that both P and L terminals are active low (contrary to some documents showing P as high, L as low). Both ground down the LED in an opto-isolator so again, while people suggest they can be modulated by PWM - yes they can, but only at low frequency (<1KHz to be practical). One is already connected to the Font-panel Laser Enable button (I labelled it La) while the other (Lb) is free to be connected to the Fan 0 O/P on Duet. The connection is duplicated on the empty 4-way block as well.
At the moment I'm not controlling the Laser power via Duet other than on/off as I'm only interested in cutting (not engraving). As I understand it, controlling power using PWM rather than using the analogue input (normally connected to the wiper of a front-panel pot) does have advantages as the laser can deliver a higher peak of power in the first instances of it striking. I hope to investigate this at some point.
One other thing worth noting is that the 5V is derived from a 7805 TO220 heatsinked to the case. So while I've seen people say don't pull more than 20mA from this terminal, I suspect it can deliver plenty more. I have a small stand-alone PIC chip running off this to act as a monostable (could have been a 555) to deliver a 10ms pulse when the test button is pressed. I find this useful for delivering a calibrated pulse that can be compared at different foci, materials etc. It conveniently plugs straight into the 4-way connector where all the signals needed are present (apart from the push-button which is now wired to the PIC).
Workflow
Swapping the standard 3D printing extrusion function for a cutting action means being able to use a workflow familiar to most 3D printer users. In my case this means creating .STL files representing 2D paths only (e.g. using 2D primitives with a small extrusion height in OpenSCAD) and setting a matching nozzle size in Slic3r to produce G-codes limited to a single layer.
Other sources of G-code generation for 3D prints should be equally applicable in addition to the more conventional 2D CAD/CAM tools. While it certainly isn't how the authors of the apps I'm using intended them to be used, it works just great for me and cuts down on the number of apps I need to be familiar with. It also makes projects that involve both 3D printed and Laser cut parts much more integrated - i.e. easily modeled in OpenSCAD as one design, with conditional modules enabled for output to the two different tools.
RS Components Reprap Ormerod No. 481
Hardware
The XY motors and endstop detectors were OK(ish) so I began by simply re-plugging them into the Duet XY connectors. The Y endstop was an opto-interrupter originally powered from 5V but it checked out OK at 3.3V making it compatible. The cable carrying both X motor and XY endstop connections is a flat flexible type and it works quite well as its own drag-chain so I de-soldered the socket from the original control PCB and wired it off to some 0.1" header sockets to plug into Duet. The X motor already had a 0.1" header so that plugged straight on.
The real key to getting it all working with the 3D printing hardware/firmware proved to be the M571 G-code command that enables Fan 0 on extruder moves (thanks to dc42 for pointing this out). Wiring this output to the Laser Enable input on the Laser PSU therefore neatly transforms the laying of filament into Laser path cutting. The only wrinkle (hardware wise) is that, while the Fan 0 Mosfet output is open-drain, there's a pull-up to the 12V~24V supply via a LED hanging on it. To block this I just soldered a series diode in the wire with the cathode to Fan 0 O/P.
The Laser tube PSU is often different in each version of the laser (generic naming K40 I, II ,III etx,) and mine looks like this:
I've seen lots of different suggestions for how these are interfaced, some of which contradicted the way mine was originally wired, so I did a bit of circuit tracing (great care is needed inside these things as they have very high voltages on capacitors which must be discharged before venturing in). I found that both P and L terminals are active low (contrary to some documents showing P as high, L as low). Both ground down the LED in an opto-isolator so again, while people suggest they can be modulated by PWM - yes they can, but only at low frequency (<1KHz to be practical). One is already connected to the Font-panel Laser Enable button (I labelled it La) while the other (Lb) is free to be connected to the Fan 0 O/P on Duet. The connection is duplicated on the empty 4-way block as well.
At the moment I'm not controlling the Laser power via Duet other than on/off as I'm only interested in cutting (not engraving). As I understand it, controlling power using PWM rather than using the analogue input (normally connected to the wiper of a front-panel pot) does have advantages as the laser can deliver a higher peak of power in the first instances of it striking. I hope to investigate this at some point.
One other thing worth noting is that the 5V is derived from a 7805 TO220 heatsinked to the case. So while I've seen people say don't pull more than 20mA from this terminal, I suspect it can deliver plenty more. I have a small stand-alone PIC chip running off this to act as a monostable (could have been a 555) to deliver a 10ms pulse when the test button is pressed. I find this useful for delivering a calibrated pulse that can be compared at different foci, materials etc. It conveniently plugs straight into the 4-way connector where all the signals needed are present (apart from the push-button which is now wired to the PIC).
Workflow
Swapping the standard 3D printing extrusion function for a cutting action means being able to use a workflow familiar to most 3D printer users. In my case this means creating .STL files representing 2D paths only (e.g. using 2D primitives with a small extrusion height in OpenSCAD) and setting a matching nozzle size in Slic3r to produce G-codes limited to a single layer.
Other sources of G-code generation for 3D prints should be equally applicable in addition to the more conventional 2D CAD/CAM tools. While it certainly isn't how the authors of the apps I'm using intended them to be used, it works just great for me and cuts down on the number of apps I need to be familiar with. It also makes projects that involve both 3D printed and Laser cut parts much more integrated - i.e. easily modeled in OpenSCAD as one design, with conditional modules enabled for output to the two different tools.
RS Components Reprap Ormerod No. 481
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