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From your proposals, This looks like it *should* work. The "thing" about this method of course is that you're effectively converting your MiniTHC into a standalone. Not sure how you'd do anti-dive but (as you've indicated) with properly good accel it's less of an issue anyway.
Is this worth pursuing or am I better just letting Mach handle the whole thing?
The advantage I see with the THC controlling the drive direct is it cuts out the middle man (Machs Up/Dn), so it should be more responsive, but would it make much difference?
Not sure if this is a slip of thetonguekey, but of course Mach3 per se is going to have nothing to do with up/down. That's going to be done by your CSMIO. So the question would then become - does the "smart" servo react any faster or slower vs the CSMIO to any degree that makes a difference? remember it's not as simple as which one's faster. Fast is good but too fast is no good at all.
OK there are good things about a fast thc and bad things about a fast thc.
A fast THC makes it much more sensitive to things like corner dive, gap dive. With a fast thc you may find yourself having to set these features based on Plate thickness. What works well with thin sheetgoods may not work well with heavy plate.
DOes the CSMIO do anti corner dive based on Mach3 settings ? Like Mach3 would do. Does the THC do anti gap dive ?? how adjustable is it ?? Does it have a spanvolt(deadband) setting ? Can you adjust these from on screen ??
(;-) TP
and rpm reading still persists when I manually stop the lathe.
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Whatever you use, i would not use motor current sensing for the IHS method, unless you cut 12mm plate all day it will buckle the sheet and give bad readings for z-zero. Since tweaking my system up with an offset switch probe and increased z motor tuning, the cuts have certainly improved and I am fairly confident it can follow pretty much any warp I will see.
I still have the floating z setup, connected to my limits chain, i would not build without this as its a good safety feature in case of a dive, a mag-break torch holder would probably be a good replacement though, i will be wiring my z limit to the e-stop circuit soon as the limits are ignored when doing a g28.1 and if my probe switch fails it will plant the torch heavily into the sheet, there is enough torque in my stepper/screw drive that it will not stall the motor and just keeps on going! The failure point is that it rips the delrin nut out of the z-axis body which means stripping it down to replace it.I was thinking about having the magnetic style break away torch holder, purchased a couple of 2mm sensing Prox's for this, intending to wire them into an E-Stop chain. If the torch hits something, as I am sure it will, especially at the start of my plasma escapades, then the machine will stop and hopefully nothing will be damaged
I admire your work on this though, I love R&D work, used to de plenty of it once in the day-job, only used servo's once though and that was step/direction to the servo drive and then closed-loop with encoder/resolver on the servo motor, this was a feed system for a stamping machine.
Proma did have an upgrade version of their THC and it took over direct control of the Z motor, switching back to Mach when stopped, I nearly tried it but splurged on the MP3000 instead. I managed to get the loop response times from Proma guy and it was certainly slow, ok for cutting thick stuff but I found it failed on thin sheet due to the speed needed.
Oh... I use floating switch...
Have a look at this table, you can use bits of the idea too.
http://m.instructables.com/id/CNC-Plasma-Table/
Rob
OH boy Hood are you in for an edumacation. With plasma you HOME z to find teh top of the material not to establish a real Z home. There are 3 main sensing methods ohmic tip, Remote offset switch, and floating Switch on Z. AND 2 possiblities of motion with each, G28.1 and G31
Now that is with the standard Mach3 methods. THere are actually many more but that is another story.
TP
Hood, thanks for the too highly rated complement, I'm really just starting out on a very long journey.You know way more than me on the subject, so that is reason enough to ask your advice
I know zero about servo drives, that being said, I like your options, they look very interesting and may have advantages of driving the THC directly.Don't think that would be an issue as I too would be touching off each new cut
However... If you drive the THC directly, the z axis DRO will have zero idea where the torch actually is until the next touch off (g28.1).... I don't think this would be a problem with my setup, as I touch off before my torch refires every time.
Another problem you may have if you control the servo directly via the THC.... You won't be able to turn the THC off when blended tradjectory is below x% of the feedrate....
) and the code will hopefully be such that even a sharp corner the cut will roll round the corner at the radius of the kerf thus never actually having to come to a stop. Maybe I will end up with a slowdown but if that is the case then I can probably integrate the Lock function.With regards to the rest of the control, I'll try to explain my setup (right, wrong, works for me). I use sheetcam, and that goes care of my touch off (I use g28.1, but you can use g31), and also via snipetts, I turn my THC on and off for small circles and corners etc.
Really, consider my setup a little further, I use an ESS, and turn my THC on and off by making and breaking the THCOK signal back from my THC, given THCUp and THCDn are ignored when THCOK is not present.
The THCOK signal is broken by feeding the THCOK feed via a relay which is controlled via m10px and m11px as these are the only mcodes that don't cause a divot and tradjectory to slow for the mcode execution.
The THC is a proma (actually its Dave's old one...) (I am awaiting a new product on the market, .... Since last sept..!!, hence I nearly built my own and have a few times nearly bought the neuron... If they dropped the pricing back to their introductory price I'd be there like a shot!). I have wasted a great deal of time exploring everyone THC that I could find on the market to try to understand what each offered.
Hence its crude (only settings are hysterysis, torch transfer voltage and target voltage), and its slow... It uses good old fashioned relays... Optoisolators would have been way faster....I would not recommend them, although for the cost it has met its needs as a very entry level thc. (Read:cheap!)
Anyway, the THC is set with a very close hysterysis (2v, the minimum), and an arc transfer voltage of only 5 volts above my target.... The reason behind this is because its acting as an anti-dive function.... Hence the THCOK signal will drop out (or not be enabled until the torch voltage is within 5v of the target voltage, and any spikes the THCOK signal will drop out. From all the info I've found on the net, 1torch volt is about 0.32 to 0.64mm of torch height... Say 0.5mm per volt.... Hence 2v will be around 1mm of cut height (+/- ~ 0.3 mm).
I leave the THC to control the torch height.
I leave sheetcam to insert my code snippets (which I may hand adjust onscreen) to turn my THC on and off via m10px and m11px, via the post processor.
I leave sheetcam to inset my pierce pause by setting up the relevant tool settings (pierce delay, pierce height, initial cut height and do my touch off before every pierce)
Code snippets in sheetcam reduce my feedrate for circular cuts to 60% of the straight line feedrate automatically also for circles less than 1.5" dia (most of my metal is under 4mm)
Hope some of that is for use to someone
Rob
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